Austenitic stainless-steel sheet and method for producing same

Abstract

This austenitic stainless-steel sheet has a prescribed chemical composition, has a δ-ferrite phase volume fraction of 1.00% or less at the thickness center of the sheet, and satisfies the average crystal grain size (μm) of the austenite phase ≥ –40 × the volume fraction of the δ-ferrite phase (%) + 80. As a result of the foregoing, provided is an austenitic stainless-steel sheet exhibiting excellent creep rupture lifespan.

Description

Austenitic stainless steel sheet and method for manufacturing the same

[0001] The present invention relates to an austenitic stainless steel sheet.

[0002] Austenitic stainless steel sheets are used in structures in high-temperature environments due to their excellent high-temperature strength. However, it is known that the presence of elemental segregation in austenitic stainless steels reduces creep rupture life at high temperatures, and there is a demand for improving creep rupture life in high-temperature environments.

[0003] Patent Document 1 states that, in consideration of creep strength in a high-temperature environment (300 to 700° C.), it is preferable that the austenite grains are large.

[0004] Patent Document 2 describes that the presence of a δ-ferrite phase, which is one form of component segregation, suppresses the coarsening of austenite grains.

[0005] JP 2021-66928 A JP 2010-196103 A

[0006] An object of the present invention is to improve the creep rupture life at high temperatures of an austenitic stainless steel sheet.

[0007] The present inventors have investigated means for improving the high temperature creep rupture life (hereinafter sometimes simply referred to as creep rupture life) of austenitic stainless steel sheets, and have obtained the following findings.

[0008] (a) With regard to the chemical composition, adding small amounts of Nb and N to an austenitic stainless steel plate promotes solid solution strengthening and improves creep rupture life.

[0009] Furthermore, since both elemental segregation and grain size affect the high-temperature creep rupture life of austenitic stainless steels, the inventors believed that controlling these factors was important for further improving creep rupture life, and conducted a detailed study on the effects of the δ-ferrite phase, which is one form of elemental segregation, and grain size on high-temperature creep rupture life, resulting in the following findings.

[0010] (b) It was found that there is a certain relationship between the volume fraction and grain size of the δ-ferrite phase and creep rupture life. That is, it was found that an excellent creep rupture life can be obtained if the grain size is equal to or greater than the value calculated from the relational expression using the volume fraction of the δ-ferrite phase.

[0011] (c) During the manufacturing process, the delta-ferrite phase generated during solidification gradually decreases through heating and hot rolling. The less delta-ferrite phase there is in the steel, the slower the reduction rate becomes, making it more difficult to reduce the delta-ferrite phase. Therefore, the subsequent solution heat treatment is generally a process that is performed at a lower temperature and for a shorter time than slab heating or soaking heat treatment, and its effect in reducing the delta-ferrite phase is limited. Furthermore, since solution heat treatment is also a process for adjusting the grain size, which is affected by the presence of delta-ferrite phase, it is effective to reduce the delta-ferrite phase primarily before the solution heat treatment.

[0012] (d) We have found that controlling the total heating time for slab heating and soaking heat treatment prior to the solution heat treatment, and further performing soaking heat treatment between the first and second hot rolling rather than before the first hot rolling, can efficiently mitigate element segregation, including the δ-ferrite phase. This is because the first hot rolling extends element segregation perpendicular to the thickness direction, increasing the surface area of ​​the δ-ferrite / austenite phase interface and promoting the dissolution of alloy elements in the δ-ferrite phase into the austenite phase. In addition, this shortens the diffusion distance of alloy elements in the thickness direction during dissolution, and increases the concentration gradient of alloy elements in the austenite phase in the thickness direction. Here, the first hot rolling is a process of hot rolling a slab to destroy the slab's structure, and as mentioned above, also serves to dissolve element segregation. It is typically performed at a cumulative reduction rate of 30 to 70%. Soaking heat treatment is a process performed separately from the slab heating for hot rolling, in order to reduce element segregation, including the δ-ferrite phase, and to diffuse the alloy elements. Secondary hot rolling is a process for destroying the slab's structure by hot rolling and forming it into the specified product dimensions. It is usually performed at a cumulative reduction rate of 50 to 95%.

[0013] (e) As the plate thickness increases, it becomes more difficult for the temperature at the center of the plate thickness to reach the target temperature, and the closer to the center of the plate thickness, the more difficult it becomes for grains to grow. Furthermore, as the plate thickness increases during solution heat treatment, the amount of δ-ferrite phase at the center of the plate thickness tends to increase, making the plate more susceptible to the inhibitory effect of the δ-ferrite phase on grain growth. Given this background, it is effective to adjust the heating time for solution heat treatment to increase as the plate thickness increases. Therefore, the inventors investigated the heating time depending on the plate thickness.

[0014] They found that there is a correlation between the grain size at the center of the plate thickness, plate thickness, and heating time. Grain growth progresses more toward the surface, but the larger the grain size, the slower the growth rate becomes, reducing the difference in grain size across the plate thickness. Controlling the solution heat treatment conditions as described above provides excellent creep rupture life.

[0015] (f) By controlling the chemical composition and manufacturing method described above, it is possible to obtain an austenitic stainless steel sheet with excellent creep rupture life at high temperatures, which not only achieves solid solution strengthening by the inclusion of trace amounts of Nb and N, but also alleviates the segregation of components including the δ ferrite phase and increases the grain size.

[0016] The present invention was made based on the above findings, and the gist of the present invention is as follows.

[0017] (1) The chemical composition, in mass%, is: C: 0.100% or less, Si: 2.00% or less, Mn: 2.50% or less, P: 0.0450% or less, S: 0.0300% or less, Ni: 9.00 to 13.00%, Cr: 19.00 to 24.00%, Mo: 0.001 to 1.00%, Nb: 0.005 to 0.100%, N: 0.100 to 0.300%, Al: 0.200% or less, B: 0.0001 to 0.0100%, Ti: 0 to 0.300%, Cu: 0 to 1.00%, V: 0 to 0.500%, Co: 0 to 1.000%, 1. An austenitic stainless steel sheet comprising: Ca: 0-0.1000%, Mg: 0-0.0050%, Sb: 0-0.200%, Sn: 0-0.100%, Se: 0-0.080%, W: 0-0.50%, Ta: 0-0.50%, Hf: 0-0.100%, Zr: 0-0.100%, Bi: 0-0.300%, Pb: 0-0.100%, REM: 0-0.200%, balance: Fe and impurities; a volume fraction of δ-ferrite phase in the center of the sheet thickness is 1.00% or less; and an average grain size (μm) of the austenite phase satisfies formula 1: average grain size (μm) of the austenite phase ≧ -40 × volume fraction of δ-ferrite phase (%) + 80... formula 1

[0018] (2) The chemical composition is, in mass%, Ti: 0.001 to 0.300%, Cu: 0.01 to 1.00%, V: 0.010 to 0.500%, Co: 0.010 to 1.000%, Ca: 0.0010 to 0.0100%, Mg: 0.0001 to 0.0050%, Sb: 0.020 to 0.200%, Sn: 0.001 to 0.100%, Se: 0.005 to 0.080%, W: 0.01 to 0.50%, Ta: 0.005 to 0.50%, Hf: 0.010 to 0.100%, Zr: 0.001 to 0.100%, The austenitic stainless steel sheet according to (1), further comprising one or more selected from Bi: 0.030 to 0.300%, Pb: 0.010 to 0.100%, and REM: 0.005 to 0.200%.

[0019] (3) A method for producing an austenitic stainless steel sheet according to (1), wherein the chemical composition, in mass%, is: C: 0.100% or less, Si: 2.00% or less, Mn: 2.50% or less, P: 0.0450% or less, S: 0.0300% or less, Ni: 9.00 to 13.00%, Cr: 19.00 to 24.00%, Mo: 0.001 to 1.00%, Nb: 0.005 to 0.100%, N: 0.100 to 0.300%, Al: 0.200% or less, B: 0.0001 to 0.0100%, Ti: 0 to 0.300%, Cu: 0 to 1.00%, V: 0 to 0.500%, a primary hot rolling process in which the slab, which contains Co: 0 to 1.000%, Ca: 0 to 0.1000%, Mg: 0 to 0.0050%, Sb: 0 to 0.200%, Sn: 0 to 0.100%, Se: 0 to 0.080%, W: 0 to 0.50%, Ta: 0 to 0.50%, Hf: 0 to 0.100%, Zr: 0 to 0.100%, Bi: 0 to 0.300%, Pb: 0 to 0.100%, REM: 0 to 0.200%, and the balance: Fe and impurities, is heated in a temperature range of 1100 to 1300°C, and then subjected to primary hot rolling; The method for producing an austenitic stainless steel sheet includes a soaking heat treatment step in which the slab that has undergone the first hot rolling step is heated in a temperature range of 1100 to 1300°C for 3 hours or more, a second hot rolling step in which the slab that has undergone the soaking heat treatment step is heated to a temperature range of 1100 to 1300°C and then subjected to second hot rolling to obtain a hot-rolled steel sheet, and a solution heat treatment step in which the hot-rolled steel sheet is heated in a temperature range of 1000 to 1300°C for a time period equal to or longer than the minimum heating time (hours) calculated by the following formula 2, wherein the cumulative slab heating time, which is the sum of the heating time in the first hot rolling step, the heating time in the soaking heat treatment step, and the heating time in the second hot rolling step, is 4.0 hours or more. Minimum heating time (hours) = 0.025 (hours / mm) × thickness (mm) of the hot-rolled steel sheet... Formula 2

[0020] According to the present invention, an austenitic stainless steel sheet having excellent creep rupture life at high temperatures can be obtained.

[0021] Hereinafter, one embodiment of the present invention (hereinafter, sometimes simply referred to as this embodiment) will be described in detail.

[0022] In this specification, "austenitic" refers to a metal structure in which the metal structure at room temperature is primarily austenite (γ phase). Therefore, it also encompasses those containing phases other than austenite (δ ferrite phase, strain-induced martensite phase, inclusions, etc.). For example, the proportion of austenite in a stainless steel sheet is greater than 70%, typically 95% or more. Furthermore, the thickness (sheet thickness) of the austenitic stainless steel sheet according to the present invention is not particularly limited, but may be, for example, 3 to 70 mm.

[0023] <Chemical Composition> The content of each element is limited for the following reasons: Unless otherwise specified, "%" for the content means "mass%" in the steel.

[0024] (C: 0.100% or less) C (carbon) promotes the stabilization of the austenite phase, but if the C content is high, there is a possibility that the creep rupture life will decrease. For this reason, the C content is set to 0.100% or less. The C content may be 0.095% or less, 0.090% or less, 0.085% or less, or 0.080% or less. The C content is preferably 0.001% or more. The C content may be 0.005% or more, 0.007% or more, 0.015% or more, 0.030% or more, 0.045% or more, or 0.050% or more. A preferred range of the C content is 0.001 to 0.100%.

[0025] (Si: 2.00% or less) Si (silicon) is an effective element for deoxidation. However, if the Si content is high, there is a risk of deterioration in weldability and creep rupture life. Therefore, the Si content is set to 2.00% or less. The Si content may be 1.85% or less, 1.65% or less, 1.30% or less, 1.10% or less, 1.00% or less, 0.80% or less, 0.65% or less, or 0.50% or less. The Si content is preferably 0.001% or more. The Si content may be 0.01% or more, 0.03% or more, 0.05% or more, 0.10% or more, 0.15% or more, or 0.20% or more. The Si content is preferably in a range of 0.01% to 2.00%, and more preferably in a range of 0.10% to 1.00%.

[0026] (Mn: 2.50% or less) Mn (manganese) is an element effective for deoxidation and stabilizes the austenite phase. However, if the Mn content is too high, oxidation resistance may deteriorate. Therefore, the Mn content is set to 2.50% or less. The Mn content may be 2.30% or less, 2.10% or less, 1.75% or less, 1.40% or less, or 1.20% or less. The Mn content is preferably 0.001% or more. The Mn content may be 0.01% or more, 0.05% or more, 0.10% or more, 0.15% or more, 0.25% or more, 0.40% or more, or 0.45% or more. The preferred range of the Mn content is 0.01% to 2.50%.

[0027] (P: 0.0450% or less) P (phosphorus) is contained as an impurity and is an element that reduces toughness and hot workability. For this reason, the P content is set to 0.0450% or less. It is preferable to reduce the P content as much as possible, and the P content may be 0.0430% or less, 0.0410% or less, 0.0380% or less, 0.0340% or less, or 0.0320% or less. On the other hand, since excessive reduction of the P content increases manufacturing costs, the P content is preferably 0.0001% or more. The P content may be 0.0020% or more, 0.0050% or more, 0.0100% or more, 0.0160% or more, or 0.0190% or more. A preferred range of the P content is 0.0001% to 0.0450%.

[0028] (S: 0.0300% or less) S (sulfur) is contained as an impurity and is an element that reduces toughness and hot workability. For this reason, the S content is set to 0.0300% or less. It is preferable to reduce the S content as much as possible, and the S content may be 0.0270% or less, 0.0240% or less, 0.0180% or less, 0.0120% or less, or 0.0100% or less. On the other hand, since excessive reduction of the S content increases the manufacturing cost, the S content is preferably 0.0001% or more. The S content may be 0.0003% or more, 0.0005% or more, or 0.0006% or more. A preferred range of the S content is 0.0001% to 0.0300%.

[0029] (Ni: 9.00 to 13.00%) Ni (nickel) is effective in stabilizing the austenite phase and improving oxidation resistance and creep rupture life. Therefore, the Ni content is set to 9.00% or more. The Ni content may preferably be 9.20% or more, 9.40% or more, 9.60% or more, 9.80% or more, 10.00% or more, 10.20% or more, 10.40% or more, or 10.80% or more. If the Ni content is too high, there is a risk of impairing weldability. Therefore, the Ni content is set to 13.00% or less. The Ni content may preferably be 12.80% or less, 12.60% or less, 12.40% or less, 12.20% or less, 12.00% or less, 11.80% or less, or 11.60% or less.

[0030] (Cr: 19.00 to 24.00%) Cr (chromium) is an element effective in improving oxidation resistance, high-temperature wear resistance, and creep rupture life. Therefore, the Cr content is set to 19.00% or more. The Cr content may preferably be 19.30% or more, 19.70% or more, 20.10% or more, 20.50% or more, 20.90% or more, 21.20% or more, 21.60% or more, 22.00% or more, or 22.50% or more. If the Cr content is too high, the austenite phase may become unstable and hot workability may deteriorate. Therefore, the Cr content is set to 24.00% or less. The Cr content may preferably be 23.80% or less, 23.70% or less, 23.50% or less, 23.30% or less, 23.20% or less, or 23.10% or less.

[0031] (Mo: 0.001 to 1.00%) Mo (molybdenum) is an element that improves corrosion resistance and also contributes to improving high-temperature strength and creep rupture life. Therefore, the Mo content is 0.001% or more. The Mo content may preferably be 0.01% or more, 0.03% or more, 0.05% or more, 0.10% or more, 0.15% or more, 0.20% or more, or 0.25% or more. A high Mo content increases raw material costs and also increases the amount of δ ferrite phase present. Therefore, the Mo content is set to 1.00% or less. The Mo content may preferably be 0.95% or less, 0.85% or less, 0.75% or less, 0.70% or less, 0.60% or less, or 0.50% or less.

[0032] (Nb: 0.005 to 0.100%) Nb (niobium) has the effect of improving high-temperature strength and creep rupture life. For this reason, the Nb content is set to 0.005% or more. The Nb content may preferably be 0.006% or more, 0.007% or more, 0.008% or more, 0.010% or more, 0.012% or more, or 0.015% or more. If the Nb content is too high, a duplex structure is formed, which actually reduces the creep rupture life. For this reason, the Nb content is set to 0.100% or less. The Nb content may preferably be 0.090% or less, 0.085% or less, 0.075% or less, 0.065% or less, 0.055% or less, 0.050% or less, or 0.040% or less.

[0033] (N: 0.100 to 0.300%) N (nitrogen) is an element effective in stabilizing the austenite phase and improving creep rupture life. For this reason, the N content is set to 0.100% or more. The N content may preferably be 0.110% or more, 0.120% or more, 0.130% or more, 0.140% or more, 0.150% or more, 0.160% or more, 0.170% or more, or 0.180% or more. A high N content promotes nitride precipitation, which in turn reduces creep rupture life. For this reason, the N content is set to 0.300% or less. The N content may preferably be 0.290% or less, 0.280% or less, 0.270% or less, 0.260% or less, 0.250% or less, 0.240% or less, 0.230% or less, 0.220% or less, 0.210% or less, or 0.200% or less.

[0034] (Al: 0.200% or less) Al (aluminum) is an element effective for deoxidation. However, if the Al content is too high, Al nitrides may be formed, which may reduce toughness. Therefore, the Al content is set to 0.200% or less. The Al content may preferably be 0.185% or less, 0.170% or less, 0.135% or less, 0.110% or less, or 0.090% or less. The Al content is preferably 0.001% or more. The Al content may be 0.004% or more, 0.008% or more, 0.015% or more, 0.020% or more, 0.025% or more, or 0.030% or more. The preferred range of the Al content is 0.001% to 0.200%.

[0035] (B: 0.0001 to 0.0100%) B (boron) is an element effective in improving creep rupture life and hot workability. Therefore, the B content is 0.0001% or more. The B content may preferably be 0.0002% or more, 0.0005% or more, 0.0010% or more, 0.0015% or more, or 0.0020% or more. If the B content is too high, there is a risk that hot workability will be impaired. Therefore, the B content is set to 0.0100% or less. The B content may preferably be 0.0090% or less, 0.0080% or less, 0.0070% or less, 0.0060% or less, or 0.0050% or less.

[0036] In addition to the above elements, one or more elements selected from Ti, Cu, V, Co, Ca, Mg, Sb, Sn, Se, W, Ta, Hf, Zr, Bi, Pb, and REM may be contained within the ranges shown below. In other words, the lower limit of the above elements is 0%. The reasons for limiting the content of each element will be explained below.

[0037] (Ti: 0 to 0.300%) Ti (titanium) is an element added to bond with C and N to improve corrosion resistance and intergranular corrosion resistance, but is not a particularly essential element, and the Ti content may be 0%. To achieve the above effects, the Ti content may be 0.001% or more, 0.002% or more, or 0.003% or more. If the Ti content is high, nozzle clogging is more likely to occur during the casting stage, and coarse Ti carbonitrides may deteriorate ductility. For this reason, the Ti content is set to 0.300% or less. The Ti content may preferably be 0.290% or less, 0.280% or less, 0.270% or less, 0.250% or less, 0.200% or less, 0.150% or less, or 0.100% or less.

[0038] (Cu: 0 to 1.00%) Cu (copper) is an element effective for stabilizing and softening the austenite phase, but is not a particularly essential element, and the Cu content may be 0%. To obtain the above effects, the Cu content may be 0.001% or more, 0.01% or more, 0.03% or more, 0.07% or more, 0.10% or more, or 0.12% or more. If the Cu content is too high, there is a risk of deterioration in oxidation resistance and hot workability. For this reason, the Cu content is set to 1.00% or less. The Cu content may preferably be 0.90% or less, 0.80% or less, 0.65% or less, 0.50% or less, or 0.40% or less.

[0039] (V: 0 to 0.500%) V (vanadium) is an element that improves corrosion resistance and promotes the formation of V carbides to improve high-temperature strength, but is not a particularly essential element, and the V content may be 0%. To achieve the above effects, the V content may be 0.001% or more, 0.005% or more, 0.010% or more, 0.015% or more, 0.030% or more, 0.045% or more, or 0.055% or more. If the V content is too high, there is a risk of a decrease in toughness due to V carbides. For this reason, the V content is set to 0.500% or less. The V content may preferably be 0.450% or less, 0.400% or less, 0.350% or less, 0.300% or less, 0.250% or less, or 0.200% or less.

[0040] (Co: 0 to 1.000%) Co (cobalt) contributes to improving high-temperature strength by stabilizing the austenite phase, but is not a particularly essential element, and the Co content may be 0%. To achieve the above effects, the Co content may be 0.001% or more, 0.010% or more, 0.015% or more, 0.030% or more, 0.060% or more, 0.080% or more, or 0.100% or more. As the Co content increases, the effect saturates and alloy costs increase. For this reason, the Co content is set to 1.000% or less. The Co content may preferably be 0.900% or less, 0.800% or less, 0.650% or less, 0.500% or less, or 0.400% or less.

[0041] (Ca: 0 to 0.1000%) Ca (calcium) is an element that improves the hot workability of steel, but is not a particularly essential element, and the Ca content may be 0%. To obtain the above effect, the Ca content may be 0.0001% or more, 0.0002% or more, or 0.0003% or more. If the Ca content is high, relatively large oxides may be formed in the steel, which may reduce the toughness of the steel. For this reason, the Ca content is set to 0.1000% or less. The Ca content may preferably be 0.0900% or less, 0.0800% or less, 0.0700% or less, 0.0600% or less, 0.0500% or less, 0.0400% or less, 0.0300% or less, 0.0200% or less, or 0.0100% or less.

[0042] (Mg: 0 to 0.0050%) Mg (magnesium) is an element that improves the hot workability of steel, but is not a particularly essential element, and the Mg content may be 0%. To obtain the above effects, the Mg content may be 0.0001% or more, 0.0002% or more, 0.0005% or more, 0.0007% or more, or 0.0008% or more. If the Mg content is too high, relatively large oxides may be formed in the steel, which may reduce the toughness of the steel. For this reason, the Mg content is set to 0.0050% or less. The Mg content may preferably be 0.0045% or less, 0.0040% or less, 0.0035% or less, 0.0030% or less, or 0.0025% or less.

[0043] (Sb: 0 to 0.200%) Sb (antimony) has the effect of improving high-temperature strength by segregating at grain boundaries, but is not a particularly essential element, and the Sb content may be 0%. To obtain the above effect, the Sb content may be 0.001% or more, 0.010% or more, 0.020% or more, 0.040% or more, 0.080% or more, 0.120% or more, or 0.140% or more. If the Sb content is too high, segregation of Sb may occur, which may cause cracks during welding. For this reason, the Sb content is set to 0.200% or less. The Sb content may preferably be 0.190% or more or 0.180% or less.

[0044] (Sn: 0 to 0.100%) Sn (tin) contributes to improving corrosion resistance and high-temperature strength, but is not a particularly essential element, and the Sn content may be 0%. To obtain the above effects, the Sn content may be 0.001% or more, 0.008% or more, 0.020% or more, 0.035% or more, 0.055% or more, or 0.060% or more. If the Sn content is too high, slab cracking may occur during steel sheet production. For this reason, the Sn content is set to 0.100% or less. The Sn content may preferably be 0.095% or less, or 0.090% or less.

[0045] (Se: 0 to 0.080%) Se (selenium) has the effect of improving machinability, but is not a particularly essential element, and the Se content may be 0%. To obtain the above effect, the Se content may be 0.001% or more, 0.005% or more, 0.007% or more, 0.015% or more, 0.030% or more, 0.045% or more, or 0.055% or more. If the Se content is too high, there is a risk of deterioration in hot workability and corrosion resistance. For this reason, the Se content is set to 0.080% or less. The Se content may preferably be 0.075% or less, or 0.070% or less.

[0046] (W: 0 to 0.50%) W (tungsten) is an element that improves high-temperature strength and corrosion resistance, but is not a particularly essential element, and the W content may be 0%. To obtain the above effects, the W content may be 0.001% or more, 0.01% or more, 0.02% or more, 0.03% or more, or 0.05% or more. If the W content is too high, toughness may be reduced. For this reason, the W content is set to 0.50% or less. The W content may preferably be 0.45% or less, 0.40% or less, 0.30% or less, 0.20% or less, or 0.15% or less.

[0047] (Ta: 0 to 0.50%) Ta (tantalum) has the effect of improving high-temperature strength, but is not a particularly essential element, and the Ta content may be 0%. To obtain the above effect, the Ta content may be 0.001% or more, 0.005% or more, 0.01% or more, 0.05% or more, 0.10% or more, 0.15% or more, 0.25% or more, or 0.30% or more. If the Ta content is too high, there is a risk of a decrease in toughness. For this reason, the Ta content is set to 0.50% or less. The Ta content may preferably be 0.49% or less, 0.48% or less, 0.47% or less, 0.46% or less, or 0.45% or less.

[0048] (Hf: 0 to 0.100%) Hf (hafnium) has the effect of improving corrosion resistance, intergranular corrosion resistance, high-temperature strength, and oxidation resistance, but is not a particularly essential element, and the Hf content may be 0%. To obtain the above effect, the Hf content may be 0.001% or more, 0.005% or more, 0.010% or more, 0.020% or more, 0.040% or more, 0.060% or more, or 0.070% or more. If the Hf content is too high, toughness may be reduced. For this reason, the Hf content is set to 0.100% or less. The Hf content may preferably be 0.099% or less, 0.098% or less, or 0.090% or less.

[0049] (Zr: 0 to 0.100%) Zr (zirconium) is an element effective for deoxidation and desulfurization and improves hot workability, but is not a particularly essential element, and the Zr content may be 0%. To obtain the above effect, the Zr content may be 0.001% or more, 0.002% or more, 0.003% or more, 0.004% or more, or 0.005% or more. If the Zr content is too high, there is a risk of deterioration of hot workability. Therefore, the Zr content is set to 0.100% or less. The Zr content may preferably be 0.090% or less, 0.080% or less, 0.060% or less, 0.040% or less, or 0.030% or less.

[0050] (Bi: 0 to 0.300%) Bi (bismuth) has the effect of improving machinability, but is not a particularly essential element, and the Bi content may be 0%. To achieve the above effect, the Bi content may be 0.001% or more, 0.010% or more, 0.020% or more, 0.030% or more, 0.050% or more, 0.100% or more, 0.150% or more, or 0.190% or more. If the Bi content is too high, there is a risk of degrading hot workability. For this reason, the Bi content is set to 0.300% or less. The Bi content may preferably be 0.295% or less, 0.290% or less, 0.285% or less, or 0.280% or less.

[0051] (Pb: 0 to 0.100%) Pb (lead) has the effect of improving machinability, but is not a particularly essential element, and the Pb content may be 0%. To achieve the above effect, the Pb content may be 0.001% or more, 0.010% or more, 0.020% or more, 0.035% or more, 0.055% or more, or 0.065% or more. A high Pb content lowers the melting point of the grain boundary and reduces the bonding strength of the grain boundary, which may lead to reduced hot workability, such as liquation cracking due to grain boundary melting. For this reason, the Pb content is set to 0.100% or less. The Pb content may preferably be 0.097% or less, 0.095% or less, or 0.090% or less.

[0052] (REM: 0 to 0.200%) REM (rare earth element) is an element effective in improving oxidation resistance and high-temperature wear resistance, but is not a particularly essential element, and the REM content may be 0%. To achieve the above effect, the REM content may be 0.001% or more, 0.005% or more, 0.0010% or more, 0.020% or more, 0.025% or more, 0.030% or more, or 0.0050% or more. If the REM content is too high, hot workability and weldability may be impaired. For this reason, the REM content is set to 0.200% or less. The REM content may preferably be 0.185% or less, 0.170% or less, 0.0150% or less, 0.130% or less, 0.100% or less, or 0.090% or less.

[0053] REM refers to a total of 17 elements, including Sc, Y, and lanthanoid elements, and the above-mentioned REM content means the total content of these elements. Industrially, REM is often added in the form of misch metal.

[0054] In the chemical composition of this embodiment, the balance is Fe and impurities. Here, "impurities" refer to components that are mixed in during industrial production of austenitic stainless steel sheets due to various factors in raw materials such as ores and scraps, and in the manufacturing process, and are acceptable within a range that does not adversely affect this embodiment.

[0055] <Relationship between Volume Fraction of δ-Ferrite Phase and Average Grain Size of Austenite Phase> In the austenitic stainless steel sheet of this embodiment, the volume fraction of the δ-ferrite phase in the center portion of the sheet thickness (hereinafter also referred to as "δ amount") is 1.00% or less, and the average grain size of the austenite phase (hereinafter also simply referred to as "average grain size") satisfies the following formula 1.

[0056] Average grain size of austenite phase (μm) ≧−40×δ volume fraction of ferrite phase (%) + 80 Formula 1

[0057] (Volume Fraction of δ-Ferrite Phase) During solidification, δ-ferrite phase is likely to form near the center of the slab's thickness. Although it gradually decreases through heating and hot rolling, it tends to remain near the center of the product's thickness. Since the higher the δ-ferrite phase content, the worse the high-temperature creep rupture life of the austenitic stainless steel sheet. Therefore, in this embodiment, the volume fraction of the δ-ferrite phase near the center of the steel sheet's thickness is set to 1.00% or less. The volume fraction of the δ-ferrite phase near the center of the steel sheet's thickness may be preferably 0.95% or less, 0.90% or less, 0.85% or less, 0.80% or less, 0.75% or less, 0.70% or less, 0.65% or less, 0.60% or less, 0.55% or less, or 0.50% or less.

[0058] The volume fraction of the δ-ferrite phase at the center of the sheet thickness is measured by the following procedure. A ferrite meter is used as the measuring device. The ferrite meter uses a magnetic induction method to measure the volume fraction of the ferrite phase near the measurement point, and can directly measure the volume fraction of the δ-ferrite phase. An example of a ferrite meter is the Fischer MP30 manufactured by Fischer Instruments. Measurements are performed at the center of the sheet thickness (within a distance of 3 / 8 to 5 / 8 of the sheet thickness from the surface of the steel sheet) in a cross section perpendicular to the surface of the steel sheet and perpendicular to the rolling direction (hereinafter referred to as the sheet width cross section). The volume fraction of the δ-ferrite phase is measured at 20 points at least 5 mm apart in the direction perpendicular to the rolling direction (hereinafter referred to as the sheet width direction) at each of the positions 3 / 8, 4 / 8, and 5 / 8 of the sheet thickness from the surface of the steel sheet, with no overlapping measurement positions. A total of 60 points are used to measure the volume fraction of the δ-ferrite phase. The average (arithmetic mean) of the measured values ​​at 60 points is taken as the volume fraction of the δ-ferrite phase. However, if the plate thickness is less than 8 mm, measurements are taken at 20 points only at a position 4 / 8 of the plate thickness from the surface of the steel plate, and the average value is obtained. If no δ-ferrite phase is detected, the volume fraction is considered to be 0.

[0059] (Average grain size of austenite phase) The grain size is calculated from the grain size measured by the comparative method in accordance with JIS G0551:2023. The measurement is performed by electrolytically etching the sheet width cross section with nitric acid, observing five fields of view under a microscope at a position halfway down the sheet thickness from the surface of the steel sheet in accordance with JIS G0551:2023, measuring the grain size in 0.5 increments, and calculating the average grain size number G of the five fields of view. Note that, in the level of the present invention, the presence of the δ-ferrite phase is minute and is ignored in the measurement. Next, the average grain size G is converted to an average grain size [μm] using the following conversion formula obtained from the correspondence table of grain size and grain size described in JIS.

[0060]

[0061] <Average grain size of austenite phase≧−40×volume fraction of δ-ferrite phase+80> The present inventors have found that excellent high-temperature creep rupture life can be obtained if the average grain size of the austenite phase is equal to or greater than the value calculated by the function (Equation 1) using the volume fraction of the δ-ferrite phase as a variable. That is, excellent creep rupture life can be obtained not only by reducing the δ-ferrite phase and increasing the grain size, but also by increasing the grain size to or greater than the value calculated by Equation 1. For this reason, the austenitic stainless steel sheet of this embodiment has a volume fraction of the δ-ferrite phase in the center portion of the sheet thickness of 1.00% or less and satisfies the following Equation 1:

[0062] Average grain size of austenite phase (μm) ≧ −40 × δ volume fraction of ferrite phase (%) + 80 Equation 1

[0063] <Creep rupture life at high temperatures> In the recent trend toward improved energy efficiency, austenitic stainless steels have been used at even higher temperatures, and there is a demand for improved creep rupture life at temperatures around 900°C. Therefore, in the present invention, austenitic stainless steel sheets are evaluated based on their creep rupture life at high temperatures (900°C). The austenitic stainless steel sheet of this embodiment achieves a sufficient reduction in the volume fraction (δ amount) of the δ ferrite phase and grain growth, thereby satisfying Equation 1, thereby achieving excellent creep rupture life.

[0064] The creep rupture life at high temperatures is measured using a test method conforming to JIS Z 2271:2019. Test specimens are taken from the width direction of the steel plate so that the center is located at half the plate thickness from the surface. Using the obtained test specimens, a constant load creep rupture test is performed at a stress of 35 MPa and a temperature of 900°C using a creep testing machine equipped with a heating furnace, and the time required to rupture is taken as the creep rupture life.

[0065] <Manufacturing Method> An example of a method for manufacturing an austenitic stainless steel sheet according to this embodiment of the present invention will be described below. In this specification, "heating" means soaking in a temperature range, and "heating temperature" and "heating time" mean the soaking temperature and soaking time, respectively.

[0066] The austenitic stainless steel sheet of this embodiment can be produced by a production method comprising, for example, a first hot rolling step in which a slab having the above-mentioned chemical composition is heated in a temperature range of 1100 to 1300°C and then subjected to first hot rolling; a soaking heat treatment step in which the slab that has been subjected to the first hot rolling step is heated in a temperature range of 1100 to 1300°C for 3 hours or more; a second hot rolling step in which the slab that has been subjected to the soaking heat treatment step is heated in a temperature range of 1100 to 1300°C and then subjected to second hot rolling to obtain a hot-rolled steel sheet; and a solution heat treatment step in which the hot-rolled steel sheet is heated in a temperature range of 1000 to 1300°C for a time equal to or longer than the minimum heating time (hours) calculated by the following equation 2, and then subjected to solution heat treatment; wherein the cumulative slab heating time, which is the sum of the heating time in the first hot rolling step, the heating time in the soaking heat treatment step, and the heating time in the second hot rolling step, is 4.0 hours or longer.

[0067] Minimum heating time (hours) = 0.025 (hours / mm) x thickness of hot-rolled steel sheet (mm) .....Equation 2

[0068] (First Hot Rolling Process) In the first hot rolling process, a slab having the aforementioned chemical composition is melted and cast, and the resulting slab is heated in a heating furnace at a temperature range of 1100 to 1300°C. After extraction from the heating furnace, the slab is subjected to first hot rolling. If the slab is heated to a temperature below 1100°C, the volume fraction (δ amount) of the δ ferrite phase cannot be sufficiently reduced. Furthermore, hot workability is reduced, and scratches and cracks are more likely to occur. Therefore, the slab heating temperature is 1100°C or higher, preferably 1130°C or higher, 1160°C or higher, 1180°C or higher, or 1200°C or higher. On the other hand, if the slab heating temperature exceeds 1300°C, the heating temperature is too high, which tends to cause surface roughness due to high-temperature oxidation and reduce yield. Therefore, the slab heating temperature is 1300°C or lower, preferably 1280°C or lower, 1260°C or lower, or 1250°C or lower. After the first hot rolling, the slab may be cooled to room temperature. The cumulative reduction rate of the first hot rolling is not particularly limited, but may be 30 to 70%.

[0069] (Soaking Heat Treatment Process) In the soaking heat treatment process, the slab after the first hot rolling is heated in a temperature range of 1100 to 1300°C for 3 hours or more. If the slab heating temperature is too low, the effect of reducing the δ-ferrite phase will be small. Therefore, the slab heating temperature is 1100°C or higher, preferably 1130°C or higher, 1160°C or higher, 1180°C or higher, or 1200°C or higher. On the other hand, if the slab heating temperature exceeds 1300°C, the heating temperature is too high, which makes it prone to roughening of the surface due to high-temperature oxidation and reduces the yield. Therefore, the slab heating temperature is 1300°C or lower, preferably 1280°C or lower, 1260°C or lower, or 1250°C or lower. After the soaking heat treatment, the slab may be cooled to room temperature.

[0070] In the present invention, the soaking heat treatment step is performed after the first hot rolling step and before the second hot rolling step, thereby making it possible to effectively reduce the δ-ferrite phase.

[0071] The reason for this is that the δ-ferrite phase is elongated after the first hot rolling. That is, the surface area of ​​the δ-ferrite / austenite phase interface is increased, which promotes the dissolution of alloy elements from the δ-ferrite phase into the austenite phase. In addition, after the first hot rolling, the diffusion distance of alloy elements in the thickness direction during dissolution is shortened, and the concentration gradient of alloy elements in the austenite phase in the thickness direction is also increased.

[0072] (Secondary Hot Rolling Process) The second hot rolling process is a process for destroying the slab structure by hot rolling and shaping it to the specified product dimensions. The slab after the first hot rolling and soaking heat treatment is loaded into a heating furnace and heated in a temperature range of 1100 to 1300°C. After being removed from the heating furnace, the second hot rolling is performed. If the slab heating temperature is less than 1100°C, the δ-ferrite phase cannot be sufficiently reduced. Furthermore, hot workability is reduced, and scratches and edge cracks are more likely to occur. For this reason, the slab heating temperature is 1100°C or higher, preferably 1130°C or higher, 1160°C or higher, 1180°C or higher, or 1200°C or higher. On the other hand, if the slab heating temperature exceeds 1300°C, the heating temperature is too high, which makes it prone to surface roughness due to high-temperature oxidation and reduces yield. Therefore, the heating temperature of the slab is 1300°C or less, preferably 1280°C or less, 1260°C or less, or 1250°C or less. After the second hot rolling, the slab may be cooled to room temperature. The cumulative reduction rate of the second hot rolling is not particularly limited, but may be 50 to 95%.

[0073] (Cumulative Slab Heating Time) In the slab heating before the first hot rolling, the slab heating before the second hot rolling, and the slab heating in the soaking heat treatment, the δ content is controlled by the cumulative slab heating time. If the cumulative slab heating time is short, the effect of reducing the δ ferrite phase is not sufficiently obtained. Therefore, the cumulative slab heating time should be 4.0 hours or more. The cumulative slab heating time may preferably be 4.2 hours or more, 4.5 hours or more, 4.8 hours or more, or 5.0 hours or more. There is no upper limit to the cumulative slab heating time. However, if the cumulative slab heating time is too long, the effect will saturate, so the cumulative slab heating time may preferably be 24.0 hours or less, 20.0 hours or less, 18.0 hours or less, or 15.0 hours or less.

[0074] In addition, in the rolling line, for example, a 2Hi roughing mill and a 4Hi finishing mill are installed on the same line, and the steel sheet is rolled by passing between the rolls of each of these two rolling mills. The first hot rolling and the second hot rolling may be performed by the same rolling mill or by different rolling mills.

[0075] (Solution Heat Treatment Process) Following the secondary hot rolling, solution heat treatment is performed. The greater the plate thickness, the more difficult it is for the temperature at the center of the plate to reach the target temperature, making it more difficult for grains to grow toward the center of the plate. Furthermore, the greater the plate thickness during solution heat treatment, the greater the amount of δ-ferrite phase near the center of the plate, making it more susceptible to the grain growth suppression effect of the δ-ferrite phase. Given this background, it is effective to adjust the heating time for solution heat treatment to promote grain growth so that the heating time increases with increasing plate thickness. The inventors have found that by setting the heating time according to the plate thickness, it is possible to grow grains near the center of the plate thickness even when the plate thickness is large. Specifically, they determined that the minimum heating time per plate thickness is 0.025 hours / mm, which allowed them to set the optimal heating time.

[0076] In the solution heat treatment process, the hot-rolled steel sheet obtained by secondary hot rolling is subjected to solution heat treatment in a temperature range of 1000 to 1300°C for a time equal to or longer than the minimum heating time calculated by the following formula 2, and then cooled to room temperature. This heat treatment allows the grain size to grow larger. If the heating temperature is less than 1000°C, grain growth slows, requiring a long heating time. Therefore, the heating temperature of the hot-rolled steel sheet is 1000°C or higher, preferably 1030°C or higher, 1060°C or higher, 1080°C or higher, or 1100°C or higher. On the other hand, if the heating temperature of the hot-rolled steel sheet exceeds 1300°C, the heating temperature is too high, which is likely to cause surface roughness due to high-temperature oxidation and reduce yield. Therefore, the heating temperature of the hot-rolled steel sheet is 1300°C or lower, preferably 1280°C or lower, 1260°C or lower, or 1250°C or lower. Furthermore, if the heating time is shorter than the heating time calculated by Equation 2, the crystals will not grow sufficiently, resulting in a small grain size. If the δ content is not sufficiently reduced before this process, grain growth will be suppressed, necessitating long heating times. Compared to slab heating and soaking heat treatment before hot rolling, solution heat treatment usually does not require long heating times due to operational issues. Therefore, it is desirable to reduce the δ content before the solution heat treatment (secondary hot rolling process).

[0077] Minimum heating time (hours) = 0.025 (hours / mm) x thickness of hot-rolled steel sheet (mm) .....Equation 2

[0078] The austenitic stainless steel sheet according to the present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples.

[0079] Example 1 Slabs having the chemical compositions shown in Steel Nos. A to Z, AA to AD, and a to d in Tables 1 to 4 (note that Tables 1 to 4 are divided from a single table) were manufactured. The resulting slabs were heated in a heating furnace at 1180°C for 1 hour, extracted from the heating furnace, and subjected to primary hot rolling. The slabs after primary hot rolling were then heated at 1250°C for 8 hours and subjected to soaking heat treatment. The slabs were then heated in a heating furnace at 1180°C for 1 hour and subjected to secondary hot rolling to be finished into hot-rolled steel sheets with a thickness of 25 mm. The cumulative slab heating time, which is the sum of the heating time in the primary hot rolling step (1 hour), the heating time in the soaking heat treatment step (8 hours), and the heating time in the secondary hot rolling step (1 hour), was 10 hours. The slabs were then subjected to solution heat treatment at 1120°C for 0.625 hours, yielding austenitic stainless steel sheets.

[0080] The volume fraction of the δ-ferrite phase and the average grain size of the austenite phase were measured for the resulting austenitic stainless steel sheets using the methods described above. The results are shown in Table 5. In Table 5, "δ amount" indicates the volume fraction (%) of the δ-ferrite phase at the center of the steel sheet, "average grain size" indicates the average grain size (μm) of the austenite phase, and the "right side of formula 1" column indicates the value of the right side of formula 1 described above, -40 × volume fraction of the δ-ferrite phase (%) + 80. Formula 1 was evaluated as "good" when formula 1 (average grain size (μm) of the austenite phase ≥ -40 × volume fraction of the δ-ferrite phase (%) + 80) was satisfied, and evaluated as "× (unacceptable)" when it was not satisfied. Furthermore, "-" in Table 5 indicates that the sample was a mixed grain and therefore could not be measured using the measurement method described above.

[0081] Using the method described above, round-bar creep test specimens with a gauge length of 30 mm were also prepared. The diameter of the parallel portion was 6 mm so that it fell within the measurement range for the volume fraction of the δ-ferrite phase. A constant-load creep rupture test was then conducted at 900°C under a stress of 35 MPa, and the time required for rupture was measured. In this example, a creep rupture life of 200 hours or more was deemed to be excellent at high temperatures, and a creep rupture life of 250 hours or more was deemed to be excellent, particularly at high temperatures. The "Creep rupture life evaluation" in Table 5 was evaluated as "Excellent" for creep rupture lives of 250 hours or more, "Good" for creep rupture lives of 200 hours or more but less than 250 hours, and "Poor" for creep rupture lives of less than 200 hours. In this example, a creep rupture life evaluation of "Excellent" or "Good" indicated excellent creep rupture life at high temperatures. The evaluation results are shown in Table 5.

[0082] Steels Nos. A to Z and AA to AD have a δ-ferrite phase volume fraction of 1.00% or less at the center of the steel plate thickness, and the average grain size of the austenite phase is large, satisfying Equation 1. As a result, austenitic stainless steel sheets with excellent high-temperature creep rupture life were obtained. Furthermore, in the examples with an Si content of 1.00% or less, austenitic stainless steel sheets with particularly excellent high-temperature creep rupture life were obtained.

[0083] Steel No. a had a low Nb content and exhibited a short creep rupture life.

[0084] Steel No. b had a high Nb content, resulting in a duplex structure and a short creep rupture life.

[0085] Steel No. c had a low N content and exhibited a short creep rupture life.

[0086] Steel No. d had a high N content and exhibited a short creep rupture life.

[0087]

[0088]

[0089]

[0090]

[0091]

[0092] Example 2 Austenitic stainless steel sheets were produced using slabs of Steel Nos. B, D, and G shown in Tables 1 to 4, under the conditions shown in Table 6, with the remaining production conditions being the same as in Example 1. In Table 6, time is represented as "h." For the resulting austenitic stainless steel sheets, the volume fraction of the δ-ferrite phase (δ amount) in the center of the steel sheet thickness, the average grain size of the austenite phase, and the creep rupture life of the steel sheets at a stress of 35 MPa and a temperature of 900°C were determined in the same manner as in Example 1. The evaluation results are shown in Table 7. In Table 7, "δ amount" refers to the volume fraction of the δ-ferrite phase, and "average grain size" refers to the average grain size of the austenite phase. The "creep rupture life evaluation" in Table 7 was evaluated using the same criteria as in Example 1.

[0093]

[0094]

[0095] The invention examples of Test Nos. 1, 8, 10, 16, and 19, which satisfy the requirements of the chemical composition and manufacturing method of the steel sheet of the present invention, have a δ-ferrite phase volume fraction of 1.00% or less, large crystal grain sizes, and satisfy Formula 1. As a result, austenitic stainless steel sheets with excellent creep rupture life at high temperatures were obtained. Furthermore, Test Nos. 1, 8, and 10, in which the Si content was 1.00% or less, also yielded austenitic stainless steel sheets with excellent creep rupture life, particularly at high temperatures.

[0096] Test Nos. 2, 7, and 9 are examples in which soaking heat treatment was performed before the first hot rolling. Therefore, the effect of reducing the δ-ferrite phase was not sufficient, and the volume fraction of the δ-ferrite phase increased. As a result, the creep rupture life was poor.

[0097] Test Nos. 3, 4, 5, and 6 were examples in which no soaking heat treatment was performed and the cumulative slab heating time was short. Therefore, the δ-ferrite phase was not sufficiently reduced, and the volume fraction of the δ-ferrite phase increased. As a result, the creep rupture life was poor.

[0098] Test Nos. 11 and 12 were examples in which the cumulative slab heating time was 4.0 hours or more, but soaking heat treatment was not performed. Test No. 15 was an example in which the cumulative slab heating time was 4.0 hours or more, but soaking heat treatment and secondary hot rolling were not performed. Therefore, the δ-ferrite phase was not sufficiently reduced, and the volume fraction of the δ-ferrite phase increased. As a result, the creep rupture life was poor.

[0099] In Test No. 13, the soaking heat treatment was performed before the first hot rolling, and the heating time of the soaking heat treatment and the cumulative slab heating time were short. Therefore, the δ-ferrite phase was not sufficiently reduced, and the volume fraction of the δ-ferrite phase increased. As a result, the creep rupture life was poor.

[0100] In Test No. 14, soaking heat treatment was performed after the first hot rolling and before the second hot rolling, but the heating time of the soaking heat treatment and the cumulative slab heating time were short. Therefore, the δ-ferrite phase was not sufficiently reduced, and the volume fraction of the δ-ferrite phase increased. As a result, the creep rupture life was poor.

[0101] Test No. 17 is an example in which the heating time of the solution heat treatment was short. As a result, the crystal grains did not grow sufficiently and the crystal grain size became small. As a result, the creep rupture life was poor.

[0102] The austenitic stainless steel sheet of the present invention can be used in various plants such as those in the steel manufacturing industry and thermal power plants, and can be used for structures used in high-temperature environments, such as heat-resistant retaining fittings, burner tubes, skid rollers, hoppers, cyclones, and pressure vessels.

Claims

The chemical composition, in mass%, is C: 0.100% or less, Si: 2.00% or less, Mn: 2.50% or less, P: 0.0450% or less, S: 0.0300% or less, Ni: 9.00-13.00%, Cr: 19.00-24.00%, Mo: 0.001-1.00%, Nb: 0.005-0.100%, N: 0.100-0.300%, Al: 0.200% or less, B: 0.0001 to 0.0100%, Ti: 0-0.300%, Cu: 0 to 1.00%, V: 0 to 0.500%, Co: 0-1.000%, Ca: 0-0.1000%, Mg: 0 to 0.0050%, Sb: 0 to 0.200%, Sn: 0-0.100%, Se: 0 to 0.080%, W: 0 to 0.50%, Ta: 0 to 0.50%, Hf: 0-0.100%, Zr: 0 to 0.100%, Bi: 0-0.300%, Pb: 0 to 0.100%, REM: 0-0.200%, Remainder: Fe and impurities and The volume fraction of the δ ferrite phase in the center of the plate thickness is 1.00% or less, The average grain size (μm) of the austenite phase satisfies formula 1.

1. An austenitic stainless steel sheet characterized by: Average grain size of austenite phase (μm) ≧ −40 × δ volume fraction of ferrite phase (%) + 80 Equation 1 The chemical composition is, in mass %, Ti: 0.001 to 0.300%, Cu: 0.01 to 1.00%, V: 0.010 to 0.500%, Co: 0.010 to 1.000%, Ca: 0.0010-0.0100%, Mg: 0.0001 to 0.0050%, Sb: 0.020-0.200%, Sn: 0.001 to 0.100%, Se: 0.005-0.080%, W: 0.01-0.50%, Ta: 0.005-0.50%, Hf: 0.010-0.100%, Zr: 0.001 to 0.100%, Bi: 0.030-0.300%, Pb: 0.010 to 0.100%, and REM: 0.005-0.200% 2. The austenitic stainless steel sheet according to claim 1, further comprising one or more selected from the following:

2. A method for producing the austenitic stainless steel sheet according to claim 1, comprising the steps of: The chemical composition, in mass%, is C: 0.100% or less, Si: 2.00% or less, Mn: 2.50% or less, P: 0.0450% or less, S: 0.0300% or less, Ni: 9.00-13.00%, Cr: 19.00-24.00%, Mo: 0.001-1.00%, Nb: 0.005-0.100%, N: 0.100-0.300%, Al: 0.200% or less, B: 0.0001 to 0.0100%, Ti: 0-0.300%, Cu: 0 to 1.00%, V: 0 to 0.500%, Co: 0-1.000%, Ca: 0-0.1000%, Mg: 0 to 0.0050%, Sb: 0 to 0.200%, Sn: 0-0.100%, Se: 0 to 0.080%, W: 0 to 0.50%, Ta: 0 to 0.50%, Hf: 0-0.100%, Zr: 0 to 0.100%, Bi: 0-0.300%, Pb: 0 to 0.100%, REM: 0-0.200%, Remainder: Fe and impurities a first hot rolling step of heating the slab in a temperature range of 1100 to 1300°C and then performing first hot rolling; a soaking heat treatment step in which the slab that has undergone the first hot rolling step is heated in a temperature range of 1100 to 1300°C for 3 hours or more; A secondary hot rolling step in which the slab that has undergone the soaking heat treatment step is heated to a temperature range of 1100 to 1300 ° C. and then subjected to secondary hot rolling to obtain a hot-rolled steel sheet; A solution heat treatment step in which the hot-rolled steel sheet is heated in a temperature range of 1000 to 1300°C for a time equal to or longer than the minimum heating time (hours) calculated by the following formula 2. Equipped with a cumulative slab heating time, which is the sum of the heating time in the first hot rolling step, the heating time in the soaking heat treatment step, and the heating time in the second hot rolling step, of 4.0 hours or more. Minimum heating time (hours) = 0.025 (hours / mm) x thickness of hot-rolled steel sheet (mm) ...Formula 2

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