Austenitic stainless hot-rolled steel sheet and method for producing same

Abstract

Provided is an austenitic stainless hot-rolled steel sheet that has small in-plane anisotropy and that contributes to workpiece shape stability and yield improvement. The austenitic stainless hot-rolled steel sheet, which has small in-plane anisotropy, has a chemical composition of, in mass%, C: 0.001-0.100%, Si: 0.01-2.00%, Mn: 0.01-10.00%, P: 0.050% or less, S: 0.0100% or less, Ni: 3.00-15.00%, Cr: 13.0-25.0%, and N: 0.001-0.300%, the balance being Fe and impurities. The strengths in the { 001 } <010> orientation, the { 112 } <111> orientation, and the { 110 } <322> orientation obtained by X-ray diffraction are all 3 or less.

Description

Austenitic stainless steel hot rolled sheet and method for manufacturing the same

[0001] The present invention relates to a hot-rolled austenitic stainless steel sheet and a method for producing the same.

[0002] In recent years, improving the fuel efficiency of transportation equipment has become an essential issue from the perspective of environmental issues. Transportation equipment refers to equipment used to transport luggage or passengers, such as automobiles, motorcycles, tricycles, bicycles, buses, and railroad cars. To improve the fuel efficiency of transportation equipment, efforts to reduce the weight of transportation equipment bodies have been actively promoted. Weight reduction of vehicle bodies is largely achieved by reducing the weight of the materials used in the components that make up the body, for example, by reducing the thickness of the materials. However, reducing the thickness of the materials reduces the rigidity and crash absorption performance of the components. To address this issue, increasing the strength of the materials that make up the components is an effective solution, and high-strength ordinary steel (high-tensile steel) is being used.

[0003] However, because ordinary steel has low corrosion resistance, it is assumed that it will be heavily painted. Therefore, ordinary steel cannot be used for unpainted or lightly painted parts, and heavy painting increases costs. On the other hand, Cr-containing stainless steel has superior corrosion resistance compared to ordinary steel, which is expected to reduce rust allowance (thickness that allows for rust formation), thereby reducing weight and simplifying painting. Furthermore, austenitic stainless steel has superior hydrogen embrittlement resistance compared to ordinary steel, making it particularly effective for components exposed to hydrogen environments and improving the safety of transportation and energy equipment. Therefore, the use of austenitic stainless steel offers significant benefits, such as weight reduction, simplified painting, and improved safety.

[0004] On the other hand, components that make up hydrogen fuel cells, such as fuel components such as piping, tanks, valves, and nozzles, are often manufactured by pressing steel sheets using techniques such as deep drawing and stretch forming. If the steel sheet has large in-plane anisotropy during this process, earrings, known as "earrings," can occur, resulting in shape defects and reduced yields. Since shape precision is particularly strict for components that make up hydrogen fuel cells, applying austenitic hot-rolled stainless steel sheets presents a major challenge.

[0005] For example, Patent Document 1 discloses a technique for reducing in-plane anisotropy by using a stable austenitic stainless steel that is resistant to the formation of work-induced martensite due to cold working strain, and by performing a double cold rolling and annealing process.

[0006] Patent Document 2 discloses a technique for reducing in-plane anisotropy by adding Al and cold rolling the steel using large diameter rolls.

[0007] Patent Document 3 discloses a technique in which hot rolling is performed under predetermined conditions, and then cold rolling and annealing are performed without annealing the hot-rolled sheet.

[0008] Patent Document 4 discloses a technique for reducing the in-plane anisotropy by setting the hot rolling reduction to 98.7% or more and performing hot-rolled sheet annealing, cold rolling, and finish annealing.

[0009] Patent Document 5 discloses a technique for hot rolling austenitic stainless steel under predetermined conditions to reduce |Δr| after annealing the hot-rolled sheet to 0.2 or less. This technique involves specifying the slab heating temperature, finish rolling temperature, and hot-rolled sheet annealing temperature to reduce Δr, which is an index of in-plane anisotropy.

[0010] Patent Document 6 also discloses a technique for omitting the annealing of the hot-rolled sheet to set |Δr| to 0.15 or less.

[0011] JP 8-165524, JP 9-263829, JP 10-128409, JP 10-158736, JP 8-41550, JP 8-260044

[0012] The techniques of Patent Documents 1 to 4 are premised on cold rolling, and therefore have problems such as the fact that a specific crystal orientation develops due to cold rolling, which tends to increase in-plane anisotropy, that it is difficult to control the reduction ratio, temperature, and shape during cold rolling, and that the costs are high.

[0013] In the examples of Patent Document 5, examples are disclosed in which |Δr| is in the range of 0.1 to 0.20, but no technology has been obtained in which |Δr| is less than 0.1.

[0014] In the examples of Patent Document 6, an example of a steel having small in-plane anisotropy, |Δr| being 0.08, is shown, but since hot-rolled sheet annealing is omitted, the steel is hard and there are problems with formability.

[0015] As described above, there are no hot-rolled austenitic stainless steel sheets with extremely small in-plane anisotropy, specifically, no products that have been annealed after hot rolling with |Δr| of less than 0.10.

[0016] The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a hot-rolled austenitic stainless steel sheet having excellent formability and a method for manufacturing the same.

[0017] The present inventors produced various hot-rolled austenitic stainless steel sheets and conducted detailed analyses and studies.

[0018] Reducing the in-plane anisotropy of a material is effective in improving its press formability. Materials with small in-plane anisotropy have a low earring rate during forming, improving yield. In order to reduce the in-plane anisotropy of steel sheets, it is necessary to control the crystal orientation of the steel sheets. However, since strength differs depending on the crystal orientation, it is necessary to weaken the strength of specific crystal orientations to form a random texture.

[0019] In the case of cold-rolled austenitic stainless steel sheets, it is possible to control the crystal orientation by adjusting the cold-rolling conditions, but it has been difficult to control the crystal orientation in hot-rolled steel sheets. The inventors identified the crystal orientation that increases the in-plane anisotropy of austenitic stainless steel material, and further controlled the chemical composition and manufacturing conditions, thereby completing a hot-rolled austenitic stainless steel sheet with small in-plane anisotropy.

[0020] The present invention relates to the following hot-rolled austenitic stainless steel sheet and a method for producing the same.

[0021] [1] Chemical composition, in mass%, C: 0.001 to 0.100%, Si: 0.01 to 2.00%, Mn: 0.01 to 10.00%, P: 0.050% or less, S: 0.0100% or less, Ni: 3.00 to 15.00%, Cr: 13.0 to 25.0%, N: 0.001 to 0.300%, Ti: 0 to 0.50%, Nb: 0 to 0.60%, Al: 0 to 1.000%, Cu: 0 to 2.00%, Mo: 0 to 3.00%, V: 0 to 0.50%, Zr: 0 to 0.50%, B: 0 to 0.0050%, Ca: 0 to 0.0100%, 1. An austenitic stainless hot-rolled steel sheet comprising: W: 0 to 3.00%, Sn: 0 to 0.50%, Co: 0 to 0.30%, Mg: 0 to 0.0100%, Sb: 0 to 0.300%, REM: 0 to 0.200%, Ga: 0 to 0.3000%, Ta: 0 to 1.000%, Hf: 0 to 1.000%, Bi: 0 to 0.02%, and the balance: Fe and impurities; and wherein the X-ray diffraction intensities of the {001}<010> orientation, the {112}<111> orientation, and the {110}<322> orientation are all 3 or less.

[0022] [2] The chemical composition is, in mass%, Ti: 0.01 to 0.50%, Nb: 0.01 to 0.60%, Al: 0.001 to 1.000%, Cu: 0.01 to 2.00%, Mo: 0.01 to 3.00%, V: 0.01 to 0.50%, Zr: 0.01 to 0.50%, B: 0.0002 to 0.0050%, Ca: 0.0005 to 0.0100%, W: 0.10 to 3.00%, Sn: 0.01 to 0.50%, Co: 0.03 to 0.30%, Mg: 0.0002 to 0.0100%, Sb: 0.005 to 0.300%, The austenitic stainless steel hot rolled sheet according to the above [1], containing one or more selected from REM: 0.002 to 0.200%, Ga: 0.0002 to 0.3000%, Ta: 0.001 to 1.000%, Hf: 0.001 to 1.000%, and Bi: 0.001 to 0.02%.

[0023] [3] The austenitic stainless steel hot rolled sheet according to the above [1] or [2], wherein |Δr| obtained by the following formula (i) is less than 0.10. Δr=(r ０ +r ９０ ) / 2-r ４５ ...(i) where the meanings of the symbols in formula (i) are as follows: ０ : Lankford value in the direction of 0° to the rolling direction r ４５ : Lankford value r at 45° to the rolling direction ９０ : Lankford value in the direction 90° to the rolling direction

[0024] [4] A method for producing austenitic stainless steel hot-rolled sheet according to the above item [3], comprising: performing slab heating under conditions of a slab heating temperature of 1200 to 1300°C and a soaking temperature of 10 minutes or more and less than 60 minutes; hot rolling under conditions of a finish rolling end temperature of 1020°C or more and a difference between the rough rolling end temperature and the finish rolling end temperature of less than 100°C; and then annealing under conditions of a heating temperature of 1100 to 1200°C.

[0025] According to the present invention, it is possible to provide a hot-rolled austenitic stainless steel sheet having excellent formability.

[0026] FIG. 1 is a diagram showing the textures of a steel according to the present invention and a comparative steel.

[0027] Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and modifications and improvements can be made to the following embodiments as appropriate based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the present invention. In the following description, "%" regarding the content of each element means "% by mass" unless otherwise specified.

[0028] The reasons for limiting the content of each element will be explained in detail below.

[0029] <C: 0.001 to 0.100%> C is an element that increases the structural stability of the austenite phase, so the lower limit of the C content is set to 0.001%. However, excessive C content reduces corrosion resistance and heat resistance, and C is an element that promotes the development of texture, so the upper limit of the C content is set to 0.100%. From the viewpoint of stretchability and deep drawability, the lower limit of the C content is preferably 0.003%. From the viewpoint of weldability, the upper limit of the C content is preferably 0.090% or 0.080%. Furthermore, in consideration of manufacturability, the lower limit of the C content is more preferably 0.005%, and in consideration of formability, the upper limit of the C content is more preferably 0.070% or 0.060%.

[0030] <Si: 0.01 to 2.00%> Si is a deoxidizing element. Furthermore, Si is a solid-solution strengthening element, and is effective in improving strength and reducing in-plane anisotropy. Therefore, the lower limit of the Si content is set to 0.01%. However, excessive Si content increases in-plane anisotropy and leads to a rapid decrease in ductility, so the upper limit of the Si content is set to 2.00%. Considering corrosion resistance, the lower limit of the Si content is preferably 0.05%. Considering manufacturability, the upper limit of the Si content is preferably 1.80%, 1.60%, 1.40%, 1.20%, 1.00%, or 0.90%. Considering weldability, the lower limit of the Si content is more preferably 0.10%, 0.20%, or 0.30%. Considering toughness, the upper limit of the Si content is more preferably 0.80%, 0.70%, or 0.60%.

[0031] <Mn: 0.01 to 10.00%> Mn is a deoxidizing element. Furthermore, Mn promotes the formation of deformation twins and is effective in improving strength and reducing in-plane anisotropy. Therefore, the lower limit of the Mn content is set to 0.01%. However, excessive Mn content increases in-plane anisotropy and leads to a decrease in corrosion resistance, so the upper limit of the Mn content is set to 10.00%. Considering oxidation resistance, the lower limit of the Mn content is preferably 0.10%, 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, or 3.00%. Considering in-plane anisotropy, the upper limit of the Mn content is preferably 9.50%. Considering manufacturability, the lower limit of the Mn content is more preferably 3.50%, 4.50%, or 5.00%. Considering weldability, the upper limit of the Mn content is more preferably 9.30%.

[0032] <P: 0.050% or less> P is an element present as an impurity in steel. Since P reduces formability, corrosion resistance, manufacturability, and the like, the lower the P content, the better. If the P content is too high, coarse phosphides are formed, which become the starting point for void formation during processing. Furthermore, it increases in-plane anisotropy. The upper limit of the P content is set to 0.050%. On the other hand, since excessive reduction of P leads to increased manufacturing costs, the lower limit of the P content is preferably 0.010%. Considering refining costs, the lower limit of the P content is more preferably 0.015%. Considering formability, the upper limit of the P content is more preferably 0.040% or 0.030%.

[0033] <S: 0.0100% or less> S is an element present as an impurity in steel. Furthermore, since S reduces formability, corrosion resistance, manufacturability, and the like, the lower the content, the better. If the S content is too high, coarse sulfides are formed, which become the starting point for void formation during high-speed deformation. Furthermore, it increases in-plane anisotropy. The upper limit of the S content is 0.0100%. On the other hand, since excessive reduction of S leads to increased manufacturing costs, the lower limit of the S content is preferably 0.0001%. Considering refining costs, the lower limit of the S content is preferably 0.0005%. Considering weldability, the upper limit of the S content is preferably 0.0080%, 0.0060%, 0.0040%, or 0.0020%.

[0034] <Ni: 3.00 to 15.00%> Ni contributes to high strength and improves formability through the stability of the austenite phase. Ni is also an element effective in reducing in-plane anisotropy. Therefore, the lower limit of the Ni content is set to 3.00%. However, since excessive Ni content increases costs, the upper limit of the Ni content is set to 15.00%. In consideration of corrosion resistance and suppression of texture development, the lower limit of the Ni content is preferably 4.00%. The upper limit of the Ni content is preferably 14.00%, 13.00%, 12.00%, 11.00%, 10.00%, 9.00%, or 8.00%. In consideration of formability, the lower limit of the Ni content is more preferably 5.00%, and in consideration of weldability, the upper limit of the Ni content is more preferably 7.00% or 7.50%.

[0035] <Cr: 13.0 to 25.0%> Cr is an element contained to improve corrosion resistance. Cr is also an element effective in reducing in-plane anisotropy. In particular, the lower limit of the Cr content is set to 13.0% to eliminate painting and improve high-temperature rigidity. On the other hand, if the Cr content is too high, toughness will be significantly reduced due to the formation of intermetallic compounds, so the upper limit of the Cr content is set to 25.0%. In consideration of suppressing texture development, the lower limit of the Cr content is preferably 14.0%, while in consideration of manufacturability, cost, and corrosion resistance of welds, the upper limit of the Cr content is preferably 23.0%, 20.0%, 17.0%, or 16.0%.

[0036] <N: 0.001 to 0.300%> N is an element effective in improving corrosion resistance and suppressing hydrogen embrittlement. Furthermore, the present inventors discovered that N is extremely important for suppressing texture development, and that random texture is formed from planar dislocation structures, etc., formed during the hot rolling stage. Therefore, the lower limit of the N content is set to 0.001%. On the other hand, excessive N content significantly hardens the steel. It also increases in-plane anisotropy. Therefore, the upper limit of the N content is set to 0.300%. From the viewpoint of strength, the lower limit of the N content is preferably 0.010%, 0.030%, or 0.050%. From the viewpoints of stretchability and deep drawability, the upper limit of the N content is preferably 0.250% or 0.200%. Furthermore, considering weldability, the lower limit of the N content is more preferably 0.060%, and from the viewpoint of manufacturability, the upper limit of the N content is more preferably 0.180%.

[0037] The chemical composition of the steel sheet of the present invention may further contain one or more elements selected from Ti, Nb, Al, Cu, Mo, V, Zr, B, Ca, W, Sn, Co, Mg, Sb, REM, Ga, Ta, Hf, and Bi within the ranges shown below. Note that these elements are not necessarily essential for the steel of the present invention, and therefore the lower limit of their content is 0%. The reasons for limiting each element will be explained below.

[0038] <Ti: 0 to 0.50%> <Nb: 0 to 0.60%> Ti and Nb bond with C and N to suppress the formation of coarse Cr carbonitrides, thereby preventing intergranular corrosion and contributing to improved formability (e.g., deep drawability). Therefore, Ti and / or Nb may be contained as needed, with the lower limit of the Ti content being preferably 0.01%, and the lower limit of the Nb content being preferably 0.01%. However, excessive Ti and Nb content causes coarse precipitation of Ti-based precipitates and Nb-based precipitates, developing a texture and increasing in-plane anisotropy. Therefore, the upper limit of the Ti content is set to 0.50%, and the upper limit of the Nb content is set to 0.60%. From the viewpoint of formability, the lower limit of the Ti content and the lower limit of the Nb content are preferably 0.05% or 0.10%, respectively, and from the viewpoints of manufacturability and cost, the upper limit of the Ti content and the upper limit of the Nb content are preferably 0.50%, 0.40%, or 0.30%, respectively. Furthermore, from the viewpoint of manufacturing cost, the upper limit of the Ti content and the upper limit of the Nb content are more preferably 0.20%.

[0039] <Al: 0 to 1.000%> Al is an element contained as a deoxidizing element. Furthermore, Al is an element effective in improving formability by forming nitrides, increasing strength by solid-solution strengthening, and improving oxidation resistance. To efficiently achieve these effects, it is preferable to contain 0.001% or more of Al as needed. However, excessive Al content can lead to reduced high-temperature rigidity, the occurrence of surface defects, reduced weldability, and reduced ductility due to coarse AlN. Furthermore, the precipitation of coarse AlN develops texture and increases in-plane anisotropy. Therefore, the upper limit of the Al content is set to 1.000%. Considering deoxidation efficiency, the lower limit of the Al content is preferably 0.020%, while considering toughness, the upper limit of the Al content is preferably 0.900%, 0.800%, 0.700%, 0.600%, or 0.500%. In addition, in consideration of weldability, the lower limit of the Al content is preferably 0.020%, the upper limit of the Al content is more preferably 0.400%, 0.300%, or 0.200%, and the Al content is further preferably less than 0.100%.

[0040] <Cu: 0 to 2.00%> Cu contributes to improving corrosion resistance and improving high-temperature rigidity and strength through the precipitation of ε-Cu, so it is preferable to include 0.01% or more of Cu as needed. However, if the Cu content is too high, ductility will be significantly reduced and in-plane anisotropy will increase. Therefore, the upper limit of the Cu content is set to 2.00%. In consideration of oxidation resistance, the lower limit of the Cu content is preferably 0.05%, and in consideration of cost, the upper limit of the Cu content is preferably 1.80%, 1.50%, or 1.30%. In consideration of toughness, the lower limit of the Cu content is preferably 0.10%, and in consideration of weldability, the upper limit of the Cu content is more preferably 1.00% or 0.50%.

[0041] <Mo: 0 to 3.00%> Mo is an element that improves corrosion resistance. Furthermore, Mo is a solid-solution strengthening element and is effective in increasing strength. Therefore, Mo is preferably contained in an amount of 0.01% or more as needed. However, excessive Mo content reduces formability, increases in planar anisotropy, and increases costs, as well as significantly reduces toughness. Therefore, the upper limit of the Mo content is set to 3.00%. From the viewpoint of high-temperature rigidity, the lower limit of the Mo content is preferably 0.05% or 0.10%, and from the viewpoint of oxidation resistance, the upper limit of the Mo content is preferably 2.50% or 2.10%. Furthermore, from the viewpoint of cost reduction, the upper limit of the Mo content is more preferably 1.50%, 1.00%, 0.50%, or 0.20%.

[0042] <V: 0 to 0.50%> <Zr: 0 to 0.50%> Like Ti and Nb, V and Zr are elements that bond with C and N and suppress the formation of coarse Cr carbonitrides. V and Zr are also effective elements for increasing strength by forming fine precipitates (Zr(C,N), V(C,N)). Therefore, it is preferable to add 0.01% or more of V and Zr as needed. However, excessive addition of V and Zr reduces toughness and increases in-plane anisotropy. Therefore, the upper limits of the V content and the Zr content are each set to 0.50%. From the viewpoint of formability, the lower limits of the V content and the Zr content are each preferably 0.05%, and the upper limits of the V content and the Zr content are each preferably 0.30%. Furthermore, in consideration of the impact absorption characteristics of the welded portion during high-speed deformation, the lower limit of the V content and the lower limit of the Zr content are each preferably 0.10%, and in consideration of bendability, the upper limit of the V content and the upper limit of the Zr content are each more preferably 0.20%.

[0043] <B: 0 to 0.0050%> B is an element effective for increasing strength and suppressing secondary processing cracking. B may also be effective in improving hot formability through grain boundary segregation. Therefore, it is preferable to add 0.0002% or more of B as needed. However, excessive B content can cause void formation, resulting in reduced formability and increased in-plane anisotropy. Therefore, the upper limit of the B content is set to 0.0050%. Considering corrosion resistance, the upper limit of the B content is preferably 0.0040% or 0.0030%. Considering weldability, the lower limit of the B content is preferably 0.0005%, and the upper limit of the B content is more preferably 0.0020%.

[0044] <Ca: 0 to 0.0100%> Ca fixes S and improves hot formability. Therefore, it is preferable to include 0.0005% or more of Ca as needed. However, excessive Ca content not only reduces corrosion resistance but also increases in-plane anisotropy due to coarse CaS. Therefore, the upper limit of the Ca content is set to 0.0100%. From the viewpoint of manufacturability, the upper limit of the Ca content is preferably 0.0080%, 0.0050%, or 0.0030%. Furthermore, the lower limit of the Ca content is more preferably 0.0010%.

[0045] <W: 0 to 3.00%> W is an element that improves corrosion resistance and also acts as a solid-solution strengthening element. Therefore, it is preferable to include 0.10% or more of W depending on the corrosion resistance level required in the usage environment. However, excessive W content leads to reduced formability and toughness, increased costs, and increased in-plane anisotropy, so the upper limit of the W content is set to 3.00%. The upper limit of the W content is preferably 2.50%, 2.00%, or 1.50%, and the lower limit of the W content is more preferably 0.50% or 1.00%.

[0046] <Sn: 0 to 0.50%> Sn contributes to improving corrosion resistance and high-temperature strength, so it is preferable to include 0.01% or more as needed. However, excessive Sn content may cause slab cracking during manufacturing, and grain boundary cracking during processing (e.g., hole expansion) becomes more pronounced. In addition, grain boundary segregation develops texture and increases in-plane anisotropy, so the upper limit of the Sn content is set to 0.50%. Considering refining costs and manufacturability, the upper limit of the Sn content is preferably 0.40% or 0.30%. Furthermore, the lower limit of the Sn content is more preferably 0.05%, 0.10%, or 0.15%.

[0047] <Co: 0 to 0.30%> Co contributes to improving high-temperature strength, so it is preferable to add 0.03% or more as needed. However, excessive Co content leads to a decrease in toughness during manufacturing, an increase in cost, and an increase in in-plane anisotropy. Therefore, the upper limit of the Co content is set to 0.30%. In consideration of refining costs and manufacturability, the upper limit of the Co content is preferably 0.20% or 0.10%. Furthermore, the lower limit of the Co content is more preferably 0.05%.

[0048] <Mg: 0 to 0.0100%> Mg is an element that is optionally contained as a deoxidizing element. Furthermore, Mg contributes to improving manufacturability by refining the structure, improving hot formability, and improving the formability of welds. To achieve these effects, it is preferable to contain 0.0002% or more of Mg. However, excessive Mg content significantly reduces corrosion resistance and increases in-plane anisotropy due to coarse MgO. Therefore, the upper limit of the Mg content is set to 0.0100%. In consideration of manufacturability, the upper limit of the Mg content is preferably 0.0080%, 0.0060%, 0.0040%, or 0.0020%. Furthermore, the lower limit of the Mg content is more preferably 0.0005%.

[0049] <Sb: 0 to 0.300%> Sb is an element that segregates at grain boundaries to increase high-temperature strength. To achieve this effect, it is preferable to add 0.005% or more Sb as needed. However, excessive Sb content can cause grain boundary cracking during processing (e.g., hole expansion), cracking during welding, and increased in-plane anisotropy due to Sb segregation, so the upper limit of the Sb content is set to 0.300%. In consideration of high-temperature properties, the lower limit of the Sb content is preferably 0.010%, 0.020%, or 0.030%. In consideration of manufacturing costs and toughness, the upper limit of the Sb content is preferably 0.200%. Furthermore, the lower limit of the Sb content is preferably 0.040% or 0.050%, and the upper limit of the Sb content is more preferably 0.100%.

[0050] <REM: 0 to 0.200%> REM (rare earth elements) are effective in improving oxidation resistance, so it is preferable to add 0.002% or more of REM as needed. However, even if REM is added excessively, the effect saturates, and REM granules cause a decrease in corrosion resistance and hole expandability and an increase in in-plane anisotropy, so the upper limit of the REM content is set to 0.200%. In consideration of formability and manufacturing costs, the upper limit of the REM content is preferably 0.100%. Furthermore, the lower limit of the REM content is more preferably 0.050%.

[0051] The term REM follows the general definition. That is, REM refers to two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu). REM may be contained alone or in the form of a mixture.

[0052] <Ga: 0 to 0.3000%> Ga is an element that is contained as needed to improve corrosion resistance and suppress hydrogen embrittlement. In particular, from the viewpoint of forming sulfides and hydrides that are effective in achieving these effects, the lower limit of the Ga content is preferably set to 0.0002%. However, excessive Ga content generates coarse sulfides, which leads to an increase in in-plane anisotropy, so the upper limit of the Ga content is set to 0.3000%. The upper limit of the Ga content is more preferably 0.2000% or 0.1000%. Furthermore, from the viewpoint of manufacturability, the lower limit of the Ga content is preferably 0.0010% or 0.0020%.

[0053] <Ta: 0 to 1.000%> <Hf: 0 to 1.000%> Ta and Hf are elements effective in improving high-temperature strength and are contained as needed. To achieve this effect, it is preferable that Ta and Hf are each contained in an amount of 0.001% or more. However, from the viewpoint of cost, the upper limit of the Ta content and the upper limit of the Hf content are each set to 1.000%. From the viewpoint of improving high-temperature strength, the upper limit of the Ta content and the upper limit of the Hf content are more preferably 0.500%, 0.100%, 0.050%, or 0.010%, respectively. Furthermore, the lower limit of the Ta content and the lower limit of the Hf content are more preferably 0.005%.

[0054] <Bi: 0 to 0.02%> Bi is an element effective in improving machinability and is contained as needed. To achieve this effect, it is preferable to contain 0.001% or more of Bi. However, from the viewpoint of cost, the upper limit of the Bi content is set to 0.02%. From the viewpoint of improving machinability, the upper limit of the Bi content is preferably 0.01%. Furthermore, the lower limit of the Bi content is more preferably 0.005%.

[0055] The balance of the chemical composition of the steel sheet of the present invention is Fe and impurities, which refer to components that are mixed in from raw materials such as ores and scraps during industrial steel production and other factors, and are acceptable within a range that does not adversely affect the properties of the steel sheet of the present invention.

[0056] <X-ray diffraction intensity> In the hot-rolled austenitic stainless steel sheet according to an embodiment of the present invention, the intensities of the {001}<010> orientation, {112}<111> orientation, and {110}<322> orientation obtained by X-ray diffraction are each 3 or less. The crystal orientation intensities of austenitic stainless steel, which affect its properties, change depending on the chemical composition, rolling, and heat treatment. There are various methods for measuring crystal orientation intensities, but the present invention specifies the crystal orientation intensities obtained by X-ray diffraction. Here, the texture was measured using an X-ray diffractometer (manufactured by Rigaku Corporation) with Mo-Kα radiation to obtain (200), (111), (220), and (311) pole figures in the region of 1 / 4 to 1 / 2 of the sheet thickness (revealed by a combination of mechanical polishing and electrolytic polishing). From these, a three-dimensional crystal orientation density function was determined using the spherical harmonic method, and then a comparison was made at a cross section (φ2=45° cross section) where the crystal orientation intensity (intensity ratio with a random sample) can be seen as contour lines in a representation of the three-dimensional texture known as the Bunge method.

[0057] 1, in the comparative steel, the intensities of the {001}<010> and {112}<111> orientations are 2, the intensity of the {110}<322> orientation is high at 5, and Δr, which indicates the in-plane anisotropy of the Lankford value, is large at -0.51. On the other hand, in the steel of the present invention, the intensities of the above crystal orientations are all small at 1, and Δr is extremely small at -0.04.

[0058] <Lankford Value> First, a JIS 13B tensile test specimen (hereinafter also referred to as "test specimen A") is taken from a hot-rolled and annealed sheet in accordance with JIS Z 2254:2021, so that the length direction of the test specimen coincides with the rolling direction of the steel sheet. Similarly, a JIS 13B tensile test specimen (hereinafter also referred to as "test specimen B") is taken so that the length direction of the test specimen coincides with the 45° direction of the rolling direction of the steel sheet, and a JIS 13B tensile test specimen (hereinafter also referred to as "test specimen C") is taken so that the length direction of the test specimen coincides with the 90° direction of the rolling direction of the steel sheet. Then, after imparting a 28% strain to each of test specimen A, test specimen B, and test specimen C, the Lankford value in each direction is calculated using the following formula (a). The gauge lengths of test specimen A, test specimen B, and test specimen C are 20 mm. r = ln(W ０ / W) / ln(t ０ / t) ...(a) where W ０ is the plate width before tension (mm), W is the plate width after tension (mm), t ０ is the plate thickness (mm) before tension, and t is the plate thickness (mm) after tension.

[0059] Then, the Lankford values ​​in each direction were substituted into the following formula (i) to calculate Δr. Δr = (r ０ +r ９０ ) / 2-r ４５ ...(i) where the meanings of the symbols in formula (i) are as follows: ０ : Lankford value in the direction of 0° to the rolling direction r ４５ : Lankford value r at 45° to the rolling direction ９０ : Lankford value in the direction 90° to the rolling direction

[0060] In the present invention, the absolute value |Δr| of Δr obtained using the above formula (i) is preferably in the range of less than 0.10. Since the steel sheet of the present invention has a random texture with weak texture development as described above, it is possible to obtain a hot-rolled and annealed sheet having such a low |Δr|.

[0061] <Thickness> The thickness of the austenitic stainless hot-rolled steel sheet according to the embodiment of the present invention may be appropriately set depending on the characteristics of the product to be used, and is not particularly limited. In consideration of weight reduction of parts, the thickness of the austenitic stainless hot-rolled steel sheet is preferably 8.0 mm or less. In consideration of manufacturability, the thickness of the austenitic stainless hot-rolled steel sheet is preferably 5.0 mm or less.

[0062] The manufacturing method will be described in detail below.

[0063] Stainless steel having the above composition is melted and forged or cast, and then hot-rolled to obtain a hot-rolled steel sheet. The hot-rolled steel sheet is then annealed and pickled in sequence to obtain a finished steel sheet. Each step can be performed using existing equipment, and the conditions are not particularly limited and can be adjusted appropriately depending on the composition of the stainless steel, etc. Furthermore, existing treatments (e.g., surface polishing, temper rolling, treatment using a tension leveler, etc.) may be performed as necessary.

[0064] During the hot rolling, the slab is heated at a temperature of 1200 to 1300°C and a soaking time of 10 to 60 minutes. If the slab is heated at a temperature less than 1200°C, the processing resistance is high, and strain accumulation during the hot rolling process is significant, resulting in excessive development of the rolling texture. As a result, specific recrystallized crystal orientations (particularly the {110}<322> orientation) develop during the subsequent annealing. Furthermore, if the soaking time is less than 10 minutes, grain growth during the slab heating stage is insufficient, resulting in significant strain accumulation during hot rolling. Subsequently, specific recrystallized crystal orientations (particularly the {110}<322> orientation) develop during the solidification stage, recrystallization during annealing, and grain growth. As a result, a non-uniform texture develops with specific recrystallized crystal orientations.

[0065] On the other hand, if the slab heating temperature exceeds 1300°C, the crystal grains become too coarse. During this grain growth process, specific recrystallized crystal orientations (particularly the {110}<322> orientation) grow, and these recrystallized crystal orientations tend to remain even during hot rolling and annealing. As a result, the strength of the {110}<322> orientation in the product increases. Furthermore, if the soaking time exceeds 60 min, precipitates tend to form during the hot rolling process. The presence of precipitates suppresses grain growth, making it easier for specific crystal orientations to remain. As a result, the strength of the {112}<111> orientation and the {110}<322> orientation increase. Furthermore, if the heating temperature and / or soaking time exceed the upper limit, hot rolling defects tend to occur, and rough surfaces tend to occur when the product sheet is processed, resulting in quality issues.

[0066] The hot rolling is a process including rough rolling consisting of multiple passes and finish rolling consisting of continuous rolling. Here, it is important to perform the hot rolling under the conditions of a finish rolling end temperature of 1020°C or higher and a difference between the rough rolling end temperature and the finish rolling end temperature of less than 100°C.

[0067] If the difference between the rough rolling end temperature and the finish rolling end temperature is 100°C or more, recrystallization occurs between the end of rough rolling and the end of finish rolling, changing the in-plane anisotropy created by hot rolling. As a result, specific crystal orientations develop. These specific crystal orientations are the {112}<111> orientation and the {110}<322> orientation.

[0068] Furthermore, if the finish rolling temperature is less than 1020°C, the deformation texture will develop excessively, and a recrystallization texture will develop during the subsequent hot-rolled sheet annealing process. Specifically, this is the development of the {110}<322> orientation. Furthermore, if the difference between the rough rolling end temperature and the finish rolling end temperature is 100°C or more and the finish rolling end temperature is less than 1020°C, the intensity of the {001}<010> orientation will increase. The upper limit of the finish rolling end temperature is not particularly limited, but may be, for example, 1200°C.

[0069] The hot-rolled steel sheet obtained in this manner is heated to 1100 to 1200°C to obtain a recrystallized structure. If the heating temperature is less than 1100°C, poor recrystallization will result in the development of a specific orientation. Specifically, the strength of the {112}<111> orientation will increase. On the other hand, if the heating temperature is more than 1200°C, excessive grain growth will occur, resulting in the development of a specific orientation. Specifically, the strength of the {001}<010> orientation will increase.

[0070] By the above annealing, the grain size number specified in JIS G0551:2013 is controlled to 5 to 9, preferably 7 to 8, thereby ensuring ductility and toughness.

[0071] The present invention will be specifically explained below with reference to examples, but the present invention should not be construed as being limited to these examples.

[0072] Austenitic stainless steel hot-rolled steel sheets were produced according to the following procedure. Stainless steel having the chemical compositions shown in Tables 1 and 2 was melted, hot-rolled, and then annealed and pickled to obtain 5.0 mm thick hot-rolled steel sheets. The strength of each crystal orientation and the Lankford value in each direction were measured for these hot-rolled steel sheets using the methods described above. In addition, formed products were produced by cylindrical drawing using a 40 mm diameter punch, and the ear shape was evaluated for pass / fail. A small earring ratio of 3% or less was evaluated as ◯, and a large earring ratio of more than 3% was evaluated as ×. These results, along with the production conditions, are shown in Tables 3 and 4.

[0073]

[0074]

[0075]

[0076]

[0077] As shown in Tables 1 and 3, the examples of the present invention had weaker development of each crystal orientation compared to the comparative examples (i.e., all orientations were 3 or less), and |Δr| was less than 0.10. Thus, the examples of the present invention had excellent in-plane anisotropy and small earing.

[0078] As shown in Tables 2 and 4, the comparative examples had intensities in at least one crystal orientation exceeding 3 and |Δr| exceeding 0.10. Thus, the comparative examples had large in-plane anisotropy and large earing.

[0079] According to the present invention, it is possible to provide a hot-rolled austenitic stainless steel sheet with excellent formability. Specifically, according to the present invention, the above-mentioned steel sheet can be efficiently produced without requiring any special new equipment. The steel sheet of the present invention is particularly suitable for use in transportation equipment that requires strength, and fuel cells, hydrogen fuel components, etc. that require hydrogen embrittlement resistance.

Claims

1. Chemical composition, by mass%, is: C: 0.001-0.100%, Si: 0.01-2.00%, Mn: 0.01-10.00%, P: 0.050% or less, S: 0.0100% or less, Ni: 3.00-15.00%, Cr: 13.0-25.0%, N: 0.001-0.300%, Ti: 0-0.50%, Nb: 0-0.60%, Al: 0-1.000%, Cu: 0-2.00%, Mo: 0-3.00%, V: 0-0.50%, Zr: 0-0.50%, B: 0-0.0050%, Ca: 0-0.0100%, 1. An austenitic stainless hot rolled steel sheet comprising: W: 0-3.00%, Sn: 0-0.50%, Co: 0-0.30%, Mg: 0-0.0100%, Sb: 0-0.300%, REM: 0-0.200%, Ga: 0-0.3000%, Ta: 0-1.000%, Hf: 0-1.000%, Bi: 0-0.02%, balance: Fe and impurities, and having X-ray diffraction intensities of 3 or less in the {001}<010> orientation, the {112}<111> orientation and the {110}<322> orientation.

2. The chemical composition is, in mass%, Ti: 0.01 to 0.50%, Nb: 0.01 to 0.60%, Al: 0.001 to 1.000%, Cu: 0.01 to 2.00%, Mo: 0.01 to 3.00%, V: 0.01 to 0.50%, Zr: 0.01 to 0.50%, B: 0.0002 to 0.0050%, Ca: 0.0005 to 0.0100%, W: 0.10 to 3.00%, Sn: 0.01 to 0.50%, Co: 0.03 to 0.30%, Mg: 0.0002 to 0.0100%, Sb: 0.005 to 0.300%, The austenitic stainless steel hot rolled sheet according to claim 1, containing one or more selected from the group consisting of REM: 0.002 to 0.200%, Ga: 0.0002 to 0.3000%, Ta: 0.001 to 1.000%, Hf: 0.001 to 1.000%, and Bi: 0.001 to 0.02%.

3. The austenitic stainless steel hot rolled sheet according to claim 1 or 2, wherein |Δr| obtained by the following formula (i) is less than 0.

10. Δr=(r ０ +r ９０ ) / 2-r ４５ ...(i) where the meanings of the symbols in formula (i) are as follows: ０ r: Lankford value in the direction of 0° to the rolling direction ４５ r: Lankford value at 45° to the rolling direction ９０ : Lankford value in the direction at 90° to the rolling direction 4. A method for producing austenitic stainless steel hot rolled steel sheet according to claim 3, comprising the steps of: performing slab heating under conditions of slab heating temperature: 1200-1300°C and soaking temperature: 10 min or more and less than 60 min; hot rolling under conditions of finish rolling end temperature: 1020°C or more and a difference between the rough rolling end temperature and the finish rolling end temperature being less than 100°C; and then annealing under conditions of a heating temperature of 1100-1200°C.

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