Technical field
[0001]
The present invention relates to a Ni-Fe-Cr alloy.
BACKGROUND
[0002]
Equipment of the heating furnace tube, such as oil refining and petrochemical plants, operating in a high temperature environment. These facilities further contact with the process fluid containing the sulfides and / or chlorides. Therefore, the materials used in these facilities, it is required excellent corrosion resistance. These facilities for example, typified Alloy825 (TM), Ni based alloys and Ni-Fe-Cr alloy having excellent corrosion resistance is used.
[0003]
　Ni based alloy for use in equipment as described above, is proposed in JP 61-227148 (Patent Document 1) and JP-A-6-240407 (Patent Document 2).
[0004]
　High nickel alloy disclosed in Patent Document 1, in weight%, C: 0.1% or less, Si: 1.0% or less, Mn: 1.5% or less, S: 0.015% or less, Ni: 30.0 ~ 30.5%, Cr: 19.0 ~ 25.0%, Cu: 1.0% or less, Al: 0.1 ~ 1.0%, Ti: 0.05 ~ 1.0%, Nb: 0.05 ~ 1.0%, the balance consists of iron and unavoidable impurities, and satisfies the condition that the (3Ti + Nb) / S ≧ 150 and (Ti + Nb) / C ≧ 15. Thus, the high nickel alloys obtained excellent intergranular corrosion resistance, it has been described as.
[0005]
　High strength clad steel disclosed in Patent Document 2, in mass%, the base material composition, C: 0.03 ~ 0.12%, Si: 0.5% or less, Mn: 1 ~ 1.8%, nb: 0.06% or less, Mo: 0.25% or less, V: 0.06% or less, Al: it contains 0.01 to 0.06%, the balance being Fe and inevitable impurities. The high-strength clad steel, the cladding material composition, C: 0.05% or less, Si: 0.5% or less, Mn: 1% or less, Cr: 19.5 ~ 23.5%, Mo: 2.5 ~ 3.5%, Al: 0.2% or less, Ti: 0.6 ~ 1.2%, Cu: 1.5 ~ 3%, Ni: 38 contained ~ 46%, the balance being Fe and inevitable impurities it is a Ni-base alloy consisting. The high-strength clad steel after heating quenching City 900 ~ 1030 ° C., by performing tempering of 500 ~ 630 ° C., are described excellent corrosion resistance is obtained, and.
CITATION
Patent Document
[0006]
Patent Document 1: JP 61-227148 Patent Publication
Patent Document 2: JP-A 6-240407 JP
Summary of the Invention
Problems that the Invention is to Solve
[0007]
　Incidentally, the Ni-based alloy or Ni-Fe-Cr alloy, when performing welding, sometimes the weld heat affected zone is sensitized. Intergranular corrosion is likely to occur by sensitization. Therefore, the Ni-based alloy or Ni-Fe-Cr alloy used in the high temperature environment as described above, excellent intergranular corrosion resistance due to sensitization suppression is required.
[0008]
　However, the materials disclosed in Patent Documents 1 and 2 described above, an insufficient suppression of sensitization, there are cases where intergranular corrosion occurs.
[0009]
　An object of the present invention is to provide a Ni-Fe-Cr alloy with good intergranular corrosion resistance.
Means for Solving the Problems
[0010]
　Ni-Fe-Cr alloy according to the present embodiment, by mass%, C: 0.005 ~ 0.015% , Si: 0.05 ~ 0.50%, Mn: 0.05 ~ 1.5%, P 0.030% or less, S: 0.020% or less, Cu: 1.0 ~ 5.0%, Ni: 30.0 ~ 45.0%, Cr: 18.0 ~ 30.0%, Mo: 2.0 ~ 4.5%, Ti: 0.5 ~ 2.0%, N: 0.001 ~ 0.015%, and, Al: 0 ~ 0.50%, containing the balance Fe and having a chemical composition consisting of impurities. The average crystal grain size d ([mu] m) satisfies the formula (1).
　d <4.386 / (C rel +0.15) (1)
　Here, C in the formula (1) rel is defined by the formula (2).
　C rel = C-0.125Ti + 0.8571N (2)
　wherein each element symbol in the formula (1) and (2), the content of the corresponding element (mass%) is substituted.
Effect of the invention
[0011]
　Ni-Fe-Cr alloy according to the present invention have excellent intergranular corrosion resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012]
[1] Figure 1 is the relative amount of solute C (C rel ), the average crystal grain size d ([mu] m), and a diagram showing the intergranular corrosion of the relationship.
FIG. 2 is an average crystal grain size d ([mu] m), F1 = 4.386 / (C rel +0.15) and the difference between d (F1-d), and the intergranular corrosion of the relationship It illustrates.
DESCRIPTION OF THE INVENTION
[0013]
　Hereinafter, with reference to the drawings, an embodiment of the present invention in detail. Later,% related to elements means "% by weight".
[0014]
　The present inventors have investigated the sensitization and intergranular corrosion resistance of the Ni-Fe-Cr alloy. As a result, the present inventors have obtained the following findings.
[0015]
　(A) sensitization occurs in the following mechanism. When Ni-Fe-Cr alloy is subjected to thermal influence of the welding enforcement, etc., Cr carbides are precipitated in the grain boundaries. The precipitation of Cr carbide Cr around the crystal grain boundaries is used. Therefore, when Cr carbide is precipitated, Cr depletion region is generated along the grain boundaries. This phenomenon is called sensitization. The Cr-depleted region, since the passive film is not sufficiently formed, the corrosion resistance is lowered, the grain boundary corrosion tends to occur. If reducing the amount of solute C Ni-Fe-Cr alloy, it is possible to suppress sensitization, it is possible to increase the intergranular corrosion resistance.
[0016]
　(B) if reducing the C content of Ni-Fe-Cr alloy, solid solution C content in the Ni-Fe-Cr alloy is reduced. Therefore, in this embodiment, the C content is from .005 to .015%.
[0017]
　(C) If the C fixed to the Ti carbides Ti, it can be further reduced amount of solute C in the Ni-Fe-Cr alloy. However, when N is present in the Ni-Fe-Cr alloy, for more of N is a strong affinity with Ti than C, Ti nitrides are precipitated earlier than Ti carbide during solidification. Consequently, Ti is insufficient, can not be fixed a C. Therefore, N content is preferably as low as. Therefore, in this embodiment, N content is 0.015% or less.
[0018]
　As described above, the actual amount of dissolved C Ni-Fe-Cr alloy is a relatively value determined from the content of C, Ti and N. Therefore, amount of dissolved C the theoretical is obtained as follows.
　Amount of solute C = C content is fixed by Ti as C content -TiC in the alloy
[0019]
　Here, if N is present, Ti is used to precipitate as Ti nitride, Ti amount that can be used for fixing the C is calculated as follows.
　Ti amount used in C fixed = Ti-48/14 × N
[0020]
　Therefore, amount of dissolved C on theoretical in the alloy (C total ) is calculated as follows.
　C total = C-(Ti-48/14 × N) × 12/48 = C-0.250Ti + 0.8571N
[0021]
　However, in the actual industrial production processes, it is necessary to consider the kinetics. In other words, in the equilibrium state, amount of solute C solid solution C amount on the aforementioned theoretical (C total becomes). On the other hand, in the actual manufacturing process, to proceed in a short time the reaction may react before reaching the equilibrium state is completed. Accordingly, since all the Ti may not form a TiC, C total is necessary to adjust the coefficients of the Ti in the formula.
[0022]
　The inventors of the result of the examination, the actual amount of dissolved C in the Ni-Fe-Cr alloy (C real ) is as follows.
　C real = C-0.125Ti + 0.8571N + k 1
　k 1 is a constant amount of solute C.
[0023]
　The actual amount of solute C (C real ) of, C the amount utilized in the Cr carbide precipitation (total deposition amount of C (C pre )) is a solid solubility limit of C k 2 when the (%), the following the as.
　C Pre = C-0.125Ti Tasu 0.8571N Tasu K 1 -K 2
[0024]
　(D) in order to increase the intergranular corrosion resistance further grain refinement is effective. The reason for this is as follows. When the crystal grains are refined, grain boundary total area increases. The total precipitation amount of C in the alloy (C pre order) does not change, the larger the grain boundary total area, which contributes C content of Cr carbide precipitation per unit grain boundary area (unit deposition amount of C (C Unit )) is reduced It is. Thus, deposition and growth of Cr carbide per unit grain boundary area is suppressed, generation of Cr-depleted region is suppressed. As a result, the sensitization is suppressed.
[0025]
　The average grain size d and the unit deposition amount of C (C Unit relationship with) is determined as follows. When the average crystal grain size of d ([mu] m), the grain boundary area of the crystal grains k 3 × d 2 [mu] m 2 (k 3 obtained in a constant). The number of crystal grains per unit volume k 4 / d 3 pieces (k 4 when a is a constant), the grain boundary the total area can be calculated as follows.
　Grain boundary Total area = (k 3 × d 2 ) × (k 4 / d 3 ) = k 3 k 4 / d
[0026]
　The grain boundary total area and total deposition amount of C (C pre using) and the unit deposition amount of C (C Unit ) is obtained as follows.
　C Unit = C pre / (k 3 k 4 / d) = d × (C pre / k 3 k 4 )
[0027]
　From this equation, the average grain size d and the unit deposition amount of C (C Unit and) are proportional. That is, as the average grain size d is reduced, the unit deposition amount of C (C Unit ) is reduced, as a result, the sensitization is suppressed.
[0028]
　(E) from the average grain size d and the Cr carbide contributing C amount to precipitation described above, was examined indicators intergranular corrosion resistance. As a result, in order to increase the intergranular corrosion resistance is not simply mean that it smaller the average crystal grain size d, the relationship between the contributing C content of Cr carbide precipitation, suitable average grain size d is the present, the present inventors have found.
[0029]
　1, Cr carbide contributing C amount to precipitation (relative amount of solute C (C rel )), the average crystal grain size d ([mu] m), and a diagram showing the intergranular corrosion of the relationship. 1, the horizontal axis represents the total deposition amount of C (C pre from the equation), k a constant 1 and k 2 are omitted (relative amount of solute C will be described later (C rel is)). Figure 1 was obtained by the Examples below. In Figure 1, "○" and shows excellent intergranular corrosion resistance were plotted which intergranular corrosion resistance is inferior as "×".
[0030]
　Than 1, in order to suppress sensitization, the total deposition amount of C (C pre more) increases, it is necessary to refine the average crystal grain size d. On the other hand, the total deposition amount of C (C pre more) becomes low, it can be increased an average crystal grain size d. In other words, the total precipitation amount of C (C pre ) is inversely related to the average grain size, represented as follows.
　= k d 5 / (C pre + k 6 )
　where, k 5 and k 6 are constants.
[0031]
　The relationship of the intergranular corrosion resistance of superiority in FIG 1 (○ and ×), as a boundary to the broken line in FIG. 1, k of the constant 1 , k 2 , k 5 and k 6 when seeking, it is possible to obtain the F1 .
　= 4.386 F1 / (C rel +0.15)
　Here, C rel is C, relatively determined amount of solute C from the content of Ti and N (relative amount of solute C (C rel as)), following It is defined as.
　C Rel = C-0.125Ti Tasu 0.8571N (2)
[0032]
　Than 1, in order to suppress sensitization, the relative amount of solute C (C rel more) increases, it is necessary to refine the average crystal grain size d. On the other hand, the relative amount of solute C (C rel more) becomes low, it can be increased an average crystal grain size d.
[0033]
　F1 is an indication of intergranular corrosion resistance. If it is less than the average grain size d is F1, the relative amount of solute C (C rel is appropriate average grain size d relative). In this case, the unit deposition amount of C (C Unit ) is sufficiently reduced, sensitization is suppressed. As a result, it is possible to increase the intergranular corrosion resistance. On the other hand, when the average grain size d equal to or greater than F1, the relative amount of solute C (C rel average grain size d is too large for). In this case, the unit deposition amount of C (C Unit ) is not sufficiently reduced, sensitization is promoted. As a result, intergranular corrosion resistance is lowered.
[0034]
　2, the average crystal grain size d ([mu] m), a diagram showing the difference (F1-d), and intergranular corrosion resistance of the relationship between F1 and d. Figure 2 is obtained from the Examples described below as in FIG. In Figure 2, "○" and shows excellent intergranular corrosion resistance were plotted which intergranular corrosion resistance is inferior as "×". Referring to FIG. 2, if the average crystal grain size d is satisfied formula (1), i.e., if F1-d is a positive value, it is larger average crystal grain size d is excellent intergranular corrosion You can have sex. If the average crystal grain size d is not satisfy Expression (1), that is, F1-d is a negative value, even with a small average crystal grain size d, intergranular corrosion resistance is lowered.
[0035]
　The Ni-Fe-Cr alloy of the present embodiment has been completed based on the above findings, by mass%, C: 0.005 ~ 0.015% , Si: 0.05 ~ 0.50%, Mn: 0. 05 ~ 1.5%, P: 0.030 % or less, S: 0.020% or less, Cu: 1.0 ~ 5.0%, Ni: 30.0 ~ 45.0%, Cr: 18.0 ~ 30.0%, Mo: 2.0 ~ 4.5%, Ti: 0.5 ~ 2.0%, N: 0.001 ~ 0.015%, and, Al: 0 ~ 0.50%, It contains, to the chemical composition the balance being Fe and impurities. The average crystal grain size d ([mu] m) satisfies the formula (1).
　d <4.386 / (C rel +0.15) (1)
　Here, C in the formula (1) rel is defined by the formula (2).
　C rel = C-0.125Ti + 0.8571N (2)
　wherein each element symbol in the formula (1) and (2), the content of the corresponding element (mass%) is substituted.
[0036]
　The chemical composition, Al: may contain from 0.05 to 0.50%.
[0037]
　[Chemical composition]
　chemical composition of Ni-Fe-Cr alloy of the present embodiment contains the following elements.
[0038]
　C: 0.005 ~ 0.015%
　carbon (C) increases the strength of the alloy. C further deoxidizing alloy. If the C content is too low, these effects can not be obtained. On the other hand, if the C content is too high, an increase in Cr carbide precipitation in the grain boundary, intergranular corrosion resistance is lowered. Therefore, C content is 0.005 to 0.015 percent. A preferred lower limit of the C content is 0.008%. The preferable upper limit of the C content is 0.013%, more preferably 0.010%.
[0039]
　Si: 0.05 ~ 0.50%
　silicon (Si), the deoxidizing alloy. If Si content is too low, the effect can not be obtained. On the other hand, if the Si content is too high, inclusions are easily generated. Therefore, Si content is from 0.05 to 0.50 percent. A preferable lower limit of Si content is 0.15%, more preferably 0.20%. The preferable upper limit of the Si content is 0.45%, more preferably 0.40%.
[0040]
　Mn: 0.05 ~ 1.5%
　manganese (Mn) stabilizes the austenite phase. Mn further deoxidizing alloy. If the Mn content is too low, these effects can not be obtained. On the other hand, if the Mn content is too high, Mn forms sulfide combines with S, becomes non-metallic inclusions to lower the pitting resistance. Therefore, Mn content is 0.05 to 1.5%. The preferable lower limit of the Mn content is 0.15%, more preferably 0.30%. The preferable upper limit of the Mn content is 1.2%, more preferably 1.0%.
[0041]
　P: 0.030% or less
　phosphorus (P) is an impurity. P is segregated at the grain boundaries during weld solidification, increasing the susceptibility to cracking due embrittlement of the heat-affected zone. Accordingly, P content is 0.030% or less. The preferable upper limit of the P content is 0.025%, more preferably 0.020%. P content is preferably as small as possible.
[0042]
　S: 0.020% or less
　sulfur (S) is an impurity. S as well as P, segregates at the grain boundaries during weld solidification, increasing the susceptibility to cracking due embrittlement of the heat-affected zone. S is further configured to form MnS, lowers the pitting corrosion resistance. Therefore, the content of S is 0.020% or less. The preferable upper limit of the S content is 0.010%, still more preferably 0.005%. S content is preferably as small as possible.
[0043]
　Cu: 1.0 ~ 5.0%
　copper (Cu) increases the corrosion resistance of the alloy. If Cu content is too low, the effect can not be obtained. On the other hand, if the Cu content is too high, decrease the hot workability of the alloy. Therefore, Cu content is 1.0-5.0%. The preferable lower limit of Cu content is 1.2%, more preferably from 1.5%. The preferable upper limit of Cu content is 4.0%, more preferably from 3.0%.
[0044]
　Ni: 30.0 ~ 45.0%
　nickel (Ni) increases the pitting resistance of the alloy. If the Ni content is too low, the effect can not be obtained. On the other hand, if the Ni content is too high, the effect is saturated. Therefore, Ni content is 30.0 to 45.0%. A preferable lower limit of Ni content is 35.0%, more preferably 38.0%. The preferable upper limit of the Ni content is 44.5%, more preferably 44.0%.
[0045]
　Cr: 18.0 ~ 30.0%
　chromium (Cr) enhances the corrosion resistance of the alloy. If the Cr content is too low, the effect can not be obtained. On the other hand, if the Cr content is too high, decrease the stability of austenite at high temperature, the high temperature strength of the alloy is lowered. Therefore, Cr content is 18.0 to 30.0%. A preferable lower limit of Cr content is 19.0%, still more preferably 20.0%. The preferable upper limit of the Cr content is 26.0%, still more preferably 24.0%.
[0046]
　Mo: 2.0 ~ 4.5%
　of molybdenum (Mo) increases the corrosion resistance of the alloy. If the Mo content is too low, the effect can not be obtained. On the other hand, if Mo content is too high, in many alloys Cr content, and precipitating Laves phase at the grain boundaries, corrosion resistance of the alloy is lowered. Therefore, Mo content is 2.0 to 4.5%. A preferable lower limit of Mo content is 2.4%, more preferably from 2.8%. The preferable upper limit of the Mo content is 4.0%, more preferably from 3.5%.
[0047]
　Ti: 0.5 ~ 2.0%
　titanium (Ti) inhibits sensitization of the alloy by forming a Ti carbide. If the Ti content is too low, the effect can not be obtained. On the other hand, if the Ti content is too high, decrease the hot workability of the alloy. Therefore, Ti content is from 0.5 to 2.0%. A preferable lower limit of the Ti content is 0.55%, more preferably 0.60%. The preferable upper limit of the Ti content is 1.5%, more preferably from 1.3%.
[0048]
　N: 0.001 ~ 0.015%
　nitrogen (N) forms fine carbonitrides in the grains may be contained because it increases the strength. On the other hand, if the N content is too high, combines with Ti to form TiN, inhibits C fixed as Ti carbide, decreases the sensitization suppression. Therefore, N content is 0.001 to 0.015%. The preferable lower limit of the N content is 0.002%, still more preferably 0.005%. The preferable upper limit of the N content is 0.013%, more preferably 0.010%.
[0049]
　The remainder of the chemical composition of the Ni-Fe-Cr alloy according to the embodiment, consists of Fe and impurities. Here, the impurity, when the industrial production of Ni-Fe-Cr alloy, ore as a raw material, there is to be mixed etc. Scrap or manufacturing environment,, Ni-Fe- of this embodiment It means what is allowed in a range that does not adversely affect the Cr alloy.
[0050]
　[For any element]
　Ni-Fe-Cr alloy of the above addition, instead of part of Fe, and may contain Al.
[0051]
　Al: 0 ~ 0.50%
　of aluminum (Al) is an optional element and may not be contained. If contained, Al is a deoxidizing the alloy. However, if the Al content is too high, decrease the cleanliness of the alloy decreases processability and ductility of the alloy. Therefore, Al content is from 0 to 0.50%. A preferable lower limit of the Al content is 0.05%. The preferable upper limit of the Al content is 0.30%, more preferably 0.20%. In this specification, Al content sol. Means Al (acid soluble Al).
[0052]
　[For formula
　(1)] F1 = 4.386 / (C rel is defined as + 0.15). F1 is an indication of intergranular corrosion resistance. If it is less than the average grain size d is F1, the relative amount of solute C (C rel is appropriate average grain size d relative). In this case, the unit deposition amount of C (C Unit ) is sufficiently reduced, sensitization is suppressed. As a result, it is possible to increase the intergranular corrosion resistance. On the other hand, when the average grain size d equal to or greater than F1, the relative amount of solute C (C rel average grain size d is too large for). In this case, the unit deposition amount of C (C Unit ) is not sufficiently reduced, sensitization is promoted. As a result, intergranular corrosion resistance is lowered.
[0053]
　[Equation (2)]
　Equation (1) relative amount of dissolved C in (C rel ), as described above C, since determined relatively from the content of Ti and N, defined as follows.
　C Rel = C-0.125Ti Tasu 0.8571N (2)
[0054]
　[Production Method]
　Ni-Fe-Cr alloy of the present embodiment is produced by various manufacturing methods. As an example of the production method, a method for manufacturing a Ni-Fe-Cr alloy tube.
[0055]
　First, prepare a material having the above chemical composition. Material is a hollow billet, for example. The hollow billet, for example, is produced by machining or vertical perforations. Implementing the hot extrusion against the hollow billet. Hot extrusion, for example, a Ugine Sejournet-Sejurune method. Through the above steps, Ni-Fe-Cr alloy pipe is manufactured. By other hot working other than hot extrusion, it may be manufactured Ni-Fe-Cr alloy tube. Hot working may be repeated several times.
[0056]
　Preferably, after between final hot working, cooling rate to 900 ° C. is 0.3 ° C. / sec or higher. After between final hot working, if the cooling rate to 900 ° C. is 0.3 ° C. / sec or more, it is possible to average crystal grain diameter d is to satisfy the equation (1), to adjust the average grain size d. As a result, it is possible to have excellent intergranular corrosion resistance.
[0057]
　After between final hot working, for example, be carried mist water cooling, it is possible to make the cooling rate to 900 ℃ 0.3 ℃ / sec or higher.
[0058]
　Further with respect to Ni-Fe-Cr alloy tube after hot working, cold working such as cold rolling and / or cold drawing may be performed. By carrying out cold working, it is possible to reduce the average crystal grain size d. In this case, it increases further intergranular corrosion resistance.
[0059]
　Further, after hot working, or, with respect to Ni-Fe-Cr alloy tube after cold working may be carried out final heat treatment such as solution treatment in order to obtain the desired mechanical properties. When carrying out the heat treatment, the preferable lower limit of the heat treatment temperature is 900 ° C., even more preferably within 915 ° C., more preferably 930 ° C.. When carrying out the solution treatment, the lower limit of the preferred heat treatment temperature is 1020 ° C.. In this case, it is possible to form a solid solution of Cr carbides. As a result, it is possible to further suppress the intergranular corrosion resistance.
[0060]
　The preferable upper limit of the heat treatment temperature is 1100 ° C., more preferably from 1080 ° C., more preferably 1060 ° C.. When carrying out the stabilization process, the preferred upper limit of the heat treatment temperature is lower than 1000 ° C.. If the heat treatment temperature is lower than 1000 ° C., it can be precipitated TiC. Further is less than the heat treatment temperature is 1000 ° C., it is possible to reduce the average crystal grain size d. In this case, it is possible to further suppress sensitization. As a result, it is possible to further suppress the intergranular corrosion resistance. And Ni-Fe-Cr alloy of the present embodiment, even if subjected to a heat treatment at a high temperature of 1000 ~ 1100 ° C., can be suppressed sensitization. A preferred thermal processing time of the final heat treatment is 2 to 30 minutes.
[0061]
　In one example of the manufacturing method described above, it has been described manufacturing method of Ni-Fe-Cr alloy tube. However, Ni-Fe-Cr alloy may be a plate, welded pipe, or may be a rod or the like. In short, the product shape of the Ni-Fe-Cr alloy is not particularly limited.
[0062]
　Ni-Fe-Cr alloy manufactured by the above manufacturing method has excellent intergranular corrosion resistance.
Example
[0063]
　The alloy of Test Nos. 1 to Test No. 23 shown in Table 1 were produced material with vacuum melting.
[0064]
[Table 1]

[0065]
　"C in Table 1 rel each of the" and "F1" column, C of Ni-Fe-Cr alloy of each test number rel values and F1 value is entered.
[0066]
　It was produced ingot from each material. In Test Nos. 1 to test No. 21, after hot forging at each ingot 1200 ° C., carried out hot rolling at a reduction of area of ​​50% at 1200 ° C., further performing cold rolling at a reduction of area of ​​67% Te, thickness 5 mm, width 80 mm, was produced a plate of length 650 mm. In Test No. 22 and Test No. 23, each ingot was hot-forged at 1200 ° C., thickness 15 mm, width 60 mm, was produced a plate of length 290 mm. In Test No. 22 and Test No. 23, the cold rolling was not conducted. For each plate, the heat treatment temperature and heat treatment time shown in Table 2, the final heat treatment was carried out. The sheet after the heat treatment was quenched (water cooling).
[0067]
[Table 2]

[0068]
　Average grain size measurement]
　cutting each sheet in the rolling direction and the direction perpendicular, thickness 5 mm, width 20 mm, were taken test piece of length 10 mm. The specimen to a plane including the rolling direction of the plate (longitudinal section of the test piece) is observed plane was filled resin, and the observation surface was mirror-polished. The polished surface was corroded with mixed acid. The corroded observation surface was observed with an optical microscope. The average grain size d is five field taken at 100 times magnification to determine the average crystal grain size d ([mu] m).
[0069]
　[Intergranular corrosion resistance test]
　from plate material of each test number, thickness 5 mm, width of 10 mm, were taken test piece of length 50 mm. Longitudinal direction of the test piece was parallel to the longitudinal direction of the plate material. On specimens were subjected to a sensitization heat treatment for 60 minutes at 700 ° C. simulating the weld heat affected zone. The surface of the subjected sensitization heat treatment test piece finished with wet emery No. 600, degreased with acetone, and dried. On specimens in accordance with ASTM A262 C method, the intergranular corrosion test, to evaluate the intergranular corrosion resistance of the corrosion test specimens. Test bath is 65% nitric acid was boiled, it was repeated three batches immersion test in which one batch for 48 hours. The corrosion weight loss of each batch was measured to calculate the average corrosion rate of the corrosion rate of 3 batches.
[0070]
　Intergranular corrosion resistance evaluation, 3 average corrosion rate of batch 1 g / m 2 when: · hr, was excellent in intergranular corrosion resistance ( "○" in Table 2). Average corrosion rate 1 g / m 2 if it exceeds · hr, was determined to intergranular corrosion is poor ( "×" in Table 2).
[0071]
　[Test Results]
　The test results are shown in Table 2.
[0072]
　Referring to Table 1, the content of each element of the plate material of Test Nos. 1 to Test No. 9 and Test No. 22 are suitable, and an average grain size d and the chemical composition satisfies the formula (1). As a result, the crystal grains become fine, showed excellent intergranular corrosion resistance.
[0073]
　In Test No. 22, because it did not implement the cold rolling, it increased average grain size d as compared with Test No. 5. However, the average grain size d is for satisfying the equation (1), showed excellent intergranular corrosive.
[0074]
　On the other hand, in Test No. 10, N content is too high. Therefore, Ti is precipitated as Ti nitride, could not be sufficiently secure the C. Thus, the relative amount of solute C (C rel ) increases, the relative amount of solute C (C rel average crystal grain size d becomes too large relative). As a result, the mean crystal grain size d is more than F1, intergranular corrosion resistance was low.
[0075]
　In Test No. 11, Ti content was too low. Therefore, Ti can not be sufficiently secure the C, relative amount of solute C (C rel ) increases, the relative amount of solute C (C rel average crystal grain size d becomes too large relative). As a result, the mean crystal grain size d is more than F1, intergranular corrosion resistance was low.
[0076]
　In Test No. 12 - Test No. 16, although the chemical composition was appropriate, the average grain size d is equal to or greater than F1. As a result, intergranular corrosion resistance was low.
[0077]
　In Test No. 17, Ti content is too low, N content is too high. Therefore, the relative amount of solute C (C rel ) increases, the relative amount of solute C (C rel average crystal grain size d becomes too large relative). As a result, the mean crystal grain size d is more than F1, intergranular corrosion resistance was low.
[0078]
　In Test No. 18, the C content is too high. Therefore, the relative amount of solute C (C rel ) increases, the relative amount of solute C (C rel average crystal grain size d becomes too large relative). As a result, the mean crystal grain size d is more than F1, intergranular corrosion resistance was low.
[0079]
　In Test No. 19, Ti content was too high. Therefore, the hot workability is deteriorated, because it could not be processed, and the outside of the test object.
[0080]
　In Test No. 20, after between final hot working, cooling rate to 900 ° C. was less than 0.3 ° C. / s. Therefore, even if the heat treatment temperature below 1000 ° C., an average grain size d as compared with test No. 2 is increased, the average grain size d is equal to or greater than F1. As a result, intergranular corrosion resistance was low.
[0081]
　In Test No. 21, after between final hot working, cooling rate to 900 ° C. was less than 0.3 ° C. / s. Therefore, the average grain size d as compared with test No. 3 is increased, the average grain size d is equal to or greater than F1. As a result, intergranular corrosion resistance was low.
[0082]
　In Test No. 23, after between final hot working, cooling rate to 900 ° C. was less than 0.3 ° C. / s. In Test No. 23 Furthermore, was not even cold rolling after hot working. Therefore, even if the heat treatment temperature below 1000 ° C., an average grain size d as compared with test No. 5 is increased, the average grain size d is equal to or greater than F1. As a result, intergranular corrosion resistance was low.
[0083]
　It has been described an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Accordingly, the present invention is not limited to the embodiments described above, it can be implemented by changing the above-described embodiments without departing from the scope and spirit thereof as appropriate.

The scope of the claims
[Requested item 1]
　By
　mass%,
　C: 0.005 ~
　0.015%, Si: 0.05 ~ 0.50%, Mn: 0.05
　~ 1.5%, P: 0.030% or
　less, S: 0.020 % or
　less,
　Cu:
　1.0 ~ 5.0%, Ni: 30.0 ~ 45.0%,
　Cr: 18.0 ~ 30.0%, Mo: 2.0 ~ 4.5%,
　Ti: 0
　~ 2.0% .5, N: 0.001 ~ 0.015%,
　and, Al: 0 ~ 0.50%, and contains, has a chemical composition the balance being Fe and impurities,
　the average crystal grain diameter d ([mu] m) satisfies the formula (1), Ni-Fe- Cr alloy.
　d <4.386 / (C rel +0.15) (1)
　Here, C in the formula (1) rel is defined by the formula (2).
　C rel = C-0.125Ti + 0.8571N (2)
　wherein each element symbol in the formula (1) and (2), the content of the corresponding element (mass%) is substituted.
[Requested item 2]
　A Ni-Fe-Cr alloy according to claim 1,
　wherein the chemical
　composition, Al: 0.05 ~ 0.50%,
containing, Ni-Fe-Cr alloy.