Steel sheet and component including same

Abstract

The present invention provides: a steel sheet that contains Ni, Cu, Cr, and Sn, that has a high N content, and that has excellent draw moldability; and a component including the same. Provided are: a steel sheet characterized by having a prescribed chemical composition in which the chemical composition satisfies [Ti]-[N]×47.88 / 14≥([N]-0.0021)0.4×0.23 where [Ti] and [N] in the formula respectively represent the contents (mass%) of Ti and N, and satisfies 0.6×[Cu]+0.1×[Ni]+0.05×[Cr]+8×[Sn]≤0.650 where [Cu], [Ni], [Cr], and [Sn] in the formula respectively represent the contents (mass%) of Cu, Ni, Cr, and Sn, and by having a metal structure in which the number density of Ti4C2S2 is 0.06 particles / μm2 or more; and a component including the steel sheet.

Description

Steel plates and parts containing them

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

[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 steel for processing 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: is 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 steel for processing that has the same excellent machinability as conventional steel.

[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.

[0005] Japanese Patent Publication No. 2000-336452, International Publication No. 2024 / 122042

[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 draw-formability, and a part containing the same.

[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 Ti ４ C ２ S ２ To appropriately control the amount of Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ We found that the formability of the material can be improved by controlling it to the above conditions. Furthermore, we found that the formability of the material can be further improved by optimizing the content of Ni, Cu, Cr, and Sn in the steel sheet, more specifically by controlling the chemical composition to satisfy 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650, thus completing the present invention.

[0009] The present invention that can achieve the above object is as follows. (1) In mass %, 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 to 0.0200%, Al: 1.000% or less, N: 0.0026 to 0.0150%, O: 0.0100% or less, Ti: 0.015 to 0.150%, Ni: 0.04 to 1.00%, Cu: 0.04 to 1.00%, Cr: 0.04 to 1.00%, Sn: 0.004 to 0.100%, Nb: 0 to 0.050%, Mo: 0 to 0.50%, B: 0 to 0.0100%, V: 0 to 0.500%, W: 0 to 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: Fe and impurities, having a chemical composition satisfying the following formulas (1) and (2), Ti ４ C ２ S ２ The number density of which is 0.06 pieces / μm ２ or more, and having a metal structure. [Ti] - [N] × 47.88 / 14 ≥ ([N] - 0.0021) ０．４× 0.23 ... Equation (1) Here, [Ti] and [N] are the mass %) of Ti and N. 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650 ... Equation (2) Here, [Cu], [Ni], [Cr] and [Sn] are the mass %) of Cu, Ni, Cr and Sn. (2) The above chemical composition is as follows, in mass%, Nb: 0.001 to 0.050%, Mo: 0.001 to 0.50%, B: 0.0001 to 0.0100%, V: 0.001 to 0.500%, W: 0.001 to 1.00%, Ta: 0.001 to 0.10%, Co: 0.001 to 1.00%, Sb: 0.001 to 0.200%, Ca: 0.0001 to 0.0500%, Mg: 0.0001 to 0.0500%, Zr: 0.0001 to 0.5000%, REM: 0.0001 to 0.0100%, Bi: 0.0001 to 0.0500%, and As: The steel plate according to (1) above, characterized in that it contains at least one of 0.001 to 0.10%. (3) Random strength ratio X of the mean orientation {001} ｛００１｝ The random intensity ratio X in the {111} <112> direction relative to the {111} direction. ｛１１１｝ The ratio (X ｛１１１｝ / X ｛００１｝ (1) or (2) above, characterized in that the ratio is 20.0 or higher. (4) A component characterized in that it includes the steel plate described in any one of the above items (1) to (3).

[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 draw-formability, and a part containing the same.

[0011] <Steel Plate> The steel plate according to the embodiment of the present invention has the following composition in mass%, 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 to 0.0200%, Al: 1.000% or less, N: 0.0026 to 0.0150%, O: 0.0100% or less, Ti: 0.015 to 0.150%, Ni: 0.04 to 1.00%, Cu: 0.04 to 1.00%, Cr: 0.04 to 1.00%, Sn: 0.004 to 0.100%, Nb: 0 to 0.050%, Mo: 0 to 0.50% The composition consists of 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 being Fe and impurities, and has a chemical composition that satisfies the following formulas (1) and (2), and Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ It is characterized by having the following metallic structure: [Ti] - [N] × 47.88 / 14 ≥ ([N] - 0.0021) ０．４ × 0.23 ... Equation (1) where [Ti] and [N] are the mass %) of Ti and N. 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650 ... Equation (2) where [Cu], [Ni], [Cr] and [Sn] are the mass %) of Cu, Ni, Cr and Sn.

[0012] As mentioned earlier, in automotive parts and other applications, part shapes are diverse and complex, and the steel sheets used as materials require good formability. However, depending on the alloying elements contained in the steel sheet, the formability, especially deep drawing formability, may be reduced. This reduction in deep drawing formability is a particular concern when the steel sheet contains all four elements Cu, Ni, Cr, and Sn simultaneously, or when the nitrogen content is high.

[0013] Furthermore, two methods are generally known for manufacturing steel sheets: one involves obtaining molten iron in a blast furnace using iron ore, a natural resource, as the main raw material, and then producing molten steel through refining in a converter or the like; and the other involves producing molten steel in an electric arc furnace using scrap material, a recycled resource, as the main raw material. In blast furnace steel, increasing the scrap content due to considerations for the global environment inevitably increases the content of scrap-derived elements such as Cu, Ni, Cr, and Sn (so-called trump elements), which is known to reduce the formability of the final steel product. In electric arc furnace steel, since scrap material is used as the main raw material, the trump element content is even higher, and it is thought that the N content is even 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 of the present invention have reduced the amount of dissolved carbon by using Ti ４ C ２ S ２ We attempted to precipitate carbon-containing precipitates and consume the dissolved C in this way. ４ C ２ S ２ To precipitate a large amount of Ti, a large amount of Ti in solid solution is required, that is, the amount of effective Ti needs to be increased. Here, the amount of effective Ti corresponds to the amount of Ti in solid solution, that is, the value obtained by subtracting the amount of Ti fixed by N from the total amount of Ti. ４ C ２ S ２The amount of Ti effective for the precipitation of carbon-containing precipitates, as shown above, is the total amount of Ti minus the amount that can be fixed as TiN, and is calculated by the following formula: Effective Ti amount (%) = [Ti] - 47.88 / 14 [N] where [Ti] and [N] are the mass %) content of each element in the hot-rolled coil.

[0015] In the process of investigating from the perspective of the chemical composition of steel sheets, it was found that, given the same amount of effective Ti in the steel sheet, the higher the N content, the greater the Ti content. ４ C ２ S ２ It was found that the precipitation of is suppressed. Therefore, in steel sheets with a relatively high N content, if there is not enough Ti, Ti ４ C ２ S ２ The precipitation of carbon is suppressed, and the dissolved carbon remains without being consumed. Although we do not intend to be bound by any particular theory, by controlling the effective Ti amount (left side of equation (1) above) to be higher than the value determined by the N content (right side of equation (1) above), even in steel plates with a relatively high N content, Ti ４ C ２ S ２ The Ti content is sufficient for adequate precipitation, and the solid-solution C is Ti ４ C ２ S ２ This allows for precipitation, reducing the amount of solid-solution carbon, and consequently improving the moldability of the material.

[0016] In addition, the inventors believe that, from the viewpoint of the metallographic structure of the steel sheet, Ti in the steel sheet ４ C ２ S ２ Ti is present in relatively large numbers. ４ C ２ S ２ Controlling the amount of Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ By controlling it to the above extent, the solid-solution C is Ti ４ C ２ S ２It was found that precipitation occurs, reducing the amount of solid-solution carbon, thereby improving the moldability of the drawing process. ４ C ２ S ２ By controlling the form and amount within this range, and in combination with the control of the chemical composition by the relationship between Ti and N described above (Equation (1)), the amount of solid-solution C is determined to be Ti ４ C ２ S ２ It precipitates as a solid, reducing the amount of dissolved carbon, and as a result, the formability of the steel sheet can be further improved.

[0017] Ti in this way ４ C ２ S ２ Even if the amount of dissolved carbon is sufficiently reduced by precipitating carbon, some dissolved carbon may remain, and this remaining dissolved carbon may form precipitates, such as carbides of Ti and / or Nb. These carbides are Ti ４ C ２ S ２Because it precipitates at a lower temperature compared to other materials, the particle size is finer. Furthermore, through the inventors' research, although the details are not yet clear, it was found that when the four elements Cu, Ni, Cr, and Sn are included, the fine carbides become even finer. In addition, it was found that the degree to which the fine carbides are refined differs depending on the type of Cu, Ni, Cr, and Sn. Generally, it is known that in order to improve the r value, not only is the amount of solid-solution 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, which lowers the r value and can lead to a decrease in draw-forming properties. 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 defined 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] From the 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 limit and upper limit, respectively, unless otherwise specified.

[0020] [C: 0.0005 to 0.0050%] Carbon (C) is an effective element for increasing the strength of steel sheets. In addition, C forms carbides and / or carbonitrides with Ti and / or Nb in the steel. To obtain these effects to the fullest, the C content should be 0.0005% or more. The C content may be 0.0010% or more, 0.0015% or more, or 0.0020% or more. On the other hand, if the C content is excessive, the amount of solid-solution C increases, which may reduce the formability of the material. Therefore, the C content should be 0.0050% or less. The C content may be 0.0045% or less, 0.0040% or less, 0.0035% or less, 0.0030% or less, or 0.0025% or less.

[0021] [Mn: 0.01-1.50%] Mn is an element effective in increasing strength as a hardenable and solid solution strengthening element. To obtain these effects fully, 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 a large amount of MnS will be generated, which will lead to Ti ４ C ２ S ２ Because the amount of precipitate decreases, the moldability may be reduced. Therefore, the Mn content should be 1.50% or less. The Mn content may also 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 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 of appearance. Therefore, the Si content should be 0.500% or less. The Si content may 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 and, like Si, is effective in increasing strength, but it is 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 to 0.0200%] S is Ti ４ C ２ S ２ This is achieved by reducing solid solution carbon and improving drawability. To obtain this effect, the sulfur content should be 0.0010% or more. The sulfur content may be 0.0020% or more, 0.0030% or more, or 0.0050% or more. On the other hand, sulfur is an impurity element that inhibits weldability and also inhibits manufacturability during casting and hot rolling. For this reason, the sulfur content should be 0.0200% or less. The sulfur 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 Al is present in excess, 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 N is present in excess, Ti ４ C ２ S ２ In some cases, sufficient precipitation may not occur. For this reason, the N content should be 0.0150% or less. The N content may also be 0.0140% or less, 0.0130% or less, 0.0120% or less, 0.0110% or less, 0.0100% or less, 0.0090% or less, 0.0080% or less, or 0.0070% or less.

[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 to 0.150%] Ti is Ti ４ C ２ S ２ These compounds form carbon sulfides and carbonitrides, reducing solid solution carbon and improving the formability of the material. To fully obtain this effect, the Ti content should be 0.015% or higher. The Ti content may 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 the formability of the material. Therefore, the Ti content should be 0.150% or lower. The Ti content may 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 contained in steel sheets when scrap is used as a raw material for steel sheets. 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 Ni is included in excess, not only will the manufacturing cost increase, but the strength may become too high, which may reduce the formability of the drawing. 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 contained in steel sheets when scrap is used as a raw material for steel sheets. The Cu content should be 0.04% or more. Cu is also 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 included in excess, fine precipitates may precipitate excessively, not only making the strength too high, but also preventing sufficient growth of the crystal grain size in the metal structure, which may reduce the formability of the deep drawing. 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 such 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 contained in steel sheets when scrap is used as a raw material for steel sheets. The Sn content should be 0.004% or more. Sn is also an effective element for 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 drawing may decrease. Therefore, the Sn content should be 0.100% or less. The Sn content may 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 draw formability. The Nb content may be 0%, but to fully obtain these effects, it is preferable that the Nb content be 0.001% or more. The Nb content may also be 0.005% or more, or 0.010% or more. On the other hand, if the Nb content is excessive, recrystallization and grain growth may be suppressed, and the draw formability may decrease. Also, including more Nb in the steel than necessary will lead to an increase in manufacturing costs. Therefore, it is preferable that the Nb content be 0.050% or less. The Nb content may also be 0.040% or less, 0.030% or less, or 0.020% or less.

[0035] [Mo: 0-0.50%] Mo is an element that enhances the hardenability of steel and contributes to improving its strength. The Mo content may be 0%, but to obtain such effects, it is preferable that the Mo content be 0.001% or more. The Mo content may 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 increase. Therefore, it is preferable that the Mo content be 0.50% or less. The Mo content may be 0.40% or less, 0.30% or less, or 0.20% or less.

[0036] [B: 0 to 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, the B content is preferably 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, the B content is preferably 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 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 generated, which may reduce toughness. Therefore, it is preferable that the V content be 0.500% or less. The V content may 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 is an element effective in improving the strength of steel sheets. The Ta content may be 0%, but to obtain these effects, it is preferable that the Ta content be 0.001% or more. The Ta content may be 0.005% or more, 0.01% or more, or 0.02% or more. On the other hand, if the Ta content is excessive, the effect will saturate, and including more Ta in the steel sheet than necessary will lead to an increase in manufacturing costs. Therefore, it is preferable that the Ta content be 0.10% or less. The Ta content may be 0.08% or less, 0.06% or less, 0.04% or less, or 0.02% or less.

[0040] [Co: 0-1.00%] Co is an element effective in improving the strength of steel plates. The Co content may be 0%, but to obtain such an effect, it is preferable that the Co content be 0.001% or more. The Co content may be 0.005% or more, 0.01% or more, or 0.05% or more. On the other hand, if the Co content is excessive, the hot workability may decrease, which can lead to an increase in raw material costs. Therefore, it is preferable that the Co content be 1.00% or less. The Co content may 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 may be present 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 Ca is present in excess, many Ca-containing sulfides will be formed and Ti ４ C ２ S ２ Because the amount of precipitate decreases, the moldability of the material may be reduced. Therefore, it is preferable that the Ca content be 0.0500% or less. The Ca content may also 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, many Mg-containing sulfides will be formed and Ti ４ C ２ S ２ Because the amount of precipitate decreases, the moldability of the material may be reduced. Therefore, it is preferable that the Mg content be 0.0500% or less. The Mg content may also 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 to 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 be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if REM is present in excess, a large amount of REM-containing sulfides will be formed and Ti ４ C ２ S ２Because the amount of precipitate decreases, the moldability of the material may decrease. 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 is a collective term for 17 elements including scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanides from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71, and 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. The Bi content may be 0%, but to obtain this effect, it is preferable that the Bi content be 0.0001% or more. The Bi content may be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if Bi is included in excess, the effect will saturate, and including more Bi in the steel sheet than necessary will lead to an increase in manufacturing costs. Therefore, it is preferable that the Bi content be 0.0500% or less. The Bi content may be 0.0400% or less, 0.0200% or less, 0.0100% or less, or 0.0050% or less.

[0047] [As: 0-0.10%] As is an element that may be present in steel plates when scrap is used as a raw material. Also, As is an element that strongly segregates at grain boundaries, so 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 an embodiment of the present invention, the balance other than the above elements consists of Fe and impurities. The impurities are components that are mixed due to various factors in the manufacturing process starting from raw materials such as ore and scrap when the steel sheet is industrially manufactured, and components included within a range that does not affect the effects of the present invention, and the like.

[0049] [[Ti] - [N] × 47.88 / 14 ≥ ([N] - 0.0021) ０．４ × 0.23] The chemical composition of the steel sheet according to an embodiment of the present invention needs to satisfy the following formula (1). [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. In the steel sheet according to an 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 described above, when the effective Ti amount is the same, the higher the N content, the more difficult it is for Ti ４ C ２ S ２ to precipitate. Therefore, in a steel sheet with a relatively high N content, when Ti is not sufficiently present, Ti ４ C ２ S ２ precipitates are difficult to precipitate, so the dissolved C remains unconsumed, and as a result, the drawing formability deteriorates. The lower limit value 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) ０．４ × 0.23, and the lower limit value of the effective Ti amount increases as the N content increases. By controlling so as to satisfy the above formula (1) for Ti and N, more specifically, by controlling the effective Ti amount (the left side of the above formula (1)) to be higher than the value determined by the N content (the right side of the above formula (1)), even in a steel sheet with a relatively high N content, Ti ４ C ２ S ２ the Ti content necessary for sufficient precipitation is ensured, and the dissolved C is Ti ４ C ２ S ２This allows for precipitation and a reduction in the amount of dissolved carbon. As a result, the r value improves, thereby improving the moldability of the material.

[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) where [Cu], [Ni], [Cr], and [Sn] are the mass %) of Cu, Ni, Cr, and Sn. Cu, Ni, Cr, and Sn are elements that may be contained in the steel sheet when scrap is used as the raw material for the steel sheet. If the content of these elements is too high, fine precipitates, such as Ti and / or Nb carbides, may precipitate. Such fine precipitates may prevent sufficient grain growth of the metal structure during annealing, thereby reducing the formability of the deep drawing. Incidentally, the degree to which these elements influence the refinement of precipitates differs depending on their type. For example, Sn tends to form fine precipitates relatively easily, while Cr tends to form fine precipitates relatively poorly. Therefore, the sum of the values ​​obtained by multiplying the content of Cu, Ni, Cr, and Sn by coefficients corresponding to their respective influences is set to 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 sum is not particularly limited, but may be 0.060 or more, 0.080 or more, or 0.100 or more.

[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 spectroscopy (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] [Ti ４ C ２ S ２ Number density: 0.06 particles / μm ２ [End of description] In the steel sheet according to the embodiment of the present invention, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ That's all. Ti ４ C ２ S ２ As a result of this formation, the dissolved carbon is consumed, 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, Ti ４ C ２ S ２ A higher number density is preferable for Ti ４ C ２ S ２ The number density is 0.10 particles / μm ２ Above, 0.15 pieces / μm ２ Above, 0.20 pieces / μm ２ More than or equal to 0.25 particles / μm ２ The above is also acceptable. On the other hand, Ti ４ C ２ S ２ There is no particular upper limit to the number density, up to 1.00 particles / μm ２ Less than or equal to 0.50, pieces / μm ２ The following is also acceptable.

[0053] [Ti ４ C ２ S ２ [Measurement of number density of Ti] ４ C ２ S ２ The average equivalent circle diameter and number density are measured by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). First, starting from the 1 / 4 thickness position of the steel plate, the SPEED method (selective constant potential electrolytic etching) is used to obtain a value of 10 coulombs / cm² at -100 mV 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 at a magnification of 30,000x or more with an EDS-equipped TEM. ２ The precipitates were then observed. In the SPEED electropolishing method, 10% acetylacetone - 1% tetramethylammonium chloride - methanol was used as the electropolishing solution. Of the observed precipitates, those with a circular equivalent diameter of 100 nm or less were analyzed using EDS, and precipitates in which peaks of 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 selected as Ti. ４ C ２ S ２ This is how it is determined. If precipitates are precipitated in combination, EDS analysis is performed on each precipitate, and if peaks for Ti, C, and S are observed in each precipitate, and the maximum peak height of Ti is 1.1 times or more than the maximum peak height of S, then each precipitate is determined to be Ti ４ C ２ S ２ This is how it is determined.

[0054] Here, with a magnification of 30,000 times or more, the observation area of ​​one field of view is 5 μm. ２ In addition, observe so that the total number of precipitates with a size of 100 nm or less in five or more fields of view is 20 or more, and Ti ４ C ２ S ２ The number of Ti was calculated. ４ C ２ S ２ The number density of each Ti identified above ４ C ２ S ２ This value is obtained by dividing the number of elements by the area of ​​the observed field of view.

[0055] [X ｛１１１｝ / X ｛００１｝ : 20.0 or more] In a steel sheet according to a preferred embodiment of the present invention, the average random strength ratio X of {001} ｛００１｝ The random intensity ratio X in the {111} <112> direction relative to the {111} direction. ｛１１１｝ The 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 is 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 the random intensity ratio X of the {111} <112> directions ｛１１１｝ This is measured by electron backscatter 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 to 45° other than φ1=0° or φ1=90° will be greater than the sum of the random intensity ratios for φ1=0°, Φ=0 to 45° (A) or the sum of the random intensity ratios for φ1=90°, Φ=0 to 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 determines the rolling direction. The sum of random intensity ratios can be calculated by calculating the random intensity ratio at Φ = 0, 5, 10... every 5° and adding them up. The sample length should be approximately 10 mm to 25 mm. From the surface of the sample, at positions 1 / 8 to 7 / 8 of the plate thickness, the thickness is 600,000 μm. ２The range is measured using EBSD at measurement intervals of 2.0 μm to obtain crystal orientation information. Here, 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 orientation distribution function (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 the direction perpendicular to the plate surface.

[0057] ODF is also used to indicate the orientation of crystal structures with low symmetry, and is generally expressed as φ1 = 0 to 360°, Φ = 0 to 180°, and φ2 = 0 to 360°, with each orientation represented as (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 to 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 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 follows. Similarly, the random intensity ratio X of the {111} <112> direction. ｛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, the analysis software "OIM Analysis" manufactured by TSL Corporation is used, and the analysis is performed 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] The present invention aims to provide a steel sheet containing Ni, Cu, Cr, and Sn, with a high N content, having excellent deep draw formability, and a part containing the same, by controlling the chemical composition to have a predetermined chemical composition, and Ti ４ C ２ S ２ The number density is 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: 10.0 μm 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 grain boundaries, which are the boundaries of 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] [Sheet Thickness] The steel sheet according to the embodiment of the present invention is not particularly limited, but for example, has a sheet thickness of 0.1 to 2.0 mm. The sheet thickness may be 0.2 mm or more, 0.3 mm or more, or 0.4 mm or more. Similarly, the sheet 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 sheet 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 sheet thickness to 1.0 mm or less, the effect of reducing the weight of the part becomes significant. The sheet 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. The hot-dip galvanized layer includes, for example, 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. The electroplated layer includes, for example, 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, 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 these parts, and therefore at least a portion of these parts will satisfy the chemical composition and metallic structure characteristics described above. In parts of the steel sheet that undergo relatively little processing during forming, such as press forming, the metallic structure 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 for Manufacturing Steel Sheets> Next, a preferred method for manufacturing steel sheets according to the embodiments of the present invention will be described. The following description is intended to illustrate characteristic methods for manufacturing steel sheets according to the 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 the 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. The slab to be used is preferably cast by continuous casting from the viewpoint of productivity, but may also be manufactured by ingot casting or thin slab casting. 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 in order to adjust the slab width, etc. Ti in the austenite region at high temperatures ４ C ２ S ２ From the viewpoint of promoting precipitation, it is preferable that the following formulas be satisfied in the sizing press: S / t ≥ 0.06, and S = 100 × (L ０ -L １ ) / L ０ In the ceremony, L ０ This is the slab width (mm) before width reduction by sizing press, L １ 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. Ti is produced by strain-induced precipitation at high temperatures. ４ C ２ S ２ In order to precipitate the material, it is important to introduce a lot of strain into the slab when it is hot, specifically when it is extracted from the hot rolling furnace and then subjected to sizing press and / or rough rolling. From the viewpoint of introducing a lot of strain, the slab width (L) before width reduction is important.０ Width reduction amount (L) for (mm) ０ -L １ It is preferable to control the slab so that (mm) is large, that is, to control it so that S is large. Also, in order to sizing press at 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 slab so that S is large and t is small, that is, to control the slab so that S / t is large, more specifically, to satisfy S / t ≥ 0.06. S / t may be 0.08 or more, 0.10 or more, or 0.12 or more. The upper limit of S / t is not particularly limited, but may be 0.30 or less, 0.25 or less, or 0.20 or less.By controlling in this way, by introducing a large amount of strain at high temperature, Ti ４ C ２ S ２ The precipitation of Ti is promoted, and thereby in the final steel sheet, ４ C ２ S ２ The number density is 0.06 particles / μm ２ It becomes possible to satisfy the above conditions.

[0071] [Rough rolling] [(a-2) (2×R1+R2) / ΔT １ ≥2.0] The heated slab or sizing-pressed slab is then subjected to rough rolling. Rough rolling may be performed using a reverse rolling mill. Ti in the austenite region at high temperatures ４ C ２ S ２ From the viewpoint of promoting precipitation, it is preferable that the following formula is satisfied during rough rolling: (2 × R1 + R2) / ΔT １ ≥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 ΔT １ This is the temperature drop from the temperature of the first pass to the temperature of the second pass. As explained above, Ti is produced by utilizing strain-induced precipitation at high temperatures. ４ C ２ S ２To precipitate it, rough rolling is performed at a high temperature, that is, the temperature drop (ΔT) between the first pass and the second pass. １ It is preferable to reduce ΔT. １ As we decrease the value of ΔT, the right-hand side of the above equation becomes larger. Therefore, ΔT １ While reducing ΔT １ It is preferable to control the reduction ratio (R1) of the first pass to be higher accordingly. Therefore, (2 × R1 + R2) / ΔT １ It is preferable to control it so that ≥ 2.0 is satisfied. By controlling it in this way, a large amount of strain can be introduced at high temperatures, and Ti ４ C ２ S ２ The precipitation of Ti is promoted, and thereby in the final steel sheet, ４ C ２ S ２ The number density is 0.06 particles / μm ２ It becomes possible to satisfy the above conditions.

[0072] The hot rolling process involves Ti ４ C ２ S ２ This is extremely important for controlling the amount of Ti. By satisfying (a-1) or (a-2) described above, Ti is produced by strain-induced precipitation at high temperatures. ４ C ２ S ２ The precipitation of Ti is promoted. ４ C ２ S ２ The number density is 0.06 particles / μm ２ The above can be achieved. In addition, by satisfying (a-1) and (a-2), Ti ４ C ２ S ２ The precipitation of Ti is further promoted, and as a result, coarser Ti ４ C ２ S ２ To precipitate a large amount of Ti ４ C ２ S ２ The number density is 0.20 particles / μm ２ You can obtain the above.

[0073] [Finish 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 metal structure and sheet 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 below 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 will become coarse, which may degrade the formability of the product. For example, an average cooling rate of 25°C / second or more is preferable, and a winding temperature of 750°C or below is preferable.

[0075] [Pickling Process] Next, the obtained hot-rolled steel sheet is pickled to remove the oxide scale formed on its surface. 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 of the oxide scale.

[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 metal structure 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 × T ２２ -1.78 × T ２ )} < 2.60] In the method for manufacturing steel sheets according to a preferred embodiment of the present invention, the following formula is satisfied in the annealing process: A = 10000 × h × σ ｔ１ / {D × (805 + 0.001 × T ２ ２ -1.78 × T ２ )} < 2.60 In the formula, h is the plate thickness (mm), D is the roll diameter (mm), and T ２ σ is the highest temperature reached (°C), 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 response 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, T ２ The larger T is, the lower the yield strain becomes, and consequently the larger the plastic strain. The larger D is, the smaller the plastic strain becomes. Therefore, from the viewpoint of reducing plastic strain, ２ It is preferable to control h to be small and D to be large; therefore, it is preferable to control the denominator of the middle term to be large. From the above, it is preferable to control the numerator of the middle term to be small and the denominator of the middle term to be large, that is, 10000 × h × σ ｔ１ / {D × (805 + 0.001 × T ２ ２ -1.78 × T ２ It is preferable to control the value such that )} < 2.60. The lower limit of the left side of the above formula 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 method for manufacturing steel sheets according to a preferred embodiment of the present invention, the following formula is satisfied in the annealing step. σ ｔ２ / σ ｔ１ <1.50 where σ 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. 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 the 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's set it to <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] For the purpose of improving corrosion resistance, etc., the surface of the obtained cold-rolled steel sheet may be plated as needed. The plating process may be hot-dip plating, alloying hot-dip plating, electroplating, etc. For example, the steel sheet may be hot-dip galvanized as a plating process, or an alloying process may be performed after hot-dip galvanizing. The specific conditions for the plating process and alloying process 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 the 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.

[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 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 as a plating treatment, and some of them were further subjected to alloying treatment.

[0085]

[0086]

[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 starts, and S is 100 × (L ０ -L １ ) / L ０ This is a value calculated from L. ０ This is the slab width (mm) before width reduction by sizing press, L １ This represents the slab width (mm) after width reduction by sizing press. In Table 2, test examples where S is 0% are test examples where sizing press treatment was not performed.

[0088] Table 2 shows the rough rolling process in the hot rolling stage. In the table, 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 ΔT １ This represents 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 This is the average tension (MPa) in the temperature range of 500-700°C after reaching the maximum temperature. ２ σ 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 × T ２ ２ -1.78 × T ２ This value is calculated from ).

[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, and X ｛００１｝ This is the random intensity ratio for the {111} <112> directions.

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

[0092] [Drawn Formability: Plastic Strain Ratio (r-value)] The plastic strain ratio (r-value) was measured in three different orientations: the longitudinal direction was the rolling direction, the longitudinal direction was perpendicular to the rolling direction, and the longitudinal direction was at a 45° angle to the rolling direction. The measurement was performed on 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 Ti ４ C２ S ２ The number density is 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 mainly 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, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When the value was less than , the r value was 1.4. In Comparative Example 2, since both the sizing press and rough rolling did not meet the specified conditions, Ti was produced by strain-induced precipitation at high temperatures. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast to this, in Example 1, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２S ２ The number density is 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, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast to this, in Example 3, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 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 to 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, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When the value was less than , the r value was 1.4. In Comparative Example 9, since both the sizing press and rough rolling did not meet the specified conditions, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Examples 5 to 8, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ As a result, a steel sheet meeting the above criteria was obtained, and the r value became higher than 1.4. Therefore, in Examples 5 to 8, despite containing Ni, Cu, Cr, and Sn, and having a high N content, the material exhibited excellent deep drawing formability.

[0098] Examples 10 and Comparative Example 11 are steel sheets made of steel D 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. As in Comparative Example 11, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast to this, in Example 10, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 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 10, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[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, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When the value was less than , the r value was 1.7. In Comparative Example 13, since both the sizing press and rough rolling did not meet the specified conditions, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast to this, in Example 12, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.7. Therefore, in Example 12, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0100] Examples 14 and Comparative Example 15 are steel sheets made of steel F that satisfy the requirements for the chemical composition of the steel sheet according to the embodiment of the present invention, and each has a GI layer. As in Comparative Example 15, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When the value was less than , the r value was 1.5. In Comparative Example 15, since both the sizing press and rough rolling did not meet the specified conditions, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 14, by appropriately controlling each condition in the manufacturing method, Ti ４ C２ S ２ The number density is 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 14, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0101] Examples 16 and Comparative Example 17 are steel sheets made of steel G that satisfy the chemical composition requirements of the steel sheet according to the embodiment of the present invention, and each has an EG layer. As in Comparative Example 17, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 16, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 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 16, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[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, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature.４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 18, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel sheet meeting the above criteria was obtained, and as a result, the r value was higher than 1.4. Therefore, in Example 18, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0103] Examples 20 and Comparative Example 21 are steel sheets made of steel I 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. As in Comparative Example 21, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When the value was less than , the r value was 1.1. In Comparative Example 21, since both the sizing press and rough rolling did not meet the specified conditions, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 20, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.1. Therefore, in Example 20, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0104] Examples 22 to 24 and Comparative Example 25 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. As in Comparative Example 25, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When the value was less than , the r value was 1.3. In Comparative Example 25, since both the sizing press and rough rolling did not meet the specified conditions, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Examples 22 to 24, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ As a result, a steel sheet meeting the above criteria was obtained, and the r value became higher than 1.3. Therefore, in Examples 22 to 24, despite containing Ni, Cu, Cr, and Sn, and having a high N content, the material exhibited excellent deep drawing formability.

[0105] Examples 26 and Comparative Example 27 are steel sheets made of steel K 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 27, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ When 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 26, by appropriately controlling each condition in the manufacturing method, Ti４ C ２ S ２ The number density is 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 Example 26, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0106] Examples 28 and Comparative Example 29 are steel sheets made of steel L 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. As in Comparative Example 29, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 28, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 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 Example 28, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0107] Examples 30 to 32 and Comparative Example 33 are steel sheets made of steel M 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. As in Comparative Example 33, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Examples 30 to 32, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel sheet meeting the above criteria was obtained, and as a result, the r value became higher than 1.3. Therefore, in Examples 30 to 32, despite containing Ni, Cu, Cr, and Sn, and having a high N content, excellent deep draw formability was observed. In particular, it had a predetermined chemical composition, and Ti ４ C ２ S ２ The number density is 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 the condition of being 20.0 or higher, the r value was further improved, and even better deep drawing properties were observed.

[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, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２It is thought that the number density of Ti decreased. In contrast, in Example 34, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel sheet meeting the above criteria was obtained, resulting in an r value higher than 1.7. Therefore, in Example 34, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep drawing formability.

[0109] Examples 36 and Comparative Example 37 are steel sheets made of steel O 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. As in Comparative Example 37, Ti ４ C ２ S ２ The number density 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, Ti was produced by strain-induced precipitation at high temperature. ４ C ２ S ２ The precipitation of Ti is not promoted, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density of Ti decreased. In contrast, in Example 36, by appropriately controlling each condition in the manufacturing method, Ti ４ C ２ S ２ The number density is 0.06 particles / μm ２ A steel sheet meeting the above criteria was obtained, and as a result, the r value became higher than 1.4. Therefore, in Example 36, despite containing Ni, Cu, Cr, and Sn, and having a high N content, it exhibited excellent deep draw formability.

[0110] Comparative Example 40 had a high carbon content, resulting in 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 was [Ti] - [N] × 47.88 / 14 ≥ ([N] - 0.0021) ０．４It does not satisfy ×0.23, and despite the relatively high N content, there is not enough Ti, therefore Ti ４ C ２ S ２ Ti does not precipitate sufficiently, and in the final steel sheet, ４ C ２ S ２ It is thought that the number density was low. Comparative Example 43 did not satisfy 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650, and therefore, compared to Example 1, which had the same chemical composition other than Cu, Ni, Cr, and Sn and the same manufacturing method, it is thought that fine precipitates were formed and the grain growth of the metal structure did not proceed sufficiently during annealing. As a result, the r value decreased. As in Reference Examples 42 and 44, when the four elements Cu, Ni, Cr, and Sn are not contained simultaneously, or when the N content is relatively low, there is no particular concern about a decrease in drawability.

Claims

1. In mass percent, 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 being Fe and impurities, having a chemical composition that satisfies the following formulas (1) and (2), and 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 ... Equation (1) where [Ti] and [N] are the mass %) of Ti and N. 0.6 × [Cu] + 0.1 × [Ni] + 0.05 × [Cr] + 8 × [Sn] ≤ 0.650 ... Equation (2) where [Cu], [Ni], [Cr] and [Sn] are the mass %) of Cu, Ni, Cr and Sn.

2. The chemical composition is as follows, 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 The steel plate according to claim 1, characterized in that it contains at least one of As: 0.001 to 0.10%.

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

4. A component characterized by comprising a steel plate as described in any one of claims 1 to 3.

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