HEAT-RESISTANT AND CORROSION-RESISTANT HIGH-CHROMIUM NICKEL-BASED ALLOY WITH SUPERIOR HOT FORGEABILITY

Abstract

Provided is a heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability, consisting of, by mass %, 43.1 to 45.5% of Cr, 0.5 to 1.5% of Mo, 0.0001 to 0.0090% of Mg, 0.001 to 0.040% of N, 0.05 to 0.50% of Mn, 0.01 to 0.10% of Si, 0.05 to 1.00% of Fe, 0.01% to 1.00% of Co, 0.01 to 0.30% of Al, 0.04 to 0.3% of Ti, 0.0003 to 0.0900% of V, 0.0001 to 0.0100% of B, 0.001 to 0.050% of Zr, and optionally one or more elements selected from (a) to (d): (a) 0.001 to 0.020% of Cu; (b) 0.001 to 0.100% of W; (c) 0.0001 or more and less than 0.0020% of Ca; and (d) 0.001% or more and less than 0.100% of Nb, and the balance of Ni with inevitable impurities.

Claims

1. A heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability, the alloy having a composition consisting of, by mass %, 43.1 to 45.5% of Cr, 0.5 to 1.5% of Mo, 0.0001 to 0.0090% of Mg, 0.001 to 0.040% of N, 0.05 to 0.50% of Mn, 0.01 to 0.10% of Si, 0.05 to 1.00% of Fe, 0.01% to 1.00% of Co, 0.01 to 0.30% of Al, 0.04 to 0.3% of Ti, 0.0003% to 0.0900% of V, 0.0001 to 0.0100% of B, 0.001 to 0.050% of Zr, and the balance of Ni with inevitable impurities.

2. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 1, wherein the composition further consists of, by mass %, 0.001% to 0.020% of Cu.

3. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 1, wherein the composition further consists of, by mass %, 0.001 to 0.100% of W.

4. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 1, wherein the composition further consists of, by mass %, 0.0001% or more and less than 0.0020% of Ca.

5. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 1, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

6. A member for a boiler of a thermal power station for use in a waste gas environment, made of the heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 1.

7. A member for a corrosion-resistant pressure vessel for use in a chemical plant, made of the heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 1.

8. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 2, wherein the composition further consists of, by mass %, 0.001 to 0.100% of W.

9. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 2, wherein the composition further consists of, by mass %, 0.0001% or more and less than 0.0020% of Ca.

10. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 3, wherein the composition further consists of, by mass %, 0.0001% or more and less than 0.0020% of Ca.

11. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according to claim 8, wherein the composition further consists of, by mass %, 0.0001% or more and less than 0.0020% of Ca.

12. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 2, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

13. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 3, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

14. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 4, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

15. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 8, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

16. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 9, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

17. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 10, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

18. The heat-resistant and corrosion-resistant high-Cr-containing Ni-based alloy having superior hot forgeability according claim 11, wherein the composition further consists of, by mass %, 0.001% or more and less than 0.100% of Nb.

Description

DESCRIPTION OF EMBODIMENTS

[0046] Next, the reasons for the content ranges of each component element in the composition of the high-Cr-containing Ni-based alloy of the present invention will be described in detail.

Cr

[0047] Cr is effective for improving corrosion resistance against high temperature corrosion including sulfuration in a high temperature environment and corrosion resistance against acids. By forming a surface film containing mostly of Cr.sub.2O.sub.3, it becomes possible to impart the superior corrosion resistance against high temperature corrosion and the superior corrosion resistance against acids. The surface film is formed as an oxide, and to what extent NiO produced from Ni, which is the main component of the alloy, has lower proportion, and to what extent the proportion of Cr.sub.2O.sub.3 approaches 100% can indicate the degree of improvement in corrosion resistance against high temperature corrosion or corrosion resistance against acids. Thus, in order to achieve sufficient effects, 43.1% by mass or more (hereinafter, % by mass is simply referred to as %) of Cr should be contained. However, if the content exceeds 45.5%, then the hot forgeability in a state in which the solidified structure is formed might significantly decrease, unfavorably. Therefore, the Cr content is set to be from 43.1 to 45.5%.

[0048] The upper limit of Cr is preferably 45.0%, and is more preferably 44.8%, whereas the lower limit of Cr is preferably 43.5%, and is more preferably 43.8%.

Mo

[0049] Mo is effective for facilitating the formation of the surface film containing mostly Cr.sub.2O.sub.3, which is essential for imparting the superior corrosion resistance against high temperature corrosion and the superior corrosion resistance against acids to the high-Cr-containing Ni-based alloy. To obtain the sufficient facilitating effect, 0.5% or more of Mo should be contained. However, if the content exceeds 1.5%, then Mo might be concentrated at dendrite boundaries in the solidified structure, so that the hot forgeability in a state in which the solidified structure has become obvious, might unfavorably decrease. Therefore, the Mo content is set to be from 0.5% to 1.5%.

[0050] The upper limit of Mo is preferably 1.4%, and is more preferably 1.2%, whereas the lower limit of Mo is preferably 0.7%, and is more preferably 0.8%.

N, Mn and Mg

[0051] By making N, Mn and Mg coexist, it is possible to reduce the formation of -Cr phases, which might decrease the hot forgeability at 1100 C. or lower. When a coarse -Cr phase is formed as the solidified structure, a fine -Cr phase is also formed. The coarse -Cr phase formed as the solidified structure does not disappear even by the homogenizing heat treatment, and becomes the principal cause of inhibition of the hot forgeability immediately after the beginning of the hot forging. When an ingot size decreases, the cooling rate increases, and accordingly, it becomes possible to reduce the coarsening, whereas when the ingot size increases, the cooling rate decreases, resulting in an unavoidable increase in occurrence of the coarse -Cr phase, correlating with the decrease in cooling rate. After melting the ingot, the melted ingot is subjected to the homogenizing heat treatment, followed by the hot forging. Here, the fine -Cr phase is once dissolved in a -Ni phase, which is the matrix, by the homogenizing heat treatment. Even in a case in which an addition of trace elements described below can successively achieve decomposition and refinement of the coarse -Cr phase without causing forging cracking immediately after the beginning of the hot forging, which is at a temperature of 1200 C. or more, then when the forging is repeated and the temperature is gradually decreased thereby to 1100 C. or less, the dissolved fine -Cr phase might be reprecipitated, so that the deformability might significantly decrease. In this case, by shifting an incubation period for the reprecipitation to a longer-period scale, the decrease in deformability at 1100 C. or less can be reduced.

[0052] N, Mn and Mg are effective for stabilizing the -Ni phase, which is the matrix, for facilitating solution of Cr, and for reducing the formation of precipitated phases, such as an -Cr phase, in a relatively short time as in the hot forging process. These advantageous effects can maintain a good hot forgeability without cracking, without a sudden increase in deformation resistance or a sudden decrease in deformability, even in a temperature range below 1100 C. However, if the N content is less than 0.001%, then there is no effect of reducing the formation of an -Cr phase, so that excessive -Cr phase might be formed during the hot forging process at 1100 C. or less, resulting in the decrease in hot forgeability. On the other hand, if the content exceeds 0.040%, then nitrides are produced in a short time, so that high temperature workability might decrease, and it might be difficult to process into a member. Therefore, the content is set to be from 0.001% to 0.040%.

[0053] The upper limit of N is preferably 0.035%, and is more preferably 0.030%, whereas the lower limit of N is preferably 0.002%, and is more preferably 0.004%.

[0054] Similarly, if the Mn content is less than 0.05%, then there is no effect of reducing the formation of an -Cr phase, resulting in decrease in hot forgeability at 1100 C. or less. On the other hand, if the content exceeds 0.50%, then the corrosion resistance against acids might decrease. Therefore, the content is set to be from 0.05% to 0.50%.

[0055] The upper limit of Mn is preferably 0.40%, and is more preferably 0.35%, whereas the lower limit of Mn is preferably 0.07%, and is more preferably 0.10%.

[0056] Similarly, if the Mg content is less than 0.0001%, then there is no effect of reducing the formation of the -Cr phase, resulting in the decrease in hot forgeability at 1100 C. or less. On the other hand, if the content exceeds 0.0090%, then the effect of reducing the formation of the -Cr phase might be saturated, and Mg might be concentrated in grain boundaries, resulting in the decrease in hot forgeability. Therefore, the content is set to be from 0.0001% to 0.0090%.

[0057] The upper limit of Mg is preferably 0.0080%, and is more preferably less than 0.0020%, whereas the lower limit of Mg is preferably 0.0003%, and is more preferably 0.0005%.

[0058] Note that the effects of these three elements are not equivalent to each other, and it has been found that the above effects cannot be achieved unless the three elements exist at the same time and are contained within the predetermined ranges.

Si

[0059] By adding Si as a deoxidant, oxides can be reduced, so that the deformability at high temperature, which concerns the hot forgeability, can be improved, and thus, Si is effective for decreasing the forging cracking. This effect can be achieved when 0.01% or more of Si is contained. However, if the content exceeds 0.10%, then the formation of an -Cr phase might be facilitated, so that a sudden decrease in deformability in the hot forgeability might be caused, and thus, the forging cracking may be likely to occur. Therefore, the Si content is set to be from 0.01% to 0.10%.

[0060] The upper limit of Si is preferably 0.09%, and is more preferably 0.08%, whereas the lower limit of Si is preferably 0.02%, and is more preferably 0.03%.

Fe and Co

[0061] Fe and Co are effective for preventing forging cracking by improving toughness in a temperature range of 1200 C. or more. This effect can be achieved when 0.05% or more of Fe is contained. However, if the content exceeds 1.00%, then the deformability at forging might decrease. Therefore, the Fe content is set to be from 0.05% to 1.00%.

[0062] The upper limit of Fe is preferably 0.90%, and is more preferably 0.80%, whereas the lower limit of Fe is preferably 0.07%, and is more preferably 0.10%.

[0063] Similarly, a comparable effect can be achieved when 0.01% or more of Co is contained. However, if the content exceeds 1.00%, then the effect might be saturated, and at the same time, a decrease in corrosion resistance against acids might be unfavorably caused. Therefore, the Co content is set to be from 0.01% to 1.00%.

[0064] The upper limit of Co is preferably 0.80%, and is more preferably 0.50%, whereas the lower limit of Co is preferably 0.02%, and is more preferably 0.05%.

Al and Ti

[0065] Al and Ti are added because they are effective for improving the hot forgeability. This is because Al and Ti combine with oxygen in molten metal, and then they float to the surface and are removed from the surface of the molten metal as slag, so that the oxygen in the metal can be removed. The deoxidation effect can be enhanced by adding Al and Ti at the same time, rather than adding them separately.

[0066] This effect can be achieved when 0.01% or more of Al is added. However, if the content exceeds 0.30%, then the incubation period for precipitation under a high temperature environment shifts to a shorter-time scale, resulting in an unfavorable increase in the possibility of forging cracking. Therefore, the Al content is set to be from 0.01% to 0.30%.

[0067] The upper limit of Al is preferably 0.26%, and is more preferably 0.20%, whereas the lower limit of Al is preferably 0.02%, and is more preferably 0.05%.

[0068] Similarly, a comparable effect can be achieved when 0.04% or more of Ti is added. However, if the content exceeds 0.30%, then the incubation period for precipitation under a high temperature environment shifts to a shorter-time scale, resulting in an unfavorable increase in the possibility of forging cracking particularly in the presence of coarse -Cr phase. Therefore, the Ti content is set to be from 0.04% to 0.30%.

[0069] The upper limit of Ti is preferably 0.28%, and is more preferably 0.25%, whereas the lower limit of Ti is preferably 0.05%, and is more preferably 0.07%.

V

[0070] V is effective for reducing the occurrence of coarse -Cr phase in a high temperature area, and thereby, in particular, the deformability regarding the hot forgeability can be improved, so that forging cracking can be suppressed. This effect can be achieved when 0.0003% or more of V is contained. However, if the content exceeds 0.0900%, then the deformability at a high temperature might decrease and the effect of suppressing forging cracking might disappear. Therefore, the V content is set to be from 0.0003% to 0.0900%.

[0071] The upper limit of V is preferably 0.0700%, and is more preferably 0.0500%, whereas the lower limit of V is preferably 0.0010%, and is more preferably 0.0050%.

Zr and B

[0072] Zr and B are effective for improving the deformability in hot forging in a temperature range of 1100 C. or more, in particular, 1200 C. or more, and thereby the cracking during hot forging can be reduced. In particular, it is effective for improving the hot forgeability in a state in which the coarse -Cr phase, which is the solidified structure that has become obvious, is present. In this case, the effect achieved by combined addition of Zr and B can be greater than that achieved by adding them separately.

[0073] This effect can be achieved when 0.0001% or more of B is contained. However, if the content exceeds 0.0100%, then the concentration in grain boundaries might occur, so that the deformability might decrease, and accordingly, cracking during hot forging might be induced. Therefore, the B content is set to be from 0.0001 to 0.0100%.

[0074] The upper limit of B is preferably 0.0080%, and is more preferably 0.0050%, whereas the lower limit of B is preferably more than 0.0005%, and is more preferably 0.0010%.

[0075] Similarly, a comparable effect can be achieved when 0.001% or more of Zr is contained. However, if the content exceeds 0.050%, then concentration at grain boundaries might occur, so that deformability might decrease, and accordingly, cracking during hot forging might be induced. Therefore, the Zr content is set to be from 0.001 to 0.05%.

[0076] The upper limit of Zr is preferably 0.040%, and is more preferably 0.030%, whereas the lower limit of Zr is preferably 0.003%, and is more preferably 0.005%.

Ca

[0077] Since Cu is effective for improving corrosion resistance to acids, Cu may be added as necessary. This effect can be achieved when 0.001% or more of Cu is contained. However, if the content exceeds 0.020%, then the hot forgeability tends to decrease. Therefore, the Cu content is set to be from 0.001 to 0.020%.

[0078] The upper limit of Cu is preferably 0.015%, and is more preferably 0.010%, whereas the lower limit of Cu is preferably 0.002%, and is more preferably 0.005%.

W

[0079] Since W is effective for improving high temperature corrosion resistance, W may be added as necessary. This effect can be achieved when 0.001% or more of W is contained. However, if the content exceeds 0.100%, then the hot forgeability tends to decrease. Therefore, the W content is set to be from 0.001 to 0.100%.

[0080] The upper limit of W is preferably 0.090%, and is more preferably 0.080%, whereas the lower limit of W is preferably 0.002%, and is more preferably 0.005%.

Ca

[0081] Ca is effective for reducing forging cracking by improving deformability in hot forgeability at, in particular, 1200 C. or more, in a state in which the coarse -Cr phase, which is the solidified structure that has become obvious, is present, and thus, Ca may be added as necessary. This effect can be achieved when 0.0001% or more of Ca is contained. However, if the content is 0.0020% or more, then the deformability might decrease, so that cracking might be induced. Therefore, the Ca content is set to be 0.0001% or more and less than 0.0020%.

[0082] The upper limit of Ca is preferably 0.0019%, and is more preferably 0.0017%, whereas the lower limit of Ca is preferably 0.0002%, and is more preferably 0.0005%.

Nb

[0083] Nb is effective for improving the hot workability at 900 C. or less, by reducing formation of M.sub.23C.sub.6 carbide by forming NbC, and thus, Nb may be added as necessary. This effect can be achieved when 0.001% or more of Nb is contained. However, if the content is 0.100% or more, then the precipitation of -Cr phase might be unfavorably promoted. Therefore, the Nb content is set to be 0.001% or more and less than 0.100%.

[0084] The upper limit of Nb is preferably 0.090%, and is more preferably 0.080%, whereas the lower limit of Nb is preferably 0.002%, and is more preferably 0.005%.

Inevitable Impurities

[0085] Although it is inevitable that P, S, Sn, Zn, Pb and C are contained as dissolved raw materials, less than 0.01% of P, less than 0.01% of S, less than 0.01% of Sn, less than 0.01% of Zn, less than 0.002% of Pb, and less than 0.01% of C do not impair the properties of the alloy of the present invention, and thus, these constituent elements with the contents thereof within the ranges described above are permitted.

[0086] Hereunder, examples of the present invention will be described.

EXAMPLES

Example 1

[0087] Each of the Ni-based alloys having predetermined component compositions was melted using a general vacuum high-frequency melting furnace, and was formed into about 15 kg of a cylindrical ingot of 10 mm diameter240 mm.

[0088] On an outer surface of the mold used to form the ingot, a Kanthal heating element was placed, thereby the maximum temperature of 1400 C. could be maintained, and a target temperature to be maintained could be varied by a thermoregulator. Thus, a solidified structure that mimics a large ingot can be obtained.

[0089] After tapping, the temperature was maintained at 1325 C., which is within the temperature range in which a solid phase and a liquid phase coexist, for 60 min, and the temperature was decreased at a cooling rate of 2 C./min, and then, when the temperature became less than 500 C., the heater was turned off to let it cool naturally.

[0090] The obtained ingots were subjected to a homogenizing heat treatment at 1230 C. for 1 hours, and then, the ingots were cooled by water, to form high-Cr-containing Ni-based alloys 1 to 42 of the present invention shown in Tables 1 to 3, Comparative high-Cr-containing Ni-based alloys 1 to 26 shown in Tables 4 and 5, and Conventional high-Cr-containing Ni-based alloys 1 to 3 shown in Table 6.

[0091] Since, in an upper end portion, shrinkage cavities occur in the casting process, a portion with the shrinkage cavities (about 4 kg from the upper surface) was cut off and removed.

[0092] Note that Conventional high-Cr-containing Ni-based alloy 1 corresponds to an alloy disclosed in Patent Document 1 (corrosion-resistant NiCr-based alloy having superior bend formability), Conventional high-Cr-containing Ni-based alloy 2 corresponds to an alloy disclosed in Patent Document 3 (Ni-based alloy having superior high temperature workability and having superior corrosion resistance with a significantly small elution amount of metal ions), and Conventional high-Cr-containing Ni-based alloy 3 corresponds to an alloy disclosed in Patent Document 4 (Ni-based alloy anti-corrosion plate having superior high-temperature corrosion resistance).

[0093] Furthermore, in order to perform evaluations described below, material preparations were carried out. That is, for high-Cr-containing Ni-based alloys 1 to 42 of the present invention, Comparative high-Cr-containing Ni-based alloys 1 to 26, and Conventional high-Cr-containing Ni-based alloys 1 to 3, one round bar of 80 mm diameter200 mm and three round bars of 15 mm diameter200 mm were subsequently cut from each ingot by wire-cut electrical discharge machining.

TABLE-US-00001 TABLE 1 Present inven- Composition ttion Ni + alloy inevitable No. Cr Mo Mg N Mn Si Fe Co Al Ti V B Zr Cu W Ca Nb impurities 1 44.2 1.0 0.0026 0.019 0.9 0.02 0.74 0.46 0.05 0.28 0.0472 0.0062 0.007 balance 2 43.1 0.8 0.0040 0.013 0.22 0.09 0.24 0.12 0.09 0.20 0.0100 0.0024 0.014 balance 3 45.5 1.4 0.0043 0.014 0.28 0.08 0.52 0.58 0.18 0.13 0.0174 0.0075 0.005 balance 4 43.7 0.5 0.0015 0.015 0.13 0.05 0.65 0.64 0.26 0.23 0.0069 0.0037 0.016 balance 5 44.6 1.5 0.0045 0.024 0.26 0.07 0.08 0.75 0.14 0.17 0.0522 0.0025 0.038 balance 6 43.8 1.2 0.0001 0.025 0.09 0.06 0.54 0.18 0.15 0.24 0.0106 0.0009 0.020 balance 7 44.3 1.3 0.0088 0.031 0.16 0.07 0.66 0.39 0.18 0.21 0.0338 0.0018 0.017 balance 8 43.8 0.9 0.0017 0.001 0.13 0.08 0.11 0.19 0.10 0.16 0.0199 0.0009 0.030 balance 9 44.7 0.8 0.0008 0.039 0.29 0.04 0.09 0.22 0.10 0.11 0.0022 0.0052 0.015 balance 10 44.6 1.3 0.0015 0.013 0.05 0.06 0.61 0.70 0.24 0.07 0.0654 0.0008 0.019 balance 11 44.7 1.0 0.0016 0.019 0.49 0.03 0.42 0.64 0.24 0.20 0.0570 0.0053 0.005 balance 12 43.7 0.9 0.0020 0.012 0.33 0.01 0.45 0.17 0.07 0.10 0.0641 0.0031 0.003 balance 13 43.7 0.9 0.0050 0.033 0.34 0.09 0.13 0.64 0.21 0.12 0.0571 0.0067 0.019 balance 14 44.3 1.0 0.0049 0.015 0.13 0.03 0.05 0.23 0.20 0.14 0.0203 0.0024 0.031 balance

TABLE-US-00002 TABLE 2 Present inven- Composition tion Ni + alloy inevitable No. Cr Mo Mg N Mn Si Fe Co Al Ti V B Zr Cu W Ca Nb impurities 15 44.8 0.8 0.0074 0.019 0.34 0.09 0.99 0.65 0.07 0.22 0.0564 0.0046 0.036 balance 16 44.0 1.0 0.0068 0.030 0.25 0.03 0.84 0.01 0.05 0.20 0.0069 0.0060 0.010 balance 17 44.2 0.8 0.0014 0.030 0.10 0.04 0.18 0.98 0.22 0.23 0.0421 0.0024 0.003 balance 18 45.0 1.2 0.0039 0.027 0.21 0.03 0.71 0.57 0.01 0.23 0.0346 0.0006 0.006 balance 19 44.9 1.2 0.0053 0.028 0.14 0.08 0.32 0.37 0.29 0.10 0.0474 0.0064 0.024 balance 20 44.3 1.2 0.0046 0.007 0.22 0.07 0.25 0.23 0.24 0.04 0.0339 0.0047 0.019 balance 21 44.5 0.8 0.0050 0.026 0.12 0.05 0.28 0.56 0.14 0.29 0.0509 0.0024 0.019 balance 22 44.7 1.1 0.0049 0.020 0.37 0.07 0.68 0.42 0.18 0.12 0.0003 0.0006 0.037 balance 23 44.6 1.2 0.0008 0.020 0.17 0.08 0.70 0.05 0.14 0.14 0.0897 0.0012 0.015 balance 24 43.5 0.9 0.0057 0.021 0.16 0.03 0.34 0.69 0.06 0.10 0.0555 0.0001 0.012 balance 25 43.7 0.8 0.0025 0.011 0.29 0.04 0.84 0.74 0.17 0.18 0.0251 0.0098 0.010 balance 26 43.6 1.2 0.0058 0.021 0.33 0.06 0.68 0.36 0.10 0.11 0.0016 0.0058 0.001 balance 27 44.3 0.9 0.0049 0.022 0.27 0.06 0.21 0.24 0.08 0.07 0.0254 0.0030 0.049 balance

TABLE-US-00003 TABLE 3 Present inven- Composition tion Ni + alloy inevitable No. Cr Mo Mg N Mn Si Fe Co Al Ti V B Zr Cu W Ca Nb impurities 28 43.9 1.1 0.0013 0.003 0.27 0.07 0.11 0.30 0.07 0.19 0.0286 0.0046 0.019 0.001 balance 29 44.3 1.3 0.0060 0.033 0.26 0.03 0.36 0.46 0.19 0.27 0.0560 0.0007 0.033 0.019 balance 30 44.6 1.3 0.0007 0.033 0.22 0.07 0.43 0.51 0.25 0.17 0.0280 0.0028 0.018 0.001 balance 31 43.9 1.3 0.0055 0.016 0.09 0.06 0.49 0.75 0.15 0.18 0.0381 0.0046 0.021 0.098 balance 32 44.1 1.2 0.0077 0.010 0.17 0.07 0.18 0.45 0.16 0.27 0.0490 0.0019 0.009 0.012 0.035 balance 33 44.0 1.2 0.0076 0.016 0.12 0.06 0.12 0.69 0.08 0.23 0.0630 0.0006 0.034 0.0001 balance 34 44.2 1.4 0.0080 0.014 0.27 0.07 0.22 0.51 0.20 0.13 0.0170 0.0024 0.023 0.0019 balance 35 44.5 1.2 0.0034 0.017 0.16 0.02 0.50 0.71 0.08 0.22 0.0493 0.0038 0.023 0.001 balance 36 44.7 1.3 0.0076 0.022 0.12 0.07 0.72 0.31 0.19 0.06 0.0478 0.0018 0.025 0.098 balance 37 44.8 1.3 0.0027 0.002 0.22 0.05 0.13 0.51 0.23 0.07 0.0102 0.0013 0.012 0.055 balance 38 44.7 1.2 0.0047 0.023 0.33 0.06 0.79 0.49 0.03 0.14 0.0354 0.0046 0.029 0.007 0.0008 0.037 balance 39 44.1 0.8 0.0068 0.025 0.22 0.07 0.29 0.39 0.17 0.16 0.0651 0.0074 0.014 0.041 0.0012 0.018 balance 40 44.5 1.1 0.0003 0.035 0.28 0.03 0.82 0.65 0.17 0.13 0.0371 0.0053 0.011 0.011 0.025 0.0016 0.005 balance 41 44.2 0.9 0.0015 0.010 0.39 0.04 0.57 0.06 0.02 0.16 0.0287 0.0072 0.023 0.014 0.013 balance 42 44.5 1.1 0.0060 0.011 0.20 0.07 0.39 0.45 0.09 0.19 0.0306 0.0025 0.009 0.006 0.004 balance

TABLE-US-00004 TABLE 4 Com- para- Composition tive Ni + alloy inevitable No. Cr Mo Mg N Mn Si Fe Co Al Ti V B Zr Cu W Ca Nb impurities 1 42.8* 1.0 0.0060 0.019 0.12 0.08 0.16 0.44 0.26 0.11 0.040 0.0076 0.022 balance 2 45.7* 0.8 0.0034 0.013 0.17 0.02 0.60 0.33 0.10 0.16 0.038 0.0036 0.038 balance 3 44.9 0.4* 0.0012 0.014 0.28 0.05 0.73 0.54 0.02 0.15 0.042 0.0011 0.007 balance 4 43.9 1.6* 0.0039 0.015 0.39 0.02 0.61 0.48 0.08 0.19 0.015 0.0009 0.009 balance 5 44.8 0.7 * 0.024 0.25 0.04 0.82 0.50 0.12 0.06 0.067 0.0075 0.033 balance 6 44.9 1.0 0.0108* 0.025 0.39 0.05 0.52 0.29 0.21 0.15 0.012 0.0013 0.034 balance 7 44.4 0.8 0.0044 * 0.33 0.05 0.23 0.08 0.19 0.12 0.050 0.0040 0.029 balance 8 44.7 1.2 0.0053 0.045* 0.14 0.06 0.27 0.30 0.08 0.13 0.015 0.0044 0.020 balance 9 43.9 1.3 0.0066 0.010 * 0.06 0.70 0.23 0.04 0.12 0.025 0.0077 0.035 balance 10 44.5 0.7 0.0037 0.013 0.54* 0.03 0.16 0.53 0.09 0.14 0.052 0.0059 0.015 balance 11 43.9 1.1 0.0059 0.019 0.25 * 0.60 0.58 0.10 0.21 0.029 0.0074 0.032 balance 12 43.7 1.4 0.0006 0.012 0.33 0.11* 0.54 0.47 0.12 0.26 0.066 0.0050 0.007 balance 13 44.5 1.4 0.0060 0.033 0.33 0.07 * 0.28 0.08 0.26 0.068 0.0033 0.029 balance 14 43.7 1.0 0.0038 0.015 0.17 0.08 1.11* 0.11 0.16 0.20 0.012 0.0022 0.011 balance 15 43.9 1.2 0.0033 0.019 0.31 0.07 0.23 * 0.16 0.12 0.021 0.0048 0.009 balance 16 44.2 1.0 0.0009 0.030 0.17 0.07 0.72 1.14* 0.10 0.23 0.014 0.0054 0.035 balance Asterisk (*) indicates out of range of composition of present invention.

TABLE-US-00005 TABLE 5 Com- para- Composition tive Ni + alloy inevitable No. Cr Mo Mg N Mn Si Fe Co Al Ti V B Zr Cu W Ca Nb impurities 17 43.9 1.2 0.0023 0.030 0.19 0.06 0.75 0.72 * 0.22 0.032 0.0025 0.020 balance 18 44.0 0.9 0.0058 0.027 0.31 0.03 0.25 0.16 0.32* 0.06 0.027 0.0009 0.033 balance 19 43.9 1.3 0.0060 0.028 0.31 0.04 0.25 0.15 0.06 0.03* 0.064 0.0033 0.040 balance 20 43.7 0.8 0.0044 0.007 0.18 0.08 0.52 0.55 0.16 0.33* 0.044 0.0020 0.025 balance 21 44.3 1.1 0.0066 0.026 0.12 0.08 0.54 0.77 0.18 0.12 * 0.0017 0.006 balance 22 43.8 1.1 0.0058 0.020 0.13 0.02 0.73 0.47 0.06 0.06 0.11* 0.0074 0.007 balance 23 44.9 1.0 0.0053 0.020 0.12 0.09 0.61 0.74 0.12 0.24 0.067 * 0.028 balance 24 45.0 0.8 0.0055 0.021 0.08 0.03 0.25 0.77 0.11 0.08 0.051 0.0121* 0.035 balance 25 44.8 0.9 0.0043 0.011 0.14 0.05 0.46 0.71 0.10 0.11 0.012 0.0053 * balance 26 43.6 0.8 0.0011 0.021 0.33 0.08 0.08 0.38 0.17 0.12 0.007 0.0039 0.055* balance Asterisk (*) indicates out of range of composition of present invention.

TABLE-US-00006 TABLE 6 Composition Conventional Ni + alloy inevitable No. Cr Mo Mg N Mn Si Fe Co Al Ti V B Zr Cu W Ca Nb C impurities 1 44.2 1.0 0.021 0.27 0.014 balance 2 44.1 0.93 0.002 0.019 0.06 0.04 0.10 0.02 balance 3 44.5 0.9 0.001 0.13 0.06 0.32 0.018 0.0022 0.010 0.05 balance

(1) Hot Forging Test

[0094] The round bar of 80 mm diameter200 mm of each of the high-Cr-containing Ni-based alloys 1 to 42 of the present invention, Comparative high-Cr-containing Ni-based alloys 1 to 26, and Conventional high-Cr-containing Ni-based alloys 1 to 3 was heated at 1230 C. in an air atmosphere furnace, and after being retained for 1 hours, the bar was taken out from the furnace, followed by hot forging with a hammer while tightening with a tap in the range of from 900 C. to 1230 C.

[0095] In the middle of the forging, the temperature might decrease below 900 C. before obtaining a predetermined shape. At that time, the bar was heated again in the furnace at 1230 C., retained for 15 min, followed by the hot forging.

[0096] The reheating in the furnace at 1230 C. and the hot forging were repeated several times, and finally, three bars of 20 mm diameter1000 mm were formed.

[0097] Alloys with significant cracks occurred in this process (hereinafter, referred to as forged cracked product) are indicated in Tables 7 to 12 as present, that is, the cracks were present after forging, and such alloys were not used in the evaluation described later.

[0098] Each of the remaining alloys without any problems occurring in the hot forging was retained at 1230 C. for 30 minutes, followed by being cooled with water, and thereby a solution heat treated material was obtained.

(2) Evaluation for Hot Forgeability

[0099] From the round bars of 15 mm diameter200 mm cut from the ingots of the high-Cr-containing Ni-based alloys 1 to 42 of the present invention, Comparative high-Cr-containing Ni-based alloys 1 to 26, and Conventional high-Cr-containing Ni-based alloys 1 to 3, round-bar tensile specimens (68 mm in total length; parallel portion having a diameter of 6 mm, a length of 15 mm) were formed.

[0100] These tensile specimens were subjected to a high speed tensile tests under a high temperature mimicking forging conditions.

[0101] Thus, only the specimens were heated at 1230 C. by direct electrification, retained for 15 minutes, and then the specimens were subjected to a tensile test at high speed at 30 mm/sec.

[0102] After occurrence of a fracture, the diameter at the site of the fracture was measured, reduction of area in high speed tensile test (reduction of area =100 (dddd)/(dd) (%), where d is a diameter before testing, d is a diameter after testing) was calculated, and the results are shown in Tables 7 to 12.

[0103] The reduction of area in the high speed tensile test can be an index for determining the deformability in a high temperature environment. In general, when assuming a large ingot, it is necessary to have a reduction of area of 60% or more.

(3) Corrosion Test

[0104] From the round bars having a diameter of 20 mm (solution heat treated materials) of the high-Cr-containing Ni-based alloys 1 to 42 of the present invention and Comparative high-Cr-containing Ni-based alloys 1 to 26 (except for the forged cracked products), plates of 20 mm diameter3 mm were obtained by cutting, the entire surfaces of these plates were polished and finished with waterproof emery paper #1000, so that corrosion specimens were obtained.

[0105] Here, since Conventional high-Cr-containing Ni-based alloys 1-3 were cracked in the forging process of the bars of 80 mm diameter200 mm, the bars of 15 mm diameter200 mm long were heated at 1230 C. in the air atmosphere furnace, retained for 10 hours, and then, the bars were taken out from the furnace, followed by hot rolling within the range of from 1000 C. to 1230 C. while pressing gradually. In the middle of the rolling, the temperature might decrease below 900 C. before obtaining a predetermined shape. At that time, the bars were heated again in the furnace at 1230 C., retained for 15 minutes, followed by hot rolling. The reheating in the furnace at 1230 C. and the hot forging were repeated several times, and finally, plates of 3 mm20 mm55 mm were obtained. From each of these plates, a plate of 20 mm diameter3 mm was obtained by cutting, and the entire surface thereof was polished and finished with waterproof emery paper #1000, to form a corrosion specimen.

[0106] As a test for high temperature corrosion including sulfuration, the specimens were retained for 24 hours under a gas flow of N.sub.2-40% CO.sub.2-40% CO-0.1% H.sub.2S, which was maintained at 800 C., and then a corrosion rate was calculated based on reduction amounts of weight, obtained from weights before and after testing.

[0107] In the measurement of the weight after testing, in order to remove scale produced by corrosion or oxidation, a removal method using an alkaline solution, known as the Gakushin-type, was adopted (the specimens were boiled in a solution of 18% NaOH+3% KMnO.sub.4, and then boiled in an aqueous solution of 10% ammonium citrate. Both boiling processes were carried out for about 30 to 40 minutes.). By using this method, the scale alone can be removed efficiently without causing damage to the ground metal.

[0108] The corrosion rate was calculated by the formula: corrosion rate (mm/year)=W/(S.Math.t)8.761/, where W is a reduction amount of weight (g) before and after testing, S is a surface area of a specimen (m.sup.2), t is a period of test (hours), is a specific gravity (g/cm.sup.3). The specific gravity was obtained by the Archimedes method. Since the obtained specific gravities were mostly about 7.9 (g/cm.sup.2), 7.9 (g/cm.sup.2) was used in every calculation.

[0109] Furthermore, a corrosion test against acids was carried out as follows: a specimen was dipped in an aqueous solution of 5% HNO.sub.3+50% H.sub.2SO.sub.4 and an aqueous solution of 50% HNO.sub.3+2% HCl, which were maintained at 80 C., the specimen being dipped for 24 hours for each solution, and then, a corrosion rate was calculated based on a weight difference between weights before and after testing.

[0110] The results obtained from the tests described above are shown in Tables 7 to 12.

TABLE-US-00007 TABLE 7 Reduction Corrosion test (mm/year) Presence of area in 80 C. 80 C. Present of crack high speed 800 C. 50% 50% invention after tensile reducing H.sub.2SO.sub.4 + HNO.sub.3 + alloy No. forging test (%) gas 5% HNO.sub.3 2% HCl 1 absent 74 0.20 0.002 0.004 2 absent 81 0.31 0.004 0.007 3 absent 63 0.14 0.001 0.002 4 absent 72 0.21 0.002 0.004 5 absent 62 0.15 0.002 0.004 6 absent 71 0.27 0.002 0.005 7 absent 69 0.28 0.002 0.006 8 absent 66 0.23 0.002 0.002 9 absent 68 0.28 0.003 0.004 10 absent 65 0.13 0.001 0.004 11 absent 78 0.36 0.004 0.005 12 absent 64 0.17 0.002 0.002 13 absent 67 0.16 0.002 0.002 14 absent 65 0.15 0.002 0.003

TABLE-US-00008 TABLE 8 Reduction Corrosion test (mm/year) Presence of area in 80 C. 80 C. Present of crack high speed 800 C. 50% 50% invention after tensile reducing H.sub.2SO.sub.4 + HNO.sub.3 + alloy No. forging test (%) gas 5% HNO.sub.3 2% HCl 15 absent 82 0.38 0.005 0.006 16 absent 64 0.27 0.002 0.001 17 absent 79 0.12 0.005 0.006 18 absent 64 0.22 0.001 0.005 19 absent 62 0.17 0.002 0.003 20 absent 67 0.12 0.002 0.004 21 absent 64 0.23 0.003 0.002 22 absent 67 0.23 0.002 0.003 23 absent 63 0.28 0.001 0.004 24 absent 64 0.30 0.002 0.004 25 absent 62 0.28 0.004 0.003 26 absent 64 0.16 0.002 0.005 27 absent 63 0.22 0.003 0.006

TABLE-US-00009 TABLE 9 Reduction Corrosion test (mm/year) Presence of area in 80 C. 80 C. Present of crack high speed 800 C. 50% 50% invention after tensile reducing H.sub.2SO.sub.4 + HNO.sub.3 + alloy No. forging test (%) gas 5% HNO.sub.3 2% HCl 28 absent 62 0.38 0.003 0.004 29 absent 63 0.13 0.003 0.005 30 absent 67 0.21 0.003 0.005 31 absent 62 0.21 0.002 0.004 32 absent 61 0.21 0.004 0.004 33 absent 78 0.30 0.003 0.005 34 absent 76 0.13 0.002 0.003 35 absent 74 0.29 0.003 0.005 36 absent 67 0.13 0.004 0.005 37 absent 81 0.14 0.002 0.006 38 absent 79 0.21 0.003 0.005 39 absent 83 0.30 0.003 0.005 40 absent 66 0.27 0.004 0.001 41 absent 78 0.29 0.002 0.004 42 absent 72 0.18 0.002 0.001

TABLE-US-00010 TABLE 10 Reduction Corrosion test (mm/year) Presence of area in 80 C. 80 C. of crack high speed 800 C. 50% 50% Comparative after tensile reducing H.sub.2SO.sub.4 + HNO.sub.3 + alloy No. forging test (%) gas 5% HNO.sub.3 2% HCl 1 absent 82 0.67 0.008 0.011 2 present 3 absent 84 0.13 0.011 0.008 4 present 5 present 6 present 7 present 8 absent 65 0.25 0.013 0.014 9 present 10 absent 72 0.13 0.021 0.016 11 present 12 present 13 present 14 absent 51 0.58 0.015 0.014 15 present 16 absent 67 0.34 0.021 0.022

TABLE-US-00011 TABLE 11 Reduction Corrosion test (mm/year) Presence of area in 80 C. 80 C. of crack high speed 800 C. 50% 50% Comparative after tensile reducing H.sub.2SO.sub.4 + HNO.sub.3 + alloy No. forging test (%) gas 5% HNO.sub.3 2% HCl 17 present 18 present 19 present 20 present 21 present 22 absent 52 0.21 0.004 0.008 23 present 24 present 25 present 26 present

TABLE-US-00012 TABLE 12 Reduction Corrosion test (mm/year) Presence of area in 80 C. 80 C. of crack high speed 800 C. 50% 50% Conventional after tensile reducing H.sub.2SO.sub.4 + HNO.sub.3 + alloy No. forging test (%) gas 5% HNO.sub.3 2% HCl 1 present 0.26 0.003 0.003 2 present 0.31 0.002 0.002 3 present 0.22 0.004 0.006

[0111] In view of the results shown above, it can be understood that the high-Cr-containing Ni-based alloys 1 to 42 of the present invention have superior corrosion resistance against high temperature corrosion and acids, equivalent to that of Conventional high-Cr-containing Ni-based alloy 1, Conventional high-Cr-containing Ni-based alloy 2 and Conventional high-Cr-containing Ni-based alloy 3, which are conventional materials.

[0112] Furthermore, it can be seen that the alloys 1 to 42 of the present invention have far superior hot forgeability even in a state in which coarse solidified structure is formed.

[0113] In contrast, as compared with the high-Cr-containing Ni-based alloys 1 to 42 of the present invention, Comparative high-Cr-containing Ni-based alloys 1 to 26, which are out of the range of the present invention, are inferior in corrosion resistance, or inferior in hot forgeability, so that the alloys were cracked during the hot forging process or had less reduction of area in the high speed tensile test (deformability (reduction of area)).

Example 2

[0114] An alloy having the same composition as that of the alloy 1 of the present invention, which was confirmed to have good hot forgeability, was subjected to 6-ton vacuum melting, which is on a mass production scale, and then poured into two 3-ton molds under a vacuum. One of them was melted again by an electro slag remelting (ESR). Thus, 3 tons of ingot of 520 mm diameter1800 mm long was formed. This weight includes that of coarse -Cr phase. The obtained ingot was subjected to a homogenizing heat treatment at 1230 C. for 10 hours, and was subsequently subjected to hot forging, to form a slab of 150 mm thick600 mm4000 mm. In the middle of the process, when the temperature decreased below 900 C., the ingot was heated again in the furnace, the temperature in which was maintained at 1230 C., and the hot forging was repeated until a predetermined size was obtained. As a result, no crack was found in the initial period of the forging process, and occurrence of cracking was not found after the end of the hot forging. Here, the occurrence of cracking in the initial period of forging was visually identified.

INDUSTRIAL APPLICABILITY

[0115] As described above, the high-Cr-containing Ni-based alloys of the present invention has superior hot forgeability, in particular, superior hot forgeability immediately after the beginning of hot forging of such a large ingot that includes a coarse -Cr phase formed at solidification, and the alloys have superior corrosion resistance against hot temperature corrosion including sulfuration and superior corrosion resistance against acids, which are equivalent to or superior to those of conventional materials. Thus, by using the high-Cr-containing Ni-based alloy of the present invention, it becomes possible to manufacture a large forged member, for example, a slab (large forged product) having a size that can be provided in a manufacturing line for stainless steel, or a large forged member required in making a large reaction vessel.

[0116] Therefore, according to the high-Cr-containing Ni-based alloys of the present invention, a slab having a size that can be provided in a manufacturing line for stainless steel, or a large forged member required in making a large reaction vessel can be provided, and accordingly, the present invention demonstrates excellent industrial effects.

[0117] In addition, since the high-Cr-containing Ni-based alloys of the present invention has superior hot forgeability, products with complicated shapes can be easily formed, so that it is expected as a new material that can be applied in a new field.