Ferritic stainless steel sheet and method of manufacturing the same

Abstract

To provide a ferritic stainless steel plate having an excellent average r value, small in-plane anisotropy, and excellent processability.SOLUTION: A ferritic stainless steel plate has a predetermined chemical composition. In a face parallel with a rolling face at plate-thickness 1 / 2 position, an intensity ratio A of a crystal orientation calculated by [I{554}<225> / I{111}<110>] is 6.0 or more, while an intensity ratio B of a crystal orientation calculated by [I{554}<225> / I{322}<236>] is 2.0-5.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a ferritic stainless steel sheet and a method for producing the same. [Background technology]

[0002] Ferritic stainless steel has excellent corrosion resistance. For this reason, it is used in applications where appearance is important, such as kitchens, and in applications exposed to corrosive environments, such as automobile exhaust system parts. For such applications, the ferritic stainless steel material must also have good workability.

[0003] The average r-value is generally used as an index of workability. Various attempts have been made to improve the average r-value. As one example, Non-Patent Document 1 states that adding elements such as Ti and Nb and immobilizing C and N is effective in improving the average r-value. In addition, it also states that a technique of growing crystal grains by performing high-temperature annealing in the final annealing process and a technique of increasing the cold rolling reduction are also effective in improving the average r-value.

[0004] On the other hand, it has been pointed out that improving the average r-value using the above method increases the in-plane anisotropy of the steel sheet, resulting in an increase in the r-value in the 45° direction. Such a change in in-plane anisotropy is undesirable because it increases the likelihood of waviness, or "ears," occurring around the edge of the drawing sheet during deep drawing, reducing yield and increasing the likelihood of forming defects.

[0005] For this reason, for example, Patent Documents 1 to 5 disclose ferritic stainless steels in which the average r-value is improved and an increase in the in-plane anisotropy is suppressed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-030078 [Patent Document 2] Japanese Patent Publication No. 2019-002053 [Patent Document 3] Japanese Patent Application Publication No. 2019-173149 [Patent Document 4] International Publication No. 2019 / 189872 [Patent Document 5] International Publication No. 2021 / 065738 [Non-patent literature]

[0007] [Non-Patent Document 1] Sawatani et al., and three others, "Workability of Ti-added low C, N-17% Cr stainless steel sheet", Iron and Steel, 63 (1977), pp. 843-854 [Non-patent document 2] RKRay et al. and 2 others, “Cold rolling and annealing texture in low carbon and extra low carbon steels”, Int. Mat. Rev., 8 (1994) p129-172 [Non-patent document 3] Hirofumi Inoue, "Three-dimensional orientation analysis of texture", Light Metals, Vol. 42, No. 6 (1992), pp. 358-367. Summary of the Invention [Problem to be solved by the invention]

[0008] However, the ferritic stainless steels disclosed in Patent Documents 1 to 5 have room for further improvement in terms of increasing the average r-value and reducing the in-plane anisotropy.

[0009] The present invention has an object to solve the above problems and to provide a ferritic stainless steel sheet having an excellent average r-value, small in-plane anisotropy, and good workability. [Means for solving the problem]

[0010] The present invention has been made to solve the above-mentioned problems, and is summarized as the following ferritic stainless steel sheet and method for producing the same.

[0011] (1) Chemical composition, in mass%, C: 0.030% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.005~0.100%, S: 0.0100% or less, Cr: 11.0~30.0%, Al: 1.00% or less, N: 0.030% or less, Ti: 0.05 to 0.50% Nb: 0 to 0.70% Sn: 0 to 0.50% Ni: 0 to 1.00% Cu: 0-1.00% Mo: 0-2.00%, W: 0~1.00%, Co: 0 to 0.50% V: 0~0.50%, Zr: 0 to 0.50% Sb: 0 to 0.50% B: 0~0.0025%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Y: 0~0.20%, Hf: 0~0.20%, REM: 0~0.10%, The balance is Fe and impurities. The following formula (i) is satisfied: A ferritic stainless steel sheet in which, in a plane parallel to the rolling surface at the 1 / 2 position in the sheet thickness, the intensity ratio A of the crystal orientation calculated by the following formula (ii) is 6.0 or more, and the intensity ratio B of the crystal orientation calculated by the following formula (iii) is 2.0 to 5.0. 0.10≦Ti+Nb≦0.70 (i) A=I{554} <225> / I{111} <110> (ii) B=I{554} <225> / I{322} <236> (iii) However, each element symbol in the above formula (i) represents the content (mass%) of each element contained in the steel, and if no element is contained, it is set to zero, and each symbol in the above formulas (ii) and (iii) is defined as follows. I{554} <225> :{554} <225> X-ray random intensity ratio of azimuth I{111} <110> :{111} <110> X-ray random intensity ratio of azimuth I{322} <236> :{322} <236> X-ray random intensity ratio of azimuth

[0012] (2) The chemical composition is in mass%: Sn: 0.005 to 0.50% Ni: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Mo: 0.05 to 2.00%, W: 0.05 to 1.00%, Co: 0.05 to 0.50%, V: 0.05 to 0.50%, Zr: 0.05 to 0.50%, and Sb: 0.005 to 0.50% The ferritic stainless steel sheet according to (1) above, containing one or more selected from the following:

[0013] (3) The chemical composition is in mass%: B: 0.0001~0.0025%, Ca: 0.0002 to 0.0050%, and Mg: 0.0002 to 0.0050%, The ferritic stainless steel sheet according to (1) or (2) above, containing one or more selected from the following:

[0014] (4) The chemical composition is in mass%: Y: 0.001 to 0.20%, Hf: 0.001 to 0.20%, and REM: 0.001~0.10%, The ferritic stainless steel sheet according to any one of (1) to (3) above, which contains one or more selected from the following:

[0015] (5) A ferritic stainless steel sheet according to any one of the above (1) to (4), which satisfies the following formula (iv): -0.20≦r0-r 45 ≦0.20 (iv) However, the symbols in the above formula (iv) are defined as follows: r0: r value in the rolling direction r 45 : r value at 45° from the rolling direction

[0016] (6) A method for producing a ferritic stainless steel sheet according to any one of (1) to (5) above, A step of finish-rolling a slab having the chemical composition described in any one of the above (1) to (4) at a hot rolling finishing temperature FT that satisfies the following formula (v): a step of cooling the steel sheet to 700°C or less within 10 seconds immediately after the finish rolling and coiling the steel sheet at a temperature of 600°C or less to obtain a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet at a cold rolling reduction rate CR in the range of 20 to 85% to obtain a cold-rolled steel sheet; and annealing the cold-rolled steel sheet, A method for producing a ferritic stainless steel sheet, in which the strain parameter R calculated by the following formula (vi) is set in the range of -0.2 to 0.2. 700≦FT(℃)≦950 (V) R=1.6-CR / 50+(FT-900) / 300―20Nb / 3 (vi) In the above formula, each symbol is defined as follows: CR: Cold rolling reduction rate (%) FT: Hot rolling finishing temperature (℃) Nb: Nb content of steel plate [Effects of the Invention]

[0017] According to the present invention, a ferritic stainless steel sheet can be obtained which has an excellent average r-value, small in-plane anisotropy, and good workability. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present inventors have investigated the r-value and in-plane anisotropy of ferritic stainless steel sheets and have obtained the following findings.

[0019] r0-r 45 By setting the range of -0.20 to 0.20 and appropriately controlling the texture, a ferritic stainless steel sheet with good workability can be obtained. In order to obtain such a ferritic stainless steel sheet, it is preferable to control various manufacturing conditions, and for example, it is preferable to cool the sheet immediately after finish rolling in the hot rolling to 700°C or less within 10 seconds.

[0020] An embodiment of the present invention has been made based on the above findings. Each requirement of this embodiment will be described in detail below.

[0021] 1.Chemical composition The reasons for limiting the content of each element are as follows: In the following description, "%" in the content means "% by mass."

[0022] C: 0.030% or less Since C is an element that reduces the r-value, it is preferable to reduce its content. Therefore, the C content is set to 0.030% or less. From the viewpoint of further improving workability, the C content is preferably set to 0.018% or less. On the other hand, excessive reduction of C increases refining costs. Therefore, the C content is preferably set to 0.001% or more, and more preferably set to 0.002% or more.

[0023] Si: 1.00% or less Although Si is an element that improves oxidation resistance, excessive Si content reduces total elongation and workability. Therefore, the Si content is set to 1.00% or less. To further improve workability, the Si content is preferably set to 0.30% or less. On the other hand, excessive reduction of Si increases raw material costs. Therefore, the Si content is preferably set to 0.01% or more, and more preferably set to 0.05% or more.

[0024] Mn: 2.00% or less Like Si, excessive Mn content reduces total elongation and workability. Therefore, the Mn content is set to 2.00% or less. To further improve workability, the Mn content is preferably set to 0.30% or less. On the other hand, excessive reduction of Mn increases raw material costs. Therefore, the Mn content is preferably set to 0.01% or more, and more preferably set to 0.05% or more.

[0025] P: 0.005 to 0.100% P is an element that reduces workability (r-value and total elongation), so it is preferable to reduce it. Therefore, the P content is set to 0.100% or less. To further improve workability, the P content is preferably set to 0.070% or less, more preferably 0.050% or less. However, the precipitation of a small amount of phosphorus-containing precipitates during annealing of the cold-rolled sheet enables texture control and also contributes to improving the r-value. Furthermore, excessive reduction of P increases raw material costs. Therefore, the P content is set to 0.005% or more. The P content is preferably set to 0.010% or more, more preferably 0.020% or more.

[0026] S: 0.0100% or less S is an impurity element contained in steel, which deteriorates corrosion resistance and promotes cracking during manufacturing, so it is preferable to reduce its content as much as possible. Therefore, the S content is set to 0.0100% or less. From the viewpoints of corrosion resistance and manufacturability, the S content is preferably set to 0.0030% or less, and more preferably 0.0020% or less. On the other hand, excessive reduction of S increases refining costs. Therefore, the S content is preferably set to 0.0003% or more, and more preferably 0.0004% or more.

[0027] Cr: 11.0 to 30.0% Cr is an element that improves corrosion resistance, a basic property of stainless steel. Therefore, the Cr content is set to 11.0% or more. To further improve corrosion resistance, the Cr content is preferably set to 14.0% or more, and more preferably set to 16.0% or more. However, excessive Cr content promotes the formation of intermetallic compounds such as the σ phase, which tends to cause cracks during manufacturing and a decrease in workability due to a decrease in total elongation. Therefore, the Cr content is set to 30.0% or less. From the viewpoint of stable manufacturing (yield, rolling defects, etc.), the Cr content is preferably set to 25.0% or less, and more preferably set to 20.0% or less.

[0028] Al: 1.00% or less Al has the effect of improving corrosion resistance and oxidation resistance. However, excessive Al content reduces total elongation and workability. Furthermore, alloy costs increase and manufacturability decreases. For this reason, the Al content is set to 1.00% or less. From the viewpoint of manufacturability, the Al content is preferably set to 0.50% or less. On the other hand, to obtain the above effects, the Al content is preferably set to 0.005% or more, and more preferably set to 0.01% or more.

[0029] N: 0.030% or less Like C, N is an element that reduces workability (r-value), and so it is preferable to reduce its content. For this reason, the N content is set to 0.030% or less. To further improve workability, the N content is preferably set to 0.015% or less. On the other hand, excessive reduction of N increases refining costs. For this reason, the N content is preferably set to 0.002% or more, and more preferably set to 0.005% or more.

[0030] Ti: 0.05 to 0.50% Ti fixes C and N as precipitates, improving the r-value and total elongation, and thereby improving workability. Therefore, the Ti content is set to 0.05% or more. To further improve workability, the Ti content is preferably set to 0.07% or more, and more preferably set to 0.1% or more. However, excessive Ti content reduces the r-value and increases alloy costs. Therefore, the Ti content is set to 0.50% or less. From the viewpoints of alloy cost and manufacturability, the Ti content is preferably set to 0.40% or less, and more preferably set to 0.30% or less.

[0031] Nb: 0 to 0.70% Like Ti, Nb fixes C and N as precipitates, improving the r-value and total elongation, thereby improving workability. Furthermore, Nb contributes to texture control through the accumulation of strain by suppressing strain recovery and recrystallization during the hot rolling process, thereby suppressing the increase in in-plane anisotropy. Therefore, Nb may be added as needed. However, excessive Nb content reduces the r-value or increases in-plane anisotropy. It also increases alloying costs. Therefore, the Nb content is set to 0.70% or less. From the standpoints of workability and alloying costs, the Nb content is preferably set to 0.50% or less, and more preferably 0.40% or less.

[0032] Here, the total content of Ti and Nb, which have the same effect, satisfies the following formula (i).

[0033] 0.10≦Ti+Nb≦0.70 (i) However, each element symbol in the above formula (i) represents the content (mass%) of each element contained in the steel, and if the element is not contained, it is set to zero.

[0034] If the value in equation (i), which is the total content of Ti and Nb, is less than 0.10, it becomes difficult to obtain the effects of improving the r-value and total elongation described above. Therefore, the value in equation (i) is set to 0.10 or more. To further improve workability, the value in equation (i) is preferably set to 0.13 or more, and more preferably set to 0.15 or more.

[0035] On the other hand, if the value in the formula (i) exceeds 0.70, the in-plane anisotropy becomes large. Also, the alloy cost increases. Therefore, the value in the formula (i) is set to 0.70 or less. From the viewpoint of workability and alloy cost, the value in the formula (i) is preferably set to 0.50 or less, and more preferably set to 0.40 or less.

[0036] In addition to the above elements, one or more elements selected from Sn, Ni, Cu, Mo, W, Co, V, Zr, and Sb (group A elements) may be contained within the ranges shown below. The reasons for limiting the amount of each element will be explained below.

[0037] Sn: 0 to 0.50% Ni: 0 to 1.00% Cu: 0 to 1.00% Mo: 0 to 2.00% W: 0 to 1.00% Co: 0 to 0.50% V: 0 to 0.50% Zr: 0 to 0.50% Sb: 0 to 0.50% Sn, Ni, Cu, Mo, W, Co, V, Zr, and Sb have the effect of improving corrosion resistance or oxidation resistance. Therefore, they may be added as needed. However, if these elements are added in excess, workability decreases. Furthermore, alloy costs increase and manufacturability decreases.

[0038] Therefore, the Sn content is set to 0.50% or less, and preferably 0.30% or less. The Ni content is set to 1.00% or less, and preferably 0.50% or less. The Cu content is set to 1.00% or less, and preferably 0.50% or less. The Mo content is set to 2.00% or less, and preferably 1.00% or less. The W content is set to 1.00% or less, and preferably 0.50% or less. The Co content is set to 0.50% or less, and preferably 0.30% or less. The V content is set to 0.50% or less, and preferably 0.30% or less. The Zr content is set to 0.50% or less, and preferably 0.30% or less. The Sb content is set to 0.50% or less, and preferably 0.30% or less.

[0039] On the other hand, in order to obtain the above effects, the Sn content is preferably 0.005% or more. The Ni content is preferably 0.05% or more. The Cu content is preferably 0.05% or more. The Mo content is preferably 0.05% or more. The W content is preferably 0.05% or more. The Co content is preferably 0.05% or more. The V content is preferably 0.05% or more. The Zr content is preferably 0.05% or more. The Sb content is preferably 0.005% or more.

[0040] In addition to the above elements, one or more elements selected from B, Ca, and Mg (B group elements) may be contained within the ranges shown below. The reasons for limiting the amount of each element will be explained below.

[0041] B: 0 to 0.0025% Ca: 0 to 0.0050% Mg: 0 to 0.0050% B, Ca, and Mg have the effect of improving hot workability and secondary workability. Therefore, they may be added as needed. However, excessive addition of these elements reduces manufacturability. Therefore, the B content is set to 0.0025% or less, and preferably 0.0012% or less. The Ca content is set to 0.0050% or less, and preferably 0.0010% or less. The Mg content is set to 0.0050% or less, and preferably 0.0010% or less.

[0042] On the other hand, to obtain the above effects, the B content is preferably 0.0001% or more, more preferably 0.0003% or more, the Ca content is preferably 0.0002% or more, and the Mg content is preferably 0.0002% or more.

[0043] In addition to the above elements, one or more elements selected from Y, Hf, and REM (C group elements) may be contained within the ranges shown below. The reasons for limiting the amount of each element will be explained below.

[0044] Y: 0 to 0.20% Hf: 0 to 0.20% REM: 0 to 0.10% Y, Hf, and REM have the effect of improving the hot workability and cleanliness of steel. They also have the effect of improving oxidation resistance. Therefore, they may be added as needed. However, because these elements are expensive, excessive addition increases the alloy cost. For this reason, the Y content is set to 0.20% or less, and preferably 0.10% or less. The Hf content is set to 0.20% or less, and preferably 0.10% or less. The REM content is set to 0.10% or less, and preferably 0.05% or less. On the other hand, to obtain the above effects, the Y content is preferably set to 0.001% or more. The Hf content is preferably set to 0.001% or more. The REM content is preferably set to 0.001% or more.

[0045] Here, REM refers to a total of 15 elements that fall under the lanthanoid group with atomic numbers 57 to 71. The REM content above refers to the total content of these elements. Industrially, REM is often added in the form of misch metal.

[0046] In the chemical composition of this embodiment, the balance is Fe and impurities. Here, "impurities" refers to components that are mixed in during the industrial production of ferritic stainless steel due to various factors in raw materials such as ores and scrap, or in the manufacturing process, and are acceptable within a range that does not adversely affect this embodiment. In addition to the above-mentioned impurity elements, other elements that may be mixed in as impurities include, for example, Bi, Pb, Se, H, and Ta. The contents of these elements are preferably within the ranges of Bi≦0.01%, Pb≦0.01%, Se≦0.01%, H≦0.01%, and Ta≦0.05%.

[0047] 2. Crystal orientation strength ratio In the ferritic stainless steel sheet of this embodiment, the random intensity ratio of the crystal orientation in a plane parallel to the rolled surface at the half-thickness position is set to the following range: Specifically, the intensity ratio A of the crystal orientation calculated by the following formula (ii) is set to 6.0 or more.

[0048] A=I{554} <225> / I{111} <110> (ii) However, the symbols in the above formula (ii) are defined as follows: I{554} <225> :{554} <225> X-ray random intensity ratio of azimuth I{111} <110> :{111} <110> X-ray random intensity ratio of azimuth

[0049] {554} <225> Orientation and <110> Both orientations increase the r-value, but as described in Non-Patent Document 2, these orientations are significantly different. <225> Compared with the direction, <110> When the random strength ratio of the orientation increases, the anisotropy of the entire steel sheet becomes {111} <110> As the orientation approaches, the anisotropy increases. <110> The direction is <225> It is necessary to control the intensity ratio A to be small compared to the orientation of r0-r1, and it is preferable to control the intensity ratio A to be large. In particular, when the intensity ratio A is less than 6.0, the in-plane anisotropy becomes large, and r0-r2 45 is smaller than −0.20. Therefore, the intensity ratio A is set to 6.0 or more, and preferably 8.0 or more.

[0050] In addition, the r-value in the direction 30° to the rolling direction becomes higher. <236> As the orientation develops, the r-value in the 30° direction decreases. <225> By developing the orientation and achieving an appropriate balance, the in-plane anisotropy can be reduced. Therefore, the crystal orientation intensity ratio B calculated by the following formula (iii) in a plane parallel to the rolling surface at the half-thickness position is set to 2.0 to 5.0. B=I{554} <225> / I{322} <236> (iii) However, the symbols in the above formula (iii) are defined as follows: I{554} <225> :{554} <225> X-ray random intensity ratio of azimuth I{322} <236> :{322} <236> X-ray random intensity ratio of azimuth

[0051] When the intensity ratio B is less than 2.0, {322} <236> The orientation is overdeveloped and the in-plane anisotropy becomes large. 45 Therefore, the intensity ratio B is set to 2.0 or more, and preferably 2.5 or more. On the other hand, when the intensity ratio B exceeds 5.0, the {554} <225> The orientation develops excessively, and the anisotropy of the entire steel sheet increases. 45is smaller than 0.20. Therefore, the intensity ratio B is set to 5.0 or less, and preferably 4.0 or less.

[0052] The intensity ratios A and B may be measured by the following procedure. First, X-ray diffraction is performed on a plane parallel to the rolled surface at a position halfway through the steel sheet thickness. Here, the measurement is performed at the position halfway through the steel sheet thickness, i.e., at a position halfway from the rolled surface when the sheet thickness is t, because this position often shows the average texture of the steel sheet and makes it easy to evaluate the workability.

[0053] Using data obtained by X-ray diffraction, three-dimensional orientation analysis is performed using the Bunge method described in Non-Patent Document 3. The random intensity ratio for each orientation can be read from a crystal orientation distribution diagram, and the intensity ratios A and B can be calculated. The X-ray random intensity ratio is a value obtained by measuring the X-ray diffraction intensity of a standard sample that does not have accumulation in a specific orientation and the test material under the same conditions using an X-ray diffraction method or the like, and dividing the obtained X-ray diffraction intensity of the test material by the X-ray diffraction intensity of the standard sample.

[0054] 3. In-plane anisotropy Conventionally, the index used to evaluate in-plane anisotropy is Δr = (r0-2 × r 45 +r 90 ) / 2 is frequently used. However, this index is more accurate than r0. 45 This is an index that can be used when the r-value is small, and in reality, it is necessary to consider the magnitude relationship of the r-value in each direction. Here, the r-value is usually divided into r0, which is the r-value in the rolling direction, and r, which is the r-value in the 45° direction from the rolling direction. 45 , r value in the direction 90° from the rolling direction 90 In many cases, the relationship between the r-values ​​in each direction is evaluated by measuring the r-value. However, in the case of ferritic stainless steel sheets, which aim to improve the r-value, 90 does not become the minimum r value (see Non-Patent Document 1), and r0 or r 45 is the minimum r value.

[0055] Therefore, in the ferritic stainless steel sheet of this embodiment, when evaluating the in-plane anisotropy, r0 and r45 Therefore, in the ferritic stainless steel sheet of this embodiment, the anisotropy of the entire steel sheet can be evaluated by considering only the relationship between r0 and r 45 Evaluation is performed using r0-r 45 The closer the value is to 0, the smaller the in-plane anisotropy is, the smaller the ears formed during deep drawing are, and the better the workability is.

[0056] So, r0-r 45 It is preferable that the following formula (iv) is satisfied: -0.20≦r0-r 45 ≦0.20 (iv) However, the symbols in the above formula (iv) are defined as follows: r0: r value in the rolling direction r 45 : r value at 45° from the rolling direction

[0057] (iv) The value of r0-r in the equation 45 If r0-r is less than -0.20, the in-plane anisotropy becomes large. 45 is preferably -0.20 or more. Similarly, r0-r 45 If r0-r exceeds 0.20, the in-plane anisotropy becomes large. 45 is preferably 0.20 or less. 45 is preferably set to -0.10 to 0.10.

[0058] In order to calculate the r-value in each of the above directions, a test is performed using the plastic strain ratio test method described in JIS Z 2254:2008, and calculations are made in accordance with the same standard.

[0059] 4. Manufacturing method A preferred method for producing the ferritic stainless steel sheet according to this embodiment will now be described. The ferritic stainless steel sheet according to this embodiment can achieve the effects described above regardless of the production method, but can be stably produced, for example, by the following production method.

[0060] 4-1.Hot rolling process A stainless steel slab having the above-described chemical composition is preferably produced by a conventional method. The resulting slab is then preferably hot-rolled. The slab is heated before hot-rolling, and the heating temperature of the slab is preferably 1100 to 1250°C. If the heating temperature of the slab is less than 1100°C, surface defects are likely to occur, and corrosion resistance is likely to decrease due to rusting from the defects. Therefore, the heating temperature of the slab is preferably 1100°C.

[0061] On the other hand, if the slab heating temperature exceeds 1250°C, the crystal grains become significantly coarse during heating, and coarse elongated grains are formed during the hot rolling process, which results in a deterioration in the workability of the steel sheet and the formation of surface irregularities, known as roping. Furthermore, Ti carbosulfide (Ti4C2S2) dissolves during heating, increasing the amount of solute carbon and making it more likely for precipitates to form again during the hot rolling process. This results in a delay in recrystallization, making poor recrystallization more likely. Such poor recrystallization also makes roping more likely. For this reason, it is preferable to set the slab heating temperature to 1250°C or less. Considering the reduction in productivity due to seizure of the rolling rolls, it is more preferable to set the slab heating temperature to 1130 to 1230°C.

[0062] The heated slab is then hot rolled. Hot rolling consists of rough rolling and finish rolling, and when hot rolling the slab, it is preferable to perform finish rolling at a hot rolling finish temperature FT that satisfies the following formula (v):

[0063] 700≦FT(℃)≦950 (V) Here, FT is the hot rolling finishing temperature (°C).

[0064] If the hot rolling finish temperature FT is less than 700°C, the reaction force increases during rolling, making it more likely that shape defects and surface defects will occur. Therefore, the hot rolling finish temperature FT is preferably 700°C or higher, and more preferably 750°C or higher.

[0065] On the other hand, if the hot rolling finishing temperature FT exceeds 950°C, strain recovery or recrystallization occurs after finish rolling, causing changes in the texture. As a result, strain recovery is suppressed and it becomes difficult to accumulate strain. In other words, the {554} <225> Orientation and {322} <236> Increase the random intensity ratio of the orientation, {111} <110> As a result, the intensity ratio A and / or B does not satisfy the range of this embodiment, and r0-r 45 Therefore, the hot rolling finishing temperature FT is preferably set to 950°C or less, and more preferably set to 920°C or less.

[0066] It is preferable to perform rapid cooling immediately after the above-mentioned finish rolling. Specifically, it is preferable to cool to 700°C or less within 10 seconds immediately after finish rolling. If the steel sheet is exposed to high temperatures for a long time after the completion of finish rolling, strain recovery and recrystallization occur. As a result, the strain accumulated during hot rolling is released, and the texture of the hot-rolled steel sheet changes. This makes it difficult to control the texture and r-value anisotropy of the product sheet. For this reason, it is preferable to cool to a temperature of 700°C or less within 10 seconds immediately after finish rolling. From the perspective of recrystallization, the temperature should be lowered to 700°C or less within 7 seconds immediately after finish rolling. As for the cooling method, water cooling is preferable.

[0067] Preferably, the steel material cooled to 700°C or less is coiled at a temperature of 600°C or less to produce a hot-rolled steel sheet. If the coiling temperature exceeds 600°C, strain recovery and recrystallization occur during the gradual cooling process of the hot-rolled steel sheet after coiling, resulting in a change in the texture. As a result, it becomes difficult to control the texture and in-plane anisotropy of the product sheet. Furthermore, the strength ratios A and / or B do not satisfy the ranges of this embodiment. For this reason, the coiling temperature is preferably 600°C or less, and more preferably 550°C or less.

[0068] For the ferritic stainless steel sheet of this embodiment, it is preferable not to perform the annealing of hot-rolled steel sheets, so-called hot-rolled sheet annealing, which is usually performed. By performing hot-rolled sheet annealing, strain accumulated during hot rolling is released due to recrystallization, and the texture of the hot-rolled steel sheet changes. As a result, it becomes difficult to control the texture and in-plane anisotropy of the product sheet. Furthermore, if scale is formed on the surface during hot rolling, surface defects and the like are likely to occur in subsequent processes. For this reason, it is desirable to perform descaling by pickling or the like, as necessary.

[0069] 4-2.Cold rolling process Subsequently, the hot-rolled steel sheet is preferably cold-rolled at a cold rolling reduction CR (%) in the range of 20 to 85% to obtain a cold-rolled steel sheet. If the cold rolling reduction CR is less than 20%, sufficient strain for recrystallization cannot be accumulated during the cold-rolled sheet annealing described below. Therefore, the cold rolling reduction CR is preferably 20% or more. From the viewpoint of effectively inducing recrystallization, the cold rolling reduction CR is more preferably 40% or more.

[0070] On the other hand, when the cold rolling reduction CR exceeds 85%, r0 decreases. More specifically, by accumulating sufficient strain, the {554} <225> Orientation and {322} <236> It becomes difficult to increase the random intensity ratio of the orientation. <110> As a result, it becomes difficult for the intensity ratio A and / or B to satisfy the range of this embodiment, and r0-r 45 becomes smaller than −0.20. Therefore, the cold rolling reduction CR is preferably set to 85% or less, and more preferably set to 80% or less.

[0071] 4-3.Cold-rolled sheet annealing After the cold rolling, the cold-rolled steel sheet is preferably annealed. That is, it is preferable to perform cold-rolled sheet annealing. The annealing temperature for the cold-rolled sheet annealing is not particularly limited, but is often performed, for example, in the range of T+50 to T+120°C, where T is the recrystallization temperature (°C). The annealing may be performed at an appropriate temperature depending on the required properties.

[0072] Annealing at a temperature exceeding T+120°C results in coarsening of the crystal grains, making the surface prone to roughness after processing. The recrystallization temperature T can be measured, for example, by the following method. Specifically, the cold-rolled steel sheet is heated to a predetermined temperature, held for one minute, cooled to room temperature, and the recrystallization rate is measured. The annealing temperature is changed in 10°C increments, and the lowest temperature at which the recrystallization rate is 98% or more is taken as the recrystallization temperature T.

[0073] The annealing time is not particularly limited, but is preferably 3 minutes or less in consideration of productivity. After that, the steel sheet is cooled in a conventional manner to obtain a steel sheet having the structure of a ferritic stainless steel sheet.

[0074] 4-4. Strain parameters The amount of accumulated strain is affected by the hot rolling finishing temperature FT, the cold rolling reduction CR, and the Nb content of the steel sheet. By setting these in appropriate ranges, the r0-r 45 can be set to a desired range. For this reason, a strain parameter R is defined, which is calculated based on the hot rolling finishing temperature FT, the cold rolling reduction CR, and the Nb content of the steel sheet. The strain parameter R is a parameter defined by the hot rolling finishing temperature FT, the cold rolling reduction CR, and the Nb content of the steel sheet as shown in the following formula (vi), and the smaller the strain parameter R, the greater the amount of accumulated strain.

[0075] By setting the strain parameter R in the range of -0.2 to 0.2, the {554} <225> Orientation and {322} <236> Increase the random intensity ratio of the orientation, {111} <110> The random intensity ratio of the orientation can be reduced. As a result, r0-r 45 can be set to a value close to 0.

[0076] R=1.6-CR / 50+(FT-900) / 300―20Nb / 3 (vi) In the above formula, each symbol is defined as follows: CR: Cold rolling reduction rate (%) FT: Hot rolling finishing temperature (℃) Nb: Nb content of steel plate

[0077] When the strain parameter R is less than -0.2, the in-plane anisotropy becomes large, i.e., r0-r 45 Therefore, the strain parameter R is preferably set to -0.2 or more, and more preferably set to -0.1 or more. On the other hand, if R exceeds 0.2, the in-plane anisotropy becomes large, and the r0-r 45 exceeds 0.20. Therefore, the strain parameter R is preferably set to 0.2 or less, and more preferably set to 0.1 or less.

[0078] In this way, by controlling the strain parameter R within an appropriate range, <225> Azimuth, {111} <110> bearings, and {322} <236> By properly controlling the random intensity ratio of the orientation, r0 and r 45 It is possible to obtain a steel sheet with small in-plane anisotropy regardless of the magnitude relationship of

[0079] The ferritic stainless steel sheet according to the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0080] Stainless steel having the chemical composition shown in Table 1 was melted, and ferritic stainless steel sheets were produced under the conditions shown in Tables 2 and 3. Note that no hot-rolled sheet annealing was performed during the production of the steel sheets. The annealing time during cold-rolled sheet annealing was 1 minute in all examples. The crystal orientation intensity ratios A and B and the r0-r 45 and total elongation were measured by the method described below.

[0081] (Intensity ratio of crystal orientations A and B) X-ray diffraction was performed on the obtained steel sheet in a plane parallel to the rolling surface at the half-thickness position. Using the data obtained by X-ray diffraction, three-dimensional orientation analysis was performed using the Bunge method described in Non-Patent Document 3. From the crystal orientation distribution diagram, it was found that {554} <225> Azimuth, {111} <110> bearings, and {322} <236> The random intensity ratio of the orientation was calculated, and the intensity ratios A and B were calculated.

[0082] (average r value and various r values, etc.) The obtained steel plates were subjected to the plastic strain ratio test method in accordance with JIS Z 2254:2008, and 45 From the measurement results, the average r value and r0-r 45 was calculated. Furthermore, a tensile test was conducted in accordance with JIS Z 2241:2011 to measure the total elongation. A total elongation of 30% or more was evaluated as having good properties. Tables 1 to 3 are shown below.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Table 3]

[0086] C1 to C18 that satisfy the requirements of this embodiment are r0-r 45 was in the range of -0.20 to 0.20, the in-plane anisotropy was small, and the workability was good. On the other hand, for c1 to c13, which do not satisfy the requirements of this embodiment, the workability was reduced.

[0087] Since c1 to c6 did not satisfy the chemical composition of this embodiment, the r-value was low. Also, c1, c2, c4, and c5 had excessive contents of Si, Mn, Al, and Cr, resulting in low total elongation of 30% or less and poor workability. Since c7 to c13 did not satisfy the preferred conditions for the manufacturing method, the texture could not be controlled, resulting in poor r0-r 45 was either too small or too large.

Claims

1. The chemical composition, in mass%, is C: 0.030% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.005-0.100%, S: 0.0100% or less, Cr: 11.0-30.0%, Al: 1.00% or less, N: 0.030% or less, Ti: 0.05-0.50%, Nb: 0 to 0.19%, Sn: 0 to 0.50%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Mo: 0-2.00%, W: 0-1.00%, Co: 0 to 0.50%, V: 0-0.50%, Zr: 0 to 0.50%, Sb: 0 to 0.50%, B: 0 to 0.0025%, Ca: 0-0.0050%, Mg: 0 to 0.0050%, Y: 0-0.20%, Hf: 0-0.20%, REM: 0-0.10%, The balance is Fe and impurities. The following formula (i) is satisfied: A ferritic stainless steel sheet in which, in a plane parallel to the rolled surface at the sheet thickness half position, the crystal orientation intensity ratio A calculated by the following formula (ii) is 6.0 or more, and the crystal orientation intensity ratio B calculated by the following formula (iii) is 2.0 to 5.

0. 0.10≦Ti+Nb≦0.66...(i) A=I{554}<225> / I{111}<110>...(ii) B=I{554}<225> / I{322}<236> ...(iii) However, each element symbol in the above formula (i) represents the content (mass%) of each element contained in the steel, and when no element is contained, it is set to zero, and each symbol in the above formulas (ii) and (iii) is defined as follows: I{554}<225>: X-ray random intensity ratio in the {554}<225> direction I{111}<110>: X-ray random intensity ratio in the {111}<110> direction I{322}<236>: X-ray random intensity ratio in the {322}<236> direction

2. The chemical composition is, in mass %, Sn: 0.005-0.50%, Ni: 0.05-1.00%, Cu: 0.05-1.00%, Mo: 0.05-2.00%, W: 0.05-1.00%, Co: 0.05-0.50%, V: 0.05-0.50%, Zr: 0.05 to 0.50%, and Sb: 0.005 to 0.50%, The ferritic stainless steel sheet according to claim 1, comprising one or more selected from the following:

3. The chemical composition is, in mass %, B: 0.0001 to 0.0025%, Ca: 0.0002 to 0.0050%, and Mg: 0.0002 to 0.0050%, The ferritic stainless steel sheet according to claim 1 or 2, comprising one or more selected from the following:

4. The chemical composition is, in mass %, Y: 0.001-0.20%, Hf: 0.001 to 0.20%, and REM: 0.001-0.10%, The ferritic stainless steel sheet according to any one of claims 1 to 3, comprising one or more selected from the following:

5. The ferritic stainless steel sheet according to any one of claims 1 to 4, which satisfies the following formula (iv): -0.20≦r ０ -r ４５ ≦0.20 ・・・(iv) However, the symbols in the above formula (iv) are defined as follows: r ０ : r value in the rolling direction r ４５ : r value in the direction 45° from the rolling direction

6. A method for producing a ferritic stainless steel sheet according to any one of claims 1 to 5, comprising: A step of finish-rolling a slab having the chemical composition according to any one of claims 1 to 4 at a hot rolling finishing temperature FT that satisfies the following formula (v) when hot-rolling; a step of cooling the steel sheet to 700°C or less within 10 seconds immediately after the finish rolling and coiling the steel sheet at a temperature of 600°C or less to obtain a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet at a cold rolling reduction rate CR of 20 to 85% without annealing the hot-rolled steel sheet to obtain a cold-rolled steel sheet; and annealing the cold-rolled steel sheet, A method for producing a ferritic stainless steel sheet, wherein the strain parameter R calculated by the following formula (vi) is in the range of -0.2 to 0.

2. 700≦FT(℃)≦950...(v) R=1.6-CR / 50+(FT-900) / 300-20Nb / 3...(vi) In the above formula, each symbol is defined as follows: CR: Cold rolling reduction rate (%) FT: Hot rolling finishing temperature (℃) Nb: Nb content of steel plate

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