JP2818319B2 - Non-ageing cold drawn high-strength cold-rolled steel sheet and method for producing same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applicable to applications requiring press formability, such as for automobiles, and is also suitable as a base sheet for galvannealed steel sheet, which has been increasing in demand in recent years. The present invention proposes a normal-temperature non-aging type high-tensile cold-rolled steel sheet having a thickness of / mm ² or more and a method for producing the same.

In recent years, required properties of cold-rolled steel sheets for drawing include: high strength for weight reduction, cost reduction, and improvement of safety; and extension of life due to improvement of corrosion resistance, so that mass production is particularly easy. Alloyed hot-dip galvanized steel sheets which are excellent in corrosion resistance are used.

[0003]

2. Description of the Related Art Heretofore, methods of increasing the strength of cold-rolled steel sheets for processing include:-solid solution strengthening by P, Mn, etc.-strengthening by forming a composite structure such as martensite,-precipitation strengthening by Cu, etc. Are known as typical examples. However, in the above, since solid solution strengthening involves deterioration in workability, there is a limit to its application to a drawing steel sheet, and P, which is the most effective strengthening element with little workability deterioration,
There is a problem that the galvanizing property is significantly impaired. Further, in the conventional strengthening of the composite structure, a relatively large amount (about 0.05 to 1.0 wt%) of C is required for processing applications in order to cause the appearance of martensite and bainite of the second phase.
Therefore, the Rankford value (r value) is significantly deteriorated, and is not suitable for drawing. Furthermore, the galvanizing alloying process (approximately 550 ° C) tempers martensite and bainite, which not only reduces the strength but also generates stretcher strain during molding. It is not suitable as an original plate. further,
Since precipitation strengthening needs to be processed under optimal precipitation conditions,
Often constrains the process. In particular, when it is necessary to incorporate a new precipitation treatment step into the process, productivity is significantly impaired.

[0004] Although not strictly precipitation hardening, steel sheets utilizing age hardening due to accumulation of solid solution C at dislocations, that is, bake hardening (BH properties) to be aged during bake coating,
Since the manufacturing process is not burdensome, it is used in exceptional cases. However, the yield strength is 3 to 5 kgf /
To increase approximately mm ^2, although tensile rigidity is improved,
There are problems that the increase in tensile strength due to BH is as small as about 1 to ² kgf / mm ² and that aging prevention means is required before working or during plating.

[0005] Therefore, there is a limit in increasing the strength of a steel sheet having drawability by the above-mentioned conventional method, and it is not suitable as an original sheet for a galvannealed steel sheet.

Under these circumstances, one of the inventors, in cooperation with the other four, disclosed in Japanese Patent Application Laid-Open No. 60-174852 a new type of cold-rolled steel sheet and a method of manufacturing the same. A composite structure cold-rolled steel sheet having a composite structure of a ferrite phase and a low-temperature transformed ferrite phase, which is excellent in deep drawability by α-γ2 phase temperature range annealing of a low carbon steel sheet, and a method of manufacturing the same have been proposed and disclosed. This steel sheet is different from the conventional composite structure steel sheet having martensite or bainite as the second phase, and the second phase is
It is characterized by low-temperature transformed ferrite having a high dislocation density.

Although the form of the low-temperature transformed ferrite varies depending on the steel composition, observation by an optical microscope shows that the grain boundaries are irregularly angular crystals, crystal grains existing along the grain boundaries such as precipitates, and scratches. One of which is distributed alone or in combination, such as a crystal grain or a group of crystal grains (having a large number of sub-grain boundaries in a relatively large second phase grain) exhibiting a scratch-like pattern. Can be clearly distinguished from normal ferrite, and furthermore, the corroded color inside the grain is almost the same as normal ferrite, unlike martensite and bainite, so it is also clearly distinguished from martensite and bainite You can do it. On the other hand, according to the observation with a transmission electron microscope, the low-temperature transformed ferrite has a very high dislocation density at the grain boundaries and / or in the grains. The lower part is layered.

In such a steel sheet having a composite structure of a ferrite phase and a low-temperature transformation ferrite phase, the low-temperature transformation ferrite of the second phase is substantially a ferrite only with a high dislocation density. Unlike martensite and bainite, they are not tempered even when exposed to temperature, and therefore are also suitable as original sheets for galvannealed steel sheets. Further, since the steel sheet having this composite structure has a mother phase of an ultra-low carbon ferrite recrystallized at a normal high temperature, the steel sheet has a higher r than conventional steel sheets having a composite structure.
Since it is a composite structure having an extremely high value and having a local strain inside, it has both BH property and resistance to aging at room temperature, that is, non-aging at room temperature.

However, the strength increase due to low-temperature transformed ferrite is smaller than that of martensite and the like.
In order to obtain higher strength, the help of reinforcing components is needed. However, when a large amount of reinforcing components such as Mn, Nb, and B are added to such a steel sheet, workability is likely to deteriorate,
In particular, there is a problem that the annealing temperature range in which good workability can be obtained is remarkably narrowed and productivity is impaired.

[0010]

SUMMARY OF THE INVENTION The present invention is intended to provide a steel sheet having a composite structure of a high-temperature transformed ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density as described above, resulting in deterioration in workability and productivity due to the increase in strength. It is an object of the present invention to propose a high-tensile cold-rolled steel sheet which is excellent in drawability, is excellent in drawability, is non-ageable at room temperature, and is also suitable as an original sheet for galvannealed steel sheet and a method for producing the same.

Here, the target characteristic values of the steel sheet are as follows.
It is as follows. TS ≧ 40Kgf / mm²  TS × El ≧ 1800Kgf / mm²・% R value (average) ≧ 1.9 Immediately after annealing, galvannealing, or temper rolling
And after leaving them at room temperature for 6 months, yield point elongation <0.5%

[0012]

The gist of the present invention is as follows. 1. C: 0.001 wt% or more, 0.025 wt% or less, Si: 1.0 wt% or less, Mn: 0.1 wt% or more, 2.0 wt% or less, Nb: 0.001 wt% or more, 0.2 wt% or less, B: 0.0003 wt% Not less than 0.01 wt%, Al: not less than 0.005 wt%, not more than 0.10 wt%, P: not more than 0.1 wt%, and N: not more than 0.007 wt%, Ni: not less than 0.05 wt%, not more than 3.0 wt%, Mo: 0.01wt% or more, 2.0wt% or less and Cu: 0z05wt% or more, selected from among 5.0wt% or less, with the balance being the composition of iron and unavoidable impurities, and high-temperature transformation of the structure A high-temperature cold-rolled steel sheet for non-aging drawing at room temperature, comprising a composite structure of a ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density.

2. C: 0.001 wt% or more, 0.025 wt% or less, Si: 1.0 wt% or less, Mn: 0.1 wt% or more, 2.0 wt% or less, Nb: 0.001 wt% or more, 0.2 wt% or less, B: 0.0003wt% or more, 0.01wt% or less, Al: 0.005wt% or more, 0.10wt% or less, P: 0.1wt% or less, N: 0.007wt% or less, Ni: 0.05wt% or more, 3.0wt% or less , Mo: 0.01 wt% or more and 2.0 wt% or less and Cu: 0.05 wt% or more and 5.0 wt% or less, and Cr: 0.05 wt% or more and 3.0 wt% or less and Ti: One or two selected from 0.005 wt% or more and 1.0 wt% or less, with the balance being the composition of iron and unavoidable impurities, the structure of which is a high-temperature transformed ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density. A cold-rolled high-strength steel sheet for non-aging at room temperature characterized by a composite structure of

3. Each of the hot-rolled sheets having the composition of the above 1 or 2 is cold-rolled at a rolling reduction of 60% or more, and then annealed in a temperature range not less than the γ transformation start temperature and less than the _Ac3 transformation point. A method for producing a high-tensile cold-rolled steel sheet for non-aging at room temperature, which is excellent in TS / El balance, characterized in that the steel sheet is cooled at a rate of 100 ° C./sec or more and 100 ° C./sec or less.

[0015]

As described above, the present invention is intended to improve the workability of steel sheets having a composite structure of a normal high-temperature transformed ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density due to high strength. This is because it was found that it is very effective to improve the content by adding an appropriate amount of at least one of Ni, Mo, and Cu, which are strengthening components.

First, the effects of Ni, Mo, and Cu will be described based on experimental results. Using continuously cast slabs having three types of component compositions shown in Table 1, cold-rolled sheets were manufactured under the following conditions, and tensile properties were investigated.

[0017]

[Table 1]

Manufacturing conditions • Hot rolling Slab heating temperature (SRT): 1200 ° C Hot rolling end temperature (FDT): 910 ° C Coil winding temperature (CT): 600 ° C Finished sheet thickness: 3.5mm • Cold rolling reduction : 77% Final thickness: 0.8mm ・ Continuous annealing Heating temperature: 880 to 950 ° C (in 10 ° C increments) Cooling rate: 30 ° C / sec

FIG. 1 shows the results of this investigation. Figure 1 shows the TS-E
l The effect of Ni, Mo or Cu on the balance is shown. As is evident from FIG. 1, the C steel containing no Ni, Mo, Cu, etc., had a sharp decrease in El near TS40 Kgf / mm ² , and although a TS higher than this value was not obtained. On the other hand, steels A and B containing Ni, Mo or Cu do not show a sharp decrease in El due to an increase in TS, have a good TS-El balance, have high strength, and have a two-phase region. It shows that the material stability in annealing is excellent.

The reasons why Ni, Mo and Cu have the above-mentioned effects are not clear, but that:-these components have a tendency to suppress grain boundary migration;-because the workability and strength of this steel sheet are optimized. In the recrystallization stage before the start of the α → γ transformation, it is easy to grow grains, and during the transformation, it is necessary to suppress the growth of grains. From the two points, Ni, Mo and Cu are just around the transformation point. It is presumed that a large amount of γ becomes a solid solution in Sakai on the high temperature side and suppresses γ grain growth.

In each of the steels in Table 1, the second phase (low-temperature transformed ferrite phase) was 1 to 1 after annealing at the γ transformation start temperature or higher.
Appeared 70% and showed normal temperature non-aging property and BH property. Depending on the contents of C, Ni, Mo and Cu, the form of the second phase may be any one of the above three forms alone or in a complex form. No significant correlation was observed between the size and the processability.

However, according to another experimental result, in a steel containing a relatively large amount of a reinforcing component, the second phase grain size tends to grow larger than the matrix phase (high-temperature transformed ferrite phase) grain size. However, in a steel sheet that is in the component composition range of the present invention and exhibits excellent workability, the average particle diameter of the second phase is an average of the diameter of the parent phase. 3 times or less. This is due to the aforementioned α grain growth promotion and
This supports the idea that suppression of γ grain growth has a favorable effect on the material.

Next, the reasons for limiting the component composition of the present invention will be described. C: 0.001 to 0.025 wt% C is soft when it is less than 0.001 wt%, not only requires a large amount of alloy addition to obtain high strength, but also industrially, less than 0.001 wt% can be realized. It is uneconomical.
On the other hand, if the content exceeds 0.025 wt%, the deterioration of the r value cannot be suppressed, and if the second phase is martensitic, the alloying hot-dip galvanizing treatment causes adverse effects such as softening and strain aging. Therefore, the content is set to 0.001 wt% or more and 0.025 wt% or less.

Si: 1.0 wt% or less If Si exceeds 1.0 wt%, the transformation point rises and high-temperature annealing is required. In addition, in applications for hot-dip galvanizing, plating is difficult to adhere. Therefore, the content is 1.0 wt% or less. However, since the strength is increased and the strength-elongation balance is slightly improved, the content is preferably 0.05 wt% or more. This is considered to promote the enrichment of C in the second phase.

Mn: 0.1 to 2.0 wt% When Mn is less than 0.1 wt%, harmful sulfide (FeS) is formed. If it exceeds 2.0% by weight, the strength-elongation balance is extremely deteriorated. Therefore, the content is 0.1 wt% or more, 2.
The content is set to 0% by weight or less, preferably 1.0% by weight or less, and it is preferable to compensate for the decrease in strength with Ni, Mo, and Cu.

Nb: 0.001 to 0.2 wt% Nb is an indispensable component for promoting the formation of low-temperature transformed ferrite in the coexistence with B, and therefore requires 0.001 wt% or more. However, if it exceeds 0.2 wt%, the adverse effect on workability becomes remarkable, and the cost increases. Therefore, the content is set to 0.001 wt% or more and 0.2 wt% or less.

B: 0.0003-0.01 wt% B is an indispensable component for promoting the formation of low-temperature transformed ferrite in the presence of Nb, and when B is less than 0.0003 wt%, there is no effect. On the other hand, if the content exceeds 0.01% by weight, the adverse effect on workability becomes significant. Therefore, its content should be 0.0003 wt% or more and 0.01 wt% or less.

Al: 0.005 to 0.10 wt% Al is a component necessary for deoxidation at the time of refining.
It is necessary to contain 5 wt% or more, but if it exceeds 0.10 wt%, inclusions increase and the material deteriorates.
Therefore, its content should be 0.005 wt% or more and 0.10 wt% or less.

P: 0.1 wt% or less P is a strengthening component of steel. If P is contained in excess of 0.1 wt%, not only surface defects due to segregation become remarkable,
In applications for hot-dip galvanizing, plating is difficult to adhere. It is also disadvantageous in that the strengthening by the second phase is weakened. Therefore, its content should be 0.1 wt% or less, but desirably
It is preferable that the content be 0.05 wt% or less, and the strength decrease is compensated for by Ni, Mo, and Cu.

N: 0.007 wt% or less N, when exceeding 0.007 wt%, deteriorates workability and non-aging property at room temperature, and deteriorates the yield of B due to formation of BN. Therefore, its content is set to 0.007 wt% or less.

Ni: 0.05-3.0 wt%, Mo: 0.01-2.0 wt%, C
u: 0.05 to 5.0 wt% Ni, Mo and Cu contain at least one of them, which is the greatest requirement of the present invention. As described above, they do not cause deterioration of the material. It is a component that can increase strength. Ni is 0.05wt%, Mo is 0.01wt%,
If Cu is less than 0.05 wt%, the effect is not obtained, and Ni is 3.0 wt%,
If Mo exceeds 2.0 wt% and Cu exceeds 5.0 wt%, the workability is adversely affected. Therefore, their content is 0.05 wt% Ni
% Or more, 3.0 wt% or less, Mo is 0.01 wt% or more, 2.0 wt% or less,
Cu should be 0.05 wt% or more and 5.0 wt% or less. For hot-dip galvanizing applications, Ni,
It is preferable that both Mo and Cu be 1.0 wt% or less.

Cr: 0.05 to 3.0 wt%, Ti: 0.005 to 1.0 wt% Cr and Ti fix C, S and N, and suppress the adverse effect of the material and B on the yield. Cr is 0.05wt%, Ti is
If the content is less than 0.005 wt%, the above effect is not obtained, and the content of Cr is 3.0 wt%,
When Ti exceeds 1.0 wt%, the effect is saturated. Therefore, the content of these should be 0.05 wt% or more and 3.0 wt% or less for Cr and 0.005 wt% or more and 1.0 wt% or less for Ti. Although the C-fixing effect of Ti is stable even at high temperatures, the C-fixing effect of Cr and Nb is weakened at high temperatures, so that Ti was not added or its content was 48/12 [C] + 48/32 [S ] +48/14 [N], the steel sheet is given a BH property while not being aged at room temperature,
This is advantageous for higher strength.

Next, the manufacturing process of the present invention will be described below. The production of the slab may be a conventional continuous casting method or ingot-making method,
Also, hot rolling may be performed at a finishing temperature equal to or higher than the Ar ₃ transformation point, as in a normal process. The winding temperature of the coil is not particularly specified, but a temperature range of 600 to 700 ° C. is preferable in order to precipitate Nb carbide to an appropriate particle size.

In cold rolling, if the rolling reduction is less than 60%,
It is considered that this is due to the delay of the start of transformation during subsequent annealing. However, the second phase is coarsened, and the ratio to the above-described matrix ferrite grain size exceeds three times, resulting in deterioration in workability. Therefore, the cold rolling reduction is required to be 60% or more.

Needless to say, if the annealing is not performed at a temperature higher than the γ transformation start temperature, the composite structure is not formed. However, α
If annealing is performed beyond the -γ coexisting temperature range, residual α grains contributing to the formation of a crystal orientation favorable to the r value are also lost during annealing, and the ratio of the second phase becomes too high. Since the second phase is coarsened to have a structure having a ratio to the matrix ferrite particle size of more than three times, the workability is significantly impaired.
Therefore, the annealing temperature is set to be equal to or higher than the γ transformation start temperature and lower than the A _C3 transformation point.

Since the cooling rate after annealing is a composite addition of Nb and B, rapid quenching is not required to form two phases. However, if the cooling rate is slower than 5 ° C./sec, the γ grains are reduced to a low temperature. It does not easily remain, and a sufficient low-temperature transformed ferrite phase does not appear. On the other hand, cooling at a rate exceeding 100 ° C./second is not required, and the shape of the plate is deteriorated. Therefore, the cooling rate after annealing is 5 ° C./sec or more and 100 ° C./sec or less.

Although temper rolling is not particularly required, there is no problem if the elongation is 3% or less for correcting the shape of the sheet.

[0038]

EXAMPLE Continuously cast slabs of 12 kinds of compatible steels and 7 kinds of comparative steels of the present invention prepared to the component compositions shown in Table 2 were hot rolled (finished sheet thickness: 1.6 to 1.6) under the conditions shown in Table 3, respectively. 3.5m
m), cold-rolled (finished sheet thickness: 0.7 mm), annealed, and a part thereof were subjected to alloyed hot-dip galvanizing or temper rolling to obtain product sheets.

[0039]

[Table 2]

The alloyed hot-dip galvanizing in Table 3 is a continuous galvanizing line (CGL) that has been subjected to an annealing-hot-dip galvanizing-alloying process (550 ° C., 20 seconds), and the adhered state of the plating Had no problem.

For the above product plate, tensile properties, r value,
BH, room temperature non-aging, organizational survey, etc. were performed. Table 4 summarizes the results of these investigations.

[0043]

[Table 3]

[0044]

[Table 4]

Here, each measurement condition is as follows. Tensile properties: Measured using a JISZ 2201 No. 5 test piece.

R value (average): 15% The value at the time of tension was measured by a three-point method, and the L direction (rolling direction) and the D method (rolling direction) were measured.
45 ° direction) and C direction (the average value of γ value of the rolling direction 90-degree direction) (average) = (was determined as _{r L + 2 r D + r} C) / 4.

BH: stress at 2% tensile strain (σ ₂ )
And after unloading after giving 2% tensile prestrain,
Yield stress (σ _Y ) after aging treatment at 0 ° C. for 20 minutes was measured and determined as BH = (σ _Y ) − (σ ₂ ).

Non-aging property at room temperature: Yield elongation (YEl) in a tensile test (tensile speed 10 mm / min) immediately after annealing, and 100 ° C.
After aging treatment for 10 hours (corresponding to 30 ° C. for 6 months), the yield elongation was determined and evaluated in the same manner as described above.

As is apparent from Table 4, the conforming examples of the present invention show that TSs are all 40 kgf / mm ² or more,
It shows excellent properties in terms of workability, and has a BH of 3.5 kgf / mm ² or more except for the sample code 8 in which all of the solid solution C is fixed by Ti. In addition, the material does not deteriorate even by alloying hot-dip galvanizing treatment by CGL or temper rolling.

On the other hand, comparative examples are as follows. 1D: The annealing temperature is lower than the γ transformation temperature, and non-aging at room temperature is not obtained because of the α single phase. 1E: Cooling rate after annealing is low and almost α single phase,
No room temperature non-aging property has been obtained. 1F: Since the cold rolling reduction is low, the particle size of the second phase is larger than that of the parent phase, and good workability is not obtained. 5B: Good workability has not been obtained because the annealing temperature is higher than the α-γ coexistence temperature. 13A, 13B: Since neither Cu, Ni nor Mo is contained, the particle size of the second phase is much larger than that of the parent phase, the workability is deteriorated, and the non-aging property at room temperature is also adversely affected. . The adverse effect on non-aging at room temperature is significant after galvannealing. 14, 15: The content of Ni, Mo or Cu is excessive, the ratio of the particle size of the second phase to the particle size of the matrix is out of the optimum range, and good workability cannot be obtained. 16: The content of Mn is excessive, the ratio of the particle size of the second phase to the parent phase is out of the optimum range, and good workability is not obtained. 17: High Nb content, adversely affecting processability. 18, 19: Since Nb or B was not added, no low-temperature transformed ferrite phase appeared, and good workability and non-aging property at room temperature were not obtained. As described above, each of the comparative examples is inferior to the conforming example in any of the characteristics.

[0051]

The present invention is intended to provide a steel sheet having a composite structure of a high-temperature transformed ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density by containing an appropriate amount of at least one of Ni, Mo and Cu. The high-tensile cold-rolled steel sheet obtained by the present invention has a good drawability in a normal temperature non-ageing type or a normal temperature non-ageing BH type, and has an alloyed melt. Even if it is subjected to a galvanizing treatment, the material does not deteriorate and can be advantageously used for automobiles and the like.

[Brief description of the drawings]

Fig. 1 Ni, which affect the TS-El balance of the annealed steel sheet
4 is a graph showing the effect of Cu or Mo.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiko Morita 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. (72) Inventor Toshiyuki Kato 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. (56) References JP-A-58-84929 (JP, A) JP-A-60-174852 (JP, A)

Claims (4)

(57) [Claims] 1. C: 0.001 wt% or more, 0.025 wt% or less, Si: 1.0 wt% or less, Mn: 0.1 wt% or more, 2.0 wt% or less, Nb: 0.001 wt% or more, 0.2 wt% or less, B: 0.0003wt% or more, 0.01wt% or less, Al: 0.005wt% or more, 0.10wt% or less, P: 0.1wt% or less, N: 0.007wt% or less, Ni: 0.05wt% or more, 3.0wt% or less , Mo: not less than 0.01 wt%, not more than 2.0 wt% and Cu: not less than 0.05 wt%, not more than 5.0 wt%, and the balance is composed of iron and unavoidable impurities, A high-temperature cold-rolled steel sheet for non-aging at room temperature, characterized in that the structure is composed of a composite structure of a high-temperature transformed ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density. 2. C: 0.001 wt% or more, 0.025 wt% or less, Si: 1.0 wt% or less, Mn: 0.1 wt% or more, 2.0 wt% or less, Nb: 0.001 wt% or more, 0.2 wt% or less, B: 0.0003wt% or more, 0.01wt% or less, Al: 0.005wt% or more, 0.10wt% or less, P: 0.1wt% or less, N: 0.007wt% or less, Ni: 0.05wt% or more, 3.0wt% or less , Mo: 0.01 wt% or more and 2.0 wt% or less and Cu: 0.05 wt% or more and 5.0 wt% or less, and Cr: 0.05 wt% or more and 3.0 wt% or less and Ti: One or two selected from 0.005 wt% or more and 1.0 wt% or less, with the balance being the composition of iron and unavoidable impurities, the structure of which is a high-temperature transformed ferrite phase and a low-temperature transformed ferrite phase having a high dislocation density. A cold-rolled high-strength steel sheet for non-aging at room temperature characterized by a composite structure of C: 0.001 wt% or more, 0.025 wt% or less, Si: 1.0 wt% or less, Mn: 0.1 wt% or more, 2.0 wt% or less, Nb: 0.001 wt% or more, 0.2 wt% or less, B: 0.0003wt% or more, 0.01wt% or less, Al: 0.005wt% or more, 0.10wt% or less, P: 0.1wt% or less, N: 0.007wt% or less, Ni: 0.05wt% or more, 3.0wt% or less , Mo: 0.01wt% or more and 2.0wt% or less and Cu: 0.05wt% or more and 5.0wt% or less. After cold rolling, above the γ transformation start temperature,
Following annealing in the temperature range A than _C3 transformation point, 5 ° C. /
A method for producing a high-tensile cold-rolled steel sheet for non-aging at room temperature, characterized in that the steel sheet is cooled at a rate of at least 100 seconds per second. 4. C: 0.001 wt% or more, 0.025 wt% or less, Si: 1.0 wt% or less, Mn: 0.1 wt% or more, 2.0 wt% or less, Nb: 0.001 wt% or more, 0.2 wt% or less, B: 0.0003wt% or more, 0.01wt% or less, Al: 0.005wt% or more, 0.10wt% or less, P: 0.1wt% or less, N: 0.007wt% or less, Ni: 0.05wt% or more, 3.0wt% or less , Mo: 0.01 wt% or more and 2.0 wt% or less and Cu: 0z05 wt% or more and 5.0 wt% or less and Cr: 0.05 wt% or more and 3.0 wt% or less and Ti: 0.005 A hot rolled sheet containing one or two selected from among wt% or more and 1.0 wt% or less,
After cold rolling with 60% reduction ratio, gamma transformation start temperature or higher, A _C3
A method for producing a high-tensile cold-rolled steel sheet for non-aging at room temperature, characterized by cooling at a rate of 5 ° C / sec or more and 100 ° C / sec or less, subsequent to annealing in a temperature range below the transformation point.