TW200532032A - High strength cold rolled steel sheet and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high strength cold rolled steel sheet consisting of 0.015% or less of C, 1.5% or less of Si, 0.4 to 3% of Mn, 0.15% or less of P, 0.02% or less of S, 0.1 to 1% of sol. Al, 0.01% or less of N, 0.2% or less of Ti, by mass%, and the balance of Fe and inevitable impurities. In this steel sheet, 1 ≤([Ti]/48)/([C]/12+[N]/14) is satisfied, in which [M] represents the content of the element M. Since having the superior deep drawability and the TS of 340 to 590 MPa, the high strength cold rolled steel sheet of the present invention is preferably used for automobiles parts difficult to be press formed, such as a side outer panel and a door inner panel.

Description

200532032 IX. Description of the invention: [Technical field to which the invention belongs] The present invention relates to high-strength cold-rolled steel sheets used in automobiles, home appliances, and the like, and in particular, has a tensile strength of 3 40 to 5 9 0 MPa ( High-strength cold-rolled steel sheet with excellent deep drawability (TS, tensile strength), and its manufacturing method. [Prior art] It is known that in automobile parts that are difficult to form on the outer panel and the inner panel of the door, φ is an IF (Interstitia 1) with excellent deep drawability using TS of about 270 MPa and an r value of 1.8 to 2.0. Free, seamless) soft cold rolled steel sheet (SPC270E, F). In recent years, as the demand for lighter weight of automobile bodies has increased, these difficult-to-form parts have also been developed using IF high-strength cold-rolled steel sheets with TS of 340 to 590 MPa. However, if these parts are to be used in the south-strength cold-rolled steel sheet whose TS is 340 to 390 MPa and r value is about 1.7, TS is about 440 MPa and r value is 1.5.

If the high-strength cold-rolled steel sheet with a TS strength of about 590 MPa and an r value of about 1.0 is formed, the high-strength cold-rolled steel sheet at the left and right will easily crack at the stretched part. The situation applies only to shallow extruded parts. In addition, a high-strength cold-rolled steel sheet having a TS of 3 40 to 590 MPa and a higher r value is required. Specifically, it is desired that TS is 340 to 400 MPa and has an r value of 1.8 or more, and TS is 400 to 590 MPa and has a value of 1.6 or more, preferably 1 or more. So far, as a method for increasing the r value, it has been known to use IF steels that reduce c and N as much as possible and add a large amount of T i and N b after hot rolling at 6 8 0 X: 5 312XP / Invention Specification (Supplementary) ) / 9 winter 05/94105020 200532032 Coiled under high temperature, so that solid solution C and N are extremely reduced and the precipitates are coarsened, and the formation and growth of recrystallized grains with an aggregated structure beneficial to r value during annealing are promoted Methods. As the same method, in Japanese Patent Laid-Open No. 6-1 0 8 1 5 5 and Japanese Patent No. 3 2 9 1 6 39, it is disclosed that IF is used to reduce C and N as much as possible and to add T i Steel, a method that allows T i (C, S) to be generated, and that the aggregate structure of r values is developed during annealing.

However, in the method disclosed in Japanese Patent Laid-Open No. 6-1 0 8 1 5 5, a soft cold-rolled steel sheet having a TS of 260 to 300 MPa is used as an object, and if it is applied to an existing When a large amount of IF high-strength cold-rolled steel sheet with TS of 340 MPa or more is added with P and Mη, a large amount of P compounds such as Fe-Ti-P and Fe-Nb-P are generated at the grain boundary during coiling after hot rolling. And because of the large number of Mη itself, the r value is significantly reduced. Also, in the method disclosed in Japanese Patent No. 3 2 9 1 6 39, a high-strength cold-rolled steel sheet for deep drawing having a TS of 340M Pa or more added with a large amount of P is proposed. At the time, cracks occurred due to the uneven structure in the plate thickness direction caused by the segregation of P in the casting. On the other hand, a method has been proposed to increase the value of r by working on the manufacturing method. For example, Japanese Patent Application Laid-Open No. 7-1 8 8 7 7 6 discloses a method of finishing rolling while lubricating in the α region during hot rolling. In Japanese Patent Application Laid-Open No. 9-2 7 9 2 4 9, a method of applying 1 to 50% of a rolling material in a temperature range of 50 to 75 ° C during annealing is disclosed. In Japanese Patent Laid-Open No. 2000-1-1 3 1 6 4 3, it is disclosed that the amounts of Si, Mn, and P of the steel to which Nb and B are added are controlled, and 0 is applied after pickling, cold-rolling L, and annealing. 3 to 5% rolling, and again pickled and passed through the hot-dip galvanizing streamline. 6 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 However, these methods all require special manufacturing steps, resulting in increased manufacturing costs and reduced productivity. That is, in the method of Japanese Patent Laid-Open No. 7-1 8 8 7 7 6, it is necessary to recrystallize and annealed the hot-rolled steel sheet that has been finished rolling in the α region. The method of Japanese Patent Laid-Open No. 9-2 7 9 2 4 9 requires rolling equipment capable of withstanding high temperatures in an incinerator. In the method of Japanese Patent Laid-Open No. 2000-1-1 3 1 6 4 3, pickling, annealing, and temper rolling must be performed twice. [Summary of the Invention]

The purpose of the present invention is to provide a high Ts of 340 to 400 MPa and an r value of 1.8 or more, a TS of 400 to 590 MPa, and an r value of 1.6 or more, preferably 1.7 or more. Strength cold-rolled steel sheet and manufacturing method thereof. The purpose is to include C: 0 · 0 15% or less, Si: 1.5% or less, M η: 0 · 4 to 3%, P: 0 · 15% or less, S: 0. 2% or less, so 1. A 1: 0.1 to 1%, N: 0.01% or less, Ti: 0.2% or less, the remainder is Fe and unavoidable impurities, and satisfies the following formula (1) High strength cold rolled steel sheet. 1 S ([T i] / 48) / ([C] / 12 + [N] / 1 4) (1) Here, [M] represents the content (mass%) of the element M. In addition, the high-strength cold-rolled steel sheet may be provided with a step of heating the flat steel blank having the above composition at 1 080 to 1350 ° C, and heating the flat steel blank to (A r 3 metamorphosis). Point -2 0) to (A r 3 abnormal point + 1 5 0) ° C the step of hot rolling to hot rolled steel sheet; the hot rolled steel sheet meets the coiling temperature of the following formula (5) Steps for coiling by CT; hot rolled steel 7 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 after coiling is cold rolled into a cold rolled steel sheet at a reduction ratio of 50 to 90% Steps; and a step of continuously annealing the cold-rolled steel sheet at 7500 to 870 ° C, or closed-box annealing at 600 to 750 ° C; a manufacturing method. 480 $ CTS 5 8 0 + 0 · 17 / {([Ti] + 0. 〇8x [sol. A1]) x [P] 丨 ... (5) Here, [Μ] is the content of element M (mass %). [Embodiment] The present inventors investigated the influence of various alloy elements on the r value of an I F high-strength cold-rolled steel sheet, and found the following.

i) Compared with the previous high-strength cold-rolled steel sheet, if a larger amount of s ο 1. A 1 is added, the r value increases significantly. This effect is particularly pronounced when Mn is added above 0.4%. ii) The addition of Si and P is effective to increase the r value. iii) By adjusting the amount of P, sol.Al, Ti, and optionally Nb and the coiling temperature after hot rolling, a higher r value can be obtained. This invention is made | formed based on the said discovery, and the detailed content is demonstrated below. 1) sol · A1 amount and r value In order to investigate the relationship between s ο 1 and A 1 amount and r value, the following tests were performed. C: 0.02%, Si: 0.25%, P: 0.08%, S: 00.07%, Nb: 0.015%, Ti: 0 · 0 3%, N: 0 · 0 0 2%, B: 0 · 0 0 1% are constant, and the amount of s ο 1. A 1 is from 0 · 0 1 to 1.2%, and the amount of η is from 0 · 6 to 1 · 8 ° /. The changing flat steel blank was heated at 1 250 ° C, and then hot rolled to form a hot rail steel plate with a thickness of 3 mm, and subjected to a simulated heat treatment of coiling at 5 80 ° C for 1 hour. This hot-rolled steel sheet was cold-rolled to form a cold-rolled steel sheet having a thickness of 0.75 mm, and was subjected to continuous annealing at 80 ° C for 60 seconds, and an elongation of 0.7% was applied. Quenching and tempering rolling 8 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032. Thereafter, the r value and TS were measured in the following manner. JIS No. 5 test pieces were taken from the rolling direction, 45 ° with respect to the rolling direction, and 90 ° with respect to the rolling direction, and the r value and TS for each direction were measured, and the following formula was obtained The average value within the steel sheet. Average = ([Τ〇] +2 [Τ45] + [Τ9〇]) / 4 Here, [Τ. ] Is the rolling direction, [Τ 4 5] is the 45 ° direction with respect to the rolling direction, and [Tw] is the r value or TS, which is 90 ° with respect to the rolling direction.

The relationship between the amount of sol. A1 and the r value and TS is shown in FIG. 1. In the figure, the black circle is the result when the amount of Mη is 1.8%, and the white circle is the result when the total amount of sol. A1 and Mη is 1.8%. When the amount of η is 1.8%, the value of r is s ο 1 · A 1 is 0.1% or more and 1.6 or more, and 0.2 to 0 · 7% is 1. 7 or more. 0.7% decreased. TS exceeds 460 MPa when sol.Al is 0.1% or more, and increases in proportion to the amount of sol.Al. At this time, the increase in TS per 1% of the amount of sol.Al was 35 MPa. Its solid solution strengthening ability is about the same as Μη, so if the total of s ο 1. A 1 and Μ η is 1.8%, the relationship between T S and r value when the white circle-like strength is kept constant is obtained. From this, it can be seen that adding s ο 1. A 1 and reducing M η can achieve a higher r value at the same strength. In addition, if s ο 1. A 1 exceeds 1%, during continuous casting of the flat steel slab, fine A 1 N precipitates at the iron grain boundary of Vostian, embrittles the grain boundary, and corrects the bending of the flat slab. During and after the rough rolling, cracks easily occur on the surface of the flat steel blank. Then, due to the cracking of the surface of the flat steel embryo, surface defects are easily caused by the scale, and the surface quality of the final product is significantly reduced. 9 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 From the above results, even if TS exceeds 400 MPa, if the amount of sol.Al is 0.1 to 1%, preferably 0.2 to 0.7% , A high r value of 1.6 or more, preferably 1.7 or more can be obtained. The reason why a high r value can be obtained when s ο 1. A 1 is 0.1 to 1% is considered as follows. That is, A 1 is an element that raises the abnormal point of A r 3. Therefore, during hot rolling, after transformation from Vostian iron to ferrous iron, the precipitation of carbides is promoted in the α region at a high temperature, and the solid solution C is reduced. In addition, the carbides are coarsened, so that a recrystallized aggregate structure favorable for the r value is formed during annealing, and the r value is increased. In addition, measuring the change of the cold-rolled structure caused by A 1 by pushing φ also contributes to the improvement of the r value. 2) The relationship between the amount of Si, P, and r was investigated, and the relationship between the amount of Si, P, and r was investigated, using C: 0.02%, Mη: 1%, and Si: 0.07 ° / 〇, s ο 1. A 1: 0.2 5 ° / 〇, N b: 0.0 2%, T i: 0.0 1%, N: 0. 0 0 2% > B: 0 · 0 0 Γ / ◦ is constant, and the flat steel billet whose S i amount is from 0.05 to 1.5% and the P amount is from 0.3 to 0.15% is subjected to the same test as in the case of 1). .

The relationship between [Si] + 10x [P] and the r value is shown in FIG. 2. The numbers in the figure indicate the amount of S i. If the steel of the present invention having a sol.Al content of 0.25% is satisfied with the following formula (2), it is found that a high r value of 1.7 or more can be obtained. 0. [Si] + 10x [P] ^ 1.4 (2) Here, [M] represents the content (mass%) of the element M. However, if the amounts of Si and 10 X P both exceed 1.5%, the value of r deteriorates greatly. Therefore, the amounts of Si and P are set to 1.5% or less and 0.15% or less, respectively. In addition, in the case where the high-strength cold-rolled steel sheet of the present invention is alloyed with hot-dip galvanizing 10 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032, these elements are likely to cause poor adhesion of the key layer, so The amount of Si is preferably not more than 5%, and the amount of P is preferably not more than 0.8%. In addition, since Si and P are effective elements for solid-solution strengthening of ferrous grain iron, the amount of Si is preferably 0.003% or more, and the amount of P is preferably 0.01% or more. 3) Other ingredients

C: C is a carbide that is combined with Ti and Nb. If the amount exceeds 0.015%, the amount of this carbide will increase and the r value will decrease significantly. Therefore, the amount of C is below 0.015%, preferably below 0.8%, and more preferably Less than 0. 0 0 4%. However, C also has the effect of increasing the strength by precipitation strengthening in the form of T i C and N b C. Therefore, it is more effective to contain a content of 0.04% or more in a steel having a TS of about 4 40 MPa. . That is, if the amount of C is 0.004 to 0.008%, and Ti and Nb are added at an atomic ratio of 1.0 or more to 1.0, it is possible to suppress a decrease in the r value and increase the design strength. In addition, in the case where the amount of C is less than 0.05%, the iron particles of the fertilizer grains are coarsened during annealing, and the surface texture is prone to be roughened during the press forming, so the amount of C is set to 0. 0 0 0 5 More than% is preferred. Μ η: Μ η is an element that increases strength through solid solution strengthening, and is an indispensable element in high-strength cold-rolled steel sheets. To obtain a TS of 340 MPa or more, the Mη amount must be 0.4% or more. On the other hand, if the amount exceeds 3%, the r value decreases significantly. Therefore, the amount of η is set to 3% or less, preferably 2 ° / 0 or less, and more preferably 1.5% or less. Although the reason why the increase in the amount of Mn decreases the r value is not necessarily clear, it is thought that the value of r decreases due to the interaction between Mn and the solid solution C. Furthermore, it is speculated that M η lowers the Ar3 abnormality point, so that the precipitated carbides are miniaturized during hot rolling, and the precipitation of carbides is delayed and the solid solution C is increased. Therefore, it is not possible to form a favorable 11 312XP / Invention Specification (Supplement) during annealing ) / 94-05 / 94105020 200532032 The recrystallized aggregate structure at the r value reduces the r value. S: S is present in steel in the form of sulfides. If the amount exceeds 0.02%, the ductility is deteriorated. Therefore, the amount of S is 0.02% or less, and preferably 0.01% or less. From the viewpoint of descaling and rust-removing properties, the amount of S is desirably 0.04% or more. N: If the amount of N exceeds 0.01%, fine A 1 N, N b N, N b (C, N) precipitates at the iron grain boundaries of the fertile grains during continuous casting of the flat steel slab, making the grain boundaries brittle It is easy to crack on the surface of the flat steel blank during casting and subsequent rough rolling. Therefore, the amount of N is set to 0.01% or less. In addition, the smaller the amount of N, the better, but the limit of φ in the current steelmaking technology is about 0.01%. T i: T i has the effect of miniaturizing crystal grains after hot rolling, and forming precipitates with C and N, reducing the solid solution C and N, and increasing the r value. To make full use of this Ti effect, it is necessary to satisfy the following formula (1) and add Ti. 1 ^ ([Ti] / 48) / ([C] / 12 + [N] / 14) ... (1) Here, [M] represents the content (mass%) of the element M.

However, even if the amount of T i exceeds 0.2%, the increase in r value is still small, so the amount of T i is made 0.2% or less. In addition, in the case where the high-strength cold-rolled steel sheet according to the present invention is alloyed with fused zinc, from the viewpoint of preventing uneven plating, the Ti amount is preferably 0.4% or less. In order to obtain a high r value due to the addition of T i, it is preferable that the amount of T i be 0.5% or more. The remainder is Fe and inevitable impurities. In addition to the above components, more than 002% of NbO is added to obtain a higher r value. In addition, at this time, the amounts of Nb, Ti, C, and N must be adjusted so as to satisfy the following formula (3). ([Nb] / 93 + [Ti] / 48) / ([C] / 12 + [N] / 14)… (3) 12 312XP / Invention Specification (Supplement) / 94-05 / 94105020

200532032 Here, [M] represents the content (mass%) of the element M. However, if the amount of Nb is more than 0.02%, fine Nb Ν, Nb (C, N) will be precipitated at the iron grain boundary in the continuous casting of the flat steel slab, making the grain boundary brittle and in the flat steel slab. During casting and subsequent rough rolling, chipping occurs on the surface of the flat steel blank. Therefore, the amount of N b is set to 0.02% or less. If B is added more than 0.01%, the secondary resistance can be improved. However, if the amount of B is more than 0.03%, the good effect of resistance to secondary working embrittlement is small, and conversely, the r value is reduced and the rolling load is increased. Therefore, the amount of B is made 0.003% or less. In addition, in order to improve the strength and improve the resistance to secondary processing brittleness, Cu: 0.03 to 0.5% or less, Ni: 0.03 to or less, and Cr: 0 · 0 3 to 0 · 5% or less can be added. At least one element selected from the group consisting of Μ0: 0 · 0.5 to 0.3% or less, and V: 0 to 0.5% or less. At this time, Cu deteriorates the surface quality, so the amount is made 0.5% or less. The addition of Ni increases the cost significantly, so its amount is 0.5% or less. Μ 〇 has a small adverse effect on the secondary additive properties and is effective for high strength. However, because the yield is increased and the surface fineness of the pressurized parts is deteriorated, the amount is 0.3%. The secondary processing brittleness has a small adverse effect and is effective in improving it. However, if it exceeds 0.5%, the cost will increase significantly, so the amount is set to 0. When Cu is added, it is desirable that Ni and Cu be contained in equal amounts. In terms of improving the appearance of bond zinc, bond zinc adhesion, fatigue properties, and toughness of the stretched part formed by pressing, it contains S b: 0.0 2 to 0.2% and S η: 0. 0 0 2 At least one element selected from 0.2% or less, and the following formula (4) is more effective. 312XP / Invention Specification (Supplement) / 94-05 / 94105020 [time, time, and brittleness change 〇 Because of spring, r 0.5% .005, C r is increased, the brittleness point is increased. Intensity 5 0 / 〇 at time and satisfies 13

200532032 0. 0 0 2 ^ [Sb] + [Sn] / 2 $ 〇 2 (4) Here, [M] represents the content (mass%) of the element M. The addition of Sb and Sn can prevent surface nitriding and oxidation during annealing caused by flat steel billet heating, coil box annealing furnace (BAF), continuous annealing streamline (CAL), continuous molten plating (CGL), etc. 'And to improve unevenness and deterioration of coating adhesion. In addition, it prevents the adhesion of zinc oxygen in the zinc bath and improves the appearance of the plating. Furthermore, Sb and Sn reduce the deterioration of the surface suppressive fatigue characteristics and the deterioration of the toughness after stretch forming. However, if the amounts of S b and S η exceed 0.2%, the galvannealed blade will deteriorate. 4) Manufacturing method The high-strength cold-rolled steel sheet of the present invention is provided with a step of heating a flat steel slab having the upper temperature at 1080 to 1350 ° C, and heating the steel slab to (A r 3 abnormal point-2) to (A r 3 abnormal point + 15 0) ° C The step of hot rolling to make a hot rolled steel sheet at the end temperature, the case where N b is added to the hot rolled steel sheet satisfies the following formula (5); when N b is added Then, the coiling temperature CT of the full-type (6) is rolled up, the rolled plate is cold rolled at a reduction ratio of 50 to 90% to make a cold rolled steel sheet, and the cold rolled steel sheet is rolled at 7 Continuous annealing at 50 to 870 ° C; or to 750. (: The manufacturing method of the closed box annealing step can produce 480SCTS 580 + 0.17 / {([Ti] + 〇.〇8x [so 1 · Α1]) χ [Ρ]} · 480580 + 0. 17 / ((0. 6x [Nb] + [Ti] + 0.08x [sol. A1]) x [P]} Here, [M] is the content (mass ° /.) Of the element M.

In order to make the Fe-Ti-P and Fe-Nb-P 312XP / Invention Specification (Supplement) / 94-05 / 94105020 in the flat steel blank, the closed zinc streamline is good for oxidation and viscosity of the mineral deposits. After the composition, the flattened milk is made without adding the following hot-rolled steel steps, and is fully solid-dissolved with P 0 14 200532032 of 600 (5)… (6). The heating temperature SRT before hot rolling must be Above 1 0 0 0 ° C. However, if it exceeds 1 350 ° C, the surface quality deteriorates, so S R T must be 1 350 ° C or less. In order to obtain excellent appearance, it is better to remove not only the primary scale but also the secondary scale generated during hot rolling. In addition, during hot rolling, heating may be performed through a rod heater. Finish rolling temperature F D T of hot rolling In order to refine the microstructure after hot rolling, it must be (A r 3 transformation point-2 0) to (A r 3 transformation point + 1 5 0) ° C.

The coiling temperature after hot rolling greatly affects the r value of the cold-rolled steel sheet of the present invention in which A1, P, T i and optionally Nb are added in combination. The reason is that the IF steel added with P is inferior to the r value as described above and easily generates P compounds such as Fe-Ti-P and Fe-Nb-P. Generally, if the coiling temperature is high, the precipitates are coarsened, and the solid solution C is reduced, the r value is significantly increased. However, if the coiling temperature exceeds the appropriate cutting temperature and becomes high, P compounds as described above are formed, and the r value is significantly reduced. Therefore, for steels with various A1, P, T i and Nb as needed, the most suitable coiling temperature was investigated. As a result, it was found that if the coiling temperature CT exceeds 580 + 0.17 / {([[ Ti] + 0.08x [sol.Al]) x [P]}, if the addition of Nb exceeds 580 + 0.17 / {(0.6x [Nb] + [Ti] + 0.08x [sol.Al]) x [P] generates P compounds and the r value decreases significantly. In addition, if the coiling temperature C T is lower than 48 ° C., even if no P compound is formed, the precipitation of carbides during coiling is insufficient, and the r value is deteriorated. Therefore, the coiling temperature C T must satisfy the above-mentioned formula (5) or (6).

In addition, in the temperature range between (upper limit value-4 0) to (upper limit value) of the above formulas (5) and (6) ° C 15 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 Which is better. In the cold rolling, from the viewpoint of increasing the r value, the reduction ratio must be 50 to 90%, preferably 65 to 80 ° / 〇.

The annealing temperature A T must be 750 to 870 ° C in the case of continuous annealing with C a 1 and C G L. At temperatures below 750 ° C, recrystallization is not sufficient to achieve high r values. In addition, characteristics such as elongation deteriorate significantly. At temperatures exceeding 870 ° C, steel sheets with a large amount of M η become annealed above the A r 3 transformation point, the strength is extremely increased and extended, and the value of η is significantly deteriorated. In order to achieve higher r value and higher elongation, it is better to anneal at a temperature above 820 ° C. In the case of BAF annealing, since the annealing time is long, the annealing temperature AT must be 600 to 75 ° C. For annealed cold-rolled steel sheets, zinc-containing coatings can also be applied via electroplating or hot-melt plating if necessary. Examples of the zinc-containing plating layer include galvanizing, galvanizing, and galvanizing nickel alloy. Moreover, you may provide an organic film treatment after plating. (Example) After melting the steels of steel Nos. A to X shown in Table 1, a 230 mm thick flat steel blank was continuously cast. This flat steel billet was reheated at the heating temperature SRT shown in Table 2, and then hot rolled at the finishing rolling temperature FDT shown in Table 2 to a plate thickness of 3.2 mm, and was applied at the coiling temperature CT shown in Table 2. Take-up. This hot-rolled sheet was cold-rolled to a sheet thickness of 0.8 mm, and then annealed at the annealing temperature AT shown in Table 2 via CAL, CGL, and BAF, and then subjected to temper rolling with an elongation of 0.8% to produce a steel sheet No. 1 to 34. In addition, in CGL, the annealed steel sheet was immersed in a hot-dip galvanizing bath at 460 ° C, and then subjected to an in-line alloying treatment furnace at 500 ° C at 16 312XP / Invention Specification ( Supplement) / 94-05 / 94105020 200532032 Alloying treatment. The apparent amount of bond layer is 45g / m2 per side. Then, the r value and TS were measured by the method described above. The surface defects were visually inspected and the surface quality was investigated. The results are shown in Table 2. [Nb] in the formulas at the top of Tables 1 and 2 is regarded as 0 when Nb is not added. The steel plates Nos. 1 to 24 of the examples of the present invention can obtain TS of 340 to 400 MPa, r value of 1.8 or more, TS of 400 to 590 MPa, and r value of 1.6 or more. The surface φ surface quality is also good. Further, when compared with a comparative example of the same strength, it can be seen that the r value of the example of the present invention is significantly higher. In particular, if the amount of M η exceeds 1%, the effect can be remarkably observed. On the other hand, in the steel plates N 0.25 to 34 of the comparative example, it was impossible to obtain a T S of 340 to 400 MPa, an r value of 1.8 or more, a TS of 400 to 590 MPa, and r

The value is 1.6 or more. Steel plates Nos. 27, 28, and 29 corresponding to conventional high-strength cold-rolled steel plates having a high M η content have low r values. In addition, in the steel plate Nos. 30, 31, 32, 33, and 34, the (Nb + Ti) / (C + N) ratio, C, Si, Mn, P, sol.Al, and Nb are all outside the scope of the present invention, and r The value is low. Among them, the amount of C and the (Nb + Ti) / (C + N) ratio have not been tailored, and the solid solution C and M η coexist, which is equivalent to the steel sheet N of the conventional low-carbon high-strength cold-rolled steel sheet 0.30 , Even if you increase s ο 1. A 1 can not achieve a high r value. Further, Nb or Nb and sol. Al are steel plates No. 3 1 > 3 4 which are out of the scope of the present invention, and have poor surface quality. In addition, if the steel plate No. 25 equivalent to the conventional soft cold-rolled steel plate SPC 2 7 0 F is compared with the steel plate No. 26 in which a large amount of sol.Al is added, it can be seen that even if the M η and P contents are low and added s ο 1. A 1, increase the value of 17 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 The effect is still small.

312XP / Invention Specification (Supplement) / 94-05 / 94105020 18 200532032

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3] 2XP / Invention Manual (Supplement) / 94-05 / 94105020 21

Claims (1)

200532032 X. Scope of patent application: 1. A high-strength cold-rolled steel plate characterized by C: 0. 15% or less, Si: K 5% or less, M η: 0.4 to 3 %, P: 0 · 15% or less, S ·· 0 · 0 2% or less, sol. Α1: 0.1 to 1%, N ·· 0. 1% or less, T i: 0.2% or less , The remaining part is F e and unavoidable impurities, and satisfies the following formula (1); ([Ti] / 48) / ([C] / 12 + [N] / 14)… (1) where [ M] represents the content (% by mass) of the element M. 2. The high-strength cold-rolled steel sheet according to item 1 of the scope of the patent application, wherein mass% is s ο 1 · A 1: 0 · 2 to 0 · 7%. 3. For example, the high-strength cold-rolled steel sheet of item 1 of the patent application scope satisfies the following formula (2); 0. [Si] + 10x [P] ^ 1.4… (2) where [M] represents an element M content (% by mass). 4. If the high-strength cold-rolled steel sheet of item 2 of the patent application is to satisfy the following formula (2); 0. [Si] + 10x [P] ^ 1.4… (2) where [M] represents an element M content (% by mass). 5. The high-strength cold-rolled steel sheet according to item 1 of the scope of patent application, which further contains N b in terms of mass%: 0 · 0 02 to 0 · 0 2% or less, and satisfies the following formula (3); ( [Nb] / 93 + [Ti] / 48) / ([C] / 12 + [N] / 14) (3) Here, [M] represents the content (mass%) of the element M. 6. If the high-strength cold-rolled steel sheet in item 4 of the scope of patent application, which further includes 22 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 step contains Nb in mass%: 0.002 to 0.02% or less, And satisfy the following formula (3); ([Nb] / 93 + [Ti] / 48) / ([C] / 12 + [N] / 14) ... (3) where [M] represents the element M Content (mass%). 7. The high-strength cold-rolled steel sheet according to item 1 of the scope of patent application, which further contains B ·· 0.0 0 0 1 to 0 · 0 0 3% by mass%. 8. The high-strength cold-rolled steel sheet according to item 6 of the scope of patent application, which further contains B in terms of mass%: 0 · 0 0 0 1 to 0. 0 3% or less. 9. The high-strength cold-rolled steel sheet according to item 1 of the scope of patent application, which further contains Cu in terms of mass%: 0 · 0 3 to 0 · 5% or less, Ni · · 0 · 0 3 to 0.5 % Or less, (: 1 *: 0.03 to 0.5% or less, 0: 0.05 to 0.3% or less, and V: 0.005 to 0.5 ° / ◦ or less. At least one element selected from the following. 1 0. The high-strength cold-rolled steel sheet according to item 8, further comprising C m 0.3 to 0.5% or less, Ni: 0.3 to 0.5% or less, and Cr: 0.03 to 0.5% in terms of mass%. At least one element selected from the following: Mo: 0.05 to 0.3% or less and V: 0.05 to 0.5% or less. 1 1. If the high-strength cold-rolled steel sheet of the first scope of the patent application, It further contains at least one element selected from the mass% of S b: 0.02 to 0.2% or less and S η · 0.2 to 0.2% or less, and satisfies the following formula (4); 0. 0 0 2 $ [Sb] + [Sn] / 2S 0 · 2… (4) where [M] represents the content (% by mass) of the element M. 1 2. If the scope of patent application is the first High-strength cold-rolled steel sheet of item 0, further containing self-quality Including Sb ·· 0 0 2 to 0.2% or less and Sn: 0.002 23 312XP / Invention Specification (Supplement) / 94-05 / 94105020 200532032 to 0 · 2% or less Element, and satisfies the following (4); 0. 0 0 2 ^ [Sb] + [Sn] / 2 ^ 0.2. (4) ~ [M] represents the content (% by mass) of the element M. 1 3. A method for manufacturing a high-strength cold-rolled steel sheet, characterized by the steps of: heating the embryo at a temperature of 1080 to 1350 ° C; The flat steel blank after heating is hot-rolled at the finishing rolling temperature of (A r 3 abnormal point-2 0) to (A r 1 φ point + 1 50) ° C to make a hot-rolled steel sheet; The rolled steel sheet meets the coiling temperature 3 of the following formula (5) or (6), and the coiling step is performed. The hot-rolled steel sheet after the coiling is applied at a reduction ratio of 50 to 90% to be cold rolled. Step of steel sheet; and step of continuously annealing the cold-rolled steel sheet at 750 to 870 ° C, or closed box annealing at 750 ° C; 480 SCTS 580 + 0. 1 7 / {([Ti] + 0 · 08x [sol · Al]) x [P]} ... (5) 480 580 + 0. 1 7 / ((0. 6x [Nb] + [Ti] + 0.08x [sol. A1]) x [P]} where [M] represents the content (% by mass) of the element M. Formula Step for steel metamorphosis: CT cold rolling 600 (6) 1] 2XP / Invention specification (Supplement) / 94-05 / 94105020