KR101143157B1 - High strength cold rolled steel sheet having aging resistance and superior workability, and process for producing the same - Google Patents

Abstract

A high strength cold rolled steel sheet used as a material for automobiles, home appliances and the like, and a manufacturing method thereof. The cold-rolled steel sheet according to claim 1, wherein the cold-rolled steel sheet contains 0.0005-0.003% of C, 0.003-0.025% of S, 0.01-0.08% of Al, 0.004% or less of N, 0.01-0.2% 0.1 to 0.8% of Si, and 0.2 to 1.2% of Cr, wherein the content of P is 0.03 to 0.2% when only one kind of P is contained, and the content of P and S Satisfies the condition 0.5 * Cu / S: 1-10 and is composed of remaining Fe and other unavoidable impurities, and the average size of CuS precipitates is 0.1 탆 or less. According to the present invention, fine CuS precipitates reduce the amount of solid carbon in the crystal grains and improve the aging characteristics and workability.

Cold rolled steel sheet, durability, high strength, plastic anisotropy index, CuS precipitate

Description

 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength cold rolled steel sheet having a high workability,

Fig. 1 is a graph showing changes in the amount of solid carbon in the crystal grains depending on the size of the CuS precipitate.

2 is a graph showing the size of CuS precipitates with respect to the cooling rate,

2 (a) shows the case of 0.5 * Cu / S: 2.56,

2 (b) shows the case of 0.5 * Cu / S: 8.1,

2 (c) shows the case of 0.5 * Cu / S: 28.

The present invention relates to a high-strength cold-rolled steel sheet used as a material for automobiles, household appliances, and the like. More particularly, the present invention relates to a cold-rolled steel sheet having improved aging resistance characteristics and workability by controlling the amount of solid carbon in the crystal by fine precipitates and a method for producing the same.

Cold rolled steel sheets used in automobiles and home appliances are required to have strength and moldability as well as resistance to aging. Aging is a kind of deformation aging phenomenon that causes defects such as stretcher strain due to hardening as the interstitial elements C and N stick to the electric potential over time.

The durability of the cold-rolled steel sheet can be ensured by the application of aluminum-killed steel. It has the disadvantage that the productivity is low due to the long annealing time and the material variation is very large in each part. Therefore, Interstitial Free Steel, which is continuously annealed by adding strong carbon and nitride forming elements such as Ti and Nb, is mainly used.

In order to produce an IF steel, Ti, Nb, etc., which are strong carbon and nitride forming elements, are added, and these elements must be annealed at a high temperature because they raise the recrystallization temperature. This lowers productivity and increases energy costs. In addition, when annealing is performed at a high temperature, various defects such as fine scratches and shape defects are likely to occur. Also, since Ti and Nb are highly oxidative, many nonmetallic inclusions are generated in steel making to cause surface defects of the steel sheet. In addition, the IF steel has a disadvantage in that so-called secondary machining brittleness occurs in which the grain boundary is weak and brittleness is generated after machining. To prevent this, efforts have been made to prevent brittleness of secondary processing by adding elements such as B and the like. Particularly, in the case of IF steel, there are disadvantages in that many defects occur in products that are subjected to surface treatment such as plating and painting.

In order to solve this problem, Ti and Nb-free alloys without Ti or Nb have been proposed. For example, in JP-A Nos. 6-093376, 6-093377 and 6-212354, Ti and Nb are not added and instead, 0.0001 to 0.003% of B is added to 0.0001 to 0.003% It is a technology to improve Hyosung. However, in this prior art, endurance is not sufficient, and quenching after annealing is recommended in order to secure endurance. In this case, since quenching is mostly water cooling, the surface is not good and additional cost is required because the pickling treatment is performed again in order to remove the oxide film generated in the water cooling. In addition, these steel types have disadvantages of low strength, high in-plane anisotropy, wrinkles, and ear inconvenience.

On the other hand, the present inventors have proposed a method of manufacturing a cold-rolled steel sheet capable of improving yield strength in a high-strength steel having a tensile strength of 340 MPa without adding Ti and Nb in Korean Patent Publication No. 2002-0049667. A method for producing a cold-rolled steel sheet comprising the steps of: C: 0.0005-0.003%, Mn: 0.1% or less, S: 0.003-0.02%, P: 0.03-0.07%, Al: 0.01-0.1% , Cu: 0.05-0.3%, and Cu / S atomic ratio of 2 to 10 are subjected to hot rolling at an Ar ₃ transformation point or higher, cold rolling at a reduction ratio of 50 to 90%, and heat treatment at a temperature of 700 For 5 minutes. The cold-rolled steel sheet thus obtained had a yield strength of 240 MPa . However, since the aging index is larger than 30 MPa, the aging property can not be guaranteed. In addition, the plastic anisotropy index (r _m ) is required to be improved to 1.8, and the in-plane anisotropy index is higher than 0.5, which causes a problem of wrinkles.

On the other hand, a cold rolled steel sheet having a high yield strength and having an increased strength of Mn and P added to the ultra low carbon steel and Ti added thereto is known. This cold-rolled steel sheet has a ductile-brittle transition temperature of 0 to 30 ° C, which is insufficient in secondary workability to such an extent that fracture occurs even at room temperature.

It is an object of the present invention to provide a cold-rolled steel sheet improved in workability and anti-aging properties without addition of Ti and Nb, and a method of manufacturing the same.

In order to achieve the above object, the cold-rolled steel sheet of the present invention is characterized in that it comprises 0.0005-0.003% of C, 0.003-0.025% of S, 0.01-0.08% of Al, 0.004% or less of N, 0.01-0.2% , Wherein the content of P is 0.2% or less, the content of Si is 0.1 to 0.8% and the content of Cr is 0.2 to 1.2%, and if the P contains only one species, the content of P is 0.03 to 0.2% The Cu and S satisfy the condition 0.5 * Cu / S: 1-10, and are composed of the remaining Fe and other unavoidable impurities. The average size of the CuS precipitates is 0.1 탆 or less.

The method for producing a cold-rolled steel sheet according to the present invention is a method for producing a cold-rolled steel sheet having a composition comprising 0.0005-0.003% C, 0.003-0.025% S, 0.01-0.08% Al, 0.004% Wherein the content of P is 0.2% or less, 0.1 to 0.8% of Si, 0.2 to 1.2% of Cr, and the content of P is 0.03 to 0.2% when only one of P is contained , The Cu and S satisfy the condition 0.5 * Cu / S: 1-10 and the remaining Fe and other unavoidable impurities are reheated to a temperature of 1100 캜 or higher, and the finish rolling temperature is set to be higher than the Ar ₃ transformation point, Rolling, cooling at a rate of 300 DEG C / min or more, winding at a temperature of 700 DEG C or less, cold rolling, and continuous annealing.

In the present invention, the content of S is preferably more than 0.02 to 0.025%. It is most preferable that Cu and S satisfy the condition 0.5 * Cu / S: 1-3. The cold-rolled steel sheet of the present invention may further contain 0.01 to 0.2% of Mo and 0.01 to 0.2% of V. It is most preferable that V and C satisfy the condition 0.25 * V / C: 1 to 20 when V is included.

Hereinafter, the present invention will be described in detail.

The present inventors have found the following new facts in the research process for improving the aging property without addition of Ti and Nb. That is, fine CuS precipitates improve the aging resistance characteristics by appropriately controlling the amount of solid carbon in the crystal grains. These precipitates also have a positive effect on strength properties, plastic anisotropy index, in-plane anisotropy index, and secondary work-hardening brittleness.

As shown in FIG. 1, it can be seen that as the precipitate of CuS is finely distributed, the amount of the solid carbon in the crystal grains decreases. Since the solid carbon remaining in the crystal grains is relatively free to move, it binds with the movable potential and affects the aging characteristics. Therefore, if the amount of the solid carbon in the crystal grains is reduced to a certain level or less, the aging resistance is improved. From the viewpoint of securing the aging property, the amount of the solid carbon in the crystal grains is preferably about 15 ppm or less. 1, when the CuS precipitate is distributed at a size of about 0.1 mu m or less, the amount of dissolved carbon in the crystal grains can be controlled to about 15 ppm or less. As described above, it is important to finely distribute CuS precipitates in order to control the amount of solid carbon in the crystal grains to about 15 ppm or less. In the present invention, by using fine CuS precipitates, the carbon content in steel can be increased to 0.003%, which is a small load in the steelmaking process, while securing the resistance to aging.

With this new fact in mind, we have been studying how to finely distribute precipitates. As a result, it is necessary to control the contents of Cu and S and their composition ratios, and it is also possible to obtain a fine precipitate by controlling the cooling rate after the rolling process. That is, (1) it is necessary to adjust the weight ratio of Cu and S (0.5 * Cu / S) to 1 to 10, while setting the content of Cu to 0.01 to 0.2% and the content of S to 0.003 to 0.025% 2) In addition, when the cooling rate is 300 ° C / min or more after completion of the pressure rolling, fine CuS precipitates of 0.1 μm or less can be obtained. Such properties are realized in a high-strength steel sheet to which at least one of solid solution strengthening elements such as P, Si, Cr and the like is added.

That is, FIG. 2 (a) is a graph showing the results of hot rolling a steel (0.5 * Cu / S: 2.56) having 0.0018% C-0.18% Si-0.01% P-0.009% S-0.05% Al-0.0015% N-0.046% And the size of the precipitate according to the cooling rate. The graph of FIG. 2 (a) shows that when the cooling rate is adjusted for the case where the composition ratio of Cu and S (0.5 * Cu / S) is 10 or less, the precipitate size of CuS can satisfy 0.1 탆 or less .

When V is additionally added to the steel in which the fine CuS precipitates are distributed, the remaining solid carbon is precipitated as carbonitride, and the non-aging property can be secured. Or, when Mo is added, the plastic anisotropy index is increased and the workability is improved.

The cold-rolled steel sheet of the present invention and its manufacturing method will be described in detail below.

[Cold rolled steel sheet of the present invention]

The content of carbon (C) is preferably 0.0005-0.003%.

When the content of carbon is more than 0.003%, it is difficult to secure endurance due to a large amount of carbon in solid in steel, and the crystal grains of the annealed plate become finer and the ductility is greatly lowered. When the content of carbon (C) is less than 0.0005%, the crystal grains of the hot-rolled steel sheet may have a low strength and an in-plane anisotropy. In the present invention, since the amount of dissolved carbon in the crystal grains can be lowered by the CuS precipitate, the content of carbon can be increased up to 0.003%, and the decarburization treatment for decreasing the carbon content can be omitted. The content of such carbon is in the range of more than 0.002% to 0.003% or less.

The content of sulfur (S) is preferably 0.003-0.025%.

When the content of sulfur (S) is less than 0.003%, the amount of precipitated CuS is not only small but also the size of precipitated CuS is very large and the anti-aging property is not good. When the content of sulfur is more than 0.025%, the content of sulfur dissolved is large, so that ductility and moldability are greatly lowered, and there is a fear of heat brittleness. When the sulfur content is in the range of 0.02 to 0.025%, it is easy to control the precipitate size of CuS to a desired range.

The content of aluminum (Al) is preferably 0.01-0.08%.

Aluminum is an element to be added as a deoxidizer, but in the present invention, nitrogen is added to the steel in order to completely prevent aging by solid nitrogen. When the content of aluminum is less than 0.01%, the amount of solute nitrogen is large and the aging phenomenon can not be completely prevented. When the content of aluminum is more than 0.08%, the amount of aluminum existing in a solid state is large.

The content of nitrogen (N) is preferably 0.004% or less.

Nitrogen is an element which is inevitably added during steelmaking. When it exceeds 0.004%, the aging index becomes high.

The content of copper (Cu) is preferably 0.01 to 0.2%.

When the content ratio of copper to sulfur (S) and the cooling rate before winding in the hot rolling process become appropriate, CuS precipitates of 0.1 탆 or less are formed to reduce the solid carbon in the crystal grain, thereby improving the aging characteristics, in-plane anisotropy and plastic anisotropy Based on the research, 0.01 to 0.2% is added. If the content of copper is 0.01% or more, CuS can be precipitated finely. If Cu content exceeds 0.2%, coarse CuS precipitates and the aging resistance characteristic becomes poor.

The weight ratio of Cu to S is preferably 0.5 * Cu / S: 1 to 10.

Cu and S are bound to form CuS, which differs depending on the amount of Cu and S added, affecting the aging index, plastic anisotropy index and in-plane anisotropy index. According to the study of the present invention, effective CuS precipitates are precipitated when the addition ratio of Cu and S (0.5 * Cu / S, wherein the content of Cu and S is in weight%) is 1 or more, The Aging Aggregate Index increases, and the properties of plastic anisotropy index and in-plane anisotropy index are not good.

As the solid solution strengthening element, one or more kinds of P, Si and Cr

The content of phosphorus (P) is preferably 0.2% or less.

Phosphorus assures a high strength in the steel which controls CuS precipitates according to the present invention as an element with a low effect of strengthening solid solubility and a decrease in r value. In order to secure high strength by phosphorus, the phosphorus content is preferably 0.2% or less. When the phosphorus content is more than 0.2%, the ductility is undesirably low. When phosphorus alone is added as a solid solution strengthening agent, the content of phosphorus is preferably 0.03 to 0.2%. When the phosphorus is added alone, the phosphorus content should be 0.03% or more so that the strength can be secured. In the case of adding phosphorus together with one or two of Si and Cr, the target strength can be secured by suitably controlling the content of phosphorus at 0.2% or less. In this case, even if phosphorus content is less than 0.015%, high strength can be ensured.

The content of silicon (Si) is preferably 0.1-0.8%.

Silicon is a low-elongation element with a high solid solution strengthening effect, which ensures high strength in the steel which controls CuS precipitates according to the present invention. If the content of silicon is 0.1% or more, the strength can be secured. If the content is more than 0.8%, the ductility is lowered.

The content of chromium (Cr) is preferably 0.2 to 1.2%.

Chromium lowers the secondary process brittle temperature and lowers the aging index due to Cr carbide, while enhancing the solid solution strengthening effect. According to the present invention, high strength is ensured in the steel which controls CuS precipitates, and the in-plane anisotropy index is also lowered. If the content of chromium is 0.2% or more, the strength can be secured. If the content of chromium exceeds 1.2%, the ductility is lowered.

At least one of molybdenum (Mo) and vanadium (V) may be further added to the steel thus formed.                     

The content of molybdenum (Mo) is preferably 0.01 to 0.2%.

Molybdenum is added as an element to increase the plastic anisotropy index. When the content is more than 0.01%, the plastic anisotropy index becomes large. When the content exceeds 0.2%, plastic anisotropy index does not increase any more and may cause hot brittleness.

The content of vanadium (V) is preferably 0.01 to 0.2%.

Vanadium is added to precipitate solute C to secure non-aging properties. When the content is more than 0.01%, non-aging characteristics can be obtained. When the content exceeds 0.2%, the plastic anisotropy index is lowered. It is more preferable that the weight ratio of V and C (0.25 * V / C, V, C content is% by weight) satisfies 1-20. If the weight ratio of V and C is less than 1, the precipitation effect of the solid solution C is not large. If the weight ratio of V and C is more than 20, the plastic anisotropy index is low.

The average size of the CuS precipitates is preferably 0.1 탆 or less.

According to the results of the present invention, the size of the CuS precipitates directly affects the aging index, the plastic anisotropy index and the in-plane anisotropy index. When the average size of the CuS precipitates exceeds 0.1 μm, the aging index increases sharply, Anisotropy index and in-plane anisotropy index are not good. Therefore, the average size of the CuS precipitates is preferably 0.1 탆 or less.

 [Production method of cold-rolled steel sheet]

The present invention is characterized in that an average size of CuS precipitates in the cold rolled steel sheet is 0.1 mu m or less through hot rolling and cold rolling. The size of the CuS precipitates in the cold rolled sheet is affected by the ratio of Cu / S and the manufacturing process, but is directly affected by the cooling rate especially after hot rolling.

[Hot rolling condition]

In the present invention, the steel satisfying the above-mentioned stress is reheated and hot-rolled. The reheating temperature is preferably 1100 DEG C or higher. When the reheating temperature is less than 1100 ° C, the coarse CuS produced during the continuous casting remains in a completely undissolved state due to the low reheating temperature, and a large amount of coarse CuS remains after the hot rolling.

The hot rolling is preferably carried out under the condition that the finishing rolling temperature is equal to or higher than the Ar ₃ transformation temperature. When the finishing rolling temperature is lower than the Ar ₃ transformation temperature, not only the workability is lowered due to the production of the pressure-relief but the ductility is greatly reduced.

The cooling rate before hot rolling is preferably 300 DEG C / min or more. According to the present invention, even if the composition ratio of Cu and S (0.5 * Cu / S) is 10 or less, if the cooling rate is less than 300 캜 / min, the precipitate size of CuS exceeds 0.1 탆. That is, as the cooling rate is increased, a large number of nuclei are generated and the CuS precipitates become finer. When the composition ratio of Cu and S (0.5 * Cu / S) is more than 10, even if the coarse CuS precipitates unreacted in the reheating process are increased, the number of new nuclei is small and the precipitates are not fine 0.006% C-0.45% Si-0.01% P-0.006% S-0.03% Al-0.0015% N-0.15% Cu). 2, it is not necessary to limit the upper limit of the cooling rate since the size of the CuS precipitates becomes finer as the cooling rate increases. However, even if the cooling rate is 1000 占 폚 / min or more, the effect of refining the precipitate does not further increase, so that the cooling rate is more preferably 300 to 1000 占 폚 / min. Figures 2A and 2B (0.0024% C-0.22% Si-0.009% P-0.008% S-0.04% Al-0.0024% N-0.09% Cu) show the size of the precipitate according to the value of 0.5 * Cu / S , CuS precipitates of 0.1 占 퐉 or less can be obtained stably than when the value of 0.5 * Cu / S is low. In the present invention, it is preferable to appropriately select the CuS precipitate under conditions of a cooling rate of 300 캜 / min or more such that the size of the CuS precipitate is 0.1 탆 or less.

[Winding condition]

After hot rolling as described above, winding is performed, and the winding temperature is preferably 700 DEG C or lower. If the coiling temperature is higher than 700 ° C, the CuS precipitates grow too coarse and the anti-aging properties are lowered.

[Cold rolling conditions]

The cold rolling is preferably performed at a reduction ratio of 50 to 90%. When the cold rolling reduction rate is less than 50%, the amount of annealed recrystallized nuclei is small, so that the grain size grows too large during annealing and the strength and formability are lowered due to coarsening of the annealed recrystallized grains. If the cold rolling reduction is more than 90%, the formability is improved but the amount of nucleation is too large, so that the annealed recrystallized grains become too fine and the ductility deteriorates.                     

[Continuous Annealing]

The continuous annealing temperature plays an important role in determining the material of the product. In the present invention, it is preferable to carry out the reaction in a temperature range of 500 to 900 ° C. When the continuous annealing temperature is less than 500 캜, the recrystallized grains are too fine to secure a desired ductility value, and when the annealing temperature exceeds 900 캜, the strength is lowered due to coarsening of the recrystallized grains. The continuous annealing time is maintained so that the recrystallization is completed. When the time is about 10 seconds or longer, the recrystallization is completed.

Hereinafter, the present invention will be described in more detail with reference to examples.

In the examples, the mechanical properties were measured by processing cold-rolled steel sheets into standard specimens according to ASTM E-8 standard. Yield strength, tensile strength, elongation, plastic anisotropy index ( _rm value), in-plane anisotropy index (Δr value) and aging index (AI) were measured using a tensile tester (INSTRON, Model 6025). In the examples, the plastic anisotropy index (r _m ) and the in-plane anisotropy index (? R) were obtained by the following formulas. _{r m = (r 0 + 2r} 45 + r 90) / 4, Δr = (r 0 -2r 45 + r 90) /

The average size of the precipitates and the number of precipitates in the specimen are the sizes and distribution numbers of all the precipitates present in the matrix.

[Example 1]

The steel slabs shown in Table 1 were reheated at 1,200 ° C. and finished by hot rolling, then cooled at a rate of 400 ° C./min, rolled at 650 ° C., cold rolled at a reduction ratio of 75% and subjected to continuous annealing. The finish rolling temperature was 910 占 폚, which is higher than the Ar3 transformation point, and continuous annealing was performed at 750 占 폚 for 40 seconds at a rate of 10 占 폚 / sec.

Psalter
number Chemical composition (% by weight) C P Si Cr S Al N Cu 0.5 *
Cu / S ≤0.003 ≤0.2 0.1-0.8 0.2-1.2 0.003-
0.025 0.01-0.1 ≤0.004 0.01-0.2 1-10 A1 0.0021 0.045 - - 0.015 0.04 0.0018 0.045 1.5 A2 0.0015 0.048 - - 0.013 0.03 0.0023 0.06 2.25 A3 0.0021 0.1 - - 0.011 0.04 0.0015 0.056 2.55 A4 0.0025 0.11 - - 0.011 0.04 0.0038 0.106 4.82 A5 0.0018 0.16 - - 0.008 0.05 0.0012 0.141 8.81 A6 0.0018 0.05 - - 0.01 0.02 0.0039 0.005 0.25 A7 0.0022 0.109 - - 0.011 0.05 0.0038 0.32 14.5 A8 0.0022 0.01 0.23 - 0.015 0.04 0.0014 0.045 1.5 A9 0.0024 0.009 0.21 - 0.012 0.05 0.0024 0.052 2.15 A10 0.0025 0.01 0.4 - 0.008 0.04 0.0018 0.045 2.81 A11 0.0015 0.012 0.43 - 0.01 0.04 0.0032 0.087 4.34 A12 0.0021 0.010 0.63 - 0.008 0.035 0.0012 0.141 8.81 A13 0.0026 0.01 0.25 - 0.01 0.03 0.0028 0.004 0.2 A14 0.0017 0.012 0.41 - 0.005 0.04 0.0032 0.221 22.1 A15 0.0024 0.01 - 0.30 0.012 0.04 0.0022 0.043 1.8 A16 0.0021 0.012 - 0.33 0.01 0.04 0.0018 0.05 2.5 A17 0.0024 0.009 - 0.60 0.009 0.05 0.0032 0.05 2.78 A18 0.0024 0.013 - 0.63 0.009 0.04 0.0028 0.078 4.33 A19 0.0016 0.009 - 0.95 0.005 0.04 0.0032 0.083 8.3 A20 0.0026 0.011 - 0.35 0.012 0.04 0.0028 0.008 0.33 A21 0.0025 0.009 - 0.61 0.011 0.05 0.0023 0.252 14

Sample number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(Δr) Aging index
(AI- (MPa) Secondary processing
Brittle
(DBTT-C) A1 265 360 49 1.85 0.24 25 - 70 0.05 Invention river A2 271 365 49 1.83 0.25 22 - 70 0.05 Invention river A3 301 410 41 1.73 0.24 21 - 50 0.06 Invention river A4 299 402 42 1.69 0.22 27 - 50 0.06 Invention river A5 352 456 35 1.53 0.18 21 - 40 0.09 Invention river A6 208 326 50 1.85 0.61 35 - 60 0.38 Comparative steel A7 278 382 39 1.59 0.58 45 - 50 0.55 Comparative steel A8 270 355 52 1.85 0.28 21 - 80 0.06 Invention river A9 271 359 48 1.75 0.28 28 - 80 0.06 Invention river A10 300 406 45 1.68 0.26 25 - 60 0.07 Invention river A11 306 409 43 1.63 0.25 22 - 60 0.07 Invention river A12 363 459 35 1.45 0.21 26 - 50 0.05 Invention river A13 231 346 45 1.79 0.61 49 - 70 0.49 Comparative steel A14 279 392 38 1.66 0.47 37 - 60 0.51 Comparative steel A15 262 356 48 1.75 0.25 19 - 80 0.07 Invention river A16 265 350 48 1.75 0.23 17 -80 0.07 Invention river A17 310 405 42 1.63 0.22 18 - 60 0.05 Invention river A18 302 408 40 1.58 0.22 20 - 60 0.05 Invention river A19 354 451 35 1.51 0.22 16 - 50 0.06 Invention river A20 212 339 47 1.74 0.49 37 - 70 0.38 Comparative steel A21 279 393 43 1.64 0.42 39 - 60 0.35 Comparative steel

[Example 2]

The steel slabs shown in Table 3 were reheated at 1,200 ° C. and finishing hot-rolled, then cooled at a rate of 550 ° C./min, rolled at 650 ° C., then subjected to cold rolling and continuous annealing at a reduction ratio of 75%. The finish rolling temperature of not less than Ar ₃ transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second.

Specimen Number Chemical composition (% by weight) 0.5
*
Cu / S C P S Cu Al N Mo 0.0005
-
0.003 0.03
-
0.2 0.003
-
0.025 0.01
-
0.2 0.01
-
0.08 ≤0.004 0.01
-
0.2 ≤10 B1 0.0025 0.052 0.012 0.054 0.023 0.0033 0.035 2.25 B2 0.0018 0.101 0.009 0.1 0.044 0.0018 0.08 5.56 B3 0.0024 0.155 0.01 0.12 0.025 0.0032 0.16 6 B4 0.0015 0.053 0.009 0.045 0.032 0.0023 0.26 2.5

Sample number Mechanical property Average size of precipitates
(탆) Remarks surrender
burglar
(Mpa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy index
(r _m ) In-plane
Anisotropy
Indices
(R) Aging index
(AI- (MPa) Secondary processing
Brittle
(DBTT-C) B1 265 355 48 2.18 0.27 25 - 80 0.06 Invention river B2 295 400 43 1.92 0.26 21 - 50 0.05 Invention river B3 362 459 36 1.77 0.24 26 - 40 0.08 Invention river B4 240 349 47 1.8 0.28 19 - 70 0.11 Comparative steel

 [Example 3]

The steel slabs shown in Table 5 were reheated at 1200 ° C and then subjected to finish hot rolling, followed by cooling at a rate of 550 ° C / min and winding at 650 ° C, followed by cold rolling and continuous annealing at a reduction ratio of 75%. The finish rolling temperature of not less than Ar ₃ transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second. The measurement of the mechanical properties was carried out in the same manner as in Example 1.

Psalter
number Chemical composition (% by weight) 0.5
*
Cu / S C Si P S Al N Cu Mo 0.0005
-
0.003 0.1
-
0.8 ≤0.2 0.003
-
0.025 0.01
-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 1-10 C1 0.0014 0.23 0.01 0.009 0.035 0.0034 0.05 0.022 2.78 C2 0.0025 0.45 0.009 0.011 0.025 0.0012 0.082 0.074 3.73 C3 0.0023 0.6 0.011 0.01 0.043 0.0022 0.1 0.17 5 C4 0.0026 0.25 0.009 0.011 0.043 0.0033 0.039 0.29 1.77

city
side
time
number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) Aging index
(AI- (MPa) Secondary processing
Brittle
(DBTT-C) C1 262 355 49 2.03 0.26 18 - 80 0.06 Invention river C2 295 394 44 1.80 0.21 25 - 60 0.08 Invention river C3 365 462 37 1.66 0.14 25 - 50 0.04 Invention river C4 261 356 46 1.75 0.26 29 - 80 0.09 Comparative steel

[Example 4]

Table 7 The steel slabs were reheated at 1200 DEG C and finishing hot rolled, then cooled at a rate of 550 DEG C / min, and then wound at 650 DEG C, followed by cold rolling and continuous annealing at a reduction ratio of 75%. Finishing rolling temperature is 910 ℃ than Ar ₃ transformation point, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second. The measurement of the mechanical properties was carried out in the same manner as in Example 1.

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S C Cr P S Al N Cu Mo 0.0005
-
0.003 0.2
-
1.2 ≤0.2 0.003
-
0.025 0.01
-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 1-10 D1 0.0014 0.33 0.011 0.01 0.034 0.0024 0.04 0.018 2 D2 0.002 0.6 0.012 0.011 0.044 0.0032 0.071 0.073 3.23 D3 0.0022 0.93 0.009 0.009 0.022 0.0012 0.08 0.15 4.44 D4 0.0016 0.33 0.01 0.01 0.032 0.0023 0.055 0.28 2.75

city
Ryo
time
number Mechanical property Precipitate
Average size
(탆) Remarks Yield strength
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) Aging index
(AI- (MPa) Secondary processing
Brittle
(DBTT-C) D1 252 356 47 2.03 0.31 15 - 80 0.06 Invention river D2 300 399 41 1.82 0.24 26 - 60 0.07 Invention river D3 361 455 34 1.73 0.19 26 - 50 0.06 Invention river D4 251 349 47 1.72 0.22 17 - 70 0.09 Comparative steel

[Example 4]                     

The steel slabs shown in Table 9 were reheated at 1200 DEG C and finishing hot-rolled, then cooled at a rate of 550 DEG C / min, rolled at 650 DEG C, and subjected to cold rolling and continuous annealing at a reduction ratio of 75%. The finish rolling temperature of not less than Ar ₃ transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second.

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S 0.25
*
V / C C P S Cu Al N V 0.0005
-
0.003 0.03
-
0.2 0.003
-
0.025 0.01
-
0.2 0.01
-
0.08 ≤0.004 0.01
-
0.2 1-10 1-20 E1 0.0015 0.055 0.01 0.052 0.043 0.0023 0.023 2.6 3.83 E2 0.0018 0.101 0.009 0.1 0.044 0.0018 0.072 5.56 10 E3 0.0024 0.155 0.01 0.12 0.025 0.0032 0.15 6 15.6 E4 0.0015 0.053 0.009 0.045 0.032 0.0023 0.26 2.5 43.3

city
Ryo
time
number Cognitive property Precipitate
Average size
(탆) Remarks surrender
burglar
(Mpa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) Aging index
(AI- (MPa) Secondary processing
Brittle
(DBTT-C) E1 224 357 47 1.82 0.32 0 - 70 0.07 Invention river E2 259 408 42 1.63 0.25 0 - 50 0.06 Invention river E3 316 460 36 1.52 0.19 0 - 40 0.09 Invention river E4 211 344 47 1.68 0.28 0 - 70 0.09 Comparative steel

 [Example 5]                     

A cold-rolled steel sheet was produced from the steel slab of Table 11 under the conditions of Example 1. Mechanical properties were also measured in the same manner as in Example 1.

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S 0.25
*
V / C C Si P S Al N Cu V 0.0005
-
0.003 0.1
-
0.8 ≤0.015 0.003
-
0.025 0.01
-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 1-10 1-20 F1 0.0012 0.25 0.009 0.011 0.023 0.0014 0.055 0.024 2.5 5 F2 0.0022 0.43 0.01 0.01 0.035 0.0032 0.078 0.069 3.9 7.84 F3 0.0027 0.63 0.008 0.008 0.034 0.0029 0.105 0.153 6.56 14.2 F4 0.0025 0.23 0.011 0.009 0.043 0.003 0.049 0.26 2.72 26

Psalter
number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) prescription
Indices
(MPa) Secondary processing
Brittle
(DBTT-C) F1 216 357 48 1.77 0.27 0 - 80 0.07 Invention river F2 259 405 43 1.62 0.24 0 - 60 0.09 Invention river F3 305 465 36 1.44 0.17 0 - 50 0.07 Invention river F4 211 356 47 1.57 0.21 0 - 80 0.09 Comparative steel

 [Example 6]

A cold-rolled steel sheet was produced from the steel slab of Table 13 under the conditions of Example 1. Mechanical properties were also measured in the same manner as in Example 1.                     

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S 0.25
*
V / C C Cr P S Al N Cu V 0.0005
-
0.003 0.2
-
1.2 ≤0.015 0.003
-
0.025 0.01
-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 1-10 1-20 G1 0.0012 0.35 0.01 0.009 0.034 0.0025 0.042 0.017 2.33 3.54 G2 0.0024 0.63 0.011 0.01 0.024 0.003 0.057 0.083 2.85 8.65 G3 0.0025 0.95 0.008 0.011 0.042 0.0032 0.082 0.16 3.73 16 G4 0.0019 0.32 0.012 0.008 0.026 0.0031 0.053 0.25 3.31 32.9

Psalter
number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) Aging index
(AI- (MPa) Secondary processing
Brittle
(DBTT-C) G1 222 350 47 1.72 0.25 0 - 80 0.08 Invention river G2 253 399 41 1.55 0.21 0 - 60 0.07 Invention river G3 321 453 35 1.49 0.21 0 - 50 0.07 Invention river G4 258 359 46 1.54 0.25 0 - 70 0.08 Comparative steel

[Example 7]

The steel slabs shown in Table 15 were reheated at 1200 ° C and finishing hot-rolled, then cooled at a rate of 550 ° C / min, rolled at 650 ° C, and subjected to cold rolling and continuous annealing at a reduction ratio of 75%. The finish rolling temperature of not less than Ar ₃ transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second.

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S 0.25
*
V / C C P S Cu Al N Mo V 0.0005
-
0.003 0.03
-
0.2 0.003
-
0.025 0.01
-
0.2 0.01-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 ≤10 1-20 H1 0.0024 0.054 0.012 0.05 0.034 0.0023 0.018 0.02 2.08 2.08 H2 0.0022 0.11 0.011 0.083 0.038 0.0028 0.074 0.081 3.77 9.2 H3 0.0026 0.153 0.012 0.1 0.023 0.0027 0.16 0.17 4.17 16.3 H4 0.0018 0.054 0.011 0.045 0.042 0.0019 0.23 0.24 2.05 33.3 H5 0.002 0.048 0.01 0.045 0.027 0.0033 0.44 0.07 2.25 8.75 H6 0.0023 0.05 0.009 0.065 0.041 0.0031 0.073 0.51 3.61 55.4

city
side
time
number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(Mpa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) prescription
Indices
(MPa) Secondary processing
Brittle
(DBTT-C) H1 210 361 48 2.12 0.38 0 - 70 0.06 Invention river H2 255 410 41 1.85 0.25 0 - 50 0.07 Invention river H3 312 463 37 1.73 0.22 0 - 40 0.08 Invention river H4 238 379 45 1.83 0.34 0 - 50 0.09 Comparative steel H5 254 375 44 1.83 0.24 0 - 70 0.09 Comparative steel H6 212 352 47 1.88 0.31 0 - 30 0.08 Comparative steel

 [Example 8]

The steel slabs shown in Table 17 were reheated at 1200 DEG C and finishing hot-rolled, cooled at a rate of 550 DEG C / min, and then rolled at 650 DEG C, followed by cold rolling and continuous annealing at a reduction ratio of 75%. The finish rolling temperature of not less than Ar ₃ transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second. The measurement of the mechanical properties was carried out in the same manner as in Example 1.

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S 0.25
*
V / C C Si P S Al N Cu Mo V 0.0005
-
0.003 0.1
-
0.8 ≤0.015 0.003
-
0.025 0.01
-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 0.01
-
0.2 1-10 1-20 I1 0.0017 0.26 0.01 0.01 0.032 0.0024 0.05 0.022 0.018 2.5 2.65 I2 0.0024 0.45 0.011 0.011 0.025 0.0028 0.082 0.069 0.08 3.73 8.33 I3 0.0026 0.62 0.012 0.009 0.024 0.0026 0.034 0.15 0.16 1.42 15.4 I4 0.0019 0.25 0.011 0.011 0.043 0.0013 0.044 0.23 0.22 2 28.9 I5 0.0024 0.21 0.01 0.01 0.044 0.0027 0.075 0.51 0.07 3.75 7.29 I6 0.0026 0.22 0.011 0.012 0.028 0.0029 0.044 0.074 0.45 1.83 43.3 I7 0.0024 0.23 0.014 0.009 0.032 0.0019 0.44 0.047 0.066 24.4 6.88

city
side
time
number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) prescription
Indices
(MPa) Secondary processing
Brittle
(DBTT-C) I1 210 355 50 2.11 0.34 0 - 70 0.08 Invention river I2 262 410 44 1.86 0.27 0 - 50 0.08 Invention river I3 315 460 36 1.62 0.24 0 - 40 0.07 Invention river I4 248 376 45 1.82 0.31 0 - 40 0.09 Comparative steel I5 233 376 44 1.79 0.32 0 - 70 0.09 Comparative steel I6 209 354 47 1.86 0.28 0 - 30 0.09 Comparative steel I7 214 356 45 1.91 0.34 27 - 70 0.36 Comparative steel

[Example 9]

The steel slabs shown in Table 19 were reheated at 1200 ° C and then subjected to finish hot rolling, followed by cooling at a rate of 550 ° C / min and winding at 650 ° C, followed by cold rolling and continuous annealing at a reduction ratio of 75% rolling temperature is Ar ₃ transformation point or higher 910 ℃, continuous annealing was performed by heating for 40 seconds to 750 ℃ to 10 ℃ / second. The measurement of the mechanical properties was carried out in the same manner as in Example 1.

city
side
time
number Chemical composition (% by weight) 0.5
*
Cu / S 0.25
*
V / C C Cr P S Al N Cu Mo V 0.0005
-
0.003 0.2
-
1.2 ≤0.015 0.003
-
0.025 0.01
-
0.08 ≤0.004 0.01
-
0.2 0.01
-
0.2 0.01
-
0.2 1-10 1-20 J1 0.0023 0.34 0.011 0.01 0.024 0.0024 0.046 0.021 0.018 2.3 1.96 J2 0.0023 0.65 0.01 0.009 0.034 0.0039 0.059 0.08 0.072 3.83 7.83 J3 0.0028 0.93 0.008 0.011 0.045 0.0019 0.08 0.15 0.16 4 14.3 J4 0.0019 0.35 0.01 0.008 0.032 0.0021 0.058 0.25 0.22 4.25 28.9 J5 0.0024 0.31 0.009 0.011 0.028 0.0027 0.081 0.48 0.087 3.68 9.06 J6 0.0024 0.36 0.009 0.008 0.044 0.0019 0.039 0.11 0.51 2.44 53.1 J7 0.0026 0.32 0.012 0.01 0.032 0.0031 0.44 0.064 0.071 22 6.83

city
Ryo
time
number Mechanical property Precipitate
Average size
(탆) Remarks surrender
burglar
(MPa) Seal
burglar
(MPa) year
God
rate
(%) Plasticity
Anisotropy
Indices
(r _m ) In-plane
Anisotropy
Indices
(R) prescription
Indices
(MPa) Secondary processing
Brittle
(DBTT-C) J1 213 355 48 2.14 0.35 0 - 70 0.08 Invention river J2 263 407 40 1.81 0.27 0 - 60 0.07 Invention river J3 318 462 35 1.71 0.24 0 - 50 0.08 Invention river J4 243 375 44 1.55 0.19 0 - 40 0.08 Comparative steel J5 251 378 43 1.79 0.27 0 - 70 0.09 Comparative steel J6 218 357 47 1.87 0.27 0 - 30 0.09 Comparative steel J7 224 355 48 1.93 0.39 27 - 70 0.42 Comparative steel

INDUSTRIAL APPLICABILITY As described above, according to the present invention, there is provided a high strength, cold-rolled steel sheet having a high anisotropic index of plasticity while securing an anti-aging property,

Claims (22)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet has a composition of C: 0.0005-0.003%, S: 0.003-0.025%, Al: 0.01-0.08%, N: 0.8% and Cr: 0.2 to 1.2%, wherein the content of P is 0.03 to 0.2% when only one kind of P is contained, and the content of Cu and S is 0.5 * Cu / S: 1 -10, the balance being Fe and other unavoidable impurities, and having an average size of CuS precipitates of 0.1 占 퐉 or less, and excellent in workability. 0.003 to 0.03% of S, 0.003 to 0.025% of S, 0.01 to 0.08% of Al, 0.004% or less of N, 0.01 to 0.2% of Cu and 0.03 to 02% of P, A high strength in-walled cold-rolled steel sheet excellent in workability wherein Cu and S satisfy the condition 0.5 * Cu / S: 1-10, the balance Fe and other unavoidable impurities, and the average size of CuS precipitates is 0.1 탆 or less. 0.003 to 0.025% of Al, 0.01 to 0.08% of Al, 0.004% or less of N, 0.01 to 0.2% of Cu, 0.015% or less of P, 0.1 to 0.8% of Si, , The Cu and S satisfying the condition 0.5 * Cu / S: 1-10, the remaining Fe and other unavoidable impurities, and the CuS precipitate having an average size of 0.1 탆 or less. 0.003 to 0.025% of Al, 0.01 to 0.08% of Al, 0.004% or less of N, 0.01 to 0.2% of Cu, 0.015% or less of P, 0.2 to 1.2% of Cr, Wherein the Cu and S satisfy the condition 0.5 * Cu / S: 1-10, the remaining Fe and other unavoidable impurities, and the CuS precipitates have an average size of 0.1 탆 or less. Cold rolled steel sheets. 5. The cold rolled steel sheet according to any one of claims 1 to 4, wherein the S is more than 0.02 to 0.025%. 5. The cold rolled steel sheet according to any one of claims 1 to 4, wherein the Cu and S satisfy the condition 0.5 * Cu / S: 1-3. The high-strength, time-aged, cold-rolled steel sheet according to any one of claims 1 to 4, further comprising 0.01 to 0.2% Mo. The high-strength, time-aged, cold-rolled steel sheet according to any one of claims 1 to 4, further comprising 0.01 to 0.2% of V. The high-strength, time-aged cold-rolled steel sheet according to claim 7, further comprising 0.01 to 0.2% of V. 9. The cold rolled steel sheet according to claim 8, wherein V and C satisfy the condition 0.25 * V / C: 1 to 20. The high-strength, time-aged cold-rolled steel sheet according to claim 9, wherein the V and C satisfy the condition 0.25 * V / C: 1 to 20. The steel sheet according to any one of claims 1 to 3, wherein the steel sheet has a composition of C: 0.0005-0.003%, S: 0.003-0.025%, Al: 0.01-0.08%, N: 0.8% and Cr: 0.2 to 1.2%, wherein the content of P is 0.03 to 0.2% when only one P is contained, and the content of Cu and S is 0.5 * Cu / S: 1-10 and the remaining Fe and other unavoidable impurities are reheated to a temperature of 1100 ° C or higher, hot rolled at a finishing rolling temperature of at least the Ar ₃ transformation point, cooled at a rate of 300 ° C / min or more, Rolled at a temperature not higher than the melting point of the steel sheet, followed by cold rolling and continuous annealing. 0.003 to 0.03% of S, 0.003 to 0.025% of S, 0.01 to 0.08% of Al, 0.004% or less of N, 0.01 to 0.2% of Cu and 0.03 to 02% of P, The steel having Cu and S satisfying the condition of 0.5 * Cu / S: 1-10 and composed of the remaining Fe and other unavoidable impurities is reheated to a temperature of 1100 ° C or higher and then subjected to hot rolling at a finishing rolling temperature of Ar ₃ transformation point or higher Cooling the steel sheet at a cooling rate of 300 DEG C / min or more and winding the steel sheet at a temperature of 700 DEG C or less, followed by cold rolling and continuous annealing. 0.003 to 0.025% of Al, 0.01 to 0.08% of Al, 0.004% or less of N, 0.01 to 0.2% of Cu, 0.015% or less of P, 0.1 to 0.8% of Si, , The Cu and S satisfy the condition 0.5 * Cu / S: 1-10 and the remaining Fe and other unavoidable impurities are reheated to a temperature of 1100 캜 or higher, and the finish rolling temperature is set to be higher than the Ar ₃ transformation point, Rolled, rolled at a temperature of not lower than 700 캜, cold-rolled, and continuously annealed. 0.003 to 0.025% of Al, 0.01 to 0.08% of Al, 0.004% or less of N, 0.01 to 0.2% of Cu, 0.015% or less of P, 0.2 to 1.2% of Cr, Wherein the Cu and S satisfy the condition 0.5 * Cu / S: 1-10 and the remaining Fe and other unavoidable impurities are reheated to a temperature of 1100 ° C or higher, and then the finish rolling temperature is adjusted to be higher than the Ar ₃ transformation point Rolled at a temperature of 700 ° C or lower, and then cold rolled and continuously annealed. The method of manufacturing a high strength cold rolled steel sheet according to claim 1, The method of manufacturing an anti-aging cold rolled steel sheet according to any one of claims 12 to 15, wherein the S is more than 0.02 to 0.025%. The method of manufacturing an anti-aging cold-rolled steel sheet according to any one of claims 12 to 15, wherein the Cu and S satisfy the condition 0.5 * Cu / S: 1-3. The method of manufacturing a high strength intrinsic age cold rolled steel sheet according to any one of claims 12 to 15, further comprising 0.01 to 0.2% of Mo. The method for producing a high strength intrinsic age steel sheet according to any one of claims 12 to 15, further comprising 0.01 to 0.2% of V. 19. The method of producing a high strength intrinsic age steel sheet according to claim 18, further comprising 0.01 to 0.2% of V. 21. The method according to claim 19, wherein the V and C satisfy the condition 0.25 * V / C: 1 to 20. 21. The method according to claim 20, wherein the V and C satisfy the condition 0.25 * V / C: 1 to 20.

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