Steel plates and parts containing them

Abstract

The present invention provides a steel sheet containing Ni, Cu, Cr, and Sn, with a high N content, and having excellent deep draw formability, as well as parts containing the same. It has a predetermined chemical composition and [Ti]-[N]×47.88 / 14≧([N]-0.0021) 0.4 The chemical composition satisfies ×0.23, where [Ti] and [N] are the mass %) of Ti and N, satisfies 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650, where [Cu], [Ni], [Cr] and [Sn] are the mass %) of Cu, Ni, Cr and Sn, and the number density of Ti4C2S2 is 0.06 particles / μm 2 A steel plate and a component containing the same are provided, characterized by having the above-described metallic structure.

Description

[Technical Field]

[0001] This invention relates to steel plates and parts containing them. [Background technology]

[0002] Many automotive parts are made by press-forming steel sheets. In recent years, part shapes have become more diverse and complex, and the steel sheets used as materials require good formability. On the other hand, it is known that the formability can be reduced depending on the alloying elements contained in the steel sheet.

[0003] In this regard, Patent Document 1 discloses a processing steel that contains C: 0.0050 mass% or less, Si: 1.5 mass% or less, Mn: 1.5 mass% or less, P: 0.10 mass% or less, Al: 0.10 mass% or less, S: 0.020 mass% or less, and O: 0.01 mass% or less, and inevitably contains Cu: 1.5 mass% or less and Ni: 2.0 mass% or less as trump elements, characterized in that it contains Ti and / or Nb: 0.001 to 0.10 mass% and N: suppressed to the range of 0.0040 to 0.0090 mass%. Patent Document 1 teaches that with the above configuration, even when using electric furnace steel containing trump elements, it is possible to obtain a processing steel with the same excellent machinability as conventional steels.

[0004] Patent Document 2 discloses a cold-rolled steel sheet having a predetermined chemical composition that satisfies formula (i) (Ti-48 / 32 × S-48 / 14 × N-48 / 12 × C≧-0.010) and formula (ii) (5.0≦11Si+33Mn+21Mo+17(Cr+Cu+Ni)-30Al≦50.0), wherein the r value rL in the rolling direction is 1.50 or more, the r value rC in the direction perpendicular to the rolling direction is 1.50 or more, the r value rD in the direction 45° from the rolling direction is 1.50 or more, mr defined as mr=(rL+2rD+rC) / 4 is 1.70 or more, and Δr defined as Δr=(rL+rC-2rD) / 2 is in the range of -0.40 to 0.40. Patent Document 2 teaches that, according to the above configuration, it is possible to obtain a cold-rolled steel sheet that has improved deep drawability while containing a certain amount or more of Sn in order to improve corrosion resistance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-336452 [Patent Document 2] International Publication No. 2024 / 122042 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As mentioned above, the formability of steel sheets can decrease depending on the elements they contain. For example, Patent Document 1 teaches that the workability of steel sheets, particularly the plastic strain ratio (r value), decreases due to elements such as Cu, Ni, and Cr. Patent Document 2 also teaches that the r value decreases with increasing Sn content. Steel sheets with low r values ​​have poor deep drawing formability, so steel sheets with high r values ​​are in demand.

[0007] Therefore, the present invention aims to provide a steel sheet containing Ni, Cu, Cr, and Sn, with a high N content, that has excellent deep drawing formability, and a part containing the same. [Means for solving the problem]

[0008] To achieve the above objective, the inventors focused on both the chemical composition and the microstructure of the steel sheet. First, the inventors optimized the chemical composition of the steel sheet and appropriately controlled the amount of Ti4C2S2, more specifically, the number density of Ti4C2S2 to 0.06 particles / μm 2 We found that controlling the process to the above extent improves the formability of the material. Furthermore, we found that optimizing the content of Ni, Cu, Cr, and Sn in the steel sheet, more specifically, controlling the chemical composition to satisfy 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650, further improves the formability of the material, thus completing the present invention.

[0009] The present invention, which has achieved the above objectives, is as follows. (1) In mass%, C: 0.0005~0.0050%, Mn: 0.01~1.50%, Si: 0.002~0.500%, P: 0.100% or less, S: 0.0010~0.0200%, Al: 1.000% or less, N: 0.0026~0.0150%, O: 0.0100% or less, Ti: 0.015~0.150%, Ni: 0.04~1.00%, Cu: 0.04~1.00%, Cr: 0.04~1.00%, Sn: 0.004~0.100%, Nb: 0~0.050%, Mo: 0~0.50%, B: 0~0.0100%, V: 0~0.500%, W: 0~1.00%, Ta: 0~0.10%, Co: 0~1.00%, Sb: 0~0.200%, Ca: 0~0.0500%, Mg: 0~0.0500%, Zr: 0~0.5000%, REM: 0~0.0100%, Bi: 0~0.0500%, As: 0~0.10%, and The remainder consists of Fe and impurities. Having a chemical composition that satisfies the following formulas (1) and (2), The number density of Ti4C2S2 is 0.06 particles / μm 2 A steel plate characterized by having the above-mentioned metallic structure. [Ti]-[N]×47.88 / 14≧([N]-0.0021) 0.4 ×0.23...Equation (1) Here, [Ti] and [N] represent the content (mass%) of Ti and N, respectively. 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650...Equation (2) Here, [Cu], [Ni], [Cr], and [Sn] represent the mass %) of Cu, Ni, Cr, and Sn. (2) The above chemical composition is in mass %, Nb: 0.001~0.050%, Mo: 0.001~0.50%, B: 0.0001~0.0100%, V: 0.001~0.500%, W: 0.001~1.00%, Ta: 0.001~0.10%, Co: 0.001~1.00%, Sb: 0.001~0.200%, Ca: 0.0001~0.0500%, Mg: 0.0001~0.0500%, Zr: 0.0001~0.5000%, REM: 0.0001~0.0100%, Bi: 0.0001~0.0500%, and As: 0.001~0.10% The steel plate according to (1) above, characterized in that it includes at least one of the following. (3) {001} Random intensity ratio of average direction X {001} {111} <112> Directional random intensity ratio X {111} Ratio (X {111} / X {001} The steel plate according to (1) or (2) above, characterized in that the ratio is 20.0 or higher. (4) A component characterized by including a steel plate as described in any one of the above items (1) to (3). [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a steel sheet containing Ni, Cu, Cr, and Sn, with a high N content, which has excellent deep draw formability, and a part containing the same. [Modes for carrying out the invention]

[0011] <Steel plate> The steel plate according to the embodiment of the present invention is, by mass %, C: 0.0005~0.0050%, Mn: 0.01~1.50%, Si: 0.002~0.500%, P: 0.100% or less, S: 0.0010~0.0200%, Al: 1.000% or less, N: 0.0026~0.0150%, O: 0.0100% or less, Ti: 0.015~0.150%, Ni: 0.04~1.00%, Cu: 0.04~1.00%, Cr: 0.04~1.00%, Sn: 0.004~0.100%, Nb: 0~0.050%, Mo: 0~0.50%, B: 0~0.0100%, V: 0~0.500%, W: 0~1.00%, Ta: 0 to 0.10%, Co: 0 to 1.00%, Sb: 0 to 0.200%, Ca: 0 to 0.0500%, Mg: 0 to 0.0500%, Zr: 0 to 0.5000%, REM: 0 to 0.0100%, Bi: 0 to 0.0500%, As: 0 to 0.10%, and the balance: consisting of Fe and impurities, having a chemical composition satisfying the following formulas (1) and (2), the number density of Ti4C2S2 is 0.06 pieces / μm 2 and having a metal structure that is at least the above. [Ti] - [N] × 47.88 / 14 ≥ ([N] - 0.0021) 0.4 × 0.23 ··· Formula (1) However, [Ti] and [N] are the contents (mass%) of Ti and N. 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650 ··· Formula (2) However, [Cu], [Ni], [Cr], and [Sn] are the contents (mass%) of Cu, Ni, Cr, and Sn.

[0012] As described above, in automotive parts and the like, the part shapes are diverse and complex, and the steel sheet used as the material is required to have formability. However, depending on the alloying elements contained in the steel sheet, the formability, particularly the drawing formability, may decrease. When the steel sheet contains the four elements of Cu, Ni, Cr, and Sn simultaneously or when the N content is high, such a decrease in drawing formability is particularly a concern.

[0013] Furthermore, there are generally known methods for manufacturing steel sheets, such as the method of producing molten steel in a blast furnace using iron ore, a natural resource, as the main raw material, and then refining it in a converter or the like to produce molten steel, and the method of producing molten steel in an electric arc furnace using scrap material, a recycled resource, as the main raw material. In blast furnace steel, it is known that if the proportion of scrap is increased due to considerations for the global environment, the content of scrap-derived elements such as Cu, Ni, Cr, and Sn (so-called trump elements) inevitably increases, and the formability of the final steel product decreases. In electric arc furnace steel, since scrap material is used as the main raw material, the content of trump elements is even higher, and it is also thought that the N content is higher than in blast furnace steel due to contamination from the atmosphere. Therefore, there are concerns about a further decrease in formability. Accordingly, the inventors focused on chemical composition and metal structure and conducted studies to provide a steel sheet that has excellent deep drawing formability even when the steel sheet contains all four elements Cu, Ni, Cr, and Sn simultaneously.

[0014] Generally, the plastic strain ratio (r-value) is used as an indicator of deep drawability, and it is known that reducing the amount of dissolved carbon in the hot-rolled sheet before annealing improves the r-value. First, the inventors attempted to reduce the amount of dissolved carbon by precipitating a carbon-containing precipitate such as Ti4C2S2 and consuming the dissolved carbon. In order to precipitate a large amount of Ti4C2S2 in this way, a large amount of dissolved Ti is required, that is, the amount of effective Ti needs to be increased. Here, the amount of effective Ti corresponds to the amount of dissolved Ti, that is, the value obtained by subtracting the amount of Ti fixed by N from the total amount of Ti. The amount of Ti effective for precipitating a carbon-containing precipitate such as Ti4C2S2 is the value obtained by subtracting the amount that can be fixed as TiN from the total amount of Ti, and is calculated by the following formula. Effective Ti content (%) = [Ti] - 47.88 / 14 [N] Here, [Ti] and [N] represent the mass %) content of each element in the hot-rolled coil.

[0015] In the process of investigating the chemical composition of steel sheets, it was found that, given the same amount of effective Ti in the steel sheet, a higher N content suppresses the precipitation of Ti4C2S2. Therefore, in steel sheets with a relatively high N content, if there is insufficient Ti, the precipitation of Ti4C2S2 is suppressed, and the dissolved C remains unconsumed. While not intended to be bound by any particular theory, by controlling the amount of effective Ti (left side of equation (1) above) to be higher than the value determined by the N content (right side of equation (1) above), it becomes possible to ensure sufficient Ti content for Ti4C2S2 precipitation even in steel sheets with a relatively high N content, allowing the dissolved C to precipitate as Ti4C2S2, reducing the amount of dissolved C, and consequently improving the formability of the deep drawing.

[0016] In addition, from the viewpoint of the metallographic structure of the steel sheet, the inventors aim to control the amount of Ti4C2S2 so that a relatively large amount of Ti4C2S2 is present in the steel sheet, more specifically, to achieve a number density of 0.06 Ti4C2S2 particles / μm 2 By controlling the conditions as described above, it is possible to reduce the amount of dissolved carbon (C) by causing it to precipitate as Ti4C2S2, thereby improving the formability of the steel sheet. By controlling the form and amount of Ti4C2S2 within this range, and combining this with the control of the chemical composition using the relationship between Ti and N (equation (1)) described above, dissolved carbon precipitates as Ti4C2S2, reducing the amount of dissolved carbon, and as a result, it is possible to further improve the formability of the steel sheet.

[0017] Even when Ti4C2S2 is precipitated in this way and the amount of dissolved carbon is sufficiently reduced, some dissolved carbon remains, and this remaining dissolved carbon may form precipitates, such as carbides of Ti and / or Nb. These carbides precipitate at a lower temperature than Ti4C2S2 and therefore have finer particle sizes. Furthermore, through the inventors' studies, although the details are not clear, it has been found that when the four elements Cu, Ni, Cr, and Sn are included, these fine carbides become even finer. In addition, it has been found that the degree to which these fine carbides become finer differs depending on the type of Cu, Ni, Cr, and Sn. In general, it is known that in order to improve the r value, not only is the amount of dissolved carbon reduced, but the grain size of the metal structure is also made coarser. However, when the four elements Cu, Ni, Cr, and Sn are included, the fine carbides become even finer, and these fine precipitates suppress the growth of the grain size of the metal structure, lowering the r value and consequently reducing the formability of the deep drawing. The inventors experimentally investigated the influence of Cu, Ni, Cr, and Sn precipitates on the particle size of steel sheets from the viewpoint of chemical composition. As a result, they found that by controlling the value of the formula determined by the content of these elements, specifically 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn] (the left side of formula (2) above), along with a coefficient that takes into account the influence on the formation of fine carbides, to 0.650 or less, further refinement of fine carbides is suppressed, the crystal grain size of the metal structure becomes coarser, and thereby the formability of the deep drawing is improved.

[0018] As described above, according to the steel sheet according to the embodiment of the present invention, even when the steel sheet contains four elements, Cu, Ni, Cr, and Sn, and has a high nitrogen content, excellent deep drawing formability can be achieved. Therefore, the steel sheet according to the embodiment of the present invention is particularly useful for use in technical fields where such properties are required.

[0019] The steel sheets according to embodiments of the present invention will be described in more detail below. In the following description, "%", which is the unit for the content of each element, means "mass%" unless otherwise specified. In this specification, "~", which indicates a numerical range, is used to mean that the numbers written before and after it are included as the lower and upper limits, respectively, unless otherwise specified.

[0020] [C:0.0005~0.0050%] Carbon (C) is an effective element for increasing the strength of steel sheets. Furthermore, C forms carbides and / or carbonitrides with Ti and / or Nb in the steel. To fully obtain these effects, the C content should be 0.0005% or higher. The C content may also be 0.0010% or higher, 0.0015% or higher, or 0.0020% or higher. On the other hand, excessive C content can increase the amount of solid-solution C, potentially reducing the formability of the steel. Therefore, the C content should be 0.0050% or lower. The C content may also be 0.0045% or lower, 0.0040% or lower, 0.0035% or lower, 0.0030% or lower, or 0.0025% or lower.

[0021] [Mn: 0.01~1.50%] Mn is an effective element for increasing strength as a hardenable and solid solution strengthening element. To obtain these effects to the fullest, the Mn content should be 0.01% or more. The Mn content may be 0.05% or more, 0.10% or more, or 0.20% or more. On the other hand, if the Mn content is excessive, the strength will become too high, and the amount of Ti4C2S2 precipitate will decrease due to the generation of a large amount of MnS, which may reduce the formability of the material. Therefore, the Mn content should be 1.50% or less. The Mn content may be 1.00% or less, 0.80% or less, 0.60% or less, or 0.40% or less.

[0022] [Si: 0.002~0.500%] Si is an effective element for increasing strength as a solid solution strengthening element. To obtain this effect fully, the Si content should be 0.002% or more. The Si content may also be 0.005% or more, 0.010% or more, 0.020% or more, 0.050% or more, or 0.100% or more. On the other hand, if the Si content is excessive, it may become difficult to remove the scale generated during hot rolling, leading to a deterioration in appearance. Therefore, the Si content should be 0.500% or less. The Si content may also be 0.400% or less, 0.300% or less, 0.200% or less, or 0.150% or less.

[0023] [P:0.100% or less] P is an impurity element that, like Si, is effective in increasing strength, but it is also an element that causes embrittlement of welds and deterioration of plating properties. For this reason, the P content should be 0.100% or less. The P content may also be 0.050% or less, 0.030% or less, 0.020% or less, or 0.010% or less. The lower limit of the P content is not particularly limited and may be 0%, but excessive reduction will lead to increased costs. Therefore, the P content may be 0.0001% or more, 0.0002% or more, or 0.0005% or more.

[0024] [S:0.0010~0.0200%] S forms Ti4C2S2, reducing solid-solution carbon and improving draw-formability. To achieve this effect, the S content should be 0.0010% or more. The S content may be 0.0020% or more, 0.0030% or more, or 0.0050% or more. On the other hand, S is an impurity element that inhibits weldability and also inhibits manufacturability during casting and hot rolling. For this reason, the S content should be 0.0200% or less. The S content may be 0.0150% or less, 0.0100% or less, or 0.0050% or less.

[0025] [Al: 1.000% or less] Al is an element that functions as a deoxidizing agent. The Al content may be 0%, but to obtain these effects sufficiently, it is preferable that the Al content be 0.001% or more. The Al content may be 0.005% or more, 0.010% or more, 0.025% or more, or 0.050% or more. On the other hand, if the Al content is excessive, coarse oxides may form, which may reduce toughness. Therefore, the Al content should be 1.000% or less. The Al content may be 0.800% or less, 0.600% or less, or 0.400% or less.

[0026] [N: 0.0026~0.0150%] N is an impurity element, and reducing the N content increases steelmaking costs. In particular, the electric arc furnace method tends to have a higher N content than the blast furnace method. For this reason, the N content should be 0.0026% or higher. The N content may also be 0.0030% or higher, 0.0035% or higher, 0.0040% or higher, 0.0045% or higher, or 0.0050% or higher. On the other hand, if the N content is excessive, Ti4C2S2 may not precipitate sufficiently. For this reason, the N content should be 0.0150% or lower. The N content may also be 0.0140% or lower, 0.0130% or lower, 0.0120% or lower, 0.0110% or lower, 0.0100% or lower, 0.0090% or lower, 0.0080% or lower, or 0.0070% or lower.

[0027] [O:0.0100% or less] O is an element that is introduced during the manufacturing process. Excessive O content can lead to the formation of coarse oxides, which can reduce the toughness of the steel sheet. Therefore, the O content should be 0.0100% or less. The O content may also be 0.0080% or less, 0.0060% or less, 0.0040% or less, or 0.0020% or less. The lower limit of the O content is not particularly limited and may be 0%, but reducing it to less than 0.0001% requires more time for refining, leading to a decrease in productivity. Therefore, the O content may be 0.0001% or more, 0.0002% or more, or 0.0005% or more.

[0028] [Ti: 0.015~0.150%] Ti forms carbon sulfides and carbonitrides such as Ti4C2S2, reducing solid-solution carbon and improving deep drawing formability. To fully obtain this effect, the Ti content should be 0.015% or higher. The Ti content may also be 0.030% or higher, 0.040% or higher, or 0.050% or higher. On the other hand, if the Ti content is excessive, fine Ti-based carbides may precipitate, preventing sufficient growth of the crystal grain size in the metal structure, which may reduce deep drawing formability. Therefore, the Ti content should be 0.150% or lower. The Ti content may also be 0.120% or lower, 0.100% or lower, 0.080% or lower, or 0.060% or lower.

[0029] [Ni: 0.04~1.00%] Ni is an element that may be present in steel sheets when scrap is used as a raw material. The Ni content should be 0.04% or more. Ni is also an element that contributes to improving strength through solid solution strengthening. To obtain such an effect, the Ni content may be 0.10% or more, 0.15% or more, or 0.20% or more. On the other hand, if the Ni content is excessive, not only will the manufacturing cost increase, but the strength may become too high, which may reduce the formability of the steel sheet. Therefore, the Ni content should be 1.00% or less. The Ni content may be 0.90% or less, 0.80% or less, 0.70% or less, 0.60% or less, 0.50% or less, 0.40% or less, or 0.30% or less.

[0030] [Cu: 0.04~1.00%] Cu is an element that may be present in steel sheets when scrap is used as a raw material. The Cu content should be 0.04% or more. Furthermore, Cu is an element that contributes to improving strength through precipitation strengthening or solid solution strengthening. To obtain such effects, the Cu content may be 0.10% or more, 0.15% or more, or 0.20% or more. On the other hand, if Cu is present in excess, fine precipitates may precipitate excessively, resulting in excessively high strength, and the growth of the crystal grain size in the metal structure may not proceed sufficiently, thereby reducing the formability of the metal. Therefore, the Cu content should be 1.00% or less. The Cu content may be 0.90% or less, 0.80% or less, 0.70% or less, 0.60% or less, 0.50% or less, 0.40% or less, or 0.30% or less.

[0031] [Cr:0.04~1.00%] Cr is an element that may be present in steel sheets when scrap is used as a raw material. The Cr content should be 0.04% or more. Cr is also an element that enhances the hardenability of steel and contributes to improving its strength. To obtain these effects, the Cr content may be 0.06% or more, 0.08% or more, or 0.10% or more. On the other hand, excessive Cr content not only increases manufacturing costs but can also lead to excessively high strength, which can reduce the ability to be drawn into shape. Therefore, the Cr content should be 1.00% or less. The Cr content may also be 0.80% or less, 0.60% or less, 0.40% or less, or 0.20% or less.

[0032] [Sn: 0.004~0.100%] Sn is an element that may be present in steel sheets when scrap is used as a raw material. The Sn content should be 0.004% or more. Furthermore, Sn is an element that is effective in improving corrosion resistance. To obtain such an effect, the Sn content may be 0.006% or more, 0.008% or more, 0.010% or more, 0.012% or more, or 0.014% or more. On the other hand, if the Sn content is excessive, the formability of the steel sheet may decrease. Therefore, the Sn content should be 0.100% or less. The Sn content may also be 0.080% or less, 0.050% or less, 0.040% or less, 0.030% or less, or 0.020% or less.

[0033] The basic chemical composition of the steel sheet according to the embodiment of the present invention is as described above. Furthermore, the steel sheet may, if necessary, contain at least one of the following optional elements in place of a portion of the remaining Fe.

[0034] [Nb:0~0.050%] Nb forms carbonitrides, reducing solid-solution carbon and improving deep draw formability. While the Nb content may be 0%, it is preferable that the Nb content be 0.001% or higher to fully obtain these effects. The Nb content may also be 0.005% or higher, or 0.010% or higher. On the other hand, excessive Nb content may suppress recrystallization and grain growth, leading to a decrease in deep draw formability. Furthermore, including more Nb in the steel than necessary increases manufacturing costs. Therefore, it is preferable that the Nb content be 0.050% or lower. The Nb content may also be 0.040% or lower, 0.030% or lower, or 0.020% or lower.

[0035] [Mo: 0~0.50%] Mo is an element that enhances the hardenability of steel and contributes to improving its strength. While the Mo content may be 0%, it is preferable that the Mo content be 0.001% or more to obtain these effects. The Mo content may also be 0.005% or more, 0.01% or more, 0.02% or more, or 0.03% or more. On the other hand, if the Mo content is excessive, the deformation resistance during hot working may increase, and the equipment load may become larger. Therefore, it is preferable that the Mo content be 0.50% or less. The Mo content may also be 0.40% or less, 0.30% or less, or 0.20% or less.

[0036] [B: 0~0.0100%] B improves low-temperature toughness by segregating at grain boundaries and increasing grain boundary strength. The B content may be 0%, but to obtain this effect, it is preferable that the B content be 0.0001% or more. The B content may be 0.0005% or more or 0.0010% or more. On the other hand, if the B content is excessive, toughness and / or weldability may decrease. Therefore, it is preferable that the B content be 0.0100% or less. The B content may be 0.0080% or less, 0.0060% or less, 0.0040% or less, or 0.0020% or less.

[0037] [V:0 ~0.500%] V is an element effective in controlling the morphology of carbides and is also effective in refining the microstructure and improving the toughness of steel sheets. The V content may be 0%, but to obtain such effects, it is preferable that the V content be 0.001% or more. The V content may also be 0.005% or more or 0.010% or more. On the other hand, if the V content is excessive, a large amount of precipitate may be formed, which may reduce toughness. Therefore, it is preferable that the V content be 0.500% or less. The V content may also be 0.400% or less, 0.200% or less, 0.100% or less, or 0.050% or less.

[0038] [W: 0~1.00%] W is an element effective in improving the strength of steel plates. The W content may be 0%, but to obtain such an effect, it is preferable that the W content be 0.001% or more. The W content may be 0.005% or more, 0.01% or more, or 0.05% or more. On the other hand, if the W content is excessive, the weldability may decrease. Therefore, it is preferable that the W content be 1.00% or less. The W content may be 0.80% or less, 0.60% or less, 0.40% or less, or 0.20% or less.

[0039] [Ta: 0~0.10%] Ta (Ta) is an element effective in improving the strength of steel sheets. While the Ta content may be 0%, it is preferable that the Ta content be 0.001% or higher to obtain these effects. The Ta content may also be 0.005% or higher, 0.01% or higher, or 0.02% or higher. On the other hand, if the Ta content is excessive, the effect will saturate, and including more Ta than necessary in the steel sheet will lead to increased manufacturing costs. Therefore, it is preferable that the Ta content be 0.10% or lower. The Ta content may also be 0.08% or lower, 0.06% or lower, 0.04% or lower, or 0.02% or lower.

[0040] [Co: 0~1.00%] Co is an effective element for improving the strength of steel sheets. While the Co content may be 0%, it is preferable that the Co content be 0.001% or more to obtain such an effect. The Co content may also be 0.005% or more, 0.01% or more, or 0.05% or more. On the other hand, excessive Co content may reduce hot workability and lead to increased raw material costs. Therefore, it is preferable that the Co content be 1.00% or less. The Co content may also be 0.80% or less, 0.60% or less, 0.40% or less, or 0.20% or less.

[0041] [Sb: 0~0.200%] Sb is an element that can be contained in steel sheets when scrap is used as a raw material. Furthermore, Sb can strongly segregate at grain boundaries, potentially leading to embrittlement of the grain boundaries. For this reason, a lower Sb content is preferable, preferably 0.200% or less. The Sb content may also be 0.100% or less, 0.040% or less, or 0.020% or less. The Sb content may be 0%, but reducing the Sb content to less than 0.001% would lead to an excessive increase in refining costs. For this reason, the Sb content may be 0.001% or more, 0.005% or more, or 0.010% or more.

[0042] [Ca: 0~0.0500%] Ca is an element that can control the morphology of nonmetallic inclusions. The Ca content may be 0%, but to obtain this effect, it is preferable that the Ca content be 0.0001% or more. The Ca content may be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if the Ca content is excessive, a large amount of Ca-containing sulfides will be formed, reducing the amount of Ti4C2S2 precipitated, which may reduce the formability of the material. Therefore, it is preferable that the Ca content be 0.0500% or less. The Ca content may be 0.0300% or less, 0.0250% or less, 0.0200% or less, 0.0150% or less, 0.0100% or less, 0.0080% or less, 0.0060% or less, 0.0040% or less, or 0.0020% or less.

[0043] [Mg: 0~0.0500%] Mg is an element that can control the morphology of nonmetallic inclusions. The Mg content may be 0%, but to obtain this effect, it is preferable that the Mg content be 0.0001% or more. The Mg content may be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if the Mg content is excessive, a large amount of Mg-containing sulfides will be formed, reducing the amount of Ti4C2S2 precipitated, which may reduce the formability of the material. Therefore, it is preferable that the Mg content be 0.0500% or less. The Mg content may be 0.0300% or less, 0.0250% or less, 0.0200% or less, 0.0150% or less, 0.0100% or less, 0.0080% or less, 0.0060% or less, 0.0040% or less, or 0.0020% or less.

[0044] [Zr:0~0.5000%] Zr is an element that can control the morphology of nonmetallic inclusions. The Zr content may be 0%, but to obtain such an effect, it is preferable that the Zr content be 0.001% or more. The Zr content may be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if the Zr content is excessive, the effect will saturate, and including more Zr in the steel sheet than necessary will lead to an increase in manufacturing costs. Therefore, it is preferable that the Zr content be 0.5000% or less. The Zr content may be 0.3000% or less, 0.1000% or less, 0.0500% or less, 0.0300% or less, 0.0100% or less, 0.0080% or less, 0.0060% or less, 0.0040% or less, or 0.0020% or less.

[0045] [REM:0~0.0100%] REM is an element that can control the morphology of nonmetallic inclusions. The REM content may be 0%, but to obtain such an effect, it is preferable that the REM content be 0.0001% or more. The REM content may also be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if the REM content is excessive, a large amount of REM-containing sulfides will be formed, reducing the amount of Ti4C2S2 precipitated, which may reduce the formability of the material. Therefore, it is preferable that the REM content be 0.0100% or less. The REM content may also be 0.0080% or less, 0.0060% or less, 0.0040% or less, or 0.0020% or less. In this specification, REM refers to the collective term for 17 elements, including scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and the lanthanides from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. The REM content is the total content of these elements.

[0046] [Bi: 0~0.0500%] Bi is an element that enhances formability by refining the solidification structure. While the Bi content may be 0%, it is preferable that the Bi content be 0.0001% or higher to obtain this effect. The Bi content may also be 0.0002% or higher, 0.0005% or higher, or 0.0010% or higher. On the other hand, if Bi is included in excess, the effect will saturate, and including more Bi than necessary in the steel sheet will lead to an increase in manufacturing costs. Therefore, it is preferable that the Bi content be 0.0500% or lower. The Bi content may also be 0.0400% or lower, 0.0200% or lower, 0.0100% or lower, or 0.0050% or lower.

[0047] [As: 0~0.10%] As is an element that can be contained in steel sheets when scrap is used as a raw material. As is also an element that strongly segregates at grain boundaries, and a lower As content is preferable. The As content is preferably 0.10% or less. The As content may be 0.08% or less, 0.06% or less, 0.04% or less, or 0.02% or less. The As content may be 0%, but reducing the As content to less than 0.001% would lead to an excessive increase in refining costs. For this reason, the As content may be 0.001% or more, 0.005% or more, or 0.01% or more.

[0048] In the steel sheet according to the embodiment of the present invention, the remainder of the elements other than those mentioned above consists of Fe and impurities. Impurities include components that are mixed in during the industrial production of steel sheets due to various factors in the manufacturing process, such as raw materials like ore and scrap, and components that are included in a range that does not affect the effects of the present invention.

[0049] [[Ti]-[N]×47.88 / 14≧([N]-0.0021) 0.4 [×0.23] The chemical composition of the steel sheet according to the embodiment of the present invention must satisfy the following formula (1). [Ti]-[N]×47.88 / 14≧([N]-0.0021) 0.4 ×0.23...Equation (1) However, [Ti] and [N] represent the content (mass%) of Ti and N, respectively. In the steel sheet according to the embodiment of the present invention, it is important to make the effective Ti amount corresponding to the left side of the above formula (1) higher than a predetermined value. As explained above, the inventors have confirmed that when the effective Ti amount is the same, the higher the N content, the less likely Ti4C2S2 is to precipitate. Therefore, in a steel sheet with a relatively high N content, if there is not enough Ti, Ti4C2S2 precipitates are less likely to precipitate, so the solid-solution C remains unconsumed, and as a result, the formability of the deep drawing decreases. The lower limit of the effective Ti amount required for the steel sheet is a value determined by the N content, and more specifically, it is the right side of the above formula (1) ([N]-0.0021). 0.4This value is calculated from ×0.23, and as the N content increases, the lower limit of the effective Ti content increases. By controlling Ti and N to satisfy the above equation (1), or more specifically, by controlling the effective Ti content (left side of the above equation (1)) to be higher than the value determined by the N content (right side of the above equation (1)), even in steel sheets with a relatively high N content, the Ti content necessary for sufficient precipitation of Ti4C2S2 can be secured, and the dissolved C precipitates as Ti4C2S2, making it possible to reduce the amount of dissolved C. As a result, the r value improves, thereby improving the formability of the deep drawing.

[0050] [0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650] The chemical composition of the steel sheet according to the embodiment of the present invention must satisfy the following (2). 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650...Equation (2) However, [Cu], [Ni], [Cr], and [Sn] represent the mass percentage of Cu, Ni, Cr, and Sn. Cu, Ni, Cr, and Sn are elements that may be present in steel sheets when scrap is used as a raw material. If the content of these elements is too high, fine precipitates, such as Ti and / or Nb carbides, may form. Such fine precipitates may prevent sufficient grain growth in the metal structure during annealing, thereby reducing the formability of the deep drawing. However, the degree to which these elements influence the refinement of precipitates differs depending on the type of element. For example, Sn tends to form fine precipitates relatively easily, while Cr does not tend to form fine precipitates relatively easily. Therefore, the sum of the values ​​obtained by multiplying the content of Cu, Ni, Cr, and Sn by coefficients corresponding to their degree of influence should be 0.650 or less, i.e., 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650. The above sum may be 0.500 or less, 0.400 or less, 0.300 or less, or 0.200 or less. The lower limit of the above total value is not particularly limited, but it may be 0.060 or higher, 0.080 or higher, or 0.100 or higher.

[0051] The chemical composition of the steel sheet according to the embodiment of the present invention can be measured by general analytical methods. For example, the chemical composition of the steel sheet can be measured using inductively coupled plasma-atomic emission spectrometry (ICP-AES). C and S can be measured using the combustion-infrared absorption method, N can be measured using the inert gas fusion-thermal conductivity method, and O can be measured using the inert gas fusion-nondispersive infrared absorption method.

[0052] [Metal structure] [Number density of Ti4C2S2: 0.06 particles / μm] 2 [End] In the steel sheet according to an embodiment of the present invention, the number density of Ti4C2S2 is 0.06 particles / μm 2 The above explains the process. The formation of Ti4C2S2 consumes the dissolved carbon, reducing the amount of dissolved carbon, improving the r value, and thereby improving the draw-molding properties. Similarly, from the viewpoint of improving draw-molding properties, a higher number density of Ti4C2S2 is preferable, with a number density of 0.10 particles / μm 2 More than 0.15 pieces / μm 2 More than 0.20 pieces / μm 2 More than or equal to 0.25 particles / μm 2 The above is also acceptable. On the other hand, there is no particular upper limit to the number density of Ti4C2S2, which is 1.00 particles / μm 2 Less than or equal to 0.50, pieces / μm 2 The following is also acceptable.

[0053] [Measurement of the number density of Ti4C2S2] The average circle equivalent diameter and number density of Ti4C2S2 particles are measured by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). First, the SPEED method (selective potential-constant electrolytic etching) is used from the 1 / 4 thickness position of the steel plate to obtain a value of 10 coulombs / cm² at -100mV vs. SCE. 2Etching is performed under these conditions, and the precipitate is extracted into a carbon film and held on a Cu mesh. Then, using the prepared extracted replica sample, the observation area of ​​one field of view is 5 μm, using a TEM with EDS at a magnification of 30,000x or more. 2 Next, the precipitates were observed. In the SPEED electropolishing method, 10% acetylacetone-1% tetramethylammonium chloride-methanol was used as the electropolishing solution. Of the observed precipitates, those with an equivalent circle diameter of 100 nm or less were analyzed using EDS. Precipitates in which peaks for Ti, C, and S were observed, and where the maximum peak height of Ti was 1.1 times or more than the maximum peak height of S, were identified as Ti4C2S2. If precipitates were found in combination, each precipitate was analyzed using EDS. If peaks for Ti, C, and S were observed in each precipitate, and the maximum peak height of Ti was 1.1 times or more than the maximum peak height of S, each precipitate was identified as Ti4C2S2.

[0054] Here, with a magnification of 30,000 times or more, the observation area of ​​one field of view is 5 μm. 2 Based on the above, observations were made to ensure that there were at least 20 precipitates with a total size of 100 nm or less in five or more fields of view, and the number of Ti4C2S2 particles was calculated. The number density of Ti4C2S2 particles is the value obtained by dividing the number of individual Ti4C2S2 particles identified as described above by the area of ​​the observed field of view.

[0055] [X {111} / X {001} [20.0 or higher] In a steel sheet according to a preferred embodiment of the present invention, the average random strength ratio X of {001} {001} {111} <112> Directional random intensity ratio X {111} Ratio (X {111} / X {001} ) is 20.0 or higher. As explained earlier, in order to improve the r value as an indicator of deep drawability, it is known that the texture can be controlled to increase the random intensity ratio of {111} and / or to decrease the random intensity ratio of {001}. Therefore, X {111} / X {001}It is preferably 20.0 or higher, and may be 22.0 or higher or 24.0 or higher. On the other hand, X {111} / X {001} While a larger value is preferable, it may be 100.0 or less, 80.0 or less, 60.0 or less, or 40.0 or less.

[0056] [X {111} / X {001} [Calculation of] {001}Random intensity ratio of average direction X {001} and {111} <112> Directional random intensity ratio X {111} This is measured by electron backscattered diffraction (EBSD). More specifically, X {001} and X {111}The orientation is determined as follows: A sample is taken from a steel plate so that the thickness cross section perpendicular to the plate surface becomes the observation surface. In displaying the crystal orientation distribution, the orientation within the plate surface is generally based on the rolling direction of the steel plate. Therefore, in order to determine the crystal orientation including the orientation within the plate surface, it is necessary to specify the rolling direction of the steel plate during orientation analysis. However, if the rolling direction of the steel plate cannot be determined, the rolling direction is determined by the following procedure. In the orientation analysis results described later, if the direction perpendicular to the plate surface and parallel to the thickness cross section of the observation sample (generally the direction specified as the rolling direction in orientation analysis) is not parallel or perpendicular to the true rolling direction, the sum of the random intensity ratios for Φ=0~45° other than φ1=0° or φ1=90° will be greater than the sum of the random intensity ratios for φ1=0°, Φ=0~45° (A) or the sum of the random intensity ratios for φ1=90°, Φ=0~45° (B). In this case, the random intensity ratio is measured by slightly shifting the direction of cross-section sampling, and the direction in which the sum of random intensity ratios for φ1=0 or φ1=90° is maximized is searched for. The direction perpendicular to the plate surface and parallel to the plate thickness cross-section in the observation sample with the maximum sum can be identified as the direction parallel or perpendicular to the true rolling direction. Furthermore, in the orientation analysis results of the observation sample with the maximum sum of random intensity ratios, random intensity ratio (A) and random intensity ratio (B) are compared. If (A)>(B), the measured cross-section is perpendicular to the rolling width direction, and if (A)<(B), the measured cross-section is perpendicular to the rolling direction. This ultimately identifies the rolling direction. The sum of random intensity ratios can be calculated by calculating the random intensity ratio at Φ=0, 5, 10, etc., every 5° and adding them up. The sample length should be approximately 10mm to 25mm. From the surface of the sample, at positions 1 / 8 to 7 / 8 of the plate thickness, the thickness is 600,000 μm. 2The crystal orientation information is obtained by measuring the range using EBSD at measurement intervals of 2.0 μm. Here, the EBSD analysis is performed using a device consisting of, for example, a thermal field emission scanning electron microscope (JEOL JSM-7001F) and an EBSD detector (TSL DVC5 detector), with an electron beam acceleration voltage of 15 kV to 25 kV and an analysis speed of 200 to 300 points / second. The crystal orientation is calculated by the degree of accumulation of each crystal orientation on the Crystallite Orientation Distribution Function (ODF) of a φ2 = 45° cross section, which is created based on the crystal orientation data obtained by EBSD measurement. Here, the measurement is performed on a cross section perpendicular to the rolling width direction, but the ODF is obtained by converting the crystal orientation data obtained on that cross section to a direction perpendicular to the plate surface.

[0057] Since ODF is also used to indicate the orientation of crystal structures with low symmetry, it is generally expressed as φ1=0~360°, Φ=0~180°, and φ2=0~360°, with each orientation represented by (hkl)[uvw]. However, in the steel sheet according to the embodiment of the present invention, a highly symmetric bcc crystal structure is targeted, so Φ and φ2 are expressed in the range of 0~90°.

[0058] Furthermore, the range of φ1 changes depending on whether or not symmetry due to deformation is considered when performing the calculation, but in the steel sheet according to the embodiment of the present invention, φ1 is expressed as φ1 = 0 to 90° after considering the symmetry of rolling deformation. In the steel sheet according to the embodiment of the present invention, the average value of the values ​​calculated in 5° increments within the range of Φ = 0° and φ1 = 0 to 90° is {001} Random strength ratio of average orientation X {001} It will be adopted as such. Similarly, {111} <112> Directional random intensity ratio X {111} This is the average of the random intensity ratios for "φ1=30°, Φ=55°" and "φ1=90°, Φ=55°".

[0059] When creating the ODF, we will use "OIM Analysis," an analysis software from TSL Corporation, and perform the analysis under the following conditions. Calculation Method:Harmonic Series Expansion Series Rank[L]:16 Gaussian Half-Width[degrees]:5 Sample Symmetry:Orthotropic(Rolled) sheet)

[0060] [Preferred average grain size of steel sheet] As described above, the present invention aims to provide a steel sheet containing Ni, Cu, Cr, and Sn, with a high N content, that has excellent deep draw formability, and a part containing the same, by controlling the chemical composition to have a predetermined chemical composition, and having a number density of Ti4C2S2 of 0.06 particles / μm 2 The objective is achieved by controlling the grain size to be as described above. Therefore, it is clear that the average grain size is not an essential technical feature for achieving the objective of the present invention. The preferred average grain size of a steel sheet according to the embodiment of the present invention will be described in detail below, but these descriptions are intended to be merely illustrative examples of preferred average grain sizes of steel sheets and are not intended to limit the present invention to steel sheets having such specific average grain sizes.

[0061] [Average grain size: 10.0μm or more] The average grain size of the steel sheet according to the embodiment of the present invention, more specifically the average grain size of ferrite, may be 10.0 μm or more. The larger the average grain size, the higher the r value, which in turn improves the formability of the drawing. Therefore, the average grain size of the steel sheet is preferably 10.0 μm or more, and may be 11.0 μm or more, 12.0 μm or more, 13.0 μm or more, 14.0 μm or more, or 15.0 μm or more. On the other hand, if the average grain size of the steel sheet is too large, it can lead to deterioration of the toughness and surface quality of the processed part, so it may be 30.0 μm or less, 25.0 μm or less, or 20.0 μm or less.

[0062] [Measurement of average crystal grain size] The average crystal grain size is X {111} / X{001} Similar to the calculation, this is performed using EBSD and the analysis software "OIM Analysis ver7.3.1" manufactured by TSL. A region enclosed by a grain boundary, which is the boundary between regions where the crystal orientations differ by 15° or more, is defined as a crystal grain. Next, the equivalent circle diameter obtained by the Area Fraction method is determined as the average crystal grain size of the ferrite.

[0063] [plate thickness] The steel sheet according to the embodiment of the present invention is not particularly limited, but for example, it has a thickness of 0.1 to 2.0 mm. The thickness may be 0.2 mm or more, 0.3 mm or more, or 0.4 mm or more. Similarly, the thickness may be 1.8 mm or less, 1.5 mm or less, 1.2 mm or less, or 1.0 mm or less. For example, by setting the thickness to 0.2 mm or more, it becomes easier to maintain the flatness of the molded product shape, and additional effects such as improved dimensional accuracy and shape accuracy can be obtained. On the other hand, by setting the thickness to 1.0 mm or less, the effect of reducing the weight of the part becomes significant. The thickness of the steel sheet is measured with a micrometer.

[0064] [plating] The steel sheet according to the embodiment of the present invention may further include a plating layer on its surface for the purpose of improving corrosion resistance, etc. The plating layer may be either a hot-dip galvanized layer or an electroplated layer. In other words, the steel sheet according to the embodiment of the present invention may be a steel sheet having a hot-dip galvanized layer or an electroplated layer on its surface. Examples of the hot-dip galvanized layer include a hot-dip galvanized layer (GI), an alloyed hot-dip galvanized layer (GA), a hot-dip aluminum galvanized layer, a hot-dip Zn-Al alloy galvanized layer, a hot-dip Zn-Al-Mg alloy galvanized layer, a hot-dip Zn-Al-Mg-Si alloy galvanized layer, etc. Examples of the electroplated layer include an electroplated zinc galvanized layer (EG), an electroplated Zn-Ni alloy galvanized layer, etc. Preferably, the plating layer is a hot-dip galvanized layer, an alloyed hot-dip galvanized layer, or an electroplated zinc galvanized layer. The amount of the plating layer is not particularly limited and may be a general amount.

[0065] The steel sheet according to the embodiment of the present invention can achieve excellent deep drawing formability even when the steel sheet contains four elements, Cu, Ni, Cr, and Sn, simultaneously and has a high nitrogen content. For this reason, the steel sheet according to the embodiment of the present invention is particularly useful for use in parts in technical fields where such properties are required. In preferred embodiments, exterior members, particularly automobile exterior members, and containers, particularly battery containers, are provided, including the steel sheet according to the embodiment of the present invention. Examples of automobile exterior members include roofs, hoods, fenders, and doors. These parts only need to include the steel sheet according to the embodiment of the present invention in at least a portion of them, and therefore at least a portion of these parts will satisfy the chemical composition and microstructure characteristics described above. In parts of the steel sheet that undergo relatively little processing during forming, such as press forming, the microstructure characteristics do not change particularly before and after forming.

[0066] [Mechanical properties] [Tensile Strength (TS)] The tensile strength (TS) of the steel sheet according to the embodiment of the present invention may be, for example, 270 MPa or more or 340 MPa or more. The upper limit of the tensile strength is not particularly limited, but may be 590 MPa or less, 540 MPa or less, or 490 MPa or less. The tensile strength is measured by taking a No. 5 tensile test specimen of JIS Z2241:2022 from the steel sheet with the test direction parallel to the rolling direction, and performing a tensile test in accordance with JIS Z2241:2022.

[0067] <Method of manufacturing steel plates> Next, preferred manufacturing methods for steel sheets according to embodiments of the present invention will be described. The following description is intended to illustrate characteristic methods for manufacturing steel sheets according to embodiments of the present invention, and is not intended to limit the steel sheets to those manufactured by the manufacturing methods described below. Steel sheets according to embodiments of the present invention can be manufactured, for example, by a casting step of casting molten steel with an adjusted chemical composition to form a slab, a hot rolling step of hot rolling the slab to obtain a hot-rolled steel sheet, a pickling step of pickling the obtained hot-rolled steel sheet, a cold rolling step of cold rolling the pickled hot-rolled steel sheet, and an annealing step of annealing the obtained cold-rolled steel sheet. Each step will be described in detail below.

[0068] [Casting Process] The conditions for the casting process are not particularly limited. For example, after melting in a blast furnace or electric furnace, various secondary smelting processes may be carried out, and then a slab having the chemical composition described above in relation to steel plates may be cast by methods such as conventional continuous casting or ingot casting.

[0069] [Hot rolling process] [Slab heating] First, a slab having the chemical composition described above in relation to the steel plate is heated. From the viewpoint of productivity, the slab to be used is preferably cast by a continuous casting method, but it may also be manufactured by an ingot casting method or a thin slab casting method. If the heating temperature of the slab is low, not only will the dissolution of carbides and the like be insufficient, but the finishing temperature will also be low, so the heating temperature is preferably 1100°C or higher, and more preferably 1200°C or higher. There is no particular upper limit to the heating temperature, but from the viewpoint of the capacity of the heating equipment and productivity, it is preferably 1300°C or lower.

[0070] [Sizing Press] [(a-1)S / t≧0.06] The heated slab may be subjected to a sizing press before rough rolling to adjust the slab width, etc. From the viewpoint of promoting the precipitation of Ti4C2S2 in the austenite region at high temperatures, it is preferable that the following formula is satisfied during the sizing press. S / t≧0.06, and S=100×(L0-L1) / L0 In the formula, L0 is the slab width (mm) before width reduction by sizing press, L1 is the slab width (mm) after width reduction by sizing press, and t is the time (seconds) from when the slab is extracted from the hot rolling furnace until the sizing press begins. In order to precipitate Ti4C2S2 using strain-induced precipitation at high temperatures, it is important to introduce a lot of strain into the slab when it is at a high temperature, specifically when it is extracted from the hot rolling furnace and subjected to sizing press and / or rough rolling. From the viewpoint of introducing a lot of strain, it is preferable to control the amount of width reduction (L0-L1) (mm) to the slab width (L0) (mm) before width reduction to be large, that is, to control it so that S is large. Also, in order to perform sizing press at a high temperature, it is preferable to sizing press the slab extracted from the hot rolling furnace in a short time, that is, it is preferable to control it so that t is small. Therefore, it is preferable to control the process so that S is large and t is small, that is, so that S / t is large, more specifically so that S / t ≥ 0.06. S / t may be 0.08 or greater, 0.10 or greater, or 0.12 or greater. There is no particular upper limit to S / t, but it may be 0.30 or less, 0.25 or less, or 0.20 or less. By controlling the process in this way, the precipitation of Ti4C2S2 is promoted by introducing a large amount of strain at high temperatures, and as a result, the number density of Ti4C2S2 in the final steel sheet is 0.06 particles / μm 2 It becomes possible to satisfy the above conditions.

[0071] [Rough rolling] [(a-2)(2×R1+R2) / ΔT1≧2.0] The heated slab or sizing-pressed slab is then subjected to rough rolling. Rough rolling may be carried out using a reverse rolling mill. From the viewpoint of promoting the precipitation of Ti4C2S2 in the austenite region at high temperatures, it is preferable that the following formula is satisfied during rough rolling. (2×R1+R2) / ΔT1≧2.0 In the formula, R1 is the reduction ratio (%) of the first pass in rough rolling, R2 is the reduction ratio (%) of the second pass in rough rolling, and ΔT1 is the temperature drop from the temperature of the first pass to the temperature of the second pass. As explained above, since Ti4C2S2 is precipitated by strain-induced precipitation at high temperatures, it is preferable to perform rough rolling at high temperatures, that is, to reduce the temperature drop (ΔT1) between the first and second passes. When ΔT1 is reduced, the right-hand side of the above formula becomes larger. Therefore, it is preferable to reduce ΔT1 while controlling the reduction ratio (R1) of the first pass to increase in proportion to ΔT1. Accordingly, it is preferable to control it so that (2×R1+R2) / ΔT1≧2.0 is satisfied. By controlling it in this way, a large amount of strain can be introduced at high temperatures, promoting the precipitation of Ti4C2S2, and as a result, the number density of Ti4C2S2 in the final steel sheet is 0.06 particles / μm 2 It becomes possible to satisfy the above conditions.

[0072] The hot rolling process is crucial for controlling the amount of Ti4C2S2. By satisfying (a-1) or (a-2) described above, strain-induced precipitation of Ti4C2S2 at high temperatures is promoted, resulting in a Ti4C2S2 number density of 0.06 particles / μm 2 The above can be achieved. In addition, by satisfying (a-1) and (a-2), the precipitation of Ti4C2S2 is further promoted, and as a result, more coarser Ti4C2S2 is precipitated, specifically, the number density of Ti4C2S2 is 0.20 particles / μm 2 You can obtain the above.

[0073] [Finishing Rolling] The roughly rolled slab is then subjected to finish rolling. The conditions for finish rolling, such as the temperature and reduction ratio, are not particularly limited and can be appropriately determined according to the desired microstructure and thickness. For example, the final temperature of finish rolling may be 850 to 1050°C, and the reduction ratio of each pass in finish rolling may be 10 to 50%.

[0074] [Cooling and winding] Next, the finish-rolled steel sheet is cooled to 780°C or lower at an average cooling rate of 20°C / second or more and then wound up. If the average cooling rate is less than 20°C / second or the winding temperature is above 780°C, the grain size of the hot-rolled steel sheet may become coarse, which may degrade the formability of the product. For example, an average cooling rate of 25°C / second or higher is preferable, and a winding temperature of 750°C or lower is preferable.

[0075] [Pickling process] Next, the obtained hot-rolled steel sheet is pickled to remove the oxide scale formed on its surface. The pickling can be carried out under conditions suitable for removing the oxide scale, and may be done once or in multiple steps to ensure complete removal.

[0076] [Cold rolling process] Pickled hot-rolled steel sheets are cold-rolled in the cold-rolling process with a reduction ratio of 50-90%. If the cold-rolling reduction ratio is less than 50%, the generation of {111} oriented crystal grains that improve the r value will be insufficient, and the r value will decrease. On the other hand, if the cold-rolling reduction ratio exceeds 90%, the rolling load will be excessive, making rolling difficult. The number of rolling passes and the reduction ratio for each pass are not particularly limited and should be set appropriately so that the overall cold-rolling reduction ratio falls within the above range.

[0077] [Annealing process] The annealing process is an operation that includes heat treatment to adjust the microstructure and properties of cold-rolled steel sheets. The maximum heating temperature in the annealing process is not particularly limited, but may be, for example, 900°C or lower. On the other hand, the maximum heating temperature is 700°C or higher in order to complete recrystallization and improve the r value.

[0078] [(b-1)A=10000×h×σ t1 / {D×(805+0.001×T2 2 (-1.78 × T²) {<2.60] In the steel sheet manufacturing method according to a preferred embodiment of the present invention, the following formula is satisfied during the annealing process. A = 10000 × h × σ t1 / {D×(805+0.001×T2 2 (-1.78 × T²) {<2.60} In the formula, h is the plate thickness (mm), D is the roll diameter (mm), T2 is the maximum temperature reached (°C), and σ t1 σ is the tension (MPa) at the highest temperature reached. Generally, it is known that reducing plastic strain in the annealing process improves the r value. The larger h is, the more plastic strain can be stored. Also, σ t1 The larger h is, the greater the plastic strain in relation to the tension applied to the steel plate. Therefore, from the viewpoint of reducing plastic strain, h should be controlled to be small, and σ t1 It is preferable to control the values ​​so that they are also small. Therefore, the molecules h and σ in the middle are preferable. t1 It is preferable to control the product of to be small. Also, the larger T2 is, the lower the yield strain, and consequently the larger the plastic strain. The larger D is, the smaller the plastic strain. Therefore, from the viewpoint of reducing plastic strain, it is preferable to control T2 to be small and D to be large, and therefore it is preferable to control the denominator of the middle part to be large. From the above, it is preferable to control the numerator of the middle part to be small and the denominator of the middle part to be large, that is, 10000 × h × σ t1 / {D×(805+0.001×T2 2 It is preferable to control the system so that (-1.78 × T2) < 2.60. The lower limit of the left side of the above equation is not particularly limited, but may be 0.10 or more, 0.50 or more, 1.00 or more, or 1.20 or more.

[0079] [(b-2)σ t2 / σ t1 <1.50] In the steel sheet manufacturing method according to a preferred embodiment of the present invention, the following formula is satisfied during the annealing process. σ t2 / σ t1 <1.50 In the formula, σ t1 σ is the tension (MPa) at the highest temperature reached. t2σ is the average tension (MPa) in the temperature range of 500-700°C after reaching the maximum temperature. The above formula defines an upper limit on the ratio of the tension at the maximum temperature to the average tension in the temperature range of 500-700°C during cooling. As explained above, the r value improves by reducing plastic strain in the annealing process. On the other hand, the tension (σ) during cooling in the annealing process t2 ) is the tension at the highest temperature reached (σ) from the viewpoint of controlling the shape of the plate, etc. t1 It needs to be higher than ). If the tension during cooling is too high, the plastic strain will become excessively large. Therefore, in order to suppress the plastic strain from becoming excessively large, σ t1 / σ t2 Let it be <1.50.

[0080] In the annealing process, by satisfying (b-1) or (b-2) described above, plastic strain can be reduced, and as a result, in the steel sheet finally obtained, X {111} / X {001} It becomes possible to set it to 20.0 or higher.

[0081] [Plating process] To improve corrosion resistance and other properties, the surface of the obtained cold-rolled steel sheet may be plated as needed. The plating treatment may be hot-dip plating, alloying hot-dip plating, electroplating, etc. For example, the steel sheet may be hot-dip galvanized as a plating treatment, or an alloying treatment may be performed after hot-dip galvanizing. The specific conditions for the plating treatment and alloying treatment are not particularly limited and may be any appropriate conditions known to those skilled in the art. For example, the alloying temperature may be 450 to 600°C.

[0082] [Temper rolling] For purposes such as correcting the shape of the steel sheet or adjusting its surface roughness, temper rolling may be applied to the steel sheet after, for example, an annealing process or a plating process. The reduction ratio of temper rolling is preferably, for example, 1.0% or less.

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to these examples. [Examples]

[0084] First, molten steel was cast using a continuous casting method to form slabs with various chemical compositions as shown in Table 1. These slabs were heated to 1100-1300°C, sizing pressed as appropriate under the conditions shown in Table 2, and then hot-rolled. Hot rolling was carried out by rough rolling and finish rolling. More specifically, the conditions for rough rolling were as shown in Table 2, while the conditions for finish rolling and winding were the same for all examples and comparative examples. The obtained hot-rolled steel sheets were pickled, and then cold-rolled under the same conditions for all examples and comparative examples to obtain cold-rolled steel sheets with a thickness of 0.60-0.95 mm. Next, the obtained cold-rolled steel sheets were annealed under the conditions shown in Table 2. Finally, hot-dip galvanizing or electro-galvanizing was applied as appropriate, and some of these were further alloyed.

[0085] [Table 1]

[0086] [Table 2]

[0087] Table 2 shows the sizing press in the hot rolling process. In the table, t is the time (seconds) from when the slab is extracted from the hot rolling furnace until the sizing press begins, and S is the value calculated from 100 × (L0 - L1) / L0. Here, L0 is the slab width (mm) before width reduction by the sizing press, and L1 is the slab width (mm) after width reduction by the sizing press. In Table 2, a test example where S is 0% is a test example in which no sizing press treatment was performed.

[0088] In Table 2, for rough rolling in the hot rolling process, R1 is the reduction ratio (%) of the first pass in rough rolling, R2 is the reduction ratio (%) of the second pass in rough rolling, and ΔT1 is the temperature drop from the temperature of the first pass to the temperature of the second pass.

[0089] Regarding the annealing process in Table 2, σ in the table t1 σ is the tension (MPa) at the highest temperature reached, t2 σ is the average tension (MPa) in the temperature range of 500-700°C after reaching the maximum temperature. T2 is the maximum temperature reached (°C), h is the plate thickness (mm), and D is the roll diameter (mm). Also, A is 10000 × h × σ t1 / {D×(805+0.001×T2 2 This value is calculated from (-1.78 × T²).

[0090] Regarding the plating types in Table 2, GA in the table represents alloyed hot-dip galvanizing, GI represents hot-dip galvanizing, and EG represents electroplated zinc. On the other hand, regarding the plating types in Table 2, "None" in the table represents no plating treatment. Also, X {111} This is the random intensity ratio of the mean direction, X {001} is {111} <112> This is the random intensity ratio for each direction.

[0091] The properties of the obtained steel plates were measured and evaluated by the following method.

[0092] [Draw-down formability: Plastic strain ratio (r value)] The plastic strain ratio (r-value) was measured using three types of test specimens: one with the rolling direction as the longitudinal direction, one perpendicular to the rolling direction as the longitudinal direction, and one at a 45° angle to the rolling direction as the longitudinal direction. Measurements were taken for each specimen in accordance with the provisions of JIS Z 2254:2021. The average of the measured values ​​was calculated, and this average value was defined as the r-value.

[0093] [Tensile Strength (TS)] Tensile strength (TS) was measured by taking a JIS No. 5 test specimen, 200 mm in length and 2.5 mm in thickness, from the direction (C direction) where the longitudinal direction of the test specimen is parallel to the direction perpendicular to the rolling direction of the steel plate, and performing a tensile test in accordance with JIS Z 2241:2022. More specifically, the test was performed at room temperature in the range of 10 to 35°C, and a tensile test force was applied to the test specimen, allowing strain to be introduced until fracture occurred.

[0094] Conventional steel sheets, specifically Ti4C2S2, have a number density of 0.06 particles / μm 2 Steel sheets with an improved r-value compared to those with an r-value less than 1.0 were evaluated as having excellent deep-draw formability. Whether a steel is of the present invention cannot be determined solely by the absolute value of the r-value. For example, if applying the present invention to a steel type with an r-value of 1.0 using the conventional technology improves the r-value to 1.2, then the steel sheet with an r-value of 1.0 using the conventional technology is a comparative steel, and the steel sheet with an r-value of 1.2 is the steel of the present invention. Also, for example, if applying the present invention to a steel type with an r-value of 1.8 improves the r-value to 2.0, then the steel sheet with an r-value of 1.8 using the conventional technology is a comparative steel, and the steel sheet with an r-value of 2.0 is the steel of the present invention. It is important to note here that in the former case, the inventive steel with an r-value of 1.2 has a lower r-value than the comparative steel with an r-value of 1.8 in the latter case. In other words, the absolute value of the r-value itself varies over a fairly wide range due to factors other than the effect of the present invention, such as chemical composition, cold rolling reduction rate, and even the final annealing temperature (grain size). Therefore, when evaluating the effect of the present invention using the r-value, it is necessary to appropriately select the steel sheet to be compared. In the examples, in order to clearly demonstrate the effects of the present invention, two steel plates were manufactured such that only the provisions of the present invention were primarily changed, and the improvement in the r value between them was confirmed.

[0095] Examples 1 and Comparative Example 2 are steel sheets made of steel A that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 2, the number density of Ti4C2S2 is 0.06 particles / μm 2When the value was less than , the r value was 1.4. In Comparative Example 2, both the sizing press and rough rolling did not meet the specified conditions, so the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 1, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.4. Therefore, in Example 1, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0096] Examples 3 and Comparative Example 4 are steel sheets made of steel B that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 4, the number density of Ti4C2S2 is 0.06 particles / μm 2 When the value was less than , the r value was 1.5. In Comparative Example 4, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 3, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.5. Therefore, in Example 3, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0097] Examples 5-8 and Comparative Example 9 are steel sheets made of steel C that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 9, the number density of Ti4C2S2 is 0.06 particles / μm 2When the value was less than , the r value was 1.4. In Comparative Example 9, both the sizing press and rough rolling did not meet the specified conditions, so the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Examples 5 to 8, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 As a result, steel plates meeting the above criteria were obtained, and the r value was higher than 1.4. Therefore, in Examples 5 to 8, despite containing Ni, Cu, Cr, and Sn, and having a high N content, the materials exhibited excellent deep drawing formability.

[0098] Examples 10 and Comparative Example 11 are steel sheets made of steel D that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 11, the number density of Ti4C2S2 is 0.06 particles / μm 2 When the value was less than , the r value was 1.5. In Comparative Example 11, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 10, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.5. Therefore, Example 10 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0099] Examples 12 and Comparative Example 13 are steel sheets made of steel E that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and neither has a plating layer. As in Comparative Example 13, the number density of Ti4C2S2 is 0.06 particles / μm 2When it was less, the r value was 1.7. In Comparative Example 13, since both the sizing press and the rough rolling did not satisfy the predetermined conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperature, and it is considered that the number density of Ti4C2S2 became low in the finally obtained steel sheet. In contrast, in Example 12, by appropriately controlling each condition in the manufacturing method, a steel sheet having a number density of Ti4C2S2 of 0.06 particles / μm 2 or more could be obtained, and as a result, the r value became higher than 1.7. Therefore, in Example 12, although it contained Ni, Cu, Cr, and Sn and had a high N content, it had excellent drawing formability.

[0100] Regarding Example 14 and Comparative Example 15, they are steel sheets made of Steel F that satisfy the requirements of the chemical composition of the steel sheet according to the embodiment of the present invention, and each has a GI layer. When the number density of Ti4C2S2 is less than 0.06 particles / μm 2 as in Comparative Example 15, the r value was 1.5. In Comparative Example 15, since both the sizing press and the rough rolling did not satisfy the predetermined conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperature, and it is considered that the number density of Ti4C2S2 became low in the finally obtained steel sheet. In contrast, in Example 14, by appropriately controlling each condition in the manufacturing method, a steel sheet having a number density of Ti4C2S2 of 0.06 particles / μm 2 or more could be obtained, and as a result, the r value became higher than 1.5. Therefore, in Example 1, although it contained Ni, Cu, Cr, and Sn and had a high N content, it had excellent drawing formability.

[0101] Regarding Example 16 and Comparative Example 17, they are steel sheets made of Steel G that satisfy the requirements of the chemical composition of the steel sheet according to the embodiment of the present invention, and each has an EG layer. When the number density of Ti4C2S2 is less than 0.06 particles / μm 2When the value was less than , the r value was 1.4. In Comparative Example 17, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 16, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.4. Therefore, Example 16 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0102] Examples 18 and Comparative Example 19 are steel sheets made of steel H that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 19, the number density of Ti4C2S2 is 0.06 particles / μm 2 When the value was less than , the r value was 1.4. In Comparative Example 19, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 18, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.4. Therefore, Example 18 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0103] Examples 20 and Comparative Example 21 are steel sheets made of steel I that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 21, the number density of Ti4C2S2 is 0.06 particles / μm 2When it was less than that, the r value was 1.1. In Comparative Example 21, since both the sizing press and the rough rolling did not satisfy the predetermined conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperature, and it is considered that the number density of Ti4C2S2 became low in the finally obtained steel sheet. In contrast, in Example 20, by appropriately controlling each condition in the manufacturing method, a steel sheet having a number density of Ti4C2S2 of 0.06 particles / μm 2 or more was obtained, and as a result, the r value became higher than 1.1. Therefore, in Example 20, although it contained Ni, Cu, Cr, and Sn and had a high N content, it had excellent drawing formability.

[0104] Regarding Examples 22 to 24 and Comparative Example 25, they are steel sheets made of Steel J that satisfy the requirements for the chemical composition of the steel sheet according to the embodiment of the present invention, and each has a GA layer. When the number density of Ti4C2S2 was less than 0.06 particles / μm as in Comparative Example 25 2 the r value was 1.3. In Comparative Example 25, since both the sizing press and the rough rolling did not satisfy the predetermined conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperature, and it is considered that the number density of Ti4C2S2 became low in the finally obtained steel sheet. In contrast, in Examples 22 to 24, by appropriately controlling each condition in the manufacturing method, a steel sheet having a number density of Ti4C2S2 of 0.06 particles / μm 2 or more was obtained, and as a result, the r value became higher than 1.3. Therefore, in Examples 22 to 24, although it contained Ni, Cu, Cr, and Sn and had a high N content, it had excellent drawing formability.

[0105] Regarding Example 26 and Comparative Example 27, they are steel sheets made of Steel K that satisfy the requirements for the chemical composition of the steel sheet according to the embodiment of the present invention, and each has a GA layer. When the number density of Ti4C2S2 was less than 0.06 particles / μm as in Comparative Example 27 2When the value was less than , the r value was 1.3. In Comparative Example 27, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 26, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.3. Therefore, Example 26 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0106] Examples 28 and Comparative Example 29 are steel sheets made of steel L that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 29, the number density of Ti4C2S2 is 0.06 particles / μm 2 When the value was less than , the r value was 1.3. In Comparative Example 29, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 28, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.3. Therefore, Example 28 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0107] Examples 30-32 and Comparative Example 33 are steel sheets made of steel M that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 33, the number density of Ti4C2S2 is 0.06 particles / μm 2When the value was less than , the r value was 1.3. In Comparative Example 33, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Examples 30 to 32, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.3. Therefore, in Examples 30-32, despite containing Ni, Cu, Cr, and Sn, and having a high N content, excellent deep draw formability was achieved. In particular, it possessed the specified chemistry, and the number density of Ti4C2S2 particles was 0.06 particles / μm. 2 In addition to the above, X {111} / X {001} In Examples 30 and 31, where the r value was controlled to satisfy a value of 20.0 or higher, the r value was further improved, and the deep drawing properties were even better.

[0108] Examples 34 and Comparative Example 35 are steel sheets made of steel N that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and neither has a plating layer. As in Comparative Example 35, the number density of Ti4C2S2 is 0.06 particles / μm 2 When the value was less than , the r value was 1.7. In Comparative Example 35, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 34, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.7. Therefore, Example 34 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0109] Examples 36 and Comparative Example 37 are steel sheets made of steel O that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has a GA layer. As in Comparative Example 37, the number density of Ti4C2S2 is 0.06 particles / μm 2 When the value was less than , the r value was 1.4. In Comparative Example 37, since both the sizing press and rough rolling did not meet the specified conditions, the precipitation of Ti4C2S2 was not promoted by strain-induced precipitation at high temperatures, and it is thought that the number density of Ti4C2S2 in the final steel sheet was low. In contrast, in Example 36, by appropriately controlling each condition in the manufacturing method, the number density of Ti4C2S2 was 0.06 particles / μm 2 A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.4. Therefore, Example 36 exhibited excellent deep drawing formability despite containing Ni, Cu, Cr, and Sn, and having a high N content.

[0110] Comparative Example 40, due to its high carbon content, showed an increased amount of solid-solution carbon and a lower r value compared to Example 1, which had the same chemical composition other than carbon and was manufactured using the same method. Comparative Example 41: [Ti]-[N]×47.88 / 14≧([N]-0.0021) 0.4 In Comparative Example 43, the requirement of ×0.23 was not met, and despite a relatively high N content, there was insufficient Ti, resulting in insufficient precipitation of Ti4C2S2. This is thought to have led to a low number density of Ti4C2S2 in the final steel sheet. In Comparative Example 43, the requirement of 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650 was not met. Compared to Example 1, which had the same chemical composition other than Cu, Ni, Cr, and Sn, and the same manufacturing method, fine precipitates were formed, and grain growth in the metal structure did not proceed sufficiently during annealing. As a result, the r value decreased. In cases where the four elements Cu, Ni, Cr, and Sn are not simultaneously present, or when the N content is relatively low, as in Reference Examples 42 and 44, a decrease in deep draw formability is not a particular concern.

Claims

1. In mass percent, C: 0.0005 to 0.0050%, Mn: 0.01 to 1.50%, Si: 0.002 to 0.500%, P: 0.100% or less, S: 0.0010-0.0200%, Al: 1.000% or less, N: 0.0026-0.0150%, O: 0.0100% or less, Ti: 0.015-0.150%, Ni: 0.04-1.00%, Cu: 0.04-1.00%, Cr: 0.04-1.00%, Sn: 0.004-0.100%, Nb: 0 to 0.050%, Mo: 0 to 0.50%, B: 0 to 0.0100%, V: 0 to 0.500%, W: 0-1.00%, Ta: 0-0.10%, Co: 0-1.00%, Sb: 0 to 0.200%, Ca: 0-0.0500%, Mg: 0 to 0.0500%, Zr: 0 to 0.5000%, REM: 0-0.0100%, Bi: 0-0.0500%, As: 0-0.10%, and The remainder consists of Fe and impurities. Having a chemical composition that satisfies the following formulas (1) and (2), Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel plate characterized by having the above-mentioned metallic structure. [Ti] - [N] × 47.88 / 14 ≥ ([N] - 0.0021) ０．４ × 0.23 ··· Formula (1) However, [Ti] and [N] represent the content (mass%) of Ti and N, respectively. 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≦0.650...Formula (2) However, [Cu], [Ni], [Cr], and [Sn] represent the content (mass%) of Cu, Ni, Cr, and Sn.

2. The aforementioned chemical composition is, in mass%, Nb: 0.001 to 0.050%, Mo: 0.001 to 0.50%, B: 0.0001 to 0.0100%, V: 0.001-0.500%, W: 0.001-1.00%, Ta: 0.001 to 0.10%, Co: 0.001 to 1.00%, Sb: 0.001-0.200%, Ca: 0.0001-0.0500%, Mg: 0.0001-0.0500%, Zr: 0.0001 to 0.5000%, REM: 0.0001-0.0100%, Bi: 0.0001 to 0.0500%, and As: 0.001~0.10% The steel plate according to claim 1, characterized in that it includes at least one of the following.

3. {001} Random intensity ratio X of the average orientation ｛００１｝ to the random intensity ratio X of the {111}<112> orientation ｛１１１｝ The ratio of (X ｛１１１｝ / X ｛００１｝ ) is 20.0 or more, and the steel sheet according to claim 1 or 2 is characterized by this.

4. A component characterized by comprising the steel plate described in claim 1 or 2.

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