Specification
Title of the invention: Ni-based alloy manufacturing method and Ni-based alloy
Technical field
[0001]
　The present invention relates to a method for producing a Ni-based alloy and a Ni-based alloy.
Background technology
[0002]
　Members used in oil well refining equipment, chemical plant equipment, geothermal power generation equipment, and the like are exposed to a high-temperature corrosive environment containing hydrogen sulfide, carbon dioxide, and various acid solutions. The high temperature corrosive environment may reach a maximum of about 1100°C. Therefore, a member used for equipment in a high temperature corrosive environment is required to have excellent strength at high temperature and also excellent corrosion resistance.
[0003]
　A Ni-based alloy containing a large amount of Cr and Mo is known as a material that can be used for the above-mentioned equipment applications. This Ni-based alloy has excellent corrosion resistance due to the inclusion of Cr and Mo.
[0004]
　By the way, a Ni-based alloy contains a plurality of types of alloy elements. Therefore, in the step of casting the melted liquid alloy, the alloy element may be concentrated between the secondary arms of the dendrite formed during solidification. In this case, segregation occurs in the Ni-based alloy. In particular, Mo, which has the effect of enhancing corrosion resistance, is easily segregated. If Mo segregates, the corrosion resistance of the Ni-based alloy decreases.
[0005]
　A method for suppressing segregation of Ni-based alloy is proposed in WO 2010/038680 (Patent Document 1). In this document, a Ni-based alloy liquid alloy is melted by vacuum melting. Then, the liquid alloy is cast to manufacture a Ni-based alloy material. Further, if necessary, secondary melting such as vacuum arc remelting (VAR) or electro-slag remelting (Electro-Slag Remelting: ESR) is performed on the Ni-based alloy material to further enhance the performance. The segregation suppression effect of is obtained. Subsequently, the Ni-based alloy material is homogenized at 1160 to 1220° C. for 1 to 100 hours. It is described in Patent Document 1 that this suppresses segregation of the Ni-based alloy.
Prior art documents
Patent literature
[0006]
Patent Document 1: International Publication No. 2010/038680
Patent Document 2: JP-A-60-211029
Summary of the invention
Problems to be Solved by the Invention
[0007]
　In Patent Document 1, primary melting is performed by vacuum melting, and further, secondary melting such as VAR or ESR is performed as necessary, and then homogenization treatment is performed for a long time. Therefore, when the manufacturing method of Patent Document 1 is adopted, the manufacturing cost may increase. Therefore, in the Ni-based alloy, there may be another method capable of reducing Mo segregation.
[0008]
　An object of the present invention is to provide a method for producing a Ni-based alloy that can reduce Mo segregation and a Ni-based alloy.
Means for solving the problem
[0009]
　In the method for producing a Ni-based alloy according to the present invention, a
　liquid alloy is cast, and the
　chemical composition is, in mass %,
　C: 0.100% or less,
　Si: 0.50% or less,
　Mn: 0.50% or less,
　P: 0.015% or less,
　S: 0.0150% or less,
　Cr: 20.0 to 23.0%,
　Mo: 8.0 to 10.0%,
　one element selected from the group consisting of Nb and Ta Above: 3.150 to 4.150%,
　Ti: 0.05 to 0.40%,
　Al: 0.05 to 0.40%,
　Fe: 0.05 to 5.00%,
　N: 0.100% Hereinafter,
　O: 0.1000% or less,
　Co: 0 to 1.00%,
　Cu: 0 to 0.50%,
　one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000% , And the
　balance is a soaking process for producing a Ni-based alloy material made of Ni and impurities , and a 　soaking treatment
　for the Ni-based alloy material produced by the casting step
, or
　A soaking treatment and a composite treatment including a hot working and a soaking treatment after the hot working
　are carried out, and a segregation reducing step satisfying the formula (1) is provided.
[

　Equation 1] Here, each symbol in the formula (1) is as follows.
　V R : Solidification cooling rate (° C./min) of the liquid alloy in the casting process
　T n : Soaking temperature (° C.) in the n-th soaking heat treatment
　t n : Holding time (hr) at the soaking temperature in the n-th soaking heat treatment )
　Rd n-1 : Cumulative area reduction rate (%) of the Ni-based alloy material before the nth soaking,
　N: Total number of soaking
[0010]
　The
　chemical composition of the Ni-based alloy according to the present invention is % by mass,
　C: 0.100% or less,
　Si: 0.50% or less,
　Mn: 0.50% or less,
　P: 0.015% or less,
　S: 0.0150% or less,
　Cr: 20.0 to 23.0%,
　Mo: 8.0 to 10.0%,
　1 element or more selected from the group consisting of Nb and Ta: 3.150 to 4.150% ,
　Ti: 0.05 to 0.40%,
　Al: 0.05 to 0.40%,
　Fe: 0.05 to 5.00%,
　N: 0.100% or less,
　O: 0.1000% or less,
　Co: 1.0% or less,
　Cu: 0.50% or less,
　one element or more selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the
　balance Ni and impurities,
　Ni In the cross section perpendicular to the longitudinal direction of the base alloy, the average concentration of Mo is 8.0% or more by mass%, the maximum value of Mo concentration is 11.0% or less by mass%, and the Mo concentration is %, the area ratio of the region of less than 8.0% is less than 2.0%.
Effect of the invention
[0011]
　The method for producing a Ni-based alloy according to the present invention can reduce Mo segregation in the Ni-based alloy. The Ni-based alloy according to the present invention has suppressed Mo segregation and has excellent corrosion resistance.
Brief description of the drawings
[0012]
FIG. 1 is a schematic view of a Ni-based alloy being solidified in a casting process.
FIG. 2 is a diagram showing the relationship between the dendrites in FIG. 1 and the Mo concentration of the Ni-based alloy.
FIG. 3 is a diagram showing the relationship between the dendrite secondary arm interval D II and the solidification cooling rate V R in the Ni-based alloy material (cast material) having the chemical composition of the present invention .
FIG. 4 is a diagram showing a relationship between F1 (=right side of formula (1)-left side of formula (1)) and a corrosion rate in a Ni-based alloy having a chemical composition of the present invention.
FIG. 5A is a microstructure observation image of a Ni-based alloy when hot working was performed once at a cross-section reduction rate of 44.6% in the segregation reduction step.
FIG. 5B is a microstructure observation image of a Ni-based alloy when hot working was performed once at a cross-section reduction rate of 31.3% in the segregation reduction step.
FIG. 6 is an EPMA image in a Ni-based alloy according to the second embodiment.
[FIG. 7] FIG. 7 shows the relationship between F2=(Ca+Nd+B)/S in a Ni-based alloy and the fracture drawing (%) obtained when a tensile test was performed in the air at 900° C. at a strain rate of 10/sec. FIG.
MODE FOR CARRYING OUT THE INVENTION
[0013]
　In order to obtain excellent corrosion resistance in a high temperature corrosive environment, the inventors of the present invention should use a Ni-based alloy having a high Mo content, specifically, in mass%, C: 0.100% or less, Si: 0.50% or less, Mn: 0.50% or less, P: 0.015% or less, S: 0.0150% or less, Cr: 20.0 to 23.0%, Mo: 8.0 to 10 0.0%, one element or more selected from the group consisting of Nb and Ta: 3.150 to 4.150%, Ti: 0.05 to 0.40%, Al: 0.05 to 0.40%, Fe : 0.05 to 5.00%, N: 0.100% or less, O: 0.1000% or less, Co: 0 to 1.00%, Cu: 0 to 0.50%, from Ca, Nd and B One or more elements selected from the group consisting of: 0 to 0.5000%, and the balance is considered to be suitable for a Ni-based alloy having a chemical composition of Ni and impurities. Therefore, the present inventors investigated and studied a method for reducing Mo segregation in a high Mo Ni-based alloy having the above-described chemical composition. As a result, the present inventors have obtained the following findings.
[0014]
　[Relationship between Dendrite Secondary Arm Interval and Solidification Cooling Rate in Casting Process]
　The concentration distribution of Mo in the Ni-based alloy having the above-mentioned chemical composition depends on the dendrite secondary arm interval formed in the final solidification stage in the casting process. Have a correlation.
[0015]
　FIG. 1 is a schematic view of a Ni-based alloy being solidified in a casting process. Referring to FIG. 1, in the casting step, the liquid alloy in mold 13 is cooled and solidification proceeds. Specifically, the portion near the mold 13 is solidified and the solid phase 11 is formed. Further, in the liquid phase 10, the dendrite 12 is formed in the portion where the solidification is in progress.
[0016]
　FIG. 2 is a diagram showing the relationship between the dendrite 12 in FIG. 1 and the Mo concentration in the Ni-based alloy. With reference to FIG. 2, in the Mo concentration distribution in the Ni-based alloy material (cast material) after casting, a portion having a high Mo concentration is defined as a positive segregation portion of Mo segregation, and a portion having a low Mo concentration is segregated with Mo. It is defined as the negative segregation part of. The interval between adjacent Mo segregations (the interval between the positive segregation portions or the interval between the negative segregation portions) is defined as the Mo segregation distance Ds. As shown in FIG. 2, the Mo inter-segregation distance Ds corresponds to the dendrite secondary arm interval D II . In FIG. 2, as an example, the Mo segregation distance Ds matches the dendrite secondary arm distance D II .
[0017]
　FIG. 3 is a diagram showing a relationship between the dendrite secondary arm interval D II and the solidification cooling rate V R in the Ni-based alloy material (cast material) having the above-described chemical composition . FIG. 3 was obtained by the following method. A liquid alloy of Ni-based alloy was melted. Then, it was cooled to room temperature (25° C.) at various solidification cooling rates V R to manufacture a plurality of Ni-based alloy materials (ingots) having the above-described chemical composition. In this experiment, the solidification cooling rate V R was defined as the average cooling rate (°C/min) in the temperature range from the temperature of the liquid solution at the start of casting to the completion of solidification (temperature range is 1290°C). The temperature of the Ni-based alloy during cooling was measured using a consumable thermocouple.
[0018]
　Here, in this specification, a cross section perpendicular to the longitudinal direction of the Ni-based alloy material is defined as a "cross section", and a width of the Ni-based alloy material in the cross section is defined as W. When the cross section has a rectangular shape, the long side of the cross section is defined as the width W. When the cross section is circular, the diameter is defined as the width W. In addition, a region at a depth position of W/4 in the width W direction from a surface perpendicular to the width W direction in the cross section is defined as “W/4 depth position”.
[0019]
　The produced Ni-based alloy material was cut in a direction perpendicular to the longitudinal direction. Then, at the W/4 depth position of the cross section, the dendrite secondary arm interval D II (μm) was measured. Specifically, a sample was taken from the W/4 depth position. After mirror-polishing the surface of the sample parallel to the above-mentioned cross section, it was etched with aqua regia. The etched surface was observed with a 400x optical microscope to produce a photographic image of a 200 [mu]m x 200 [mu]m viewing field. Using the obtained photographic image, the dendrite secondary arm interval (μm) at any 20 points within the observation visual field was measured. The average of the measured dendrite secondary arm spacing was defined as the dendrite secondary arm spacing D II (μm). FIG. 3 was created using the solidification cooling rate V R and the dendrite secondary arm interval D II thus obtained.
[0020]
　Referring to FIG. 3, in the Ni-based alloy material having the above-described chemical composition , the dendrite secondary arm interval D II becomes narrower as the solidification cooling rate V R becomes faster . Based on the results of FIG. 3, in the Ni-based alloy material having the above-described chemical composition, the dendrite secondary arm interval D II (μm) was calculated using the solidification cooling rate V R (° C./min) as the following formula (A ) Can be defined. 　D II =182V R -0.294　(A)
[0021]
　[Mo Diffusion Distance in Soaking Treatment] It
　is assumed that the soaking treatment is performed on the Ni-based alloy material produced by the casting process. At this time, the diffusion distance of Mo in the Ni-based alloy material can be defined as follows.
[0022]
　The diffusion equation is defined by the following equation (B).
　σ 2 =2D×t (B)
　Here, σ in the formula (B) is an average distance (hereinafter referred to as a diffusion distance) that Mo moves at a time t (hr) in the Ni-based alloy material having the above-described chemical composition. : The unit is μm). Further, D in the formula (B) is a diffusion coefficient of Mo and is defined by the Arrhenius formula of the formula (C).
　D=D 0 exp(−Q/R(T+273)) (C)
　Q in the formula (C) is activation energy for Mo diffusion. R is a gas constant and T is a temperature (°C). D 0 is a Mo constant (frequency factor) in the Ni-based alloy.
[0023]
　Do was determined by the following experiment. The Ni-based alloy material having the above chemical composition was subjected to soaking at 1248° C. for 48 hours. Then, the diffusion distance σ of Mo in the Ni-based alloy after soaking was determined. More specifically, the following experiment was conducted. By the above-described method, the dendrite secondary arm interval D II of the Ni-based alloy material before soaking was measured. After the measurement, the Ni-based alloy material was kept at a soaking temperature of 1248°C. At this time, soaking was carried out at various holding times. After the soaking, the difference in Mo concentration between the positive segregation portion and the negative segregation portion of Mo was measured at the W/4 depth position of the Ni-based alloy material. The concentration difference between the positive segregation portion and the negative segregation portion of Mo was determined for each holding time in the soaking treatment. Then, the holding time t at which the concentration difference becomes 1.0 mass% or less was obtained. The dendrite secondary arm spacing D II of the Ni-based alloy of the Ni-based alloy material used in the test was 120.6 μm. Since the diffusion distance σ of Mo=D II /2, the Mo diffusion distance σ was set to 60.3 μm. As a result of the above-mentioned test, when the soaking temperature was 1248° C. and the soaking time was set to 48 hours, the difference in concentration between the positive segregation portion and the negative segregation portion of Mo was 1.0 mass% or less. ..
[0024]
　Matters obtained by the above experiment (when the diffusion distance σ is 60.3 μm, if the temperature T=1248° C. and the holding time t=48 hours, the concentration difference between the positive segregation portion and the negative segregation portion of Mo is 1. 0% by mass or less), Mo activation energy Q=240 kJ/mol in the range of 1050 to 1360° C., and the soaking temperature T( C) and the diffusion time σ of Mo at the holding time t(hr) are as in the following formula (D). Regarding the activation energy, the activation energy value of Mo in the above temperature range in austenitic steel is substituted as the activation energy value of Mo in the Ni-based alloy.
[Number 2]

[0025]
　[ Relationship between Dendrite Secondary Arm Spacing D II and Mo Diffusion Distance σ] With
　reference to the formulas (A) and (D), the diffusion length of Mo during soaking is defined by the above formula (D). If σ becomes 1/2 or more of the dendrite secondary arm spacing D II (that is, the Mo segregation distance Ds) defined by the formula (A), it is considered that Mo segregation can be sufficiently improved by soaking. .. That is, when the soaking temperature T (° C.), the holding time t (hr), and the solidification cooling rate V R (° C./min) satisfy the equation (0), Mo segregation is sufficiently reduced in the soaking process.
[Number 3]

[0026]
　[Further improvement of Mo segregation by hot working] If
　the Ni-base alloy material before soaking is subjected to hot working, the Mo segregation distance Ds can be further narrowed before soaking. This is because the dendrite arm grows by extending in the direction normal to the surface of the Ni-based alloy material, as shown in FIG. In hot working, reduction is applied in the normal direction of the surface of the Ni-based alloy material. Therefore, when hot working is performed, the dendrite secondary arm distance D II (that is, Mo segregation distance Ds) becomes narrower than when hot working is not performed . Therefore, when performing soaking at the same soaking temperature T (° C.) and the same holding time t (hr), it is better to carry out hot working before soaking when not performing hot working before soaking. Compared with, it becomes easier to reduce the segregation of Mo.
[0027]
　Here, it is assumed that hot working is performed on the Ni-based alloy material after the casting process at a surface reduction ratio Rd, and soaking is performed on the Ni-based alloy material after the hot working. In this case, it is considered that the Mo inter-segregation distance Ds is reduced by the area reduction ratio Rd. Conversely speaking, it can be considered that the Mo diffusion distance σ in the soaking treatment is extended by the area reduction ratio Rd.
[0028]
　In consideration of the above matters, when hot working is performed at the surface reduction ratio Rd before soaking, the following expression (E) is established based on the expression (D).
[Number 4]

[0029]
　Based on the above examination, if hot working is performed before soaking, Mo segregation can be further reduced. Here, a series of treatments in which hot working is performed and then soaking is performed after hot working (that is, one hot working and one soaking performed after the hot working) The processing of combination) is defined as "composite processing". When the composite treatment is performed once or a plurality of times on the Ni-based alloy material, the following expression (1) is established based on the expression (E).
[

　Equation 5] Here, each symbol in the formula (1) is as follows.
　V R : solidification cooling rate in the casting process (° C. /
　min) T n : soaking temperature in n-th soaking (°
　C.) t n : retention time at the soaking temperature in the n-th soaking
　(hr) Rd n −1 : Cumulative area reduction rate (%) of the Ni-based alloy material before the n-th soaking treatment
　N: Total number of soaking treatments
　Here, n is a natural number of 1 to N, and N is a natural number.
[0030]
　The cumulative area reduction rate Rd n-1 is defined by the following equation (F).
　Rd n-1 =(1-(S n-1 /S 0 ))×100 (F)
　Here, S n-1 is a cross section of the Ni-based alloy material before the n-th soaking treatment, which is perpendicular to the longitudinal direction ( (Cross section) area (mm 2 ). S 0 is the area of ​​the cross section (transverse cross section) perpendicular to the longitudinal direction of the Ni-based alloy material after the casting step and before the first hot working (that is, after the casting step and before the segregation reduction step) (Mm 2 ). The area S 0 is defined as follows when the Ni-based alloy material targeted for S 0 is an ingot and the cross section perpendicular to the longitudinal direction is not constant in the longitudinal direction, as typified by a truncated pyramid shape. To be done. 　S 0 =V 0 /L 　where V 0 is the volume of the Ni-based alloy material (mm 3

) And L is the length (mm) of the Ni-based alloy material in the longitudinal direction.
　When hot working is not performed, the cumulative area reduction rate Rd n-1 =0 (as cast material).
[0031]
　The manufacturing method of the Ni-based alloy of the present embodiment completed based on the above findings and the Ni-based alloy manufactured by the manufacturing method of the present embodiment have the following configurations.
[0032]
　In the method for manufacturing the Ni-based alloy of the present embodiment having the configuration [1], a
　liquid alloy is cast, and the
　chemical composition is mass%,
　C: 0.100% or less,
　Si: 0.50% or less,
　Mn. : 0.50% or less,
　P: 0.015% or less,
　S: 0.0150% or less,
　Cr: 20.0 to 23.0%,
　Mo: 8.0 to 10.0%,
　consisting of Nb and Ta One or more elements selected from the group: 3.150 to 4.150%,
　Ti: 0.05 to 0.40%,
　Al: 0.05 to 0.40%,
　Fe: 0.05 to 5.00% ,
　N: 0.100% or less,
　O: 0.1000% or less,
　Co: 0 to 1.00%,
　Cu: 0 to 0.50%,
　one or more elements selected from the group consisting of Ca, Nd and B : 0 to 0.5000%, and
　the balance a casting step of producing a Ni based alloy material consisting of Ni and impurities,
　with respect to the Ni-base alloy material produced by the casting process,
　soaking, or,
　A soaking treatment and a combined treatment including a hot working and a soaking treatment after the hot working
　are carried out, and a segregation reducing step satisfying the formula (1) is provided.
[

　Equation 6] Here, each symbol in Formula (1) is as follows.
　V R : Solidification cooling rate (° C./min) of the liquid alloy in the casting process
　T n : Soaking temperature (° C.) in the n-th soaking heat treatment
　t n : Holding time (hr) at the soaking temperature in the n-th soaking heat treatment )
　Rd n-1 : Cumulative area reduction rate (%) of the Ni-based alloy material before the nth soaking,
　N: Total number of soaking
[0033]
　The method for manufacturing the Ni-based alloy of the present embodiment having the configuration [2] is the method for manufacturing the Ni-based alloy according to [1], and the
　soaking temperature is 1000 to 1300°C.
[0034]
　The method for producing the Ni-based alloy of the present embodiment having the configuration [3] is the method for producing the Ni-based alloy according to [2], wherein the
　segregation reducing step includes
　performing the composite treatment one or more times, and Hot working is performed at least once at a cross-section reduction rate of 35.0% or more for the Ni-based alloy material heated to 1000 to 1300°C.
[0035]
　In this case, the grain size number of the manufactured Ni-based alloy according to ASTM E112 is 0.0 or more.
[0036]
　The method for producing the Ni-based alloy of the present embodiment having the configuration [4] is the method for producing the Ni-based alloy according to [2] or [3], and in the
　segregation reducing step, the uniform
　heating at 1000 to 1300° C. Soaking is performed at least once for 1 hour or more at the temperature.
[0037]
　In this case, the total number of Nb carbonitrides having a maximum length of 1 to 100 μm is 4.0×10 −2 /μm 2 or less. As a result, hot workability is further enhanced.
[0038]
　The method for producing a Ni-based alloy having the configuration of [5] is the method for producing a Ni-based alloy according to any one of [1] to [4], wherein
　the chemical composition of the Ni-based alloy material is
　Ca, One or more elements selected from the group consisting of Nd and B are contained in a content satisfying the formula (2).
　(Ca+Nd+B)/S≧2.0 (2)
　Here, the content of the corresponding element in atomic% (at) is substituted for the element symbol in the formula (2).
[0039]
　In this case, the hot workability of the manufactured Ni-based alloy is further enhanced.
[0040]
　The
　chemical composition of the Ni-based alloy according to the configuration of [6] is % by mass,
　C: 0.100% or less,
　Si: 0.50% or less,
　Mn: 0.50% or less,
　P: 0.015% or less. ,
　S: 0.0150% or less,
　Cr: 20.0 to 23.0%,
　Mo: 8.0 to 10.0%,
　1 element or more selected from the group consisting of Nb and Ta: 3.150 to 4 150%,
　Ti: 0.05 to 0.40%,
　Al: 0.05 to 0.40%,
　Fe: 0.05 to 5.00%,
　N: 0.100% or less,
　O: 0.1000 % 　Or less,
　Co:0 to 1.0%,
　Cu:0 to 0.50%,
one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the
　balance Ni and
　An average concentration of Mo is 8.0% or more by mass% and a maximum value of Mo concentration is 11.0% or less by mass% in a cross section perpendicular to the longitudinal direction of the Ni-based alloy. The area ratio of the region where the Mo concentration is less than 8.0% by mass% is less than 2.0%.
[0041]
　Mo segregation is suppressed in the Ni-based alloy according to the present embodiment. Therefore, the Ni-based alloy of this embodiment has excellent corrosion resistance.
[0042]
　The Ni-based alloy having the configuration [7] is the Ni-based alloy according to [6], and has a
　chemical composition of
　one or more elements selected from the group consisting of Ca, Nd, and B expressed by the formula (2 ) It is contained in a content that satisfies the above.
　(Ca+Nd+B)/S≧2.0 (2)
　Here, the content of the corresponding element in atomic% (at) is substituted for the element symbol in the formula (2).
[0043]
　In this case, the hot workability of the Ni-based alloy is further enhanced.
[0044]
　The Ni-based alloy having the configuration [8] is the Ni-based alloy according to [6] and [7], and has a
　grain size number of 0.0 or more in accordance with ASTM E112.
[0045]
　In this case, the hot workability of the Ni-based alloy is further enhanced.
[0046]
　The Ni-based alloy having the configuration [9] is the Ni-based alloy according to any one of [6] to [8],
　wherein the Nb carbonitride has a maximum length of 1 to 100 μm in the Ni-based alloy. Is 4.0×10 −2 /μm 2 or less.
[0047]
　In this case, the hot workability of the Ni-based alloy is further enhanced.
[0048]
　Here, in the present specification, “Nb carbonitride” is a concept including Nb carbide, Nb nitride, and Nb carbonitride, and the total content of Nb, C, and N is 90% by mass. The above precipitates are meant. Further, the maximum length of Nb carbonitride means the maximum length of the straight lines connecting at any two points on the interface (boundary) between the Nb carbonitride and the mother phase.
[0049]
　Hereinafter, the method for manufacturing the Ni-based alloy and the Ni-based alloy according to the present embodiment will be described.
[0050]
　[First Embodiment]
　[Ni-based alloy manufacturing method]
　The Ni-based alloy manufacturing method according to the present embodiment includes a casting step and a segregation reducing step. Hereinafter, each step will be described.
[0051]
　[Casting Step] In the
　casting step, a liquid alloy of a Ni-based alloy material is melted, and the liquid alloy is cast to manufacture a Ni-based alloy material having the following chemical composition.
[0052]
　[Chemical composition] The chemical composition of the
　Ni-based alloy material contains the following elements. Hereinafter,% relating to elements means mass% unless otherwise specified. The chemical composition of the Ni-based alloy manufactured by the method for manufacturing the Ni-based alloy of the present embodiment is the same as the chemical composition of the Ni-based alloy material.
[0053]
　C: 0.100% or less
　Carbon (C) is inevitably contained. That is, the C content is more than 0%. If the C content is too high, carbides typified by Cr carbides precipitate at grain boundaries after long-term use at high temperatures. In this case, the corrosion resistance of the Ni-based alloy decreases. Precipitation of carbides at grain boundaries further reduces mechanical properties such as toughness of Ni-based alloys. Therefore, the C content is 0.100% or less. The preferable upper limit of the C content is 0.070%, more preferably 0.050%, further preferably 0.030%, further preferably 0.025%, further preferably 0.023. %. It is preferable that the C content is as low as possible. However, the extreme reduction of the C content increases the manufacturing cost. Therefore, the preferable lower limit of the C content is 0.001%, more preferably 0.005%, and further preferably 0.010%.
[0054]
　Si: 0.50% or less
　Silicon (Si) is unavoidably contained. That is, the Si content is more than 0%. Si deoxidizes the Ni-based alloy. However, if the Si content is too high, Si combines with Ni or Cr to form an intermetallic compound, or promotes the formation of an intermetallic compound such as a sigma phase (σ phase). As a result, the hot workability of the Ni-based alloy decreases. Therefore, the Si content is 0.50% or less. The preferable upper limit of the Si content is 0.40%, more preferably 0.30%, further preferably 0.25%, further preferably 0.20%, further preferably 0. 19%. The lower limit of the Si content is 0.01%, more preferably 0.02%, and most preferably 0.04% in order to more effectively obtain the above deoxidizing action.
[0055]
　Mn: 0.50% or less
　Manganese (Mn) is inevitably contained. That is, the Mn content is more than 0%. Mn deoxidizes the Ni-based alloy. Mn further fixes S, which is an impurity, as Mn sulfide, and improves the hot workability of the Ni-based alloy. However, if the Mn content is too high, the formation of a spinel type oxide film is promoted during use in a high temperature corrosive environment, and as a result, the oxidation resistance at high temperatures decreases. If the Mn content is too high, the hot workability of the Ni-based alloy further deteriorates. Therefore, the Mn content is 0.50% or less. The preferable upper limit of the Mn content is 0.40%, more preferably 0.30%, and further preferably 0.23%. A preferable lower limit of the Mn content for effectively improving hot workability is 0.01%, more preferably 0.02%, further preferably 0.04%, further preferably 0. It is 08%, and more preferably 0.12%.
[0056]
　P: 0.015% or less
　Phosphorus (P) is an impurity. The P content may be 0%. P reduces the toughness of the Ni-based alloy. Therefore, the P content is (not less than 0%) and not more than 0.015%. The preferable upper limit of the P content is 0.013%, more preferably 0.012%, and further preferably 0.010%. The P content is preferably as low as possible. However, the extreme reduction of P content increases the manufacturing cost. Therefore, the lower limit of the P content is preferably 0.001%, more preferably 0.002%, and further preferably 0.004%.
[0057]
　S: 0.0150% or less
　Sulfur (S) is an unavoidable impurity. That is, the S content is more than 0%. S reduces the hot workability of the Ni-based alloy. Therefore, the S content is 0.0150% or less. The preferable upper limit of the S content is 0.0100%, more preferably 0.0080%, further preferably 0.0050%, further preferably 0.0020%, further preferably 0.0015. %, more preferably 0.0010%, further preferably 0.0007%. It is preferable that the S content is as low as possible. However, the extreme reduction of the S content increases the manufacturing cost. Therefore, the preferable lower limit of the S content from the viewpoint of manufacturing cost is 0.0001%, and more preferably 0.0002%.
[0058]
　Cr: 20.0 to 23.0%
　Chromium (Cr) enhances corrosion resistance such as oxidation resistance, steam oxidation resistance, and high temperature corrosion resistance of the Ni-based alloy. Cr further combines with Nb to form an intermetallic compound and precipitates at the grain boundaries, increasing the creep strength of the Ni-based alloy. If the Cr content is too low, the above effects cannot be sufficiently obtained. On the other hand, if the Cr content is too high, a large amount of M 23 C 6 type carbide is precipitated, and the corrosion resistance is rather deteriorated. Therefore, the Cr content is 20.0 to 23.0%. The preferable lower limit of the Cr content is 20.5%, more preferably 21.0%, and further preferably 21.2%. The preferable upper limit of the Cr content is 22.9%, more preferably 22.5%, further preferably 22.3%, further preferably 22.0%.
[0059]
　Mo: 8.0-10.0%
　Molybdenum (Mo) enhances the corrosion resistance of the Ni-based alloy when used in a high temperature corrosive environment. Mo further forms a solid solution in the parent phase and enhances the creep strength of the Ni-based alloy by solid solution strengthening. This enhances the strength of the Ni-based alloy in a high temperature corrosive environment. On the other hand, if the Mo content is too high, the hot workability deteriorates. Therefore, the Mo content is 8.0 to 10.0%. The preferable lower limit of the Mo content is 8.1%, more preferably 8.2%, further preferably 8.3%, further preferably 8.4%, further preferably 8.5. %. The preferable upper limit of the Mo content is 9.9%, more preferably 9.5%, further preferably 9.2%, further preferably 9.0%, and further preferably 8.8. %.
[0060]
　One or more elements selected from the group consisting of Nb and Ta: 3.150 to 4.150%
　Niobium (Nb) and tantalum (Ta) both promote the formation of intermetallic compounds and Contributes to precipitation strengthening. As a result, creep strength is increased. If the total content of one or more elements selected from the group consisting of Nb and Ta is too low, the above effect cannot be sufficiently obtained. On the other hand, if the total content of one or more elements selected from the group consisting of Nb and Ta is too high, the precipitates become coarse and the creep strength decreases. Therefore, the total content of one or more elements selected from the group consisting of Nb and Ta is 3.150 to 4.150%. The preferable lower limit of the total content of one or more elements selected from the group consisting of Nb and Ta is 3.200%, more preferably 3.210%, and further preferably 3.220%. The preferable upper limit of the total content of one or more elements selected from the group consisting of Nb and Ta is 4.120%, more preferably 4.000%, further preferably 3.800%, and further preferably Is 3.500%, and more preferably 3.450%. Note that only Nb may be contained and Ta may not be contained. Moreover, only Ta may be contained and Nb may not be contained. Both Nb and Ta may be contained. When only Nb is contained among Nb and Ta, the above-mentioned total content (3.150 to 4.150%) means the content of Nb. When only Ta is contained among Nb and Ta, the above-mentioned total content (3.150 to 4.150%) means the content of Ta.
[0061]
　Ti: 0.05 to 0.40%
　Titanium (Ti) deoxidizes the Ni-based alloy together with Si, Mn, and Al. Further, Ti forms a gamma prime phase (γ′ phase) together with Al and enhances the creep strength of the Ni-based alloy under a high temperature corrosive environment. If the Ti content is too low, the above effect cannot be sufficiently obtained. On the other hand, if the Ti content is too high, a large amount of carbides and/or oxides are generated, and the hot workability and creep strength of the Ni-based alloy are reduced. Therefore, the Ti content is 0.05 to 0.40%. The preferable lower limit of the Ti content is 0.08%, more preferably 0.10%, further preferably 0.13%, further preferably 0.15%. The preferable upper limit of the Ti content is 0.35%, more preferably 0.30%, further preferably 0.25%, further preferably 0.22%.
[0062]
　Al: 0.05 to 0.40%
　Aluminum (Al) deoxidizes the Ni-based alloy together with Si, Mn and Ti. Further, Al forms a gamma prime phase (γ′ phase) together with Ti to enhance the creep strength of the Ni-based alloy under a high temperature corrosive environment. If the Al content is too low, the above effects cannot be sufficiently obtained. On the other hand, if the Al content is too high, a large amount of oxide-based inclusions are produced, and the hot workability and creep strength of the Ni-based alloy are reduced. Therefore, the Al content is 0.05 to 0.40%. The preferable lower limit of the Al content is 0.06%, more preferably 0.07%, further preferably 0.08%. The preferable upper limit of the Al content is 0.35%, more preferably 0.32%, further preferably 0.30%, further preferably 0.27%. In addition, in this specification, Al content is sol. It means the content of Al (acid-soluble Al).
[0063]
　Fe: 0.05 to 5.00%
　Iron (Fe) substitutes for Ni. Specifically, Fe enhances the hot workability of the Ni-based alloy. Fe further precipitates a Laves phase at the grain boundaries and strengthens the grain boundaries. If the Fe content is too low, the above effect cannot be sufficiently obtained. On the other hand, if the Fe content is too high, the corrosion resistance of the Ni-based alloy decreases. Therefore, the Fe content is 0.05 to 5.00%. The preferable lower limit of the Fe content is 0.10%, more preferably 0.50%, further preferably 1.00%, further preferably 2.00%, further preferably 2.50. %. The preferable upper limit of the Fe content is 4.70%, more preferably 4.50%, further preferably 4.00%, further preferably 3.90%.
[0064]
　N: 0.100% or less
　Nitrogen (N) is unavoidably contained. That is, the N content is more than 0%. N stabilizes austenite in the Ni-based alloy. N further enhances the creep strength of Ni-based alloys. However, if the N content is too high, the hot workability of the Ni-based alloy deteriorates. Therefore, the N content is 0.100% or less. The preferable upper limit of the N content is 0.080%, more preferably 0.050%, further preferably 0.030%, further preferably 0.025%. Extreme reduction of N content increases manufacturing costs. Therefore, the preferable lower limit of the N content from the viewpoint of manufacturing cost is 0.001%, more preferably 0.002%, and further preferably 0.005%.
[0065]
　O: 0.1000% or less
　Oxygen (O) is an impurity. The O content may be 0%. O forms an oxide and reduces the hot workability of steel. Therefore, the O content is (not less than 0%) and not more than 0.1000%. The preferable upper limit of the O content is 0.0800%, more preferably 0.0500%, further preferably 0.0300%, further preferably 0.0150%. The O content is preferably as low as possible. However, the extreme reduction of O content increases the manufacturing cost. Therefore, the preferable lower limit of the O content from the viewpoint of manufacturing cost is 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
[0066]
　The balance of the Ni-based alloy material according to the present invention is nickel (Ni) and impurities. It should be noted that the term "impurity" as used herein means an element mixed from an ore or scrap used as a raw material when manufacturing a Ni-based alloy industrially, or an element mixed from the environment of the manufacturing process or the like.
[0067]
　Note that Ni stabilizes austenite in the structure of the Ni-based alloy and enhances the corrosion resistance of the Ni-based alloy. As described above, the rest of the chemical composition other than the above elements is Ni and impurities. The preferable lower limit of the Ni content is 58.0%, more preferably 59.0%, and further preferably 60.0%.
[0068]
　The Ni-based alloy material of the present embodiment may further contain one or more elements selected from the group consisting of Co and Cu, instead of part of Ni. Both Co and Cu enhance the high temperature strength of the Ni-based alloy.
[0069]
　Co: 0 to 1.00%
　Cobalt (Co) is an optional element. That is, the Co content may be 0%. When included, Co enhances the high temperature strength of the Ni-based alloy. If Co is contained even a little, the above effect can be obtained to some extent. However, if the Co content is too high, the hot workability of the Ni-based alloy deteriorates. Therefore, the Co content is 0 to 1.00%. The preferable upper limit of the Co content is 0.90%, more preferably 0.80%, further preferably 0.70%, further preferably 0.60%. The preferable lower limit of the Co content is 0.01%, more preferably 0.10%, further preferably 0.20%, further preferably 0.30%.
[0070]
　Cu: 0 to 0.50%
　Copper (Cu) is an optional element. That is, the Cu content may be 0%. When contained, Cu precipitates to enhance the high temperature strength of the Ni-based alloy. If Cu is contained even a little, the above effect can be obtained to some extent. However, if the Cu content is too high, the hot workability of the Ni-based alloy deteriorates. Therefore, the Cu content is 0 to 0.50%. The preferable upper limit of the Cu content is 0.45%, more preferably 0.40%, further preferably 0.30%, further preferably 0.20%, further preferably 0.15%. %. The preferable lower limit of the Cu content is 0.01%, more preferably 0.02%, and further preferably 0.05%.
[0071]
　The Ni-based alloy material of the present embodiment may further contain one or more elements selected from the group consisting of Ca, Nd and B, instead of part of Ni.
[0072]
　At least one element selected from the group consisting of Ca, Nd, and B: 0 to 0.5000% in total content of
　calcium (Ca), neodymium (Nd), and boron (B) are all optional elements Yes, and may not be contained. That is, the Ca content may be 0%, the Nd content may be 0%, and the B content may be 0%. When at least one element of Ca, Nd and B is contained, all of these elements enhance the hot workability of the Ni-based alloy. As long as it contains at least one element selected from the group consisting of Ca, Nd, and B, for example, only Ca may be contained, only Nd may be contained, or only B may be contained. May be done. Ca and Nd may be contained, Ca and B may be contained, or Nd and B may be contained. Ca, Nd and B may be contained. If at least one element selected from the group consisting of Ca, Nd and B is contained at least, the above effect can be obtained to some extent. However, Ca, Nd, and B are easily absorbed by the slag or the like during the melting of the liquid alloy and are unlikely to remain in the Ni-based alloy material. Therefore, the total content of Ca, Nd and B is unlikely to exceed 0.5000%. Therefore, the total content of at least one element selected from the group consisting of Ca, Nd and B is 0 to 0.5000%. The preferable upper limit of the total content of one or more elements selected from the group consisting of Ca, Nd and B is 0.4500%, more preferably 0.4200%. The preferable lower limit of the total content of one or more elements selected from the group consisting of Ca, Nd and B is 0.0001%, more preferably 0.0003%, further preferably 0.0005%.
[0073]
　The liquid alloy is melted so that the Ni-based alloy material has the above-described chemical composition. The liquid alloy may be melted by a known method. The liquid alloy is produced, for example, by electric furnace melting. The liquid alloy may be melted by vacuum melting. From the viewpoint of manufacturing cost, it is preferable to manufacture the liquid alloy by electric furnace melting.
[0074]
　A Ni-based alloy material having the above-described chemical composition is manufactured by a casting method using the melted liquid alloy. The Ni-based alloy material may be an ingot manufactured by the ingot making method or a cast piece (slab or bloom) manufactured by the continuous casting method.
[0075]
　The solidification cooling rate V R from the liquid alloy to the solidification of the Ni-based alloy material in the casting process is determined by measuring the dendrite secondary arm distance D II of the Ni-based alloy material after the casting process and before the segregation reduction process. It can be calculated. The dendrite secondary arm distance D II can be measured by the following method. A sample is taken at the W/4 depth position of the cross section (transverse cross section) perpendicular to the longitudinal direction at the central position in the longitudinal direction of the Ni-based alloy material. Of the surface of the sample, the surface parallel to the above-mentioned cross section is mirror-polished and then etched with aqua regia. The etched surface is viewed under a 400X optical microscope to produce a photographic image of a 200 [mu]m x 200 [mu]m viewing field. Using the obtained photographic image, the dendrite secondary arm interval (μm) at any 20 points in the observation visual field is measured. The average of the measured dendrite secondary arm spacing is defined as the dendrite secondary arm spacing D II (μm).
[0076]
　The solidification cooling rate V R (° C./min) is obtained by substituting the obtained dendrite secondary arm distance D II into the equation (A) . 　D II =182V R -0.294　(A)
[0077]
　[Segregation reduction step] In the
　segregation reduction step, Mo segregation is reduced with respect to the Ni-based alloy material produced in the casting step. Specifically, the Ni-based alloy material produced in the casting step is
　subjected to (I) soaking treatment, or
　(II) soaking treatment, and combined treatment after soaking treatment
　.
[0078]
　In the present specification, the “composite treatment” means a series of treatments in which hot working is performed and soaking is further performed after hot working. In other words, the “composite treatment” means a treatment that combines one hot working and one soaking treatment after the hot working. The one-time soaking treatment means a process of inserting into a heating furnace or soaking furnace, holding at a predetermined soaking temperature and a predetermined holding time, and then performing extraction. One-time hot working means a treatment that starts hot working on a Ni-based alloy material heated to 1000 to 1300°C and finishes hot working without reheating in the middle. To do. Hot working means, for example, hot extrusion, hot forging, and hot rolling.
[0079]
　In the segregation reducing step, the soaking treatment may be performed only once and the composite treatment may not be performed, or the soaking treatment may be performed only once and the soaking treatment is not performed. Moreover, you may implement a composite process repeatedly in multiple times. The soaking treatment may be performed once or more and then the composite treatment may be performed once or more. The soaking treatment may be performed once or more after the composite treatment is performed once or more. In short, in the segregation reduction step, at least one soaking treatment, or at least one soaking treatment and at least one combined treatment may be performed.
[0080]
　After the soaking treatment, the composite treatment may be carried out as it is, or after the soaking treatment, the Ni-based alloy material may be once cooled and then the soaking treatment may be carried out again, and then the composite treatment may be carried out (that is, in this case, , Soaking treatment, soaking treatment, and composite treatment in this order). In addition, after the soaking treatment, the composite treatment may be performed, and then the composite treatment may be further performed (in this case, the soaking treatment, the composite treatment, and the composite treatment are sequentially performed). The soaking treatment and the composite treatment may be appropriately combined. For example, soaking treatment, compounding treatment, soaking treatment may be carried out in this order, or soaking treatment, compounding treatment, soaking treatment and compounding treatment may be carried out in this order. The hot working during soaking and composite processing will be described below.
[0081]
　[Soaking Treatment] In the
　n-th soaking treatment, the Ni-based alloy material produced in the casting step is held at the soaking temperature T n (° C.) for the holding time t n (hr). Here, n is 1 to N (N is a natural number), and the soaking temperature T n is the soaking temperature of the n-th soaking process (including the soaking process of (I) and the soaking process of (I)). It means the heat temperature (° C.), and the holding time t n means the holding time (hr) of the n-th soaking treatment. N is the total number of soaking treatments (I) and (II).
[0082]
　If the soaking temperature T n is too low, the diffusion distance σ of Mo cannot be increased and Mo does not easily diffuse during soaking . On the other hand, if the soaking temperature T n is too high, a part of the Ni-based alloy material may be redissolved. Therefore, the soaking temperature T n is not particularly limited, but the preferable soaking temperature T n is 1000 to 1300°C. It suffices to carry out the soaking treatment in a known heating furnace or soaking furnace.
[0083]
　[Hot Working]
　As described above, the hot working may be hot extrusion, hot forging, or hot rolling. The type of hot working is not particularly limited. In the manufacturing method of the present embodiment, when hot working is performed, the soaking treatment described above is performed after hot working (composite treatment). The inter-segregation distance Ds of Mo in the Ni-based alloy material is shortened by the hot working. Therefore, Mo is more likely to diffuse in the soaking treatment after the hot working, and the holding time t n required for reducing Mo segregation can be reduced. In the segregation reduction step, when the composite treatment is performed without performing the soaking treatment in the previous stage, the Ni-based alloy material is heated to 1000 to 1300° C. in the heating furnace or the soaking furnace, and then the hot working is performed. carry out.
[0084]
　[Regarding Formula (1)]
　As described above, in the segregation reducing step, one or more soaking treatments or one or more soaking treatments and one or more combined treatments are performed. At this time, the soaking temperature T n (° C.), the holding time t n (hr), and the cross-section reduction rate Rd n-1 (%) are adjusted so as to satisfy the formula (1) .
[Number 7]

[0085]
　When the soaking treatment is performed only once in the segregation reduction step and the composite treatment is not performed (that is, when n=1 and N=1), hot working is not performed in the segregation reduction step. Therefore, the cumulative area reduction rate Rd n-1 =Rd 0 is 0 (%). Therefore, based on the following equation obtained by substituting Rd 0 =0 in the equation (1) , the solidification cooling rate V R (° C./min), the soaking temperature T n (° C.), and the holding time t n (hr) Adjust.
[Number 8]

[0086]
　If the segregation reduction step (soaking treatment, or soaking treatment and combined treatment) is performed so as to satisfy Expression (1), a Ni-based alloy in which Mo segregation is suppressed can be manufactured. After performing the segregation reducing step, other steps such as a hot working step, a cold working step, and a cutting step may be further performed.
[0087]
　[Ni-based alloy according to the
　present embodiment ] The shape of the Ni-based alloy according to the present embodiment is not particularly limited. The Ni-based alloy manufactured by the above manufacturing method is, for example, a billet. The cross section (transverse cross section) perpendicular to the longitudinal direction of the Ni-based alloy may be circular, rectangular, or polygonal. The Ni-based alloy may be a pipe material or a solid material.
[0088]
　The chemical composition of the Ni-based alloy according to the present embodiment is% by mass, C: 0.100% or less, Si: 0.50% or less, Mn: 0.50% or less, P: 0.015% or less, S: : 0.0150% or less, Cr: 20.0 to 23.0%, Mo: 8.0 to 10.0%, one or more elements selected from the group consisting of Nb and Ta: 3.150 to 4.150 %, Ti: 0.05 to 0.40%, Al: 0.05 to 0.40%, Fe: 0.05 to 5.00%, N: 0.100% or less, O: 0.1000% or less , Co: 0 to 1.00%, Cu: 0 to 0.50%, one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the balance Ni and impurities Become. That is, the chemical composition of the Ni-based alloy of the present embodiment is the same as the chemical composition of the Ni-based alloy material described above. In the Ni-based alloy of the present embodiment, the average concentration of Mo is 8.0% or more by mass% in the cross section perpendicular to the longitudinal direction of the Ni-based alloy, and the maximum value of Mo concentration is 11.0% by mass. % Or less, and the area ratio of the region where the Mo concentration is less than 8.0% by mass% is less than 2.0%. In the Ni-based alloy according to the present embodiment, Mo segregation is suppressed. Hereinafter, the Ni-based alloy of this embodiment will be described. In addition, regarding the content (including the preferable upper limit and the preferable lower limit) of each element of the chemical composition of the Ni-based alloy of the present embodiment and the action and effect, the chemical composition of the Ni-based alloy material in the above-described Ni-based alloy manufacturing method is used. It is the same as the content of each element (including the preferable upper limit and the preferable lower limit) and the action and effect.
[0089]
　[Suppression of Mo Segregation] In
　the Ni-based alloy of the present embodiment, Mo segregation is suppressed. Specifically, in a cross section (hereinafter referred to as a cross section) perpendicular to the longitudinal direction of the Ni-based alloy, the average concentration of Mo is 8.0% or more by mass% and the maximum value of the Mo concentration is 11% by mass. Further, the area ratio of the region where the Mo concentration is less than 8.0% in mass% is less than 2.0%.
[0090]
　The average concentration of Mo in the cross section of the Ni-based alloy, the maximum value of Mo concentration, and the region where the Mo concentration is less than 8.0% by mass are obtained by the following method. In the present specification, a region where the Mo concentration is less than 8.0% by mass% is also referred to as a “Mo low concentration region”.
[0091]
　A sample is taken from the cross section of the Ni-based alloy. Specifically, when the Ni-based alloy is a solid material having a rectangular cross section, the long side of the cross section is defined as the width W. When the cross section is a circular solid material (that is, a bar material), the diameter is defined as the width W. When the Ni-based alloy is a solid material, a sample is taken from the surface perpendicular to the width W direction in the width W direction from the W/4 depth position (W/4 depth position). On the other hand, when the Ni-based alloy is a pipe material, a sample is taken from the center position of the wall thickness. After mirror-polishing the surface corresponding to the cross section (observation surface) of the surface of the sample, the beam diameter is 10 μm, the scanning length is 2000 μm, and the irradiation time per point is 3000 ms in any one visual field in the observation surface. A line analysis is performed by an electron beam micro analyzer (EPMA: Electron Probe Micro Analyzer) with an irradiation pitch of 5 μm. In the scanning range of 2000 μm where the line analysis was performed, an average value of a plurality of Mo concentrations measured at a pitch of 5 μm, a maximum value of the Mo concentration among the measured Mo concentrations, and a minimum value of the Mo concentration are obtained. Furthermore, in the scanning length of 2000 μm, which is the measurement range, the total length of the range where the Mo concentration becomes less than 8.0% is continuous (range where two or more points are continuous) is obtained. The total length thus obtained is defined as the total length (μm) of the Mo low concentration region. Using the obtained total length of the Mo low concentration region, the Mo low concentration region ratio (%) is calculated by the following formula.
　Mo low concentration region ratio=Mo low concentration region total length (μm)/scan length (=2000 μm)×100
[0092]
　The Mo low-concentration region ratio obtained by the above formula is defined as "area ratio of region where Mo concentration is less than 8.0% by mass%". More specifically, in the cross section of the Ni-based alloy, a line diameter was measured by EPMA with a beam diameter of 10 μm, a scanning length of 2000 μm, an irradiation time per point: 3000 ms, and an irradiation pitch: 5 μm. The average concentration of Mo obtained at a pitch of 2000 μm and 5 μm is 8.0% or more by mass%, the maximum value of Mo concentration is 11.0% or less by mass%, and the Mo concentration is 2000 μm at a scanning length of 2000 μm. When the total length of the range in which the measurement points that are less than 8.0% are continuous (range in which two or more points are continuous) is defined as the Mo low-concentration region, the total length of the Mo low-concentration region with respect to the scanning length is defined. The ratio is less than 2.0%.
[0093]
　In the Ni-based alloy of the present embodiment, the average value of Mo concentration obtained by the above measurement is 8.0% or more by mass %, and the maximum value of Mo concentration is 11.0% or less by mass %. Furthermore, the ratio of the region where the Mo concentration is less than 8.0% in mass%, that is, the Mo low concentration region ratio is less than 2.0%.
[0094]
　As described above, in the Ni-based alloy of this embodiment, Mo segregation is suppressed. As a result, the corrosion resistance of the Ni-based alloy is enhanced. Specifically, intergranular corrosion and stress corrosion cracking can be suppressed as follows.
[0095]
　[Reduction of Intergranular Corrosion] In the
　Ni-based alloy according to the present embodiment, the corrosion rate is 0.075 mm/month or less when the corrosion test specified by ASTM G28 Method A is performed. The corrosion test based on ASTM G28 Method A is performed by the following method. A test piece is taken from any position of the Ni-based alloy. The size of the test piece is, for example, 40 mm×10 mm×3 mm. Measure the weight of the test piece before starting the corrosion test. After the measurement, the test piece is immersed for 120 hours in a solution (50% sulfuric acid/ferric sulfate solution) in which 25 g of ferric sulfate is added to 600 mL of a 50% by mass sulfuric acid solution. After 120 hours, the weight of the test piece after the test is measured. The test weight loss is determined based on the measured change in the weight of the test piece. The test weight loss is converted to a volume loss using the density of the test piece. The volume reduction is divided by the surface area of ​​the test piece to obtain the corrosion depth. The corrosion depth is divided by the test time to obtain the corrosion rate (mm/month).
[0096]
　In the Ni-based alloy of the present embodiment, the corrosion rate is 0.075 mm/month or less, intergranular corrosion is suppressed, and the corrosion resistance is excellent.
[0097]
　[Suppression of Stress Corrosion Cracking]
　The Ni-based alloy of the present embodiment not only has excellent intergranular corrosion resistance, but also can suppress stress corrosion cracking. Specifically, a low strain rate tensile test piece is sampled from an arbitrary position of the Ni-based alloy. The length of the low strain rate tensile test piece is 80 mm, the parallel part length is 25.4 mm, and the parallel part diameter is 3.81 mm. The longitudinal direction of the low strain rate tensile test piece is parallel to the longitudinal direction of the Ni-based alloy. While immersing the low strain rate tensile test piece in a 25% NaCl+0.5% CH 3 COOH aqueous solution saturated with 0.7 MPa of hydrogen sulfide and having a pH of 2.8 to 3.1 and 232° C. , a strain rate of 4.0× A low strain rate tensile test (SSRT) is performed at 10 -6 S -1 to break the test piece. In the test piece after the test, it is visually confirmed whether or not cracks (sub-cracks) are generated in the parts other than the fractured part. If a crack has occurred, it is determined that stress corrosion cracking has occurred. If no crack is confirmed, it is determined that stress corrosion cracking has not occurred. In the Ni-based alloy produced by the present production method, cracks are not confirmed in the low strain rate tensile test, and stress corrosion cracking is suppressed. Therefore, the Ni-based alloy manufactured by the manufacturing method of this embodiment has excellent corrosion resistance.
[0098]
　As described above, the Ni-based alloy manufactured by the manufacturing method of the present embodiment has the above-described chemical composition, and further, the average concentration of Mo is 8.0% or more by mass %, and the maximum value of Mo concentration is Is 11.0% or less by mass %. Further, the area ratio of the region where the Mo concentration is less than 8.0% in mass% (Mo low concentration region) is less than 2.0%. Therefore, the Ni-based alloy of this embodiment has excellent corrosion resistance. Specifically, the corrosion rate obtained by the Method A test of ASTM G28 is 0.075 mm/month or less, and the corrosion resistance (intergranular corrosion resistance) is excellent. Furthermore, in the SSRT test, cracks do not occur in regions other than the fractured part of the test piece, and the corrosion resistance (specifically, SCC resistance) is excellent.
[0099]
　[Production Method
　of Ni-Based Alloy of Present Embodiment ] The production method of the Ni-based alloy of the present embodiment is not particularly limited as long as the Ni-based alloy having the above-described configuration can be produced. However, the above-described Ni-based alloy production method is a suitable example for producing the Ni-based alloy of the present embodiment. Specifically, the manufacturing method of the Ni-based alloy of the present embodiment includes the above-mentioned casting step and the above-mentioned segregation reduction step. In the casting process described above, a liquid alloy is cast, and the chemical composition is C: 0.100% or less, Si: 0.50% or less, Mn: 0.50% or less, P: 0.015 in mass%. % Or less, S: 0.0150% or less, Cr: 20.0 to 23.0%, Mo: 8.0 to 10.0%, and one or more elements selected from the group consisting of Nb and Ta: 3.150. Up to 4.150%, Ti: 0.05 to 0.40%, Al: 0.05 to 0.40%, Fe: 0.05 to 5.00%, N: 0.100% or less, O:0 1000% or less, Co:0 to 1.00%, Cu:0 to 0.50%, one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the balance A Ni-based alloy material composed of Ni and impurities is manufactured. In the segregation reduction step, (I) one or more soaking treatments or (II) one or more soaking treatments and one or more combined treatments are applied to the Ni-based alloy material produced in the casting step. Is carried out and the formula (1) is satisfied.
[Numerical equation 9]

[0100]
　According to the above-mentioned manufacturing method, the chemical composition in mass% is C: 0.100% or less, Si: 0.50% or less, Mn: 0.50% or less, P: 0.015% or less, S: 0.0150. % Or less, Cr: 20.0 to 23.0%, Mo: 8.0 to 10.0%, one or more elements selected from the group consisting of Nb and Ta: 3.150 to 4.150%, Ti: 0.05-0.40%, Al: 0.05-0.40%, Fe: 0.05-5.00%, N: 0.100% or less, O: 0.1000% or less, Co:0 1 to more than 1.00%, Cu: 0 to 0.50%, one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the balance Ni and impurities. In a cross section perpendicular to the longitudinal direction of the alloy, the average concentration of Mo is 8.0% or more by mass%, the maximum value of Mo concentration is 11.0% or less by mass%, and the Mo concentration is% by mass. It is possible to manufacture a Ni-based alloy in which the area ratio of the area of ​​less than 8.0% is less than 2.0%.
[0101]
　FIG. 4 is a diagram showing the relationship between F1 and the corrosion rate in the Ni-based alloy having the chemical composition of the present invention. Here, F1 is an expression obtained by subtracting the left side of expression (1) from the right side of expression (1), and is defined as follows.
[Number 10]

[0102]
　Referring to FIG. 4, when F1 is less than 0, that is, when the manufacturing conditions in the segregation reduction step do not satisfy the formula (1), the corrosion rate is significantly higher than 0.075 mm/month, and the F1 value fluctuates. However, the corrosion rate does not fluctuate much. On the other hand, when F1 is 0 or more, that is, when the manufacturing conditions in the segregation reducing step satisfy the formula (1), the corrosion rate is significantly reduced to 0.075 mm/month or less. Therefore, the Ni-based alloy manufactured under the manufacturing conditions satisfying the formula (1) has excellent corrosion resistance. The method for manufacturing the Ni-based alloy of the present embodiment is not particularly limited as long as the Ni-based alloy having the above-described configuration can be manufactured. The above-described method for manufacturing the Ni-based alloy using the formula (1) is a suitable example for manufacturing the Ni-based alloy of the present embodiment.
[0103]
　[Preferable Form (1) of
　Ni-Based Alloy of First Embodiment] In the Ni-based alloy, it is known that finer crystal grains are superior in strength and ductility. Preferably, in the Ni-based alloy of this embodiment, the grain size number according to ASTM E112 is 0.0 or more. If the grain size number is 0.0 or more, it indicates that the solidification structure is eliminated and the microstructure is substantially crystallized in the Ni-based alloy. The preferred grain size number is 0.5 or more, and more preferably 1.0 or more. The upper limit of the grain size number is not particularly limited.
[0104]
　The method for measuring the grain size number in the Ni-based alloy of this embodiment is as follows. The Ni-based alloy is divided into five equal parts in the axial direction (longitudinal direction), and the axial center position of each section is specified. At the specified position of each section, four sampling positions are specified at a 90° pitch around the central axis of the Ni-based alloy. For example, when the Ni-based alloy is a pipe material, the sampling positions are specified at a pitch of 90 degrees in the pipe circumferential direction. A sample is collected from the specified sample collection position. When the Ni-based alloy is a pipe material, a sample is taken from the center position of the wall thickness of the specified sample taking position. When the Ni-based alloy is a rod material or an alloy material having a rectangular cross section, a sample is taken from the W/4 depth position at the selected sampling position. The observation surface of the sample is a cross section perpendicular to the axial direction of the Ni-based alloy, and the area of ​​the observation surface is 40 mm 2 .
[0105]
　According to the above method, 4 samples in each section and 20 samples in all sections are collected. The observation surface of the collected sample is corroded with glyceresia, a curling reagent, a marble reagent, or the like to expose the crystal grain boundaries on the surface. The corroded observation surface is observed and the grain size number is determined according to ASTM E112.
[0106]
　The average value of the grain size numbers obtained from 20 samples is defined as the grain size number according to ASTM E112 in the Ni-based alloy.
[0107]
　The Ni-based alloy of the present embodiment, which has a crystal grain size number of 0.0 or more according to ASTM E112, is manufactured by the following method, for example.
[0108]
　In the method for manufacturing a Ni-based alloy, which includes the above-described casting step and segregation reduction step, the composite treatment is performed at least once in the segregation reduction step. In the composite treatment, hot working is performed at least once on the Ni-based alloy material heated to 1000 to 1300° C. at a cross-section reduction rate of 35.0% or more. The hot working under these conditions is called "specific hot working". If the specific hot working is performed at least once in the segregation reducing step, the grain size number according to ASTM E112 of the manufactured Ni-based alloy becomes 0.0 or more. The cross-section reduction rate in this item means not the cumulative cross-section reduction rate, but the cross-section reduction rate in one hot working.
[0109]
　FIG. 5A is a microstructure observation of a Ni-based alloy produced by performing hot working once on a Ni-based alloy material having the above chemical composition at a cross-sectional reduction rate of 44.6% in the segregation reduction step. It is an image. FIG. 5B is a microstructure observation of a Ni-based alloy produced by performing hot working once on the Ni-based alloy material having the above-described chemical composition at a cross-sectional reduction rate of 31.3% in the segregation reduction step. It is an image. In FIG. 5A, the grain size number according to ASTM E112 was 2.0, which was 0.0 or more. On the other hand, in FIG. 5B, the grain size number according to ASTM E112 was −2.0, which was less than 0.0. As described above, in the segregation reduction step, hot working is performed at least once on the Ni-based alloy material having the above-described chemical composition at a cross-section reduction rate of 35.0% or more, thereby obtaining a crystal conforming to ASTM E112. A Ni-based alloy having a grain size number of 0.0 or more can be produced. The specific hot working may be performed multiple times.
[0110]
　[Preferred Form (2) of Ni-Based Alloy of First Embodiment]
　Preferably, in the Ni-based alloy of the present embodiment, the total number of Nb carbonitrides having a maximum length of 1 to 100 μm is further included in the Ni-based alloy. Is 4.0×10 −2 pieces/μm 2 or less.
[0111]
　Here, in the present specification, “Nb carbonitride” is a concept including Nb carbide, Nb nitride, and Nb carbonitride, and the total content of Nb, C, and N is 90% by mass. The above precipitates are meant. Further, the maximum length of Nb carbonitride means the maximum length of the straight lines connecting at any two points on the interface (boundary) between the Nb carbonitride and the mother phase.
[0112]
　When the total number of coarse Nb carbonitrides is 4.0×10 −2 /μm 2 or less, the Nb carbonitride is sufficiently dissolved in the matrix. Therefore, the starting points of cracks during hot working are reduced, and hot workability is further enhanced.
[0113]
　The total number of coarse Nb carbonitrides can be obtained by the following method. The Ni-based alloy is divided into five equal parts in the axial direction, and the central position in the axial direction of each section is specified. In each section, the sampling position is specified at a 90° pitch in the pipe circumferential direction at the axial center position. A sample is collected from the specified sample collection position. When the Ni-based alloy is a pipe material, a sample is taken from the center position of the wall thickness of the specified sample taking position. When the Ni-based alloy is a rod material or an alloy material having a rectangular cross section, a sample is taken from the W/4 depth position of the specified sample taking position. The observation surface of the sample is a cross section perpendicular to the axial direction of the Ni-based alloy. Nb carbonitrides are specified by EPMA (Electron Probe Micro Analyzer) in one arbitrary visual field (400 μm×400 μm) in each observation surface (20 in total). Specifically, the surface analysis of EPMA identifies a precipitate having a total content of Nb, C, and N of 90% or more, and defines the identified precipitate as Nb carbonitride. FIG. 6 is an EPMA image in an example of the one visual field. The precipitate 100 shown in white in FIG. 6 is Nb carbonitride. The maximum length of the specified Nb carbonitride is measured. As described above, the value of the maximum straight line among the straight lines connecting any two points on the interface between the Nb carbonitride and the parent phase is defined as the maximum length of the Nb carbonitride. After measuring the maximum length of each Nb carbide, an Nb carbonitride having a maximum length of 1 to 100 μm (coarse Nb carbonitride) is specified, and the total number of coarse Nb carbonitrides in all 20 fields of view is obtained. The total number of coarse Nb carbonitrides (number/μm 2 ) is determined based on the obtained total number .
[0114]
　The above Ni-based alloy having a maximum length of 1 to 100 μm and a total number of Nb carbonitrides of 4.0×10 −2 /μm 2 or less can be produced, for example, by the following manufacturing method. Can be manufactured.
[0115]
　A method for manufacturing a Ni-based alloy including the above-mentioned casting step and segregation reduction step, wherein in the segregation reduction step, a soaking treatment is carried out at least once at a soaking temperature of 1000 to 1300°C for 1.0 hour or more. .. The soaking treatment under these conditions is called "specific soaking treatment". If the specific soaking treatment is performed at least once in the segregation reducing step, the total number of Nb carbonitrides having a maximum length of 1 to 100 μm in the manufactured Ni-based alloy is 4.0×10 −2 /μm. It will be 2 or less. The specific soaking treatment may be performed multiple times.
[0116]
　[Preferred Form (3) of Ni-Based Alloy of First Embodiment] The
　above-mentioned Ni-based alloy further has a grain size number of 0.0 or more in accordance with ASTM E112, and is the largest in the Ni-based alloys. The total number of Nb carbonitrides having a length of 1 to 100 μm may be 4.0×10 −2 /μm 2 or less.
[0117]
　In this case, preferably, in the segregation reducing step, hot working is performed at least once at a cross-section reduction rate of 35.0% or more with respect to the Ni-based alloy material heated to 1000 to 1300° C., and In the segregation reducing step, soaking is performed at least once at a soaking temperature of 1000 to 1300° C. for 1.0 hour or more. That is, in the segregation reducing step, the specific hot working is performed at least once, and the specific soaking treatment is performed at least once.
[0118]
　[Second Embodiment]
　Preferably, the above Ni-based alloy further contains at least one element selected from the group consisting of Ca, Nd, and B in a content satisfying the formula (2).
　(Ca+Nd+B)/S≧2.0 (2)
　Here, the content of the corresponding element in atomic% (at %) is substituted for the element symbol in the formula (2).
[0119]
　Calcium (Ca), neodymium (Nd), and boron (B) all enhance the hot workability of the Ni-based alloy as described above. It is defined as F2=(Ca+Nd+B)/S. F2 is an index of hot workability. When the total content F2 of at least one selected from the group consisting of Ca, Nd, and B is 2.0 or more, that is, when F2 satisfies the formula (2), the Ni-based alloy having the above-described chemical composition In, further excellent hot workability can be obtained. Specifically, the drawing (breaking drawing) is 35.0% or more when the tensile test is performed at 900° C. in the air at a strain rate of 10/sec.
[0120]
　FIG. 7 is a diagram showing the relationship between F2 and the fracture drawing (%) obtained when the Ni-based alloy of the present embodiment is subjected to a tensile test at a strain rate of 10/sec at 900° C. in the atmosphere. is there. FIG. 7 was obtained by the test described in Example 2 below. With reference to FIG. 7, until F2 became 1.0, the fracture reduction at 900° C. did not change so much even if F2 increased. On the other hand, when F2 exceeds 1.0, the breaking reduction at 900° C. sharply increases as F2 increases, and when F2 is 2.0, it exceeds 35.0% and becomes about 50.0%. After that, the breakage reduction further increased with the increase of F2, but at F2 of 8.0 or more, the breakage reduction became almost constant at about 80.0%. That is, the curve in FIG. 7 had an inflection point near F2=1.0 to 2.0. From the above results, if F2 is 2.0 or more, a sufficient fracture reduction (35.% or more) can be obtained at 900°C. The preferable lower limit of F2 is 2.5, more preferably 3.0, and further preferably 3.5.
[0121]
　The upper limit of the total content (mass %) of Ca, Nd, and B in the Ni-based alloy is 0.5000% as in the first embodiment.
[0122]
　[Production Method of Ni-based Alloy of
　Second Embodiment ] The production method of Ni-based alloy of the second embodiment described above is particularly limited as long as the Ni-based alloy of the second embodiment having the above-described configuration can be produced. Not done. Preferably, the manufacturing method of the Ni-based alloy of the second embodiment is the same as the manufacturing method of the Ni-based alloy of the first embodiment.
[0123]
　Specifically, the manufacturing method of the Ni-based alloy of the second embodiment includes a casting step and a segregation reducing step. In the casting step, a liquid alloy is cast to produce a Ni-based alloy material having the above chemical composition and F2 satisfying the formula (2).
[0124]
　In the segregation reduction step,
　(I) soaking treatment or
　(II) soaking treatment and combined treatment
　is performed on the Ni-based alloy material produced in the casting step . In the segregation reducing step, soaking may be performed only once, or the composite treatment may be performed only once. Moreover, you may implement a composite process repeatedly in multiple times. A composite treatment may be performed after the soaking.
[0125]
　As described above, in the segregation reducing step, soaking treatment, or soaking treatment and combined treatment is performed. At this time, the soaking temperature T n (° C.), the holding time t n (hr), and the cross-section reduction rate Rd n-1 (%) are set so that the solidification cooling rate V R in the casting process satisfies the expression (1). adjust. [Numerical equation 11]

[0126]
　When the soaking treatment is performed only once in the segregation reduction step, hot working is not performed, and thus the cross-section reduction rate R d0 is 0 (%). Therefore, based on the following equation obtained by substituting R d0 =0% into the equation (1) , the solidification cooling rate V R (° C./min), the soaking temperature T n (° C.), and the holding time t n (hr ) Is adjusted.
[Number 12]

[0127]
　If the segregation reduction step (soaking treatment, or soaking treatment and combined treatment) is performed so as to satisfy Expression (1) for the Ni-based alloy material having the chemical composition that satisfies Expression (2), the second implementation A form of Ni-based alloy can be produced. After performing the segregation reducing step, other steps such as a hot working step, a cold working step, and a cutting step may be further performed.
[0128]
　In addition, in the manufacturing method of the Ni-based alloy of the second embodiment, after the Ni-based alloy material is manufactured in the casting step, the Ni-based alloy material is melted again, that is, so-called secondary melting is not performed. That is, in the present manufacturing method, it is preferable that after the casting step, the segregation reducing step is performed without performing the secondary melting in which the Ni-based alloy manufactured by the casting step is melted again.
[0129]
　In the Ni-based alloy of the second embodiment, Ca, Nd, B and the like generally combine with S in the steel material to form sulfides, so that the solid solution S concentration in the steel material (particularly the grain boundary) is increased. By reducing it, hot workability is improved. However, if secondary melting is performed on a Ni-based alloy material containing these elements, Ca, Nd, and B will be discharged from the Ni-based alloy material to the outside during the secondary melting. For example, if the electroslag remelting method (ESR) is applied as the secondary melting, Ca, Nd, and B are taken into the molten slag when the Ni-based alloy material is melted. As a result, Ca, Nd, and B are discharged from the Ni-based alloy material, and the chemical composition of the Ni-based alloy material after the secondary melting does not satisfy the formula (2). Similarly, if the vacuum arc remelting method (VAR) is applied as the secondary melting, when Ni-based alloy material is melted, Ca, Nd, and B, which are effective elements for improving hot workability, are melted during melting. The CO bubbles that are generated cause floating separation. As a result, Ca, Nd, and B are discharged from the Ni-based alloy material, and the chemical composition of the manufactured Ni-based alloy material after the secondary melting does not satisfy the formula (2). On the other hand, in this manufacturing method, as described above, the Ni-based alloy material is manufactured only by the primary melting without performing the secondary melting (omitting the secondary melting). Therefore, in the Ni-based alloy, at least one element of Ca, Nd, and B can be maintained at a content satisfying the formula (2), and hot workability can be improved. Furthermore, since the above-described segregation reducing step is performed on the Ni-based alloy material, Mo segregation can also be suppressed.
[0130]
　[Preferred Form (1) of Ni-based Alloy of
　Second Embodiment] As in the first embodiment, preferably, in the Ni-based alloy of the second embodiment, the grain size number according to ASTM E112 is used. Is 0.0 or more.
[0131]
　When the grain size number in the Ni-based alloy is set to 0.0 or more, preferably, in the segregation reduction step, the cross-section reduction is 35.0% or more with respect to the Ni-based alloy material heated to 1000 to 1300°C. Hot working (specific hot working) at least once. If the specific hot working is performed at least once in the segregation reducing step, the grain size number according to ASTM E112 of the manufactured Ni-based alloy becomes 0.0 or more. The specific hot working may be performed multiple times.
[0132]
　[Preferred Form (2) of Ni-Based Alloy of Second Embodiment] As in
　the first embodiment, preferably, in the Ni-based alloy of the second embodiment, the maximum length in the Ni-based alloy is The total number of Nb carbonitrides having a grain size of 1 to 100 μm is 4.0×10 −2 /μm 2 or less. In this case, hot workability is further enhanced.
[0133]
　In the Ni-based alloy, when the total number of Nb carbonitrides having a maximum length of 1 to 100 μm is 4.0×10 −2 /μm 2 or less, preferably 1000 to 1300° C. in the segregation reduction step. The soaking process (specific soaking process) in which the soaking temperature is maintained for 1.0 hour or more is performed at least once. When the specific soaking treatment is performed at least once, the total number of Nb carbonitrides having a maximum length of 1 to 100 μm in the manufactured Ni-based alloy becomes 4.0×10 −2 /μm 2 or less. The specific soaking treatment may be performed multiple times.
[0134]
　[Preferred Form (3) of Ni-based Alloy of Second Embodiment] The
　above-mentioned Ni-based alloy further has a grain size number of 0.0 or more in accordance with ASTM E112, and is the largest in the Ni-based alloys. The total number of Nb carbonitrides having a length of 1 to 100 μm may be 4.0×10 −2 /μm 2 or less.
[0135]
　In this case, preferably, in the segregation reducing step, hot working is performed at least once at a cross-section reduction rate of 35.0% or more with respect to the Ni-based alloy material heated to 1000 to 1300° C., and In the segregation reducing step, soaking is performed at least once at a soaking temperature of 1000 to 1300° C. for 1.0 hour or more.
Example 1
[0136]
　The liquid alloy was melted by electric furnace melting. The melted liquid alloy was solidified by a continuous casting method or an ingot making method to manufacture a Ni-based alloy material (cast piece or ingot) having the chemical composition shown in Table 1. The Ni-based alloy materials of Test Nos. 1 to 5 and 8 were cast pieces. The cross section of the cast slab perpendicular to the longitudinal direction was 600×285 mm. The Ni-based alloy materials of Test Nos. 6 and 7 were ingots. The cross section of the ingot perpendicular to the longitudinal direction was 500 mm×500 mm.
[0137]
[table 1]

[0138]
　Against a Ni-based alloy material produced (slab), by the following method, secondary dendrite arm spacing D II by measuring the solidification cooling rate of the Ni-base alloy material of each test number V R (° C. / min ) Was asked. Specifically, a sample was taken at the W/4 depth position of the cross section perpendicular to the longitudinal direction at the central position in the longitudinal direction of the Ni-based alloy material. After mirror-polishing the surface of the sample parallel to the above-mentioned cross section, it was etched with aqua regia. The etched surface was observed with a 400x optical microscope to produce a photographic image of a 200 [mu]m x 200 [mu]m viewing field. Using the obtained photographic image, the dendrite secondary arm interval (μm) at any 20 points within the observation visual field was measured. The average of the measured dendrite secondary arm spacing was defined as the dendrite secondary arm spacing D II (μm). The solidification cooling rate V R (° C./min) was obtained by substituting the obtained dendrite secondary arm interval D II into the formula (A) . 　D II =182V R -0.294　(A)
[0139]
　Further, the segregation reduction process shown in Table 2 was performed on the Ni-based alloys of test numbers 2 to 5, 7 and 8. In test numbers 2 and 3, soaking treatment was performed once as a segregation reducing step. In test number 4, soaking was carried out (soaking 1), then hot rolling was carried out (hot working 1), and soaking was carried out again after hot rolling (soaking 2). In Test No. 5, soaking treatment 1, hot working 1, soaking treatment 2, hot working 2 (hot rolling), soaking treatment 3 were performed in this order. In test number 7, soaking treatment 1 was performed. In Test No. 8, soaking treatment 1, hot working 1, and soaking treatment 2 were performed in this order. That is, in test numbers 2, 3 and 7, only one soaking treatment was performed. Test No. 4 carried out one soaking treatment and one composite treatment. Test No. 5 carried out one soaking treatment and two composite treatments. Test No. 8 carried out the composite treatment once. In addition, in the test numbers 1 and 6, the segregation reduction process was not implemented.
[0140]
　In addition, in each of the test numbers 4, 5 and 8, a solid material having a circular cross section (that is, a round bar material) was manufactured. In all of the test numbers 4, 5, and 8, after the soaking treatment 1 was carried out, the hot working 1 was carried out immediately. In Test No. 5, after the soaking treatment 2 was carried out, the hot working 2 was carried out immediately.
[0141]
[Table 2]

[0142]
　The soaking temperature (° C.) and soaking time (hr) in each soaking treatment 1 to 3 are shown in Table 2. The cross-section reduction rate Rd n-1 (%) in each of the hot workings 1 and 2 is as shown in Table 2. For each test number, F1 (=right side of expression (1)-left side of expression (1)) was obtained. Table 2 shows the obtained F1.
[0143]
　[Evaluation Test]
　[Mo Concentration Measurement Test]
　A sample for Mo concentration measurement test was taken in a cross section (transverse cross section) perpendicular to the longitudinal direction of the Ni-based alloy of each test number after the segregation reduction step. Specifically, in each test number, a sample was taken from the W/4 depth position of the cross section, and the surface (observation surface) corresponding to the cross section of the sample surface was mirror-polished and then In any one field of view, line analysis by EPMA was performed with a beam diameter of 10 μm, a scanning length of 2000 μm, an irradiation time per point: 3000 ms, and an irradiation pitch: 5 μm. An average value of a plurality of Mo concentrations measured at a pitch of 5 μm in a scanning range of 2000 μm where the line analysis was performed, and a maximum value of the Mo concentrations of the plurality of measured Mo concentrations were obtained. Furthermore, in the scan length of 2000 μm, which is the measurement range, the total length of the range where the Mo concentration is less than 8.0% is continuous (the range where two or more points are continuous) (that is, the Mo low concentration is low). The total area length) was calculated. Using the obtained total length of the Mo low concentration region, the Mo low concentration region ratio (%) was calculated by the following formula.
　Mo low concentration area ratio=Mo low concentration total length (μm)/scan length (=2000 μm)×100
[0144]
　[Low Strain Rate Tensile Test (SSRT)] From the
　same position as the sampling position in the Mo concentration measurement test on the cross section perpendicular to the longitudinal direction of the Ni-based alloy of each test number after the segregation reduction step, the low strain rate tensile test A piece was taken. The length of the low strain rate tensile test piece was 80 mm, the parallel portion length was 25.4 mm, and the parallel portion diameter was 3.81 mm. The longitudinal direction of the low strain rate tensile test piece was parallel to the longitudinal direction of the Ni-based alloy. While immersing the low strain rate tensile test piece in a 25% NaCl+0.5% CH 3 COOH aqueous solution saturated with 0.7 MPa of hydrogen sulfide and having a pH of 2.8 to 3.1 and 232° C. , a strain rate of 4.0× A low strain rate tensile test (SSRT) was carried out at 10 -6 S -1 to break the test piece. In the test piece after the test, it was visually confirmed whether or not cracks (sub-cracks) were generated in parts other than the fractured part. When cracks were found, it was judged that stress corrosion cracking had occurred, and when cracks were not confirmed, stress corrosion cracking did not occur and it was judged that excellent corrosion resistance (SCC resistance) was obtained.
[0145]
　[Grain Boundary Corrosion Test] A
　test piece was sampled from the same sample sampling position in the Mo concentration measurement test in a cross section perpendicular to the longitudinal direction of the Ni-based alloy of each test number after the segregation reduction step. The size of the test piece was 40 mm×10 mm×3 mm. A corrosion test specified by ASTM G28 Method A was performed using the collected test piece. Specifically, the weight of the test piece before the start of the corrosion test was measured. After the measurement, the test piece was immersed in a 50% sulfuric acid/ferric sulfate solution for 120 hours. After 120 hours, the weight of the test piece after the test was measured. The corrosion rate (mm/month) of each test piece was obtained from the measured change in the weight of the test piece.
[0146]
　[Test Results] The
　test results are shown in Table 2. With reference to Table 2, in Test Nos. 3 to 5, 7 and 8, the chemical composition of the Ni-based alloy was appropriate, F1 was 0 or more, and the formula (1) was satisfied in the segregation reduction step. Therefore, in the cross section perpendicular to the longitudinal direction of the Ni-based alloy, the average concentration of Mo is 8.0% or more by mass%, the maximum value of the Mo concentration is 11.0% or less by mass%, and further, Mo The area ratio (Mo low concentration region ratio) of the region having a concentration of less than 8.0% by mass% was less than 2.0%. As a result, no crack was confirmed in the SSRT test. Further, the corrosion rate was 0.075 mm/month or less, which showed excellent corrosion resistance. In the Ni-based alloys of Test Nos. 3 to 5, 7, and 8, the total number of Nb carbonitrides having a maximum length of 1 to 100 μm was 4.0×10 −2 /μm 2 or less.
[0147]
　Furthermore, in test numbers 4, 5 and 8, in the segregation reducing step, hot working was performed before the final soaking treatment. As a result, the corrosion rate was lower than that of Test No. 3 in which hot working was not performed before soaking, and the corrosion rate was 0.055 mm/month or less.
[0148]
　On the other hand, in Test Nos. 1 and 6, after the Ni-based alloy material was manufactured by the casting process, the segregation reduction process was not performed. Therefore, in the cross section perpendicular to the longitudinal direction of the Ni-based alloy, the maximum Mo concentration exceeds 11.0% by mass% and the area ratio (Mo The low concentration area ratio) was 2.0% or more. As a result, cracks were confirmed in the SSRT test. Furthermore, the corrosion rate exceeded 0.075 mm/month.
[0149]
　In the test number 2, although the soaking treatment was performed in the segregation reduction step, F1 was less than 0, and the formula (1) was not satisfied. Therefore, the Mo low concentration region ratio was 2.0% or more. As a result, cracks were confirmed in the SSRT test. Furthermore, the corrosion rate exceeded 0.075 mm/month.
Example 2
[0150]
　The liquid alloy produced by melting in an electric furnace was solidified by a continuous casting method or an ingot making method to manufacture a Ni-based alloy material (cast piece or ingot) having the chemical composition shown in Table 3. The Ni-based alloy materials of test numbers 9 to 21 were cast pieces, and the cross section (transverse section) perpendicular to the longitudinal direction of the cast pieces was 600×285 mm. In the column F2 in Table 3, the F2 value (=(Ca+Nd+B)/S) of each test number is described. In addition, the blank part in Table 3 shows that the content of the corresponding element was less than the detection limit.
[0151]
[Table 3]

[0152]
　Against a Ni-based alloy material produced (slab) by the method described above, secondary dendrite arm spacing D II by measuring the solidification cooling rate of the Ni-base alloy material of each test number V R (° C. / min ) Was asked. As a result, as shown in Table 4, the solidification cooling rate V R was 5 (° C./min) in all test numbers .
[0153]
[Table 4]

[0154]
　The segregation reduction step was performed on the Ni-based alloy of each test number. Specifically, in test numbers 9 and 11, the soaking treatment was performed only once, and the hot working step was not performed. The soaking temperature of the soaking treatment was 1200° C., and the holding time was 96 hours. As a result, each of F1 was 0.06, which satisfied the formula (1).
[0155]
　In each of test numbers 10 and 12 to 18, soaking treatment was carried out (soaking treatment 1), then hot rolling was carried out (hot working 1), and soaking treatment was carried out again after hot rolling (soaking treatment). 2). The soaking temperature in soaking treatment 1 was 1200°C, and the holding time was 48 hours. The cross-section reduction rate in hot working 1 was 47.3%. The soaking temperature in soaking heat treatment 2 was 1200°C, and the holding time was 24 hours. As a result, F1 (=right side of expression (1)−left side of expression (1)) was 0.33, which satisfied expression (1).
[0156]
　In test numbers 19 to 21, soaking treatment 1, hot working 1, soaking treatment 2, hot working 2, soaking treatment 3 were performed in this order. The soaking temperature in soaking treatment 1 was 1200°C, and the holding time was 48 hours. The cumulative area reduction rate in hot working 1 was 47.3%. The soaking temperature in soaking heat treatment 2 was 1200°C, and the holding time was 24 hours. The cumulative area reduction rate in hot working 2 was 85.0%. The soaking time in soaking treatment 3 was 1200°C, and the holding time was 0.08 hours. As a result, each of F1 was 0.38, which satisfied the formula (1).
[0157]
　Through the above steps, Ni-based alloys of test numbers 9 to 21 were manufactured. In Test Nos. 9 to 21, no secondary melting was performed on the Ni-based alloy material after the casting process. The Ni-based alloys of Test Nos. 9 and 11 were cast pieces, and the Ni-based alloys of Test Nos. 10 and 12 to 21 were solid materials having a circular cross section (that is, round bar materials). In Test Nos. 10 and 12 to 21, after the soaking treatment 1 was carried out, the hot working 1 was carried out immediately. In test numbers 19 to 21, after the soaking treatment 2 was carried out, the hot working 2 was carried out immediately.
[0158]
　[Hot Workability Evaluation Test] The
　following tensile tests were performed using the Ni-based alloys of the respective test numbers. Tensile test pieces were taken from the Ni-based alloy. The tensile test piece corresponded to JIS standard No. 14A test piece. For each test number, a tensile test piece was taken from the W/4 depth position of the cross section. The tensile test piece was heated to 900°. Using a tensile test piece at 900° C., a tensile test was carried out in the atmosphere at a strain rate of 10/sec to measure the breaking reduction (%). If the breaking reduction was 35.0% or more, it was judged that the hot workability was excellent. The measurement results are shown in Table 3.
[0159]
　[Test Results]
　Referring to Table 3, all of Test Nos. 9 to 21 satisfied the formula (1). Therefore, in the cross section perpendicular to the longitudinal direction of the Ni-based alloy, the average concentration of Mo is 8.0% or more by mass% and the maximum value of Mo concentration is 11.0% or less by mass%. The area ratio of the region where the concentration was less than 8.0% by mass% was less than 2.0%. As a result, no crack was confirmed in the SSRT test. Further, the corrosion rate was 0.075 mm/month or less, which showed excellent corrosion resistance. In the Ni-based alloys of test numbers 9 to 21, the total number of Nb carbonitrides having a maximum length of 1 to 100 μm was 4.0×10 −2 /μm 2 or less.
[0160]
　Furthermore, in Test Nos. 11, 12, and 16 to 20, the chemical composition was appropriate, F2 was 2.0 or more, and the formula (2) was satisfied. Therefore, the breakage reductions were all 35.0% or more (more specifically, 45.0% or more), indicating excellent hot workability.
Example 3
[0161]
　The grain size numbers of the Ni-based alloys of Test No. 5 of Example 1 and Test No. 12 of Example 2 were determined by the following method. The Ni-based alloy was divided into five equal parts in the axial direction, and the axial center position of each section was specified. In each section, the sampling position was specified at a 90° pitch around the axis (around the longitudinal direction) at the central position in the axial direction. A sample was collected from the W/4 depth position of the specified sampling position. The observation surface of the sample was a cross section perpendicular to the axial direction of the Ni-based alloy, and the area of ​​the observation surface was 40 mm 2 . By the above method, 4 samples were collected in each section and 20 samples were collected in all sections. The observation surface of the collected sample was corroded using a curling reagent to expose the crystal grain boundaries on the surface. The corroded observation surface was observed, and the crystal grain size number was determined according to ASTM E112. The average value of the crystal grain size numbers obtained from 20 samples was defined as the crystal grain size number according to ASTM E112 in the Ni-based alloy.
[0162]
　As a comparative example, a Ni-based alloy material of test number 22 having the chemical composition shown in Table 5 was prepared. The Ni-based alloy material was a slab, and the cross section perpendicular to the longitudinal direction of the slab was 600×285 mm. The chemical composition of test number 22 was the same as the chemical composition of test number 5.
[0163]
[Table 5]

[0164]
　For the Ni-based alloy material (cast slab) of test number 22, the dendrite secondary arm interval D II was measured by the same method as in Example 1, and the solidification cooling rate V R of the Ni-based alloy material of each test number was measured. (°C/min) was determined. As a result, the solidification cooling rate V R was 5° C./min as shown in Table 6.
[0165]
[Table 6]

[0166]
　The segregation reduction process shown in Table 6 was performed on the Ni-based alloy material of test number 22. As compared with the manufacturing conditions of Test No. 5, the cross-section reduction rate in the first hot working was 31.3%. The cumulative cross-section reduction rate in the second hot working was 62.6%, and the cross-section reduction rate in the second hot working was 31.3%. That is, in the test number 22, the cross-sectional reduction rate in each hot working was less than 35.0%. Also for the test number 22, the crystal grain size number was obtained by the same method as the test number 5.
[0167]
　As a result of obtaining the crystal grain size number, in the test number 5, the crystal grain size number according to ASTM E112 was 0.0 or more (2.0), and in the test number 12, the crystal grain size number according to ASTM E112 was 0.0. Became. On the other hand, in the test number 22, the crystal grain size number according to ASTM E112 was less than 0.0 (−2.0).
Example 4
[0168]
　The total number of coarse Nb carbonitrides of the Ni-based alloy of Test No. 4 of Example 1 was determined by the following method. The Ni-based alloy was divided into five equal parts in the axial direction, and the axial center position of each section was specified. In each section, the sampling position was specified at a 90° pitch around the axis (around the longitudinal direction) at the central position in the axial direction. A sample was collected from the center position of the wall thickness of the specified sampling position. The observation surface of the sample was a cross section perpendicular to the axial direction of the Ni-based alloy. Nb carbonitrides were specified by EPMA in one arbitrary visual field (400 μm×400 μm) in each observation surface (20 pieces in total). The maximum length of the specified Nb carbonitride was measured. As described above, the maximum straight line value among the straight lines connecting any two points on the interface between the Nb carbonitride and the parent phase was defined as the maximum length of the Nb carbonitride. After measuring the maximum length of each Nb carbide, an Nb carbonitride having a maximum length of 1 to 100 μm (coarse Nb carbonitride) was specified, and the total number of coarse Nb carbonitrides in all 20 fields of view was determined. The total number of coarse Nb carbonitrides (number/μm 2 ) was determined based on the obtained total number .
[0169]
　As a comparative example, a Ni-based alloy of test number 23 shown in Table 7 was prepared. The Ni-based alloy material was a slab, and the cross section perpendicular to the longitudinal direction of the slab was 600×285 mm. The chemical composition of test number 23 was the same as the chemical composition of test number 4.
[0170]
[Table 7]

[0171]
　The segregation reduction process shown in Table 8 was performed on the Ni-based alloy material of test number 23. Specifically, in test number 23, the first soaking treatment was performed at the same temperature as in test number 4 (soaking treatment 1), and then hot rolling was performed at the same cross-section reduction rate as in test number 4 (hot After the hot working 1) and hot rolling, the second soaking treatment was performed again at the same temperature as the test number 4 (soaking treatment 2). However, the soaking time in each of soaking heat treatment 1 and soaking heat treatment 2 was 50 minutes (0.83 hours), which was less than 1 hour. Also in Test No. 23, as in Test No. 4, the total number of coarse Nb carbonitrides was determined.
[0172]
[Table 8]

[0173]
　Further, the Ni-based alloys of Test No. 4 and Test No. 23 were subjected to a hot workability evaluation test in the same manner as in Example 2 to determine the breaking reduction (%).
[0174]
　The total number of coarse Nb carbonitrides was 4.0×10 −2 pieces/μm 2 or less in test number 4, but exceeded 4.0×10 −2 pieces/μm 2 in test number 23 . As a result, in the test number 4, the breaking reduction exceeded 35.0%, whereas in the comparative example, the breaking reduction was less than 35.0%.
[0175]
　The embodiments of the present invention have been described above. However, the above-described embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.
The scope of the claims
[Claim 1]
　A liquid alloy is cast and has a
　chemical composition of mass%
　C: 0.100% or less,
　Si: 0.50% or less,
　Mn: 0.50% or less,
　P: 0.015% or less,
　S:0. 0.0150% or less,
　Cr: 20.0 to 23.0%,
　Mo: 8.0 to 10.0%,
　one or more elements selected from the group consisting of Nb and Ta: 3.150 to 4.150%,
　Ti: 0.05 to 0.40%,
　Al: 0.05 to 0.40%,
　Fe: 0.05 to 5.00%,
　N: 0.100% or less,
　O: 0.1000% or less,
　Co : 0 to 1.00%,
　Cu: 0 to 0.50%,
　one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the
　balance Ni consisting of Ni and impurities A casting step for producing a
　base alloy material, and a
　soaking treatment for the Ni-based alloy material produced by the casting step , or the
　soaking treatment, and after the soaking treatment, after hot working and after hot working Combined treatment including soaking of
　And a segregation reduction step that satisfies the formula (1)
　.
[

　Equation 1] Here, each symbol in the formula (1) is as follows.
　V R : solidification cooling rate (° C./min) of the liquid alloy in the casting step
　T n : soaking temperature (° C.) in the n-th soaking process
　t n : at the soaking temperature in the n-th soaking process Holding time (hr)
　Rd n-1 : Cumulative area reduction rate (%) of the Ni-based alloy material before the n-th soaking treatment
　N: Total number of soaking treatments
[Claim 2]
　A method of producing a Ni based alloy according to claim 1,
　wherein the soaking temperature is 1000 ~ 1300 °
　C., A method of producing a Ni based alloy.
[Claim 3]
　The method for producing a Ni-based alloy according to claim 2,
　wherein, in the segregation reducing step, the
　composite treatment is performed once or more, and the Ni-based alloy material heated to 1000 to 1300° C. A
　method for manufacturing a Ni-based alloy, wherein hot working is performed at least once with a cross-section reduction rate of 35.0% or more .
[Claim 4]
　The method for producing a Ni-based alloy according to claim 2 or 3,
　wherein in the segregation reducing step, the
　soaking treatment for holding at the soaking temperature of 1000 to 1300°C for 1.0 hour or more is performed at least once. A method for producing a Ni-based alloy, which is performed.
[Claim 5]
　The method for producing a Ni-based alloy according to any one of claims 1 to 4,
　wherein the chemical composition includes at
　least one element selected from the group consisting of Ca, Nd, and B, A
　method for producing a Ni-based alloy , the content of which satisfies the formula (2) .
　(Ca+Nd+B)/S≧2.0 (2)
　Here, the content of the corresponding element in atomic% (at %) is substituted for the element symbol in the formula (2).
[Claim 6]
　Ni-based alloy having a
　chemical composition of mass%,
　C: 0.100% or less,
　Si: 0.50% or less,
　Mn: 0.50% or less,
　P: 0.015% or less,
　S:0. 0.0150% or less,
　Cr: 20.0 to 23.0%,
　Mo: 8.0 to 10.0%,
　one or more selected from the group consisting of Nb and Ta: 3.150 to 4.150%,
　Ti: 0.05 to 0.40%,
　Al: 0.05 to 0.40%,
　Fe: 0.05 to 5.00%,
　N: 0.100% or less,
　O: 0.1000% or less,
　Co 0 to 1.00%,
　Cu: 0 to 0.50%,
　one or more elements selected from the group consisting of Ca, Nd and B: 0 to 0.5000%, and the
　balance Ni and impurities,
　In a cross section perpendicular to the longitudinal direction of the Ni-based alloy, the average concentration of Mo is 8.0% or more by mass% and the maximum value of the Mo concentration is 11.0% or less by mass%. A
　Ni-based alloy having an area ratio of less than 2.0% in a region whose concentration is less than 8.0% in mass% .
[Claim 7]
　The Ni-based alloy according to claim 6,
　wherein the chemical composition contains
　one or more elements selected from the group consisting of Ca, Nd, and B in a content satisfying the formula (2).
　Ni-based alloy.
　(Ca+Nd+B)/S≧2.0 (2)
　Here, the content of the corresponding element in atomic% (at %) is substituted for the element symbol in the formula (2).
[Claim 8]
　The Ni-based alloy according to claim 6 or 7, wherein the
　grain size number according to ASTM E112 is 0.0 or more
　.
[Claim 9]
　The Ni-based alloy according to any one of claims 6 to 8,
　wherein the total number of Nb carbonitrides having a maximum length of 1 to 100 μm is 4.0×10 − in the Ni-based alloy. 　Ni-based alloy having 2 pieces/μm 2 or less