Technical field
[0001]The present invention relates to a Ni-base heat-resistant alloy and a manufacturing method thereof.
[0002]Recently, for high efficiency, new construction of ultra-supercritical boiler elevated temperature and pressure of the steam is proceeding around the world. These ultra supercritical pressure boiler, a conventional 600 ° C. The steam temperature 650 ° C. or higher was around, yet are also planned to increase to over 700 ° C., technology has been developed at home and abroad.
[0003]
　This efficient use of energy-saving and resources, and CO for environmental conservation 2 gas emissions has become one of the solving problems of energy problems, it is based on has become an important industrial policies. In the case of reactors such as for power boiler and chemical industry to burn fossil fuels, high efficiency, ultra-supercritical boiler and the reactor is for advantageous.
[0004]
　High temperature and high pressure of the steam, at the time of actual operation, the reactor tube for superheater tubes and chemical industry boiler, as well as raise the temperature of such planks and forgings as heat and pressure-resistant member above 700 ° C.. Therefore, the alloy is used for a long time in such a harsh environment, not a high temperature strength and high temperature corrosion resistance only, the stability of long-term metal structure, it is required that good creep rupture ductility and creep fatigue that.
[0005]
　For the above stringent requirements, the Fe-based alloy such as austenitic stainless steel, the creep rupture strength is insufficient. Therefore, use of a Ni-based alloy utilizing the precipitation of such γ'-phase is essential. Also required to further have excellent weldability because welding is unavoidable as boilers and chemical industrial plants steel.
[0006]
　With respect to the strict requirements, for example, Patent Document 1, excellent in both of the HAZ of resistance to weld cracking resistance and toughness, discloses further austenitic heat resistant alloy is also excellent in creep strength at high temperatures.
CITATION
Patent Document
[0007]
Patent Document 1: Japanese Patent No. 4697357
Summary of the Invention
Problems that the Invention is to Solve
[0008]
　Meanwhile, a large structural members, such as a device material such as boilers and chemical plants, after hot rolling or hot forging, since the final heat treatment is used in practice without being subjected to cold working, the grain size There relatively large. Therefore, usually, 0.2% proof stress and tensile strength at normal temperature is defined as a specification of the material, there is a problem of lower than those subjected to final heat treatment after cold working.
[0009]
　In addition, the structural members of a large, since the cooling rate in the heat treatment may vary greatly depending on the site, the amount of which contributes solid solution elements to strengthen as a precipitate at the time of use at high temperature varies depending on the site. Due to its, there is also a problem that variations in the creep rupture strength occurs. Therefore, the alloy according to Patent Document 1, it is difficult to apply to a structural member of a large.
[0010]
　The present invention solves the above problems, 0.2% proof stress and tensile strength at a sufficient room temperature as a structural member of a large, well, the Ni-base heat-resistant alloy and a manufacturing method thereof expressing creep rupture strength at high temperatures an object of the present invention is to provide.
Means for Solving the Problems
[0011]
　The present invention has been made to solve the above problems, and the gist of the Ni-base heat-resistant alloy and a manufacturing method thereof below.
[0012]
　(1) the chemical composition of the alloy, in
　weight%, C: 0.005 ~
　0.15%, Si: 2.0% or
　less, Mn: 3.0% or
　less, P: 0.030% or
　less, S: 0.010% or
　less, N: 0.030% or
　less, O: 0.030% or
　less,
　Ni: 40.0 ~ 60.0%, Co: 0.01
　~ 25.0%, Cr: 15.0% or more and less than%
　28.0, Mo: 12.0% or
　less, W: less than%
　4.0,
　B: 0.0005 ~ 0.006%, Al:
　0 ~ 3.0%, Ti: 0 ~ 3.0
　%,
　Nb:
　0 ~ 3.0%, REM: 0 ~ 0.1%,
　Mg: 0 ~ 0.02%, Ca: 0 ~ 0.02%,
　the balance is Fe and impurities,
　the following (i) satisfied ~ (iii) formula,
　in the longitudinal direction perpendicular to the cross section of the alloy, the shortest distance from the center portion to the outer surface portion is not less 40mm or more,
　The austenite grain size number at the outer surface portion is the -2.0 ~ 4.0,
　Al existing as a precipitation product obtained by the extraction residue analysis, the total content of Ti and Nb satisfy the following (iv) type,
　mechanical properties at normal temperature satisfy the (v) below formula and (vi) expression,
　Ni-base heat-resistant alloy.
　≦ Mo + 0.1 W ≦ 12.0 · · ·
　(i) 1.0 ≦ 4 × Al + 2 × Ti + Nb ≦ 12.0 · · ·
　(ii) P + 0.2 × Cr × B <0.035 · · · (iii ) (Al
+ Ti + Nb) PB / (Al + Ti + Nb) PS ≦ 10.0 · · · 　(iv) YS S / YS B ≦ 1.5 · · · (v) TS S / TS B ≦ 1.2 · · · (vi) 　However, the (i) ~ (iii) each element symbol in the formulas represents the content of each element (mass%), the meaning of each symbol in the above (iv) ~ (vi) expression is as follows. 　(Al Tasu Ti Tasu Nb) PB

: The total content of Al, Ti and Nb which exists as a precipitate obtained by extraction residue analysis at the center
　(Al + Ti + Nb) PS : Al existing as a precipitation product obtained by the extraction residue analysis the outer surface portion, the sum of Ti and Nb content
　YS B : 0.2% proof stress at the center
　YS S : 0.2% proof stress on the outer surface portion
　TS B : tensile at the center strength
　TS S : tensile at the outer surface portion strength
[0013]
　(2) the chemical composition, by
　mass%, Mg: 0.0001 ~ 0.02%,
　and, Ca: 0.0001 ~ 0.02%,
　containing one or two kinds selected from
　the Ni-base heat-resistant alloy according to (1).
[0014]
　(3) 10,000 h creep rupture strength at 700 ° C. of the longitudinal direction in the center portion is not less than 150 MPa,
　Ni-based heat resistant alloy according to (1) or (2).
[0015]
　(4) above (1) or a steel ingot or slab having a chemical composition according to (2), a step of performing hot working,
　then heated to the heat treatment temperature T in the range of 1070 ~ 1220 ° C. (° C.) and, after holding 1150D / T ~ 1500D / T ( min), and a step of performing heat treatment of
　water-cooled, the manufacturing method of Ni-base heat-resistant alloy.
　However, D is, in the longitudinal direction perpendicular to the cross section of the alloy is the maximum value of the linear distance between any other point on the arbitrary point and the outer edge of a outer edge of the cross section (mm).
[0016]
　(5) In the step of subjecting the hot working is subjected hot working in the longitudinal direction substantially perpendicular to the hot working one or more times,
　the manufacturing method of Ni-base heat-resistant alloy according to (4).
The invention's effect
[0017]
　Ni-base heat-resistant alloy of the present invention has less variation in mechanical properties by site, also excellent in creep rupture strength at high temperatures.
DESCRIPTION OF THE INVENTION
[0018]
　It will be described in detail below each requirement of the present invention.
[0019]
　1. Chemical composition
　reasons for limiting each element are as follows. Incidentally, "%" for the content in the following description means "mass%".
[0020]
　C: 0.005 ~ 0.15%
　C serves to stabilize the austenite structure to form fine carbides in the grain boundaries and improves the creep strength at high temperatures. Therefore, C content should be 0.005% or more. However, if the content becomes excessive, carbides become coarse, and a large amount of precipitation, reduce the grain boundary ductility, leading to deterioration of the toughness and creep strength. Therefore, C content is 0.15% or less. C content is preferably 0.01% or more. Further, it is preferable C content is 0.12% or less, and more preferably not more than 0.10%.
[0021]
　Si: 2.0% or less
　Si is contained as a deoxidizing element. Moreover, Si is an element effective in improving the corrosion resistance and oxidation resistance at high temperatures. However, when the Si content exceeds 2.0%, the stability of the austenite phase is reduced, lowering the toughness and creep strength. Therefore, Si content is 2.0% or less. Si content is preferably 1.5% or less, more preferably 1.0% or less. It is not necessary to particularly specify any lower limit for the Si content, an extreme reduction, together with the deoxidizing effect can degrade the cleanliness of the well obtained without alloy, it causes an increase in manufacturing cost. Therefore, it is preferable Si content is 0.02% or more, more preferably 0.10% or more.
[0022]
　Mn: 3.0% or less
　Mn, as well as has a deoxidizing effect similar to the Si, an element which contributes to stabilization of austenite. However, if the Mn content exceeds 3.0%, lead to embrittlement, causing a reduction in toughness and creep ductility. Therefore, Mn content is 3.0% or less. Mn content is preferably not more than 2.5%, more preferably 2.0% or less, even more preferably 1.5% or less. Incidentally, it is not necessary to provide a lower limit for the Mn content, extreme reduction, together with deoxidizing effect degrades the cleanliness of the well obtained without alloy, it causes an increase in manufacturing cost. Therefore, it is preferable Mn content is 0.02% or more, more preferably 0.10% or more, even more preferably 0.15% or more.
[0023]
　P: 0.030% or less
　P is contained in the alloy as an impurity, it segregates in the grain boundaries of the HAZ during welding, with adverse effect element in long toughness after use to increase the liquation cracking susceptibility is there. Therefore, it is preferable to reduce as much as possible, extreme reduction causes an increase in steelmaking cost. Therefore, P content is set to 0.030% or less, preferably not more than 0.020% or.
[0024]
　S: 0.010% or less
　S is included in the alloy as an impurity, segregates in the grain boundaries of the HAZ during welding, with adverse effect element in long toughness after use to increase the liquation cracking susceptibility is there. Therefore, it is preferable to reduce as much as possible, extreme reduction causes an increase in steelmaking cost. Therefore, S content is 0.010% or less, preferably 0.005% or less.
[0025]
　N: 0.030% or less
　N is an effective element for stabilizing the austenite phase in a range of Cr content of the present invention, a large amount of fine nitride in use in the contained excessively high temperatures object was precipitated in the grains, lowering the creep ductility or toughness. Therefore, the N content more than 0.030%, preferably at 0.020% or less, and more preferably 0.015% or less. It is not necessary to particularly specify any lower limit for the N content, extreme reduction leads to increase in manufacturing cost. Therefore, it is preferable N content is 0.0005% or more, more preferably 0.001% or more, even more preferably 0.005% or more.
[0026]
　O: 0.030% or less
　O is contained in the alloy as an impurity, causing to be within the excessive decrease in hot workability, deterioration of toughness and ductility. Therefore, O content is set to 0.030% or less, preferably at 0.020% or less, more preferably 0.010% or less, further preferably 0.005% or less. It is not necessary to particularly specify any lower limit for the content of O, extreme reduction leads to increase in manufacturing cost. Therefore, O content is preferably 0.001% or more.
[0027]
　Ni: 40.0 ~ 60.0% Ni
　is an element effective for obtaining an austenitic structure, is an essential element for ensuring a long structural stability after use. Further, Ni is, Al, combined with Ti and Nb, forms fine intermetallic compound phase, also has effect of improving the creep strength. In order to obtain a sufficient effect in the range above the Ni and Cr contents of the present invention, it is necessary that the Ni content is 40.0% or more. However, since Ni is an expensive element, the cost is increased when the content exceeds 60.0%. Therefore, Ni content is 40.0 to 60.0%. Ni content is preferably at least 42.0%, more preferably at 45.0% or more, more preferably at least 48.0%, preferably not more than 58.0%.
[0028]
　Co: 0.01 ~
　25.0% Co is the same austenite-forming element and Ni, which contributes to the improvement of creep strength by increasing the stability of the austenite phase. To obtain this effect, Co content should be 0.01% or more. However, Co is because it is a very expensive element, leading to increase in significant cost if its content exceeds 25.0%. Therefore, Co content is from 0.01 to 25.0%. Co content is preferably at least 0.1%, more preferably from 2.0% or more, even more preferably 8.0% or more. Further, it is preferable Co content is less 23.0%, and more preferably not more than 21.0 percent.
[0029]
　Cr: 15.0% or more and less than 28.0%
　Cr is an essential element for ensuring the oxidation resistance and corrosion resistance at high temperatures. To obtain a Ni content range the effect of the above Cr of the present invention, it is necessary that the Cr content is 15.0% or more. However, when the Cr content is more than 28.0%, stability is deteriorated austenite phase at high temperatures, leading to reduction in creep strength. Therefore, Cr content is less than 28.0% to 15.0%. Cr content is preferably 17.0% or more, more preferably 19.0% or more. Further, it is preferable Cr content is less 26.0%, and more preferably not more than 24.0%.
[0030]
　Mo: 12.0% or less
　W: less than 4.0%
　Mo and W are both an element contributing to the improvement of creep strength at high temperatures by solid solution in the austenite tissue matrix. To obtain this effect, it is necessary to include one or both of Mo and W. However, if the content of these elements is excessive, the stability of the austenite phase conversely lowering the creep strength decreases. Therefore, Mo content is at most 12.0 percent. Mo content is preferably at most 10.0%.
[0031]
　Further, W is due to the large atomic weight as compared to Mo, in order to obtain the same effect as Mo must be larger quantities contained is disadvantageous in terms of cost and phase stability ensured. Therefore, W content is less than 4.0%. Mo and W does not need to be contained in combination. In case of containing Mo or W alone, preferably its content is respectively 0.1% or more.
[0032]
　B: 0.0005 ~ 0.006%
　B, by finely dispersing a grain boundary carbides with segregated to the grain boundaries in use to strengthen grain boundaries, is the element necessary for improving the creep strength . In addition, to improve the fixing strength segregated in the grain boundary also has a contributing effect to toughness improvement. To obtain these effects, B content and needs to be 0.0005% or more. However, in particular more than 0.006% or an increasing number B content, the welding heat cycle during welding, a large amount of segregated at a high temperature HAZ molten near the boundary reduces the melting point of the grain boundary so as to overlap with the P , enhance the HAZ liquation cracking susceptibility. Therefore, B content is 0.0005 to 0.006%. B content is preferably 0.001% or more is preferably 0.005% or less.
[0033]
　Al:
　0 ~
　3.0% Ti: 0 ~ 3.0% Nb: 0 ~
　3.0% Al, Ti and Nb are both by finely precipitated intragranular intermetallic compound bound to Ni, is an element that improves the creep strength at high temperatures. However, too much content thereof exceeds 3.0% for any of the elements, with the effect described above is saturated, the toughness is reduced after the creep ductility and prolonged heating. Therefore, Al, Ti, the content of each of Nb and 3.0% or less. The content of these elements is preferably equal to or less than 2.8%, and more preferably 2.5% or less.
[0034]
　REM: 0 ~ 0.1%
　rare earth elements (REM), the strong P and affinity, to greater high-temperature melting point that forms a compound with stable P, fixing the P, for the HAZ liquation cracking and toughness It has the effect of removing the adverse effects of P. Further, it precipitated as carbides, an element which contributes to the improvement of high-temperature strength. Therefore it may be contained as needed. However, the content of REM is excessive, exceeds 0.1%, in addition to the effect of reducing the adverse effects of P is saturated, large amount precipitates as a carbide, rather lowering the toughness. Therefore, REM content is 0.1% or less. REM content is preferably 0.08% or less, and more preferably not more than 0.06%. To obtain the above effect, REM content is preferably at 0.001% or more, more preferably 0.005% or more, even more preferably at least 0.01%.
[0035]
　Incidentally, REM is, Sc, refers to a total of 17 elements of Y and lanthanoids, the content of the REM means the total content of these elements.
[0036]
　Mg: 0 ~ 0.02% Mg
　is a strong affinity for S, has the effect of improving the hot workability, was also attributable to S, to reduce both the incidence and toughness decrease in the HAZ liquation cracking It is having an effect. Therefore it may be contained as needed. However, excessive addition of Mg will cause a decrease in cleanliness due to the binding of oxygen, in particular, the decrease in detergency and content exceeds 0.02% is significantly causes rather deteriorates the hot workability. Thus, Mg content is 0.02% or less. Mg content is preferably 0.01% or less. Meanwhile, in order to obtain the above-mentioned effects, it is preferable Mg content is 0.0001% or more, more preferably 0.0005% or more, even more preferably 0.001% or more.
[0037]
　Ca: 0 ~ 0.02% Ca
　has a strong affinity for S, has the effect of improving the hot workability, was also attributable to S, to reduce both the incidence and toughness decrease in the HAZ liquation cracking It is having an effect. Therefore it may be contained as needed. However, excessive addition of Ca will cause a decrease in cleanliness due to the binding of oxygen, in particular, the decrease in detergency and content exceeds 0.02% is significantly causes rather deteriorates the hot workability. Therefore, Ca content is 0.02% or less. Ca content is preferably 0.01% or less. Meanwhile, in order to obtain the above-mentioned effects, it is preferred Ca content is 0.0001% or more, more preferably 0.0005% or more, even more preferably 0.001% or more.
[0038]
　Alloy according to the present invention the content of each element in addition to the above range, it is necessary to satisfy the following (i) ~ (iii) expression. Note that each element symbol below (i) ~ (iii) in formula represents a content of each element (mass%).
[0039]
　0.1 ≦ Mo + W ≦ 12.0 ··· (i)
　as described above, Mo and W are both are elements contributing to the improvement of creep strength at high temperatures by solid solution in austenite structure is the matrix but the other hand, when the content of these elements is excessive, the stability of the austenite phase conversely lowering the creep strength decreases. Therefore, the total content of Mo and W should satisfy the above formula (i). Side values in the above equation (i) is preferably 1.0 or more, is preferably 10.0 or less.
[0040]
　1.0 ≦ 4 × Al + 2 × Ti + Nb ≦ 12.0 ··· (ii)
　by Ni and bound intermetallic compounds finely intragranular precipitation, good, after creep strength and prolonged heating at high temperatures in order to ensure the toughness, Al, together with the inclusion of one or more selected from Ti and Nb, the content thereof is required to satisfy the above (ii) expression. (Ii) above side value in the formula is preferably from 3.0 or more, and preferably 11.0 or less.
[0041]
　+ 0.2 × P Cr × B <0.035 · · · (iii)
　P and B segregate in the HAZ grain boundary melting near the boundary by thermal cycling during the welding, liquation cracking susceptibility of the HAZ to lower the melting point it is an element to increase. On the other hand, in the long busy, the P segregated in the grain boundary to reduce the fixing force of the grain boundaries, since B is to strengthen the grain boundary Conversely, P adversely affects toughness, B is reversed to reduce the toughness decreased to. Furthermore, Cr affects grain boundary polarization析挙motion of P and B, is an element that indirectly affect these properties. In other words, degree of influence of B on the HAZ liquation cracking becomes significant higher the Cr content. Also, the HAZ toughness long after use, but the adverse effects of P is large, if it contains approximately equal amounts of P, B, tends decrease is greater in toughness as Cr content is low.
[0042]
　Controls grain boundary segregation of P and B in the HAZ, for superior liquid-reduction cracking resistance and reduce toughness decrease after prolonged heating, it is necessary to satisfy (iii) above equation. (Iii) above formula lvalue is preferably 0.030 or less. Note that (iii) above formula lower limit of the left side value is not particularly limited, the content of P as an impurity is extremely low, Cr: 15.0%, B: close to 0.0015 when it is 0.0005% it may be a value.
[0043]
　In the chemical composition of the Ni-base heat-resistant alloy of the present invention, the balance being Fe and impurities. Here, the "impurities", when producing the alloy industrially, ores, raw material scraps, a component mixed by various factors of the manufacturing process, is allowed to the extent that the present invention does not adversely affect means shall.
[0044]
　2. Grain size
　austenite grain size number in the outer surface: -2.0 to 4.0
　when the austenite grain size at the outer surface is too coarse, low 0.2% proof stress and tensile strength at room temperature, whereas, if too fine , it is impossible to hold a high creep rupture strength at high temperatures. Thus, the austenite grain size number at the outer surface portion is set to -2.0 to 4.0.
[0045]
　In the present invention, the grain size number is determined by the intersection line (grain size) defined in JIS G 0551 (2013). In the production process of the Ni-based alloy, the heat treatment temperature and holding time and cooling method after hot working by appropriately adjusting, and the grain size number of the outer surface portion after the final heat treatment can be in the range of the .
[0046]
　3. Dimensions
　shortest distance from the center to the outer surface: 40 mm or more
　as described above, the structural members of a large, in addition to 0.2% proof stress and tensile strength at room temperature is low, variations in the creep rupture strength by site there is also a problem that may occur. However, Ni-based heat resistant alloy according to the present invention, 0.2% proof stress and tensile strength at a sufficient room temperature as a structural member of a large, well, express creep rupture strength at high temperatures. That is, the effect of the present invention is remarkably exhibited with respect to members of thick.
[0047]
　Accordingly, in the Ni-base heat-resistant alloy of the present invention, in the longitudinal direction and a section perpendicular to the shortest distance from the center portion to the outer surface portion or more 40 mm. In order to obtain the effect of the present invention more remarkably is preferably the shortest distance to the outer surface portion is 80mm or more from the center, more preferably 100mm or more. Here, the shortest distance from the center portion to the outer surface portion, for example, if the alloy is cylindrical, the cross section of radius (mm), and when a square pillar shape, the half of the short side of the cross-section length (mm) to become.
[0048]
　Incidentally, heat-resistant alloy according to the present invention, as described later, for example, obtained by subjecting a steel ingot or slab obtained by continuous casting or the like, a hot working such as hot forging or hot rolling . And generally the longitudinal direction of the heat-resistant alloy, in the case of using a steel ingot becomes a direction connecting the top portion and the bottom portion of the steel ingot, when using a cast slab, the length direction.
[0049]
　4. Precipitation amount of γ'-phase obtained by extraction residue analysis (Al
+ Ti + Nb) PB / (Al + Ti + Nb) PS ≦ 10.0 · · · (iv) 　where the meaning of each symbol in (iv) expression is as follows. 　(Al + Ti + Nb) PB : total content of existing Al, Ti and Nb as a precipitate obtained by extraction residue analysis at the center 　(Al + Ti + Nb) PS : existing as a precipitation product obtained by the extraction residue analysis the outer surface portion Al, Ti the total content of and Nb

[0050]
　In the manufacturing process of alloy, gamma prime phase is mainly within the grains after the heat treatment after hot working undissolved (Ni 3 (Al, Ti, Nb)) is generated. In particular, since the cooling rate is slower than the outer surface portion at the center of the alloy tends to amount of γ'-phase of undissolved increases. Therefore, the number precipitation amount of Al, Ti and Nb precipitate as γ'at the center portion with respect to the outer surface portion of the alloy, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS at high temperature exceeds 10.0 the value of it is not possible to hold a high creep rupture strength. On the other hand, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS lower limit value of need not be determined, it is preferably the central portion to the fact that there is a tendency to increase the amount of precipitates than the outer surface portion 1.0 above.
[0051]
　Incidentally, the precipitate obtained by extraction residue analysis is γ'-phase of undissolved contained in the alloy. Extraction residue analysis to those carried out by the following procedure. First from the central portion and the outer surface portion in the longitudinal direction perpendicular to the cross section of the alloy samples, taken test pieces for measuring the γ'-phase. After having determined the surface area of the test piece, 20 mA / cm in each 1% tartaric -1% ammonium sulfate aqueous solution 2 completely electrolyzed only the base material of the heat-resistant alloy electrolysis conditions. The solution after electrolysis was filtered through a 0.2μm filter, to extract the precipitates as a residue. Thereafter, Al contained as γ'-phase of undissolved by ICP-AES measurement of extracted residue from the decomposing acid, measured content of Ti and Nb (mass%), based on the measured value (Al + Ti + Nb ) PB / (Al + Ti + Nb) PS determine the value of.
[0052]
　5. Mechanical Properties
　YS S / YS B ≦ 1.5 · · · (v)
TS S / TS B ≦ 1.2 · · · (vi) 　where the meaning of each symbol in the formula is as follows. 　YS B : 0.2% proof stress at the center 　YS S : 0.2% proof stress on the outer surface portion 　TS B : tensile at the center strength 　TS S : tensile at the outer surface portion Strength

[0053]
　The structural member of a large, due to the cooling rate of the heat treatment varies depending on the site, there is a tendency that large variations in mechanical properties of each region. In large structural members, in its central portion and the outer surface portion, the 0.2% proof stress and tensile strength at room temperature is greatly different, a problem that does not meet the specification by site occurs. Thus, Ni-base heat resistant alloy according to the present invention, the mechanical properties at room temperature is assumed to satisfy the above (v) expression and (vi) expression. Incidentally, it is not necessary to lower limit defined respectively, towards the mechanical properties of the heart from that tends to inferior mechanical properties of the outer surface portion, and (v) expression and (vi) 1.0 or more in the expression of both it is preferable.
[0054]
　0.2% yield strength and tensile strength, from the central portion and the outer surface portion of the alloy, parallel to the longitudinal direction, cut out by machining a is 40mm round bar tensile test specimen of length of the parallel portion, a tensile test at room temperature seek by the practice. In addition, tensile test to be carried out in conformity with JIS Z 2241 (2011).
[0055]
　6. Creep rupture strength
　Ni-base heat-resistant alloy of the present invention, for use in high temperature environments, high temperature strength, in particular, high creep rupture strength is required. Therefore, the alloy of the present invention, in its central part, there is a need for 10,000 hours creep rupture strength in the longitudinal direction of 700 ° C. is not less than 150 MPa.
[0056]
　Creep rupture strength is determined by the following method. First, cut from the center of the alloy, parallel to the longitudinal direction, the diameter 6mm described JIS Z 2241 (2011), a round bar creep rupture test piece gauge length 30mm by machining. Then, 700 ° C., a creep rupture test conducted at 750 ° C., 800 ° C. in air, 700 ° C. using Larson-Miller parameter method, obtaining the creep rupture strength of 10,000 hours. Furthermore, the creep rupture test shall be done in conformity with JIS Z 2271 (2010).
[0057]
　7. Production process
　the Ni-base heat-resistant alloy of the present invention, the steel ingot or slab having a chemical composition described above is prepared by subjecting the hot working. In the above-described hot working step, the longitudinal direction of the final shape of the alloy, processing is performed to match the longitudinal direction of the steel ingot or slab as a material. Hot working, may be performed only in the longitudinal direction, giving a higher degree of processing, to a more homogeneous structure, with respect to the longitudinal direction substantially perpendicular, one or more times a hot working it may be subjected. Further, after the hot working, it may be further subjected to a hot working different methods such as extrusion hot as necessary.
[0058]
　In the production of Ni-base heat-resistant alloy of the present invention, in order after the above step, to suppress variations in the metal structure and mechanical properties of each region, to retain the high creep rupture strength, final heat treatment described below the applied.
[0059]
　First, the alloy after hot working, heating to the heat treatment temperature T in the range of 1070 ~ 1220 ℃ (℃), within its scope, 1150D / T ~ 1500D / T (min) holds. Here, D is, for example, if the alloy is cylindrical, the alloy having a diameter (mm), and when a square pillar, a distance of the diagonal (mm). That D is in the longitudinal direction perpendicular to the cross section of the alloy is the maximum value of the linear distance between any other point on the arbitrary point and the outer edge of a outer edge of the cross section (mm).
[0060]
　When the heat treatment temperature is lower than 1070 ° C., creep rupture strength γ'-phase of undissolved increases is reduced. On the other hand, if it exceeds 1220 ° C., the ductility is reduced by the grain boundaries or significantly coarsened crystal grains or molten. The heat treatment temperature is more preferably set to a 1100 ° C. or higher, and more preferably, 1200 ° C. or less. Further, the holding time is less than 1150D / T (min), γ'-phase is increased in the center portion, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS outside the range prescribed by the present invention. On the other hand, the crystal grain coarsening of the outer surface portion exceeds 1500D / T (min), the austenite grain size number is outside the range specified in the present invention.
[0061]
　After heating and holding is immediately water-cooled alloy. When the cooling rate is slow, because the particular large quantity caused mainly undissolved γ'-phase in the grains is at the center of the alloy, there may not meet the above (iv) expression.
[0062]
　The following examples illustrate the present invention more specifically, the present invention is not limited to these examples.
Example
[0063]
　An alloy having a chemical composition shown in Table 1 were melted in a high frequency vacuum melting furnace, an outer diameter of 550 mm, the weight is a steel ingot of 3t.
[0064]
[Table 1]

[0065]
　The resulting steel ingot, and processed into a cylindrical shape having an outer diameter of 200 ~ 480 mm by hot forging, the final heat treatment performed under the conditions shown in Table 2, to obtain an alloy member samples. Incidentally, after the longitudinal hot forging for the alloys 1, 2, 3 and 5, before the final heat treatment, it carried out forging in the longitudinal direction substantially perpendicular to then further longitudinally final hot forging went.
[0066]
[Table 2]

[0067]
　For each sample, we collect specimens for structure observation from the outer surface portion, after polishing a longitudinal section with emery paper and buff, was light microscopy corroded with mixed acid. Grain size number of the observation plane is determined according to the determination method according to the intersection line (grain size) defined in JIS G 0551 (2013).
[0068]
　Then, from the central portion and the outer surface portion in the longitudinal direction perpendicular to the cross section of each sample were taken test pieces for measuring the γ'-phase. After having determined the surface area of the test piece, 20 mA / cm in each 1% tartaric -1% ammonium sulfate aqueous solution 2 was only preform heat-resistant alloy completely electrolyzed in electrolysis conditions. The solution after electrolysis was filtered through a 0.2μm filter, to extract the precipitate as a residue. Thereafter, Al contained as γ'-phase of undissolved by ICP-AES measurement of extracted residue from the decomposing acid, measured content of Ti and Nb (mass%), based on the measured value (Al + Ti + Nb ) PB / (Al + Ti + Nb) PS was determined value of.
[0069]
　Further, from the central portion and the outer surface portion of each sample, parallel to the longitudinal direction, cut out by machining a tensile test specimen of 40mm length of the parallel portion, and a tensile test at room temperature, 0.2% proof stress and tensile to determine the strength. Furthermore, from the center of each sample, parallel to the longitudinal direction, were cut 6mm diameter described JIS Z 2241 (2011), a round bar creep rupture test piece gauge length 30mm by machining. Then, 700 ° C., 750 ° C., a creep rupture test conducted at 800 ° C. in air, 700 ° C. using Larson-Miller parameter method to determine the creep rupture strength of 10,000 hours. The results are summarized in Table 3.
[0070]
　The results are summarized in Table 3.
[0071]
[table 3]

[0072]
　Alloy 1-8 are examples of the present invention, the alloy composition, grain size number, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS , YS S / YS B , TS S / TS B defined, and creep rupture strength in the present invention must be within a range of the variation of mechanical properties is small, creep rupture strength was also favorable.
[0073]
　On the other hand, Alloy A and B are substantially equal alloy 1 and the chemical composition is obtained by the same final shape by hot forging. However, the retention time of the heat treatment is outside the range of manufacturing conditions defined in the present invention. In the due to its grain size number of the outer surface portion is outside the specified range of the present invention for alloy A, YS S / YS B and TS S / TS B value of has become outside the specified range of the present invention , resulted in variation of mechanical properties is increased by site. As for the alloy B, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS value of becomes outside a specified range of the present invention, the creep rupture strength becomes significantly lower results as compared with the alloys 1.
[0074]
　Alloy C, D and E are substantially equal alloy 2 and the chemical composition is obtained by the same final shape by hot forging. Alloy C is for less than the specified range of heat treatment temperature present invention, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS has a range defined in the present invention and the value of the crystal grain size number of the outer surface portion, an alloy creep rupture strength as compared with 2 becomes significantly lower results. Alloy D is the higher than the specified range of heat treatment temperature present invention, the grain size number of the outer surface portion, YS S / YS B and TS S / TS B is the value of has a specified range of the present invention, creep rupture strength as compared with the alloy 2 becomes significantly lower results. Further, the alloy E is air-cooled rather than cooling method at the time of the final heat treatment water cooling, due to the cooling rate was significantly slower, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS value of becomes outside a specified range of the present invention as a result, the creep rupture strength as compared to alloy 3 was significantly lower.
[0075]
　Alloys F, G, H, the chemical composition are comparative examples departing from the provisions of the present invention. Specifically, the alloy F has a high W content, alloy G is (i) Formula sides value is high, the alloy H is an example low side value in formula (ii). Therefore, in these examples, resulted in creep rupture strength is lowered.
Industrial Applicability
[0076]
　Ni-base heat resistant alloy according to the present invention has less variation in mechanical properties by site, also excellent in creep rupture strength at high temperatures. Therefore, Ni heat-resistant alloy of the present invention can be suitably used as a large structural members such as boilers and chemical plants used in high temperature environments.

The scope of the claims
[Requested item 1]Chemical composition of the alloy, in
　weight%, C: 0.005 ~
　0.15%, Si: 2.0% or
　less, Mn: 3.0% or
　less, P: 0.030% or
　less, S: 0.010 % or
　less, N: 0.030% or
　less, O: 0.030% or
　less,
　Ni: 40.0 ~ 60.0%, Co: 0.01
　~ 25.0%, Cr: 15.0% or more 28. less than%
　0, Mo: 12.0% or
　less, W: less than%
　4.0,
　B: 0.0005 ~ 0.006%,
　Al: 0 ~ 3.0%, Ti: 0 ~
　3.0%, Nb :
　0
　~ 3.0%, REM: 0 ~ 0.1%,
　Mg: 0 ~ 0.02%, Ca: 0 ~ 0.02%,
　the balance is Fe and impurities,
　the following (i) ~ (iii ) satisfies the formula,
　in the longitudinal direction perpendicular to the cross section of the alloy, the shortest distance from the center portion to the outer surface portion is not less 40mm or more,
　austenite in the outer surface Ito grain size number is -2.0 to 4.0,
　Al existing as a precipitation product obtained by the extraction residue analysis, the total content of Ti and Nb satisfy the following (iv) type,
　mechanical properties at normal temperature satisfy the (v) below formula and (vi) expression ,
　Ni-base heat-resistant alloy.
　≦ Mo + 0.1 W ≦ 12.0 · · ·
　(i) 1.0 ≦ 4 × Al + 2 × Ti + Nb ≦ 12.0 · · ·
　(ii) P + 0.2 × Cr × B <0.035 · · · (iii ) (Al
+ Ti + Nb) PB / (Al + Ti + Nb) PS ≦ 10.0 · · · 　(iv) YS S / YS B ≦ 1.5 · · · (v) TS S / TS B ≦ 1.2 · · · (vi) 　However, the (i) ~ (iii) each element symbol in the formulas represents the content of each element (mass%), the meaning of each symbol in the above (iv) ~ (vi) expression is as follows. 　(Al + Ti + Nb) PB : total content of existing Al, Ti and Nb as a precipitate obtained by extraction residue analysis at the center 　(Al + Ti + Nb)

PS : the total content of an existing Al, Ti and Nb as a precipitate obtained by extraction residue analysis in the outer surface portion
　YS B : 0.2% proof stress at the center
　YS S : 0.2% proof stress on the outer surface portion
　TS B : tensile at the center of strength
　TS S : tension in the outer surface strength
[Requested item 2]
　The chemical composition, by
　mass%, Mg: 0.0001 ~ 0.02%,
　and, Ca: 0.0001 ~ 0.02%,
　containing one or two kinds selected from,
　in claim 1 Ni-base heat-resistant alloy according.
[Requested item 3]
　It said longitudinal 700 10,000 hours creep rupture strength at ℃ is more than 150 MPa, in the center
　Ni-base heat-resistant alloy according to claim 1 or claim 2.
[Requested item 4]
　A steel ingot or slab having a chemical composition according to claim 1 or claim 2, the step of performing hot working,
　then heated to the heat treatment temperature T in the range of 1070 ~ 1220 ℃ (℃), 1150D / after T ~ 1500D / T (min) retention, and a step of performing heat treatment of
　water-cooled, the manufacturing method of Ni-base heat-resistant alloy.
　However, D is, in the longitudinal direction perpendicular to the cross section of the alloy is the maximum value of the linear distance between any other point on the arbitrary point and the outer edge of a outer edge of the cross section (mm).
[Requested item 5]
　In the step of performing processing between the heat applied in the longitudinal direction substantially perpendicular to the direction of hot working hot working one or more times,
　the manufacturing method of Ni-base heat-resistant alloy according to claim 4.