Bending member and austenitic stainless steel foil

Abstract

Provided are a bending member having excellent fatigue strength, and an austenitic stainless steel foil used in the bending member. In this bent member, a base material is composed of an austenitic stainless steel foil comprising, in mass%, 0.150% or less of C, 1.00% or less of Si, 2.00% or less of Mn, 0.045% or less of P, 0.0300% or less of S, 16.00-20.00% of Cr, 6.00-10.50% of Ni, and 0.100% or less of N, with the remainder being Fe and impurities, and in a plane perpendicular to the direction in which the bent member is bent in the base material, along lt; 111gt, 111gt; the volume fractions Vf111 and lt of the azimuthally oriented grains; 001gt, 001gt; the volume fraction Vf001 of the azimuthally oriented crystal grains satisfies formula (1). 0.6 < = Vf111 / Vf001 < = 12.0 (1)

Description

Technical Field

[0001] The present disclosure relates to a bent member and an austenitic stainless steel foil for the bent member. Background Art

[0002] With the development of electronic devices, materials that can be used in more harsh environments than before are needed. For example, in recent years, the development of electronic devices using deformable displays has made progress. Specifically, smartphones with bendable bodies using deformable displays (foldable smartphones), smartphones that can change the screen size by sliding a part of the body (slidable smartphones), and smartphones that can roll up the body from the end (rollable smartphones) have been developed. In recent years, deformable displays have also been applied to tablet terminals and notebook computers with larger screen sizes than smartphones.

[0003] Electronic devices using deformable displays are subject to repeated bending stress. Therefore, these electronic devices require flexible components with excellent fatigue strength. In this specification, a flexible component refers to a component that is designed to bend. Specifically, a flexible component in an electronic device using a deformable display is, for example, the substrate of an organic EL (Electro-Luminescence) panel.

[0004] Until now, organic EL panels have used resins and other materials as substrates. Therefore, there is a need to replace curved members based on resins and other materials with austenitic stainless steel foil, which has excellent fatigue strength. It should be noted that in this specification, "steel foil" refers to steel sheets with a thickness of 150 μm or less.

[0005] In recent years, technologies for further improving the fatigue strength of austenitic stainless steel foil have been proposed. For example, Japanese Patent Application Laid-Open No. 1-309919 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2005-307295 (Patent Document 2) propose technologies for improving the fatigue strength of austenitic stainless steel foil.

[0006] The stainless steel foil disclosed in Patent Document 1 is made by repeatedly cold-rolling and annealing stainless steel containing, by weight, 0.02-0.2% C, 0.1-2% Si, 0.1-2% Mn, 0.006% or less S, 6.0-10.5% Ni, 16-20% Cr, 0.01% or less Al, 0.01% or less O, 0.001% or less Mg, 0.0001-0.005% Ca, 0.01-0.2% N, and the balance Fe. The result is a total cold-rolling reduction of 98% or more, a final sheet thickness of 100 μm or less, and inclusions of 7 μm or less. Patent Document 1 describes the excellent fatigue properties of this stainless steel foil.

[0007] The austenitic stainless steel foil for springs disclosed in Patent Document 2 is a stainless steel strip for springs conforming to JIS Z 4313SUS301-CSP. The average peak spacing Sm of the surface cross-section curve perpendicular to the rolling direction is 40 μm. Patent Document 2 describes the excellent durability (fatigue properties) of this austenitic stainless steel foil for springs.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 1-309919

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-307295 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] Austenitic stainless steel foils with excellent fatigue strength can be obtained using the techniques proposed in Patent Documents 1 and 2. However, bent components using austenitic stainless steel foils with excellent fatigue strength as a base material can also be obtained using techniques other than those proposed in Patent Documents 1 and 2.

[0014] An object of the present disclosure is to provide a bent member having excellent fatigue strength, and an austenitic stainless steel foil for the bent member.

[0015] Solutions for solving problems

[0016] In the curved member disclosed in the present invention,

[0017] The base material of the bent member is composed of austenitic stainless steel foil.

[0018] The austenitic stainless steel foil is calculated in mass %.

[0019] C: 0.150% or less,

[0020] Si: 1.00% or less,

[0021] Mn: 2.00% or less,

[0022] P: 0.045% or less,

[0023] S: 0.0300% or less,

[0024] Cr: 16.00~20.00%,

[0025] Ni: 6.00~10.50%,

[0026] N: 0.100% or less,

[0027] Mo: 0-2.50%,

[0028] Nb: 0-0.12%,

[0029] V: 0~1.00%

[0030] Ta: 0~0.50%,

[0031] Hf: 0~0.10%

[0032] Co: 0-0.50%,

[0033] B: 0~0.0100%,

[0034] Ca: 0~0.0200%,

[0035] Mg: 0~0.0200%,

[0036] Rare earth elements: 0~0.0100%,

[0037] Al: 0-0.010%,

[0038] Ti: 0~0.500%,

[0039] Zr: 0~0.100%,

[0040] Cu: 0-3.00%, and

[0041] The balance is Fe and impurities.

[0042] In the surface of the base material perpendicular to the direction in which the bending member is bent, <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 Satisfying the following formula (1),

[0043] 0.6≤Vf 111 / Vf 001 ≤12.0 (1).

[0044] The austenitic stainless steel foil disclosed in the present invention is an austenitic stainless steel foil for the above-mentioned bent member, and its mass % is

[0045] C: 0.150% or less,

[0046] Si: 1.00% or less,

[0047] Mn: 2.00% or less,

[0048] P: 0.045% or less,

[0049] S: 0.0300% or less,

[0050] Cr: 16.00~20.00%,

[0051] Ni: 6.00~10.50%,

[0052] N: 0.100% or less,

[0053] Mo: 0-2.50%,

[0054] Nb: 0-0.12%,

[0055] V: 0~1.00%

[0056] Ta: 0~0.50%,

[0057] Hf: 0~0.10%

[0058] Co: 0-0.50%,

[0059] B: 0~0.0100%,

[0060] Ca: 0~0.0200%,

[0061] Mg: 0~0.0200%,

[0062] Rare earth elements: 0~0.0100%,

[0063] Al: 0-0.010%,

[0064] Ti: 0~0.500%,

[0065] Zr: 0~0.100%,

[0066] Cu: 0-3.00%, and

[0067] The balance is Fe and impurities.

[0068] In the austenitic stainless steel foil, the surface perpendicular to the direction inclined 5 to 65 degrees from the Brass direction along the rolling surface is <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 Satisfying the following formula (2),

[0069] 0.6≤Vf 111 / Vf 001 ≤12.0 (2).

[0070] Effects of the Invention

[0071] The bent member of the present disclosure has excellent fatigue strength. The austenitic stainless steel foil of the present disclosure can be used for a bent member having excellent fatigue strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 Is the Fn1 (= Vf 111 / Vf 001 ) and the number of fatigue times as an indicator of fatigue strength.

[0073] Figure 2A This is a diagram showing a bent state of the bent member 1 when the bent member 1 is applied to an electronic device.

[0074] Figure 2B This is a diagram showing another example of how the bent member 1 is bent when the bent member 1 is applied to an electronic device.

[0075] Figure 2C This is a diagram showing another example of how the bent member 1 is bent when the bent member 1 is applied to an electronic device.

[0076] Figure 3A This is a schematic diagram for explaining the incident direction of X-rays when the test piece 10 is viewed from the side in the XRD measurement of the present embodiment.

[0077] Figure 3B This is a schematic diagram for explaining the incident direction of X-rays when the test piece 10 is viewed from above in the XRD measurement of the present embodiment. DETAILED DESCRIPTION

[0078] To obtain a bent member having excellent fatigue strength, the present inventors first focused on the chemical composition of the austenitic stainless steel foil serving as the base material of the bent member. Specifically, they believed that the fatigue strength of the bent member could be improved by using as the base material an austenitic stainless steel foil having the following chemical composition (in mass %): C: 0.150% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.0300% or less, Cr: 16.00-20.00%, Ni: 6.00-10.50%, N: 0.100% or less, Mo: 0-2.50% or less. %, Nb: 0~0.12%, V: 0~1.00%, Ta: 0~0.50%, Hf: 0~0.10%, Co: 0~0.50%, B: 0~0.0100%, Ca: 0~0.0200%, Mg: 0~0.0200%, rare earth elements: 0~0.0100%, Al: 0~0.010%, Ti: 0~0.500%, Zr: 0~0.100%, Cu: 0~3.00%, and the balance is Fe and impurities.

[0079] The present inventors further focused on the relationship between the direction in which a bent member is bent and the austenitic stainless steel foil having the aforementioned chemical composition, and conducted detailed research. Their results revealed that, in a bent member based on an austenitic stainless steel foil having the aforementioned chemical composition, the crystal orientation of the foil affects the fatigue strength of the bent member.

[0080] Here, focusing on crystal orientation, the austenitic stainless steel foil with the aforementioned chemical composition contains slip planes {111}. It should be noted that slip planes refer to specific crystallographic planes where a crystal experiences slip displacement when subjected to stress. Furthermore, if the direction of the slip plane of the foil is parallel or perpendicular to the direction in which the bent member is bent, slip deformation is less likely to occur, and as a result, cracking may be more likely to occur. Specifically, in the austenitic stainless steel foil with the aforementioned chemical composition, if the direction of the slip plane of the foil is somewhat tilted relative to the direction in which the bent member is bent, slip deformation is more likely to occur, and cracking may be less likely to occur. In this case, fatigue strength in the bending direction of the bent member may be increased.

[0081] Based on the above findings, the present inventors have focused on the crystal orientation of the austenitic stainless steel foil having the above chemical composition and have conducted detailed research on methods for improving the fatigue strength of bent parts. As a result, it was found that in the austenitic stainless steel foil having the above chemical composition as the base material of the bent part, if the surface perpendicular to the direction in which the bent part is bent is aligned with the surface perpendicular to the direction in which the bent part is bent, the fatigue strength of the bent part is improved. <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 When the following formula (1) is satisfied, the fatigue strength of the bent member is improved.

[0082] 0.6≤Vf 111 / Vf 001 ≤12.0 (1)

[0083] This point will be described in detail using the drawings. Figure 1 Is the Fn1 (= Vf 111 / Vf 001 ) and the number of fatigue times as an indicator of fatigue strength. Figure 1 The thickness of the austenitic stainless steel foil having the above chemical composition is obtained on a plane perpendicular to the bending direction. <111> Volume fraction of azimuthally oriented grains Vf 111 ,along <001> Volume fraction of azimuthally oriented grains Vf 001 , and the number of bending times (fatigue times) in the bending direction.

[0084] Reference Figure 1, when Fn1 is 0.6 to 12.0, the fatigue times are more than 12,000 times, showing excellent fatigue strength. Figure 1 Furthermore, it was found that when Fn1 was less than 0.6 or exceeded 12.0, the fatigue cycle was less than 12,000, indicating that excellent fatigue strength was not achieved. Therefore, in the bent member of this embodiment, the austenitic stainless steel foil serving as its base material satisfies the aforementioned chemical composition, and Fn1 is within the range of 0.6 to 12.0. As a result, the bent member of this embodiment exhibits excellent fatigue strength.

[0085] The details of the mechanism by which the fatigue strength of a bent member is improved by having an austenitic stainless steel foil with an Fn1 value of 0.6 to 12.0 are not yet clear. However, the examples described below demonstrate that when an austenitic stainless steel having the aforementioned chemical composition has an Fn1 value of 0.6 to 12.0, the fatigue strength of a bent member using the austenitic stainless steel foil as a base material is improved.

[0086] The gist of the bent member of the present embodiment and the austenitic stainless steel foil used therefor, which were completed based on the above findings, are as follows. [1]

[0088] A curved member, wherein

[0089] The base material of the bent member is composed of austenitic stainless steel foil.

[0090] The austenitic stainless steel foil is calculated in mass %.

[0091] C: 0.150% or less,

[0092] Si: 1.00% or less,

[0093] Mn: 2.00% or less,

[0094] P: 0.045% or less,

[0095] S: 0.0300% or less,

[0096] Cr: 16.00~20.00%,

[0097] Ni: 6.00~10.50%,

[0098] N: 0.100% or less,

[0099] Mo: 0-2.50%,

[0100] Nb: 0-0.12%,

[0101] V: 0~1.00%

[0102] Ta: 0~0.50%,

[0103] Hf: 0~0.10%

[0104] Co: 0-0.50%,

[0105] B: 0~0.0100%,

[0106] Ca: 0~0.0200%,

[0107] Mg: 0~0.0200%,

[0108] Rare earth elements: 0~0.0100%,

[0109] Al: 0-0.010%,

[0110] Ti: 0~0.500%,

[0111] Zr: 0~0.100%,

[0112] Cu: 0-3.00%, and

[0113] The balance is Fe and impurities.

[0114] In the surface of the base material perpendicular to the direction in which the bending member is bent, <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 Satisfying the following formula (1),

[0115] 0.6≤Vf 111 / Vf 001 ≤12.0 (1). [2]

[0117] The curved member according to [1], wherein

[0118] The austenitic stainless steel foil contains

[0119] Mo: 0.01~2.50%,

[0120] Nb: 0.01-0.12%,

[0121] V: 0.01~1.00%,

[0122] Ta: 0.01~0.50%,

[0123] Hf: 0.01~0.10%,

[0124] Co: 0.01-0.50%,

[0125] B: 0.0001~0.0100%,

[0126] Ca: 0.0001~0.0200%,

[0127] Mg: 0.0001~0.0200%,

[0128] Rare earth elements: 0.0001~0.0100%,

[0129] Al: 0.001~0.010%,

[0130] Ti: 0.001~0.500%,

[0131] Zr: 0.001~0.100%, and

[0132] Cu: One or more elements selected from the group consisting of 0.01 to 3.00%. [3]

[0134] The curved member according to [1] or [2], wherein

[0135] The curved member comprises:

[0136] the first end,

[0137] the second end, and

[0138] a curved portion disposed between the first end portion and the second end portion,

[0139] The bending member is bent in a direction parallel to a direction in which the first end portion, the bent portion, and the second end portion are arranged. [4]

[0141] An austenitic stainless steel foil for use in a bent member according to any one of [1] to [3], wherein the austenitic stainless steel foil is

[0142] C: 0.150% or less,

[0143] Si: 1.00% or less,

[0144] Mn: 2.00% or less,

[0145] P: 0.045% or less,

[0146] S: 0.0300% or less,

[0147] Cr: 16.00~20.00%,

[0148] Ni: 6.00~10.50%,

[0149] N: 0.100% or less,

[0150] Mo: 0-2.50%,

[0151] Nb: 0-0.12%,

[0152] V: 0~1.00%

[0153] Ta: 0~0.50%,

[0154] Hf: 0~0.10%

[0155] Co: 0-0.50%,

[0156] B: 0~0.0100%,

[0157] Ca: 0~0.0200%,

[0158] Mg: 0~0.0200%,

[0159] Rare earth elements: 0~0.0100%,

[0160] Al: 0-0.010%,

[0161] Ti: 0~0.500%,

[0162] Zr: 0~0.100%,

[0163] Cu: 0-3.00%, and

[0164] The balance is Fe and impurities.

[0165] In the austenitic stainless steel foil, the surface perpendicular to the direction inclined 5 to 65 degrees from the Brass direction along the rolling surface is <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 Satisfying the following formula (2),

[0166] 0.6≤Vf 111 / Vf 001 ≤12.0 (2). [5]

[0168] The austenitic stainless steel foil according to [4] contains a

[0169] Mo: 0.01~2.50%,

[0170] Nb: 0.01-0.12%,

[0171] V: 0.01~1.00%,

[0172] Ta: 0.01~0.50%,

[0173] Hf: 0.01~0.10%,

[0174] Co: 0.01-0.50%,

[0175] B: 0.0001~0.0100%,

[0176] Ca: 0.0001~0.0200%,

[0177] Mg: 0.0001~0.0200%,

[0178] Rare earth elements: 0.0001~0.0100%,

[0179] Al: 0.001~0.010%,

[0180] Ti: 0.001~0.500%,

[0181] Zr: 0.001~0.100%, and

[0182] Cu: One or more elements selected from the group consisting of 0.01 to 3.00%.

[0183] Hereinafter, the bent member and the austenitic stainless steel foil of the present embodiment will be described in detail. Unless otherwise specified, "%" related to an element means mass %.

[0184] [Curved member]

[0185] The base material of the curved member of this embodiment is composed of austenitic stainless steel foil. That is, the curved member of this embodiment may also include structures other than austenitic stainless steel foil. Furthermore, as mentioned above, the curved member is suitable, for example, for use as a substrate for an organic EL panel. In this case, the curved member can be used in smartphones, tablet computers, and even notebook computers. In other words, the curved member of this embodiment only needs to have a base material composed of austenitic stainless steel foil having the characteristics described below, and its application is not limited.

[0186] As described above, a curved member refers to a member that is intended to bend. Therefore, those skilled in the art will naturally be able to determine the direction in which the curved member is bent. It should be noted that the direction in which the curved member is bent can sometimes be defined as follows. Specifically, the description will be of a curved member having a first end, a second end, and a curved portion. The curved portion of a curved member refers to the portion of the curved member that is deformed. Furthermore, the curved portion is disposed between the first and second ends. In this case, the direction in which the curved member is bent is parallel to the direction in which the first end, the curved portion, and the second end are arranged. It should be noted that the curved member of this embodiment may have only a first end and no second end, or may have neither a first end nor a second end. Even in this case, as described above, those skilled in the art will naturally be able to determine the direction in which the curved member is bent.

[0187] More specifically, a case where a curved member is applied to an electronic device will be described using the drawings. Figure 2A This is a diagram showing a curved state of the curved member 1 when the curved member 1 is applied to an example of an electronic device (a foldable smartphone). Figure 2A The up-down direction corresponds to the thickness direction of the bent member 1 (the thickness direction of the austenitic stainless steel foil). Figure 2A (A) shows the state of the bent member 1 before bending. Figure 2A (B) shows the state of the bending member 1 during the bending process. Figure 2A (C) shows the state of the bent member 1 after bending. Figure 2A The bending direction of the bending member 1 corresponds to the left-right direction of the drawing. Figure 2A It is further concluded that in the curved member 1, Figure 2A The left-right center position of (A) corresponds to the deformed portion (curved portion), and the curved portion is sandwiched between the non-deformed portions. Figure 2A The first end portion, the bent portion, and the second end portion of the illustrated bending member 1 are arranged in the bending direction (left-right direction in the figure) of the bending member 1 .

[0188] Figure 2B This is a diagram showing a curved state of the curved member 1 when the curved member 1 is applied to another example of an electronic device (a slidable smartphone). Figure 2B The up and down directions are also Figure 2A Likewise, it corresponds to the thickness direction of the curved member 1 . Figure 2B (A) shows the state of the bent member 1 before bending. Figure 2B (B) shows the state of the bending member 1 during the bending process. Figure 2B (C) shows the state of the bent member 1 after bending. Figure 2B The bending direction of the bending member 1 corresponds to the left-right direction of the drawing. Figure 2B Further conclusion is drawn, Figure 2B (C) The bending member 1 is except Figure 2B The portion other than the straight line portion on the upper side of (C) corresponds to the curved portion, and the straight line portion on the upper side of the drawing corresponds to the non-deformed portion. Figure 2B The first end portion and the bent portion of the illustrated bending member 1 are arranged in the bending direction (left-right direction in the figure) of the bending member 1 .

[0189] Figure 2C This is a diagram showing a bent state of the bending member 1 when the bending member 1 is applied to another example of an electronic device (a rollable smartphone). Figure 2C The up and down directions are also Figure 2A and Figure 2B Likewise, it corresponds to the thickness direction of the curved member 1 . Figure 2C (A) shows the state of the bent member 1 before bending. Figure 2C (B) shows the state of the bending member 1 during the bending process. Figure 2C (C) shows the state of the bent member 1 after bending. Figure 2C The bending direction of the bending member 1 corresponds to the left-right direction of the drawing. Figure 2C It is further concluded that the entire curved member 1 corresponds to the curved portion. Figure 2C The curved member 1 shown as an example includes only a curved portion and does not have a first end portion and a second end portion.

[0190] [Austenitic stainless steel foil]

[0191] The base material of the bent member of the present embodiment is made of austenitic stainless steel foil.

[0192] [Chemical composition of austenitic stainless steel foil]

[0193] The austenitic stainless steel foil of the present embodiment contains the following elements.

[0194] C: 0.150% or less

[0195] Carbon (C) is inevitably contained. That is, the lower limit of the C content exceeds 0%. C forms carbides and increases the strength of the steel. However, if the C content is too high, even if the content of other elements is within the range of this embodiment, carbides will precipitate at the grain boundaries, the amount of precipitation of intermetallic compounds at the grain boundaries will decrease, and the stability of the grain boundaries will decrease. If the C content is too high, carbides will further precipitate excessively, and the toughness of the steel will decrease. Therefore, the C content is 0.150% or less. The preferred upper limit of the C content is 0.140%, more preferably 0.130%, and more preferably 0.120%. Here, an extreme reduction in the C content will significantly increase the manufacturing cost. Therefore, considering industrial production, the preferred lower limit of the C content is 0.001%, and more preferably 0.005%.

[0196] Si: 1.00% or less

[0197] Silicon (Si) is inevitably contained. That is, the lower limit of the Si content exceeds 0%. Si deoxidizes the steel. However, if the Si content is too high, even if the contents of other elements are within the range of this embodiment, coarse oxides will remain in the steel, and the hot workability of the steel will be reduced. Therefore, the Si content is 1.00% or less. The preferred upper limit of the Si content is 0.95%, more preferably 0.90%, and more preferably 0.80%. Here, an extreme reduction in the Si content will significantly increase the manufacturing cost. Therefore, considering industrial production, the preferred lower limit of the Si content is 0.01%, and more preferably 0.05%.

[0198] Mn: 2.00% or less

[0199] Manganese (Mn) is inevitably contained. That is, the lower limit of the Mn content exceeds 0%. Mn deoxidizes the steel. Mn also stabilizes the austenite phase. Mn also fixes S in the steel in the form of sulfides, improving the hot workability of the steel. However, if the Mn content is too high, even if the contents of other elements are within the range of this embodiment, the formation of a spinel-type oxide film is promoted, and the oxidation resistance of the steel at high temperatures is reduced. Therefore, the Mn content is 2.00% or less. The preferred upper limit of the Mn content is 1.90%, more preferably 1.80%, and more preferably 1.70%. The preferred lower limit of the Mn content for effectively obtaining the above-mentioned effect is 0.30%, and more preferably 0.50%.

[0200] P: 0.045% or less

[0201] Phosphorus (P) is an impurity. That is, the lower limit of the P content exceeds 0%. If the P content is too high, even if the contents of other elements are within the range of this embodiment, the grain boundaries become embrittled and the stress relaxation crack sensitivity of the steel increases. Therefore, the P content is 0.045% or less. The preferred upper limit of the P content is 0.040%, and more preferably 0.035%. The P content is preferably as low as possible. However, an extreme reduction in the P content will significantly increase the manufacturing cost. Therefore, considering industrial production, the preferred lower limit of the P content is 0.001%, and more preferably 0.003%.

[0202] S: 0.0300% or less

[0203] Sulfur (S) is an impurity. That is, the lower limit of the S content exceeds 0%. If the S content is too high, even if the contents of other elements are within the range of this embodiment, S will segregate at the grain boundaries, and the stress relaxation cracking sensitivity of the steel will increase. Therefore, the S content is 0.0300% or less. The preferred upper limit of the S content is 0.0200%, more preferably 0.0150%, and more preferably 0.0100%. The S content is preferably as low as possible. However, an extreme reduction in the S content will significantly increase manufacturing costs. Therefore, considering industrial production, the preferred lower limit of the S content is 0.0001%, and more preferably 0.0003%.

[0204] Cr: 16.00~20.00%

[0205] Chromium (Cr) improves the corrosion resistance of steel, such as oxidation resistance, steam oxidation resistance, and high-temperature corrosion resistance. Cr also forms carbides to increase the strength of steel. If the Cr content is too low, even if the contents of other elements are within the range of the present embodiment, the above-mentioned effects cannot be fully obtained. On the other hand, if the Cr content is too high, even if the contents of other elements are within the range of the present embodiment, α-Cr phase and σ phase will precipitate excessively, and the corrosion resistance of the steel will be reduced. Therefore, the Cr content is 16.00 to 20.00%. The preferred lower limit of the Cr content is 16.05%, more preferably 16.10%, and more preferably 16.20%. The preferred upper limit of the Cr content is 19.95%, more preferably 19.90%, and more preferably 19.80%.

[0206] Ni: 6.00~10.50%

[0207] Nickel (Ni) stabilizes austenite. Ni also improves the ductility of steel. If the Ni content is too low, even if the contents of other elements are within the range of the present embodiment, the above-mentioned effects cannot be fully obtained. On the other hand, if the Ni content is too high, even if the contents of other elements are within the range of the present embodiment, the deformation resistance within the grains increases and the ductility of the steel decreases. Therefore, the Ni content is 6.00 to 10.50%. The preferred lower limit of the Ni content is 6.10%, more preferably 6.20%, and more preferably 6.30%. The preferred upper limit of the Ni content is 10.40%, more preferably 10.20%, and more preferably 10.00%.

[0208] N: 0.100% or less

[0209] Nitrogen (N) is inevitably contained. That is, the N content exceeds 0%. N dissolves in the steel and increases the strength of the steel. N also stabilizes the austenite phase. However, if the N content is too high, even if the contents of other elements are within the range of this embodiment, the strength of the steel will become too high and the ductility of the steel will decrease. Therefore, the N content is 0.100% or less. The preferred lower limit of the N content for effectively obtaining the above-mentioned effect is 0.001%, more preferably 0.005%, and more preferably 0.010%. The preferred upper limit of the N content is 0.090%, more preferably 0.080%, and more preferably 0.060%.

[0210] The balance of the chemical composition of the austenitic stainless steel foil of this embodiment is Fe and impurities. Impurities are substances that enter the austenitic stainless steel foil during industrial production from raw material ores, scrap, or the production environment, and are permitted to the extent that they do not adversely affect the austenitic stainless steel foil of this embodiment.

[0211] [Any element]

[0212] The austenitic stainless steel foil of the present embodiment may further contain one or more elements selected from the group consisting of Mo, Nb, V, Ta, Hf, and Co, in place of a portion of Fe. These elements are arbitrary elements and improve the strength of the steel material.

[0213] Mo: 0~2.50%

[0214] Molybdenum (Mo) is an arbitrary element and may not be contained. That is, the Mo content may be 0%. When contained, Mo dissolves in the steel and improves the strength of the steel. In this case, Mo also forms carbides in the steel and improves the strength of the steel. As long as a small amount of Mo is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Mo content is too high, even if the content of other elements is within the range of this embodiment, the strength of the steel will become too high and the hot workability of the steel will decrease. Therefore, the Mo content is 0 to 2.50%. The preferred lower limit of the Mo content exceeds 0%, more preferably 0.01%, more preferably 0.05%, and more preferably 0.10%. The preferred upper limit of the Mo content is 2.20%, more preferably 2.00%, and more preferably 1.70%.

[0215] Nb: 0~0.12%

[0216] Niobium (Nb) is an arbitrary element and may not be contained. That is, the Nb content may be 0%. When contained, Nb refines the grains of the steel and improves the corrosion resistance of the steel. As long as a small amount of Nb is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Nb content is too high, even if the contents of other elements are within the range of this embodiment, coarse carbides will be formed, and the strength, ductility and hot workability of the steel will be reduced. Therefore, the Nb content is 0 to 0.12%. The preferred lower limit of the Nb content exceeds 0%, more preferably 0.01%, and more preferably 0.02%. The preferred upper limit of the Nb content is 0.10%, and more preferably 0.09%.

[0217] V: 0~1.00%

[0218] Vanadium (V) is an arbitrary element and may not be contained. That is, the V content may be 0%. When contained, V forms carbonitrides and / or intermetallic compounds, thereby improving the strength of the steel. In this case, the grains of the steel are also refined. As long as a small amount of V is contained, the above-mentioned effect can be obtained to a certain extent. However, if the V content is too high, even if the content of other elements is within the range of this embodiment, the ductility and toughness of the steel are reduced due to the occurrence of high-temperature corrosion and the precipitation of brittle phases. Therefore, the V content is 0 to 1.00%. The preferred lower limit of the V content exceeds 0%, more preferably 0.01%, and more preferably 0.03%. The preferred upper limit of the V content is 0.90%, and more preferably 0.80%.

[0219] Ta: 0~0.50%

[0220] Tantalum (Ta) is an arbitrary element and may not be contained. That is, the Ta content may be 0%. When contained, Ta strengthens the grain boundaries and improves the strength of the steel. As long as a small amount of Ta is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Ta content is too high, the hot workability will be reduced even if the content of other elements is within the range of this embodiment. Therefore, the Ta content is 0 to 0.50%. The preferred lower limit of the Ta content exceeds 0%, more preferably 0.01%, and more preferably 0.03%. The preferred upper limit of the Ta content is 0.45%, and more preferably 0.40%.

[0221] Hf: 0~0.10%

[0222] Hafnium (Hf) is an arbitrary element and may not be contained. That is, the Hf content may be 0%. When contained, Hf strengthens the grain boundaries and improves the strength of the steel. As long as a small amount of Hf is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Hf content is too high, the hot workability will be reduced even if the content of other elements is within the range of this embodiment. Therefore, the Hf content is 0 to 0.10%. The preferred lower limit of the Hf content exceeds 0%, more preferably 0.01%, and more preferably 0.03%. The preferred upper limit of the Hf content is 0.09%, and more preferably 0.08%.

[0223] Co: 0-0.50%

[0224] Cobalt (Co) is an arbitrary element and may not be contained. That is, the Co content may be 0%. When contained, Co dissolves in the steel and improves the strength of the steel. As long as a small amount of Co is contained, the above-mentioned effect can be obtained to some extent. However, if the Co content is too high, even if the contents of other elements are within the range of this embodiment, the strength of the steel will become too high and the hot workability of the steel will decrease. Therefore, the Co content is 0 to 0.50%. The preferred lower limit of the Co content exceeds 0%, more preferably 0.01%, and more preferably 0.05%. The preferred upper limit of the Co content is 0.45%, and more preferably 0.40%.

[0225] The austenitic stainless steel foil of this embodiment may further contain one or more elements selected from the group consisting of B, Ca, Mg, and rare earth elements in place of a portion of Fe. These elements are arbitrary elements that improve the hot workability of the steel material.

[0226] B: 0~0.0100%

[0227] Boron (B) is an arbitrary element and may not be contained. That is, the B content may be 0%. When contained, B improves the high-temperature toughness of the steel by suppressing the precipitation of carbides and miniaturizing the precipitates. As long as a small amount of B is contained, the above-mentioned effect can be obtained to a certain extent. However, if the B content is too high, even if the content of other elements is within the range of this embodiment, boron nitride (BN) will be generated, which will reduce the toughness of the steel. Therefore, the B content is 0 to 0.0100%. The preferred lower limit of the B content exceeds 0%, more preferably 0.0001%, more preferably 0.0005%, and more preferably 0.0010%. The preferred upper limit of the B content is 0.0080%, more preferably 0.0070%, and more preferably 0.0050%.

[0228] Ca: 0~0.0200%

[0229] Calcium (Ca) is an arbitrary element and may not be contained. That is, the Ca content may be 0%. When contained, Ca fixes the S in the steel in the form of sulfides, thereby improving the hot workability of the steel. As long as a small amount of Ca is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Ca content is too high, even if the contents of other elements are within the range of this embodiment, coarse oxides will be formed, and the hot workability and ductility of the steel will be reduced. Therefore, the Ca content is 0 to 0.0200%. The preferred lower limit of the Ca content exceeds 0%, more preferably 0.0001%, and more preferably 0.0003%. The preferred upper limit of the Ca content is 0.0180%, and more preferably 0.0150%.

[0230] Mg: 0~0.0200%

[0231] Magnesium (Mg) is an arbitrary element and may not be contained. That is, the Mg content may be 0%. When contained, Mg fixes the S in the steel in the form of sulfides, thereby improving the hot workability of the steel. As long as a small amount of Mg is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Mg content is too high, even if the contents of other elements are within the range of this embodiment, coarse oxides will be formed, and the hot workability and ductility of the steel will be reduced. Therefore, the Mg content is 0 to 0.0200%. The preferred lower limit of the Mg content exceeds 0%, more preferably 0.0001%, and more preferably 0.0003%. The preferred upper limit of the Mg content is 0.0180%, and more preferably 0.0150%.

[0232] Rare earth elements: 0-0.0100%

[0233] Rare earth elements (REM) are arbitrary elements and may not be contained. That is, the REM content may be 0%. When contained, REM fixes the S in the steel in the form of sulfides, thereby improving the hot workability of the steel. REM also improves the adhesion of the Cr2O3 protective film on the surface of the steel and improves the oxidation resistance of the steel. REM also strengthens the grain boundaries and improves the strength and fracture strain of the steel. As long as a small amount of REM is contained, the above-mentioned effects can be obtained to a certain extent. However, if the REM content is too high, even if the content of other elements is within the range of this embodiment, coarse oxides will be formed, and the hot workability of the steel will be reduced. Therefore, the REM content is 0 to 0.0100%. The preferred lower limit of the REM content exceeds 0%, more preferably 0.0001%, and more preferably 0.0003%. The preferred upper limit of the REM content is 0.0090%, and more preferably 0.0080%.

[0234] It should be noted that REM in this specification refers to one or more elements selected from the group consisting of scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanide elements ranging from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. The REM content in this specification refers to the total content of these elements.

[0235] The austenitic stainless steel foil of this embodiment may further contain one or more elements selected from the group consisting of Al, Ti, and Zr in place of a portion of Fe. These elements are arbitrary elements and serve to deoxidize the steel material.

[0236] Al: 0~0.010%

[0237] Aluminum (Al) is an arbitrary element and may not be contained. That is, the Al content may be 0%. When contained, Al deoxidizes the steel. As long as a small amount of Al is contained, the above-mentioned effect can be obtained to a certain extent. However, if the Al content is too high, even if the contents of other elements are within the range of this embodiment, coarse inclusions will be formed, and the fatigue strength of the steel will be reduced. Therefore, the Al content is 0 to 0.010%. The preferred lower limit of the Al content exceeds 0%, more preferably 0.001%, and more preferably 0.002%. The preferred upper limit of the Al content is 0.009%, and more preferably 0.008%.

[0238] Ti: 0~0.500%

[0239] Titanium (Ti) is an arbitrary element and may not be contained. That is, the Ti content may be 0%. When contained, Ti deoxidizes the steel. As long as a small amount of Ti is contained, the above-mentioned effect can be obtained to some extent. However, if the Ti content is too high, even if the contents of other elements are within the range of this embodiment, coarse inclusions will be formed, and the hot workability of the steel will be reduced. Therefore, the Ti content is 0 to 0.500%. The preferred lower limit of the Ti content exceeds 0%, more preferably 0.001%, and more preferably 0.002%. The preferred upper limit of the Ti content is 0.450%, and more preferably 0.400%.

[0240] Zr: 0~0.100%

[0241] Zirconium (Zr) is an arbitrary element and may not be contained. That is, the Zr content may be 0%. When contained, Zr deoxidizes the steel. As long as a small amount of Zr is contained, the above-mentioned effect can be obtained to a certain extent. On the other hand, if the Zr content is too high, the toughness and hot workability of the steel will be reduced even if the contents of other elements are within the range of this embodiment. Therefore, the Zr content is 0 to 0.100%. The preferred lower limit of the Zr content exceeds 0%, more preferably 0.001%, and more preferably 0.002%. The preferred upper limit of the Zr content is 0.090%, and more preferably 0.080%.

[0242] The austenitic stainless steel foil of the present embodiment may further contain Cu in place of a portion of Fe.

[0243] Cu: 0-3.00%

[0244] Copper (Cu) is an arbitrary element and may not be contained. That is, the Cu content may be 0%. When contained, Cu improves the corrosion resistance and oxidation resistance of the steel. As long as a small amount of Cu is contained, the above-mentioned effect can be obtained to some extent. However, if the Cu content is too high, even if the content of other elements is within the scope of the present embodiment, it will promote grain boundary embrittlement at high temperatures and reduce the hot workability of the steel. Therefore, the Cu content is 0 to 3.00%. The preferred lower limit of the Cu content exceeds 0%, more preferably 0.01%, more preferably 0.05%, and more preferably 0.10%. The preferred upper limit of the Cu content is 2.20%, more preferably 2.00%, and more preferably 1.70%.

[0245] [Method for determining the chemical composition of austenitic stainless steel foil]

[0246] The chemical composition of the austenitic stainless steel foil of this embodiment can be measured using known compositional analysis methods. Specifically, cuttings are collected from the austenitic stainless steel foil. The collected cuttings are dissolved in acid to obtain a solution. The solution is subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) to perform elemental analysis of the chemical composition. The C and S contents are determined using the known high-frequency combustion method (combustion-infrared absorption method). The N content is determined using the known inert gas fusion-thermal conductivity method.

[0247] It should be noted that the content of each element is set to the numerical value obtained by rounding off the mantissa of the element content specified in the present embodiment (the number of the next digit of the lowest digit). For example, the C content is set to the numerical value obtained by rounding off the fourth decimal place of the value obtained by the above method to the third decimal place. In the present embodiment, for the element content other than the C content, the numerical value obtained by rounding off the mantissa of the element content specified in the present embodiment to the value obtained by the above method is used as the element content. It should be noted that rounding means that if the mantissa is less than 4, it is discarded, and if the mantissa is more than 5, it is carried.

[0248] [Crystal Orientation of Austenitic Stainless Steel Foil]

[0249] In the austenitic stainless steel foil of this embodiment, in a plane perpendicular to the direction in which the bent member is bent, <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 The following formula (1) is satisfied.

[0250] 0.6≤Vf 111 / Vf 001 ≤12.0 (1)

[0251] Here, we focus on the surface of the austenitic stainless steel foil having the above chemical composition that is perpendicular to the direction in which the bent member is bent. Hereinafter, in this specification, the surface of the austenitic stainless steel foil having the above chemical composition that is perpendicular to the direction in which the bent member is bent is also referred to as a "specific surface."

[0252] In the austenitic stainless steel foil having the above chemical composition, examples of the crystal orientation in a specific plane include: <001> position, <101> position, <111> Direction, and <112> Direction. It should be noted that {110} <112> The bearing is also called the Brass bearing, {110} <001> Bearing is also called Goss bearing.

[0253] In addition, in the austenitic stainless steel foil having the above chemical composition, the distribution of the volume fraction of the crystal orientation in a specific plane and the direction of the slip plane of the steel foil are constrained by the chemical composition and vary with a certain degree of correlation. <112> Volume fraction Vf of grains oriented in Brass orientation 112 When the content exceeds 42.00%, the direction of the slip plane of the steel foil becomes nearly parallel to the direction in which the bent member is bent. As a result, the bent member may be prone to cracking, and the fatigue strength of the bent member may not be sufficiently improved.

[0254] Likewise, specifically, along a particular face <001> Volume fraction Vf of grains oriented in the Goss direction 001 When the slip ratio is less than 2.50%, the direction of the slip plane of the steel foil is close to perpendicular to the direction in which the bent member is bent. As a result, the bent member may be prone to cracking and the fatigue strength of the bent member may not be sufficiently improved. <111> Volume fraction of azimuthally oriented grains Vf 111 When the content is less than 21.00%, the direction of the slip plane of the steel foil becomes nearly parallel to the direction in which the bent member is bent, and as a result, the fatigue strength of the bent member may not be sufficiently improved.

[0255] Based on these findings, the present inventors have studied the relationship between the volume fraction of grains oriented in a specific direction on a specific surface and the fatigue strength of the bent member. As a result, the bent member of this embodiment has the following characteristics. Specifically, in the bent member of this embodiment, on a specific surface of the austenitic stainless steel foil having the above-mentioned chemical composition as the base material, <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction Vf of grains oriented in the Goss direction 001 The following formula (1) is satisfied.

[0256] 0.6≤Vf 111 / Vf 001 ≤12.0 (1)

[0257] In this case, further attention is paid to austenitic stainless steel foil, and the specific surface is equivalent to the foil. <112> The surface perpendicular to the direction inclined 5 to 65 degrees from the rolling surface in the direction (Brass direction) is defined as follows. That is, in the austenitic stainless steel foil of the present embodiment used in the bent member, the surface perpendicular to the direction inclined 5 to 65 degrees from the Brass direction is defined as follows. <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001The following formula (2) is satisfied.

[0258] 0.6≤Vf 111 / Vf 001 ≤12.0 (2)

[0259] Fn1(=Vf 111 / Vf 001 ) is an indicator of the fatigue strength of a bent member. When Fn1 is less than 0.6 or exceeds 12.0, the fatigue cycle is less than 12,000, failing to demonstrate excellent fatigue strength. Therefore, the bent member of this embodiment, while the austenitic stainless steel foil serving as the base material satisfies the aforementioned chemical composition, has Fn1 on a specific surface set to 0.6 to 12.0. As a result, the bent member of this embodiment exhibits excellent fatigue strength.

[0260] The preferred lower limit of Fn1 on a specific surface of the steel foil serving as the base material for the bent member of this embodiment is greater than 0.6, more preferably 0.7, and even more preferably 0.8. The preferred upper limit of Fn1 on a specific surface of the steel foil serving as the base material for the bent member of this embodiment is 11.5, more preferably 11.0, and even more preferably 10.5. It should be noted that in this embodiment, the volume fraction of grains oriented in a specific orientation on the specific surface of the steel foil is not particularly limited. However, the following volume fractions are also acceptable.

[0261] In the specific surface of the austenitic stainless steel foil of this embodiment, <001> Volume fraction of azimuthally oriented grains Vf 001 The preferred lower limit of is 2.50%, more preferably 3.00%, more preferably 4.00%, and more preferably 5.00%. <001> Volume fraction of azimuthally oriented grains Vf 001 The upper limit of is not particularly limited, and may be, for example, 60.00%, 55.00%, or 50.00%.

[0262] In the specific surface of the austenitic stainless steel foil of this embodiment, <111> Volume fraction of azimuthally oriented grains Vf 111 The preferred lower limit of is 21.00%, more preferably 22.00%, more preferably 23.00%, more preferably 24.00%, and more preferably 25.00%. In the specific surface of the austenitic stainless steel foil of this embodiment, along <111> Volume fraction of azimuthally oriented grains Vf 111 The upper limit of is not particularly limited, and may be, for example, 70.00%, 65.00%, or 60.00%.

[0263] In the specific surface of the austenitic stainless steel foil of this embodiment, <112> Volume fraction of azimuthally oriented grains Vf 112 The preferred upper limit of is 42.00%, more preferably 41.00%, more preferably 40.00%, and more preferably 35.00%. <112> Volume fraction of azimuthally oriented grains Vf 112 The lower limit of is not particularly limited, and may be, for example, 3.00%, 5.00%, or 7.00%.

[0264] In the specific surface of the austenitic stainless steel foil of this embodiment, <101> Volume fraction of azimuthally oriented grains Vf 101 The lower limit of is not particularly limited, and may be, for example, 0.00%. <101> Volume fraction of azimuthally oriented grains Vf 101 The upper limit of the content is not particularly limited, and may be, for example, 60.00%.

[0265] In the present embodiment, Fn1 in a specific surface of the austenitic stainless steel foil can be obtained by the following method. Specifically, a test piece is made from the bent member of the present embodiment. At this time, in the test piece, the bending direction of the bent member is predetermined. The size of the test piece is not particularly limited, and the thickness of the test piece is set to the same thickness as the bent member. An X-ray diffraction device (XRD device) is used to perform 0-dimensional measurement (XRD measurement) on the observation surface (surface of the bent member) of the test piece. Specifically, the X-ray source is set to a Mo tube ball, the tube voltage is set to 45kV, and the tube current is set to 200mA. In the XRD measurement, the X-ray is incident along the surface of the test piece including the direction perpendicular to the bending direction of the bent member and the thickness direction of the steel foil.

[0266] The incident direction of X-rays will be described in detail using the drawings. Figure 3A This is a schematic diagram for explaining the incident direction of X-rays when the test piece 10 is viewed from the side in the XRD measurement of the present embodiment. Figure 3B This is a schematic diagram for explaining the incident direction of X-rays when the test piece 10 is viewed from above in the XRD measurement of this embodiment. Figure 3A and Figure 3B , the incident direction of the X-ray is set to be perpendicular to the bending direction of the bending member. Figure 3A and Figure 3B Furthermore, in this embodiment, X-rays are incident at a certain angle of incidence on the surface of the test piece 10. In this case, appropriate conditions can be set for the angle of incidence on the surface of the test piece 10 when measuring using an XRD device.

[0267] Furthermore, a MA slit (0.5 mm) and a CBO mirror were used on the incident side to collimate the X-ray beam. Specifically, the incident side long-side limiting slit was set to 0.5 mm, and the receiving Soller slit was set to 5°. The step size was set to 5°, and the scanning speed was set to 200° / min.

[0268] The data measured by the above method for the {111} plane, {200} plane, and {220} plane are analyzed, and the full pole figures and inverse pole figures are analyzed. The software used for analysis is not particularly limited, and for example, the Texture plug-in of SmartLab Studio II included with the Rigaku X-ray diffraction device SmartLab can be used. In this case, background correction, absorption correction, and defocus correction using Ni powder as a standard sample are implemented. Based on the obtained inverse pole figure, the <111> position, <001> position, <112> Direction and <101> The cumulative value of the orientation is defined as the volume fraction of the grains in each orientation. Note that, in this embodiment, the volume fraction of the grains in each orientation is obtained by rounding off the third decimal place.

[0269] [Fatigue strength]

[0270] In the bent member of this embodiment, the austenitic stainless steel foil serving as the base material of the bent member is formed along a plane perpendicular to the direction in which the bent member is bent. <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 The above formula (1) is satisfied. As a result, the bent member of this embodiment has excellent fatigue strength. Here, in this embodiment, excellent fatigue strength is defined as follows.

[0271] A repeated bending test was performed on the bending member of the present embodiment. Specifically, a test piece was made from the bending member of the present embodiment. The size of the test piece was 50 mm × 40 mm, and the thickness of the test piece was set to be the same as the thickness of the bending member. At this time, the test piece was made in such a way that the long side direction of the test piece was parallel to the bending direction of the bending member. The produced test piece was set in a universal repeated bending tester, and bending stress was repeatedly applied until the test piece broke. The direction of applying the bending stress was set to be parallel to the direction in which the bending member was bent. At this time, the bending cycle was set to 1.25 Hz, the bending radius was set to 1.8 mm, and the bending angle was set to 0 to 130°. The number of repeated bendings until fracture is defined as the fatigue number. In the case where the fatigue number based on the above definition is 1.2×10 4 If the number of times or more is greater, it is determined that the fatigue strength is excellent.

[0272] (Manufacturing Method)

[0273] An example of a method for manufacturing a bent member according to the present embodiment having the above-described structure will be described below. It should be noted that the method for manufacturing a bent member according to the present embodiment is not limited to the method described below.

[0274] An example of a method for producing a bent member according to the present embodiment includes a step of producing an austenitic stainless steel foil and a step of producing a bent member from the austenitic stainless steel foil.

[0275] [Austenitic Stainless Steel Foil Manufacturing Process]

[0276] In this embodiment, the process for producing austenitic stainless steel foil may include an intermediate steel material preparation step, an intermediate cold rolling step, a bright annealing step, a final cold rolling step, and a tension annealing step. Furthermore, the intermediate cold rolling step and the bright annealing step may be repeated multiple times. Each step is described below.

[0277] [Intermediate steel material preparation process]

[0278] In the intermediate steel material preparation step, an intermediate steel material having the aforementioned chemical composition is prepared. The intermediate steel material is an intermediate product used to produce the austenitic stainless steel foil of this embodiment and refers to a steel plate having a thickness ranging from several hundred μm to several mm. For example, the intermediate steel material is a cold-rolled coil obtained by cold-rolling a hot-rolled coil. The intermediate steel material can be manufactured or purchased from a third party. The process for preparing the intermediate steel material is not particularly limited.

[0279] When producing intermediate steel, for example, the following method is used. Molten steel having the above-described chemical composition is produced. The molten steel is used to produce a cast billet (slab, bloom, or billet) by continuous casting. Alternatively, the molten steel can be used to produce an ingot (ingot) by ingot casting. If necessary, the slab, bloom, or ingot can be subjected to bloom rolling to produce a billet.

[0280] The produced ingot or slab (slab, bloom, billet, or ingot) is hot-worked to produce steel plates with a thickness of several hundred μm to several mm. The hot working method is not particularly limited, and known methods can be used. An example of hot working is hot rolling. When producing intermediate steel by hot rolling, for example, the following method can be used.

[0281] After heating the produced slab or ingot, rough rolling and finish rolling are performed. The hot rolling conditions are not particularly limited; known conditions may be appropriately selected. The intermediate steel material after hot rolling can be repeatedly cold rolled and annealed as needed. The intermediate steel material after hot rolling can also be further subjected to skin pass rolling as needed. The intermediate steel material after hot rolling can also be further annealed as needed. Through the above steps, the intermediate steel material of this embodiment is prepared.

[0282] [Intermediate cold rolling process]

[0283] In the intermediate cold rolling step, the intermediate steel material prepared in the intermediate steel material preparation step is cold rolled. In this embodiment, the cold rolling in the intermediate cold rolling step can be performed using known equipment. For example, a tandem rolling mill equipped with multiple cold rolling stands can be used. The cold rolling ratio in the intermediate cold rolling step is not particularly limited. For example, the cold rolling ratio in the intermediate cold rolling step is 30 to 85%.

[0284] [Bright annealing process]

[0285] In the bright annealing process, the intermediate steel material, cold-rolled in the intermediate cold rolling process, is bright annealed. Bright annealing is performed in an extremely low-oxygen atmosphere. Because of this extremely low-oxygen atmosphere, the surface of the intermediate steel material undergoing bright annealing is virtually free of oxidation, maintaining its surface gloss.

[0286] The preferred annealing temperature in the bright annealing step is 900-1200°C. If the annealing temperature is too low, the constituent elements are unevenly distributed and recrystallization does not occur, resulting in an inhomogeneous structure. On the other hand, if the annealing temperature is too high, the grains may coarsen, and the fatigue strength of the produced austenitic stainless steel foil may be reduced. Therefore, in the bright annealing step of this embodiment, the annealing temperature is preferably set to 900-1200°C. The lower limit of the annealing temperature in the bright annealing step is more preferably 920°C. The upper limit of the annealing temperature in the bright annealing step is more preferably 1180°C.

[0287] The preferred annealing time in the bright annealing step is 5 to 60 seconds. If the annealing time is too short, a recrystallized structure cannot be obtained, making final cold rolling difficult. On the other hand, if the annealing time is too long, the grains coarsen, reducing fatigue properties. Therefore, in the bright annealing step of this embodiment, the annealing time is preferably set to 5 to 60 seconds.

[0288] In the bright annealing process, a mixed gas atmosphere of H2 gas and N2 gas is preferably used. In this case, the preferred N2 fraction in the atmosphere is 35-65% by volume. If the N2 fraction in the atmosphere is too low, manufacturing costs will increase significantly. On the other hand, if the N2 fraction in the atmosphere is too high, the furnace body will be severely nitrided, which may promote furnace damage and reduce productivity. Therefore, in the bright annealing process of this embodiment, the atmosphere is preferably a mixed gas of 35-65% by volume of N2 gas and the balance of H2 gas.

[0289] It should be noted that, as described above, intermediate cold rolling and bright annealing can be repeated multiple times. For example, when intermediate cold rolling and bright annealing are repeated twice, the second intermediate cold rolling and bright annealing are performed after the first intermediate cold rolling and bright annealing. Even in this case, intermediate cold rolling and bright annealing are preferably performed under the above-mentioned conditions.

[0290] [Final cold rolling process]

[0291] In the final cold rolling process, the intermediate steel material bright annealed in the bright annealing process is subjected to final cold rolling. The cold rolling in the final cold rolling process can be performed using known equipment, similar to the cold rolling in the intermediate cold rolling process. For example, a rolling mill equipped with multiple cold rolling stands can be used.

[0292] In the final cold rolling process of this embodiment, the preferred cold rolling ratio CR is 45% or greater. Here, the cold rolling ratio CR (%) refers to the reduction in thickness (%) of the intermediate steel material from before the final cold rolling process begins to after the final cold rolling process ends. Specifically, the cold rolling ratio CR in the final cold rolling process is defined by the following formula (A).

[0293] CR (%) = 100 - (thickness of intermediate steel material after final cold rolling process) / (thickness of intermediate steel material before final cold rolling process) × 100 (A)

[0294] If the cold rolling ratio CR in the final cold rolling process is too low, <112> The number of azimuthally oriented grains becomes too small. <001> The number of orientationally oriented grains becomes excessive. In this case, Fn1 becomes too small in the manufactured bent member, reducing the fatigue strength of the bent member. Therefore, in the final cold rolling process of this embodiment, the cold rolling ratio CR is preferably set to 45% or higher. The lower limit of the cold rolling ratio CR in the final cold rolling process is more preferably 47%, and even more preferably 50%. The upper limit of the cold rolling ratio CR in the final cold rolling process is not particularly limited, but is, for example, 85%.

[0295] In the final cold rolling process of this embodiment, it is preferable to further perform rolling with the rolling direction inclined by 5 to 65 degrees with respect to the rolling direction in the intermediate cold rolling process. If the inclination of the rolling direction is too small, a specific surface of the steel foil after production may be deformed along the direction of the rolling direction. <112> Azimuthally oriented grains become excessive, along <111> The number of azimuthally oriented grains becomes too small. In this case, Fn1 becomes too small in the manufactured bent member, and the fatigue strength of the bent member decreases. On the other hand, if the inclination in the rolling direction is too large, sometimes a specific surface of the manufactured steel foil may be <001> The number of azimuthally oriented grains becomes too small. In this case, Fn1 becomes too small in the manufactured bent member, and the fatigue strength of the bent member decreases.

[0296] Therefore, in the final cold rolling process of this embodiment, the inclination of the rolling direction is preferably set to 5 to 65° based on the rolling direction in the intermediate cold rolling process. The more preferred lower limit of the inclination of the rolling direction in the final cold rolling process is 10°, more preferably 15°, and even more preferably 20°. The more preferred upper limit of the inclination of the rolling direction in the final cold rolling process is 60°, more preferably 55°, more preferably 50°, more preferably 45°, and even more preferably 40°.

[0297] [Tension annealing process]

[0298] In the tension annealing step, the intermediate steel material, which has been cold-rolled in the final cold rolling step, is subjected to tension annealing. Tension annealing is performed while applying tension. The tension in the intermediate steel material maintains its flatness.

[0299] The preferred annealing temperature in the tension annealing process is 350 to 850°C. If the annealing temperature is too low, sufficient strain aging may not be achieved. On the other hand, if the annealing temperature is too high, the structure of the intermediate steel may recrystallize and the steel may be deformed. <001> The number of orientationally oriented grains becomes excessive. In this case, Fn1 becomes too small in the manufactured curved member, reducing the fatigue strength of the curved member. Therefore, in the bright annealing step of this embodiment, the annealing temperature is preferably set to 350-850°C. The lower limit of the annealing temperature in the tension annealing step is more preferably 360°C. The upper limit of the annealing temperature in the tension annealing step is more preferably 800°C.

[0300] In the tension annealing process, the annealing time is not particularly limited. The annealing time is, for example, 2 to 60 seconds. In addition, in the tension annealing process, the tension applied to the intermediate steel material is not particularly limited. The tension is, for example, 1.0 to 10.0 N / mm. 2 .

[0301] The austenitic stainless steel foil of this embodiment can be manufactured through the above steps. It should be noted that the above manufacturing method is only one example of a method for manufacturing the austenitic stainless steel foil of this embodiment. That is, the manufacturing method of the austenitic stainless steel foil of this embodiment is not limited to the above manufacturing method, and other manufacturing methods may also be used.

[0302] [Bent member manufacturing process]

[0303] The bent member manufacturing process of this embodiment is not particularly limited. For example, if the bent member is composed solely of austenitic stainless steel foil, the bent member manufacturing process may not be performed. If the bent member is composed solely of austenitic stainless steel foil, the bent member manufacturing process may include a step of cutting the manufactured austenitic stainless steel foil into a shape suitable for use as a bent member, or a step of performing an etching process.

[0304] The above steps allow the production of the bent member of this embodiment. It should be noted that the above-described production method is merely an example of a method for producing the bent member of this embodiment. That is, the production method of the bent member of this embodiment is not limited to the above-described production method; other production methods are also possible. The following examples further illustrate the bent member and austenitic stainless steel foil of this embodiment. It should be noted that the following examples are merely examples for verifying the effects of the bent member and austenitic stainless steel foil of this embodiment and do not limit the present invention.

[0305] Example

[0306] Slabs were produced by continuous casting from molten steel having the chemical compositions shown in Table 1-1 and Table 1-2.

[0307] [Table 1-1]

[0308] Table 1-1

[0309]

[0310] [Table 1-2]

[0311] Table 1-2

[0312]

[0313] The steel slabs listed in Table 1-1 were hot rolled and annealed to produce 4 mm thick hot rolled coils. The produced hot rolled coils were repeatedly cold rolled and annealed to produce 300 μm thick foil-shaped intermediate steel materials (cold rolled coils).

[0314] Intermediate steel materials of each steel were subjected to intermediate cold rolling under the conditions listed in Table 2. Specifically, intermediate cold rolling and bright annealing were repeated the number of times listed in Table 2 for the intermediate steel materials of each test number. More specifically, when "1 time" is listed in the "Number of Intermediate Cold Rolling (times)" column of Table 2, it means that intermediate cold rolling and bright annealing were each performed once. When "2 times" is listed in the "Number of Intermediate Cold Rolling (times)" column of Table 2, it means that the combination of intermediate cold rolling and bright annealing was repeated twice.

[0315] [Table 2]

[0316] Table 2

[0317]

[0318] The cold rolling ratio of the intermediate cold rolling performed on the intermediate steel materials of each test number was within the range of 30-85%. It should be noted that in the test numbers in which the intermediate cold rolling was performed twice, the cold rolling ratio of the intermediate cold rolling was the same both times. Bright annealing was performed on the intermediate steel materials of each test number that had undergone intermediate cold rolling. The annealing temperature of the bright annealing performed on the intermediate steel materials of each test number was within the range of 900-1200°C, and the annealing time was within the range of 5-60 seconds. In addition, a mixed gas of 35-65% by volume of N2 gas and the balance of H2 gas was used as the atmosphere gas for bright annealing.

[0319] Final cold rolling was performed on the intermediate steel materials of each test number that had been bright annealed. The cold rolling rate CR (%) of the final cold rolling performed on the intermediate steel materials of each test number and the inclination (°) of the rolling direction of the final cold rolling are shown in the "Rolling angle (°)" column of Table 2. It should be noted that the inclination of the rolling direction of the final cold rolling is defined as the angle with the rolling direction of the intermediate cold rolling. Tension annealing was performed on the intermediate steel materials of each test number that had been final cold rolled. The annealing temperature (°C) of the tension annealing performed on the intermediate steel materials of each test number is shown in the "Annealing temperature (°C)" column of the "TA" column of Table 2. In addition, the annealing time of the tension annealing performed on the intermediate steel materials of each test number satisfies the range of 2 to 60 seconds, and the tension satisfies 1.0 to 10.0 N / mm. 2 In addition, the rolling direction of the intermediate cold rolling performed on the intermediate steel material of each test number was defined as the bending direction, and the obtained austenitic stainless steel foil was used as a bent member.

[0320] [Evaluation test]

[0321] The bent member of each test number was subjected to a crystal orientation measurement test and a repeated bending test.

[0322] [Crystal orientation measurement test]

[0323] For the curved components of each test number, the volume fraction of grains oriented in each direction was calculated by the above method. Specifically, for the test pieces made from the curved components of each test number, a 0-dimensional measurement was performed under the above conditions using the X-ray diffraction device SmartLab manufactured by Rigaku. The data measured for the obtained {111} plane, {200} plane and {220} plane were analyzed, and the full pole figure and inverse pole figure were analyzed. The Texture plug-in of SmartLab Studio II included with the X-ray diffraction device SmartLab manufactured by Rigaku was used for the analysis. Based on the inverse pole figure obtained on the surface perpendicular to the bending direction (specific surface), the volume fraction of grains oriented in each direction was calculated. <111> position, <001> position, <112> Direction and <101> The volume fraction of azimuthally oriented grains. <111> position, <001> position, <112> Direction and <101> The volume fraction of azimuthally oriented grains is shown in Table 3 as Vf 111 (%) column, Vf 001 (%) column, Vf 112 (%) column, Vf 101 (%) column. In addition, the Vf 111 (%) and Vf 001 (%) The obtained Fn1(=Vf 111 / Vf 001 ) are shown in Table 3. It should be noted that along <111> position, <001> position, <112> Direction and <101> The sum of the volume fractions of the azimuthally oriented grains is 100.00%.

[0324] [Table 3]

[0325] Table 3

[0326]

[0327] [Repeated bending test]

[0328] The bending member of each test number is subjected to repeated bending tests by the above method. Specifically, a test piece with a thickness of 50 mm in the bending direction, 40 mm in the width direction, and the same thickness as the bending member is made from the bending member of each test number. It should be noted that the long side direction of the test piece is set to a direction parallel to the bending direction of the bending member. For the test piece, bending stress is repeatedly applied in a direction perpendicular to the direction in which the bending member is bent. The bending cycle is set to 1.25 Hz, the bending radius is set to 1.8 mm, and the bending angle is set to 0 to 130°. The number of times the bending stress is applied until the test piece breaks is set to "fatigue number". The fatigue number (times) obtained is shown in Table 3.

[0329] [Evaluation results]

[0330] Referring to Tables 1-1, 1-2, 2, and 3, the chemical composition of the austenitic stainless steel foils of the bent members of Test Nos. 1 to 15 was appropriate, and the manufacturing methods also met the conditions of the preferred manufacturing method described above. As a result, the Fn1 of these bent members was in the range of 0.6 to 12.0. As a result, the fatigue number of these bent members was 1.2×10 4 times or more, with excellent fatigue strength.

[0331] On the other hand, the cold rolling ratio CR in the final cold rolling of the bent members of test numbers 16 and 17 was too low. As a result, the Fn1 of these bent members was less than 0.6. As a result, the fatigue number of these bent members was less than 1.2×10 4 Second, it does not have excellent fatigue strength.

[0332] The rolling angle in the final cold rolling of the bent members of test numbers 18 and 19 was too small. As a result, the Fn1 of these bent members was less than 0.6. As a result, the fatigue number of these bent members was less than 1.2×10 4 Second, it does not have excellent fatigue strength.

[0333] The rolling angle in the final cold rolling of the bent members of test numbers 20 and 21 was too large. As a result, the Fn1 of these bent members exceeded 12.0. As a result, the fatigue number of these bent members was less than 1.2×10 4 Second, it does not have excellent fatigue strength.

[0334] The annealing temperature of the tension annealing of the bent members of test numbers 22 and 23 was too high. As a result, the Fn1 of these bent members was less than 0.6. As a result, the fatigue number of these bent members was less than 1.2×10 4 Second, it does not have excellent fatigue strength.

[0335] The above describes the embodiments of the present disclosure. However, the above embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above embodiments, and the above embodiments can be implemented by appropriately modifying them within the scope of the present disclosure.

Claims

1. A curved member, wherein: The base material of the bent member is composed of austenitic stainless steel foil. The austenitic stainless steel foil contains C in a mass % ratio of 0.150% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.0300% or less, Cr：16.00～20.00％、 Ni: 6.00~10.50%, N: 0.100% or less, Mo: 0-2.50%, Nb: 0-0.12%, V：0～1.00％、 Ta: 0~0.50%, Hf: 0~0.10% Co: 0-0.50%, B：0～0.0100％、 Ca: 0~0.0200%, Mg: 0~0.0200%, Rare earth elements: 0~0.0100%, Al：0～0.010％、 Ti: 0~0.500%, Zr：0～0.100％、 Cu: 0-3.00%, and The balance is Fe and impurities. In the surface of the base material perpendicular to the direction in which the bending member is bent, <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 Satisfying the following formula (1), 0.6≤Vf 111 / Vf 001 ≤12.0 (1)。 2. The curved member according to claim 1, wherein The austenitic stainless steel foil contains Mo: 0.01~2.50%, Nb: 0.01-0.12%, V：0.01～1.00％、 Ta: 0.01~0.50%, Hf: 0.01~0.10%, Co: 0.01-0.50%, B：0.0001～0.0100％、 Ca: 0.0001~0.0200%, Mg: 0.0001~0.0200%, Rare earth elements: 0.0001~0.0100%, Al：0.001～0.010％、 Ti: 0.001~0.500%, Zr: 0.001~0.100%, and Cu: One or more elements selected from the group consisting of 0.01 to 3.00%.

3. The curved member according to claim 1, wherein The curved member comprises: the first end, the second end, and a curved portion disposed between the first end portion and the second end portion, The bending member is bent in a direction parallel to a direction in which the first end portion, the bent portion, and the second end portion are arranged.

4. An austenitic stainless steel foil for use in the bent member according to any one of claims 1 to 3. The austenitic stainless steel foil contains C in a mass % ratio of 0.150% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.0300% or less, Cr：16.00～20.00％、 Ni: 6.00~10.50%, N: 0.100% or less, Mo: 0-2.50%, Nb: 0-0.12%, V：0～1.00％、 Ta: 0~0.50%, Hf: 0~0.10% Co: 0-0.50%, B：0～0.0100％、 Ca: 0~0.0200%, Mg: 0~0.0200%, Rare earth elements: 0~0.0100%, Al：0～0.010％、 Ti: 0~0.500%, Zr：0～0.100％、 Cu: 0-3.00%, and The balance is Fe and impurities. In the austenitic stainless steel foil, the surface perpendicular to the direction inclined 5 to 65 degrees from the Brass direction along the rolling surface is <111> Volume fraction of azimuthally oriented grains Vf 111 He Yan <001> Volume fraction of azimuthally oriented grains Vf 001 Satisfying the following formula (2), 0.6≤Vf 111 / Vf 001 ≤12.0 (2)。 5. The austenitic stainless steel foil according to claim 4, comprising Mo: 0.01 to 2.50%, Nb: 0.01-0.12%, V：0.01～1.00％、 Ta: 0.01~0.50%, Hf: 0.01~0.10%, Co: 0.01-0.50%, B：0.0001～0.0100％、 Ca: 0.0001~0.0200%, Mg: 0.0001~0.0200%, Rare earth elements: 0.0001~0.0100%, Al：0.001～0.010％、 Ti: 0.001~0.500%, Zr: 0.001~0.100%, and Cu: One or more elements selected from the group consisting of 0.01 to 3.00%.

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