KR101304703B1 - Ultra low carbon cold rolled steel sheet having excellent workability and method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention is a cold rolled steel sheet having excellent workability in weight%, C: 0.0005 to 0.0015%, Si: 0.003 to 0.007%, Mn: 0.05 to 0.2%, Al: 0.02 to 0.05%, Nb: 0.04 to 0.14% , N: 0.001% to 0.005%, P: 0.008% or less, S: 0.008% or less, the rest includes Fe and inevitable impurities,
The average grain size of the microstructure grains is 7-11 μm, the occupancy area of the grains having a particle size of 10 μm or less is 30-60% of the total grain area ratio, and the number of precipitates having an aspect ratio of 2.0 or less is the total number of precipitates. Contains more than 75% of the time.
Another aspect of the present invention is a method for manufacturing a cold rolled steel sheet having excellent workability, in terms of weight%, C: 0.0005 to 0.0015%, Si: 0.003 to 0.007%, Mn: 0.05 to 0.2%, Al: 0.02 to 0.05%, and Nb: 0.04 to 0.14%, N: 0.001 to 0.005%, P: 0.008% or less, S: 0.008% or less Reheating the steel slab containing Fe and unavoidable impurities to 1100 ° C. or more, hot reheating the reheated steel slab Rolling, finishing hot rolling at a temperature of Ar3 or more to produce a hot rolled steel sheet, winding the hot rolled steel sheet at a temperature of 650 to 750 ° C, and cold rolling the hot rolled steel sheet at a rolling reduction ratio of 50 to 90% after the winding. Preparing a cold rolled steel sheet and annealing the cold rolled steel sheet at a temperature of 800 ~ 900 ℃.

Description

Cold rolled steel sheet with excellent workability and manufacturing method {ULTRA LOW CARBON COLD ROLLED STEEL SHEET HAVING EXCELLENT WORKABILITY AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a cold-rolled steel sheet used as a material for automobiles, home appliances, and the like, and a manufacturing method thereof.

Recently, cold rolled steel sheets used in automobiles, home appliances, and the like are required to have excellent formability with strength. In the past, high strength steel plates with high tensile strength have been actively used to lighten the weight of automobile bodies and ensure passenger stability. Such high strength steel plates are closely related to various legal regulations surrounding the automobile industry such as automobile safety regulation law, fuel efficiency regulation law, And the fuel economy regulation by the high oil price has been strengthened, and weight reduction of automobiles has become a main concern of the automobile industry, so research and development have been accelerated and many types of high strength steel plates have been developed.

In the case of a steel sheet requiring workability, there are P-containing Al killed and high tensile strength steel for deep drawing. Since the Al-killed steel is manufactured by subjecting the Al-killed steel to an annealing, the annealing time is long, the productivity is low, and the material variation is large in each part.

Therefore, research and development of IF (Interstitial Free Steel) steel, which is a high tensile strength steel, which has improved workability by continuous annealing by adding strong carbon and nitride forming elements, is actively progressing.

In order to manufacture such IF steel, strong carbon and nitride forming elements such as Ti and Nb are added. However, these elements increase the recrystallization temperature, so they have to be annealed at a high temperature, thereby making it difficult to obtain desirable tensile strength and elongation. .

In addition, ultra-low carbon steel using CuS precipitates without Ti and Nb has been proposed, but there is a problem that a large amount of material defects are generated due to aging.

The present invention is to provide a cold rolled steel sheet excellent in material uniformity and workability and a method of manufacturing the same.

One aspect of the present invention is a cold rolled steel sheet having excellent workability in weight%, C: 0.0005 to 0.0015%, Si: 0.003 to 0.007%, Mn: 0.05 to 0.2%, Al: 0.02 to 0.05%, Nb: 0.04 to 0.14% , N: 0.001-0.005%, P: 0.008% or less, S: 0.008% or less The remainder contains Fe and unavoidable impurities, and the average grain size of the microstructure grains is 7-11 μm, and the occupancy rate of the grains having a particle size of 10 μm or less 30 to 60% of the total grain occupancy and the number of precipitates having an aspect ratio of 2.0 or less include 75% or more of the total precipitates.

Another aspect of the present invention is a method for manufacturing a cold rolled steel sheet having excellent workability, in terms of weight%, C: 0.0005 to 0.0015%, Si: 0.003 to 0.007%, Mn: 0.05 to 0.2%, Al: 0.02 to 0.05%, and Nb: 0.04 to 0.14%, N: 0.001 to 0.005%, P: 0.008% or less, S: 0.008% or less Reheating the steel slab containing Fe and unavoidable impurities to 1100 ° C. or more, hot reheating the reheated steel slab Rolling, finishing hot rolling at a temperature of Ar3 or more to produce a hot rolled steel sheet, winding the hot rolled steel sheet at a temperature of 650 to 750 ° C, and cold rolling the hot rolled steel sheet at a rolling reduction ratio of 50 to 90% after the winding. To prepare a cold rolled steel sheet and annealing the cold rolled steel sheet at a temperature of 800 ~ 900 ℃.

According to the present invention, through the present invention, the average grain size of the microstructure grains of the steel sheet is 7-11 μm, the occupancy area ratio of the grains having a particle size of 10 μm or less is 30-60% of the total grain occupancy area, and the aspect ratio Precipitates less than or equal to 2.0 may provide more than 75% of the total number of precipitates. Through the production of the structured steel, it is possible to provide a cold rolled steel sheet having excellent machinability having TS × El of 10,000 MPa% or more.

The present inventors have conducted extensive research to derive a cold rolled steel sheet having workability characteristics. As a result, by appropriately controlling the component system of the steel sheet and the cooling method after rolling, the microstructure of the steel sheet is controlled by ferrite, thereby providing excellent workability and excellent material uniformity. It has been confirmed that the cold rolled steel sheet having can be produced, which has led to the present invention.

Hereinafter, a cold-rolled steel sheet as one aspect of the present invention will be described in detail.

Carbon (C): 0.0005 to 0.0015 wt%

Carbon is the most effective element for reinforcing steel but, when added in large amounts, it degrades weldability and low temperature toughness. When the carbon content is less than 0.0005%, the grains of the hot rolled sheet are coarse to lower the strength and to increase the in-plane anisotropy. On the other hand, when the carbon content exceeds 0.0015%, the amount of solid carbon in steel is high, making it difficult to secure aging resistance, and the grain size of the annealed plate becomes fine, resulting in significantly lower ductility. Therefore, the content of C is preferably set to 0.0005 to 0.0015%.

Silicon (Si): 0.003-0.007 wt%

Silicon is a solid solution strengthening element, and is advantageous in terms of strength improvement. In the present invention, it is preferable that 0.003% by weight or more is included to exhibit such an effect. However, when the content of silicon exceeds 0.007% by weight, the Si-based oxide may be eluted on the surface during annealing to deteriorate the surface properties. Therefore, the silicon is preferably included in 0.003 ~ 0.007% by weight.

Manganese (Mn): 0.05-0.2 wt%

Manganese is an element that prevents hot shortness caused by solid solution sulfur by precipitation of solid solution sulfur in steel as MnS. In the present invention, by appropriately Mn and S content, fine MnS is precipitated to obtain yield strength and in-plane anisotropy while securing aging resistance. In the present invention, in order to exhibit such an effect, the Mn content is preferably included at 0.05% or more. Through this, it is possible to secure a fine MnS precipitate. However, if the content exceeds 0.2%, the high Mn content may cause coarse MnS to precipitate, resulting in poor aging resistance. Therefore, the Mn is preferably contained in 0.05 to 0.2% by weight.

Aluminum (Al): 0.02-0.05 wt%

Aluminum participates as a deoxidizer and has the effect of preventing aging by solid nitrogen by precipitating nitrogen in steel. When the Al content is less than 0.02%, the amount of solid solution nitrogen is high so that aging may not be prevented. When the amount of Al is more than 0.05%, the amount of aluminum present in the solid solution state is high and the ductility decreases. Therefore, it is preferable that Al is contained in 0.02-0.05 weight%.

Niobium (Nb): 0.04 to 0.14 wt%

Nionium is an element that forms precipitates, is located in the grain boundaries and in the grains of the microstructure, thereby inhibiting the growth of grains and making grains finer, thereby improving workability. It is preferable to add at least 0.04% by weight or more because it serves to improve the NbC precipitation effect. However, when the content of Nb exceeds 0.14% by weight, not only is it economically disadvantageous, but also the plating property may be reduced during plating. Therefore, the niobium is preferably contained in 0.04 ~ 0.14% by weight.

Nitrogen (N): 0.001-0.005 wt%

Nitrogen is an element inevitably contained in steelmaking. It is known that the more nitrogen in steel, the toughness is greatly reduced, and it is a general trend to reduce nitrogen content as much as possible. In the present invention, it is preferable to limit the content of nitrogen to 0.005% by weight or less. When the content of nitrogen exceeds 0.005% by weight, the aging index is high, and moldability and processability may be reduced. On the other hand, the nitrogen content is as low as possible, but the lower limit is preferably 0.001% by weight in consideration of steelmaking cost.

Phosphorus (P): 0.008 wt% or less

If the content of phosphorus exceeds 0.08% by weight, the ductility and moldability is lowered, it is preferable to limit the phosphorus to 0.08% by weight or less.

Sulfur (S): 0.008 wt% or less

When the content of sulfur exceeds 0.008% by weight, the content of solid solution of sulfur is largely lowered in ductility and formability, and there is a fear of red brittleness, so the sulfur is preferably limited to 0.008% by weight or less.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.

According to an aspect of the present invention, by satisfying the component system, it is possible to provide a steel sheet excellent in material uniformity and workability. On the other hand, in order to further improve the effect of the present invention, Cu, Cr, Mo and Ni may further include one or more selected from the group consisting of.

Copper (Cu): 0.01-0.03 wt%

Copper acts as a solid solution element, contributing to the increase in strength. In the present invention, it is preferable to include 0.01% by weight or more in order to exhibit such an effect. However, when the content of copper exceeds 0.03% by weight, there is a problem that a surface defect occurs by forming a low melting point phase during hot rolling. Therefore, the copper is preferably contained in 0.01 to 0.03% by weight.

Chromium (Cr): 0.01-0.03 wt%

Chromium is an effective element in securing strength. In the present invention, it is preferable to include 0.01% by weight or more in order to exhibit such an effect. However, when the content of chromium exceeds 0.03% by weight, moldability and processability are lowered. Therefore, the chromium is preferably contained in 0.01 to 0.03% by weight.

Molybdenum (Mo): 0.001 to 0.005 wt%

Molybdenum, like Cr, is an effective element in securing strength. In order to exhibit such an effect, it is preferable that 0.001% by weight or more is contained in the present invention. However, when the content of molybdenum exceeds 0.005 wt%, the recrystallization in the gamma region (austenite region) is delayed during hot rolling to increase the rolling load. Therefore, the molybdenum is preferably contained in an amount of 0.001 to 0.005% by weight.

Nickel (Ni): 0.001-0.03 wt%

Nickel is an effective element for simultaneously improving strength and toughness. In the present invention, it is preferable that 0.001% by weight or more is contained in order to exhibit the solid solution strengthening effect. However, when the content of nickel is more than 0.03% by weight, there is a problem that the transformation point greatly decreases and a low-temperature transformation phase appears at the time of hot rolling. Accordingly, the amount of the nickel is preferably 0.001 to 0.03% by weight.

According to an aspect of the present invention, by satisfying the above component system, it is possible to provide a cold rolled steel sheet excellent in workability. Since the present invention corresponds to ultra low carbon steel having a C content of 15 ppm or less, the microstructure is composed of a ferrite single phase structure. The ferrite single phase tissue may include other tissues inevitably generated.

Moreover, it is preferable that the average particle size of the microstructure grain of a cold rolled steel sheet is 7-11 micrometers.

In the microstructure, it is preferable that the occupancy area ratio of the crystal grains having a grain size of 10 µm or less is 30 to 60% of the total grain occupancy area.

If the average grain size of the microstructure is less than 7 μm, there is an improvement in strength due to the refinement of the structure, but it is disadvantageous in terms of processability, and if it exceeds 11 μm, it is difficult to secure desired strength by coarse grains. Therefore, it is preferable that the average particle size of the microstructure grains of a cold rolled steel sheet is 7-11 micrometers.

It is preferable that the said average grain size satisfy | fills 7-11 micrometers, and the area ratio of the crystal grains which have a crystal grain size of 10 micrometers or less in a crystal grain is 30 to 60%. In other words, when the fine grains of 10 µm or less exceed 60%, the overall structure is too fine to secure the required elongation, and when less than 30%, the entire structure is coarse to secure the desired strength. Therefore, it is preferable that the grains of the cold rolled steel sheet have a grain size of 10 μm or less and the occupancy area of the grains is 30 to 60%.

Further, the cold-rolled steel sheet of the present invention includes a precipitate. It is preferable that the number of precipitates having an aspect ratio of 2.0 or less is 75% or more of the total number of precipitates. When the aspect ratio exceeds 2.0, it is located at the grain boundary at the time of growth of the precipitate microstructure, and rather, promotes grain growth, thereby coarsening the grains. Therefore, the aspect ratio of the precipitate is preferably 2.0 or less.

The precipitate has a precipitation strengthening effect on the base steel sheet, that is, the precipitate improves the strength through pinning effect which suppresses the growth of the crystal grains. In order to obtain the precipitation strengthening effect intended in the present invention, it is preferable that the precipitate having an aspect ratio of the precipitate of 2.0 or less is 75% or more of the total number of precipitates. It is more preferable that the precipitate is NbC.

Hereinafter, a method of manufacturing a cold rolled steel sheet which is an aspect of the present invention will be described in detail.

Heating stage

By heating the steel slab satisfying the above-described component system, a ferrite having workability and material uniformity is realized. In the present invention, in order to exhibit such an effect, it is preferable to heat the steel slab to 1100 ° C or more.

Hot rolling

The steel slab heated as above is hot rolled. At this time, it is preferable to perform hot finishing rolling at the temperature of Ar3 or more. If the finish rolling is carried out at a temperature below Ar3, there is a high possibility that the hot deformation resistance is sharply increased, and there is a high possibility of microcracks due to high temperature brittleness.

Coiling

The hot-rolled steel sheet produced by hot rolling as described above is wound. At this time, it is preferable that winding temperature is 650-750 degreeC. When the said coiling temperature is less than 650 degreeC, since the grain of a hot rolled steel sheet does not fully grow in the cooling process after winding, the workability of steel is reduced. On the other hand, when the coiling temperature exceeds 750 캜, the precipitates grow too coarse to degrade processability, resulting in a large scale on the surface of the steel sheet, resulting in poor pickling in the pickling process. Therefore, it is preferable that a coiling temperature is 650-750 degreeC.

Cold rolling

The hot rolled steel sheet thus wound is cold-rolled. At this time, it is preferable to make the rolling reduction rate of cold rolling into 50 to 90%. When the reduction ratio of the cold rolling is less than 50%, since the annealing recrystallization nucleation amount is small, the grains grow too large during annealing, resulting in a decrease in strength and workability due to coarsening of the annealing recrystallization grains. On the other hand, when the reduction ratio of the cold rolling exceeds 90%, the workability is improved, but the nucleation amount is too large, the annealing recrystallized grain is too fine to decrease the ductility. Therefore, it is preferable that the rolling reduction ratio of cold rolling is 50 to 90%.

Annealing

The cold-rolled steel sheet as described above is annealed. At this time, the annealing temperature is preferably limited to a temperature of 800 ~ 900 ℃. If the temperature of the annealing is less than 800 ° C., recrystallization is not completed and thus a target ductility value cannot be secured. On the other hand, when the annealing temperature exceeds 900 ° C., the strength decreases due to coarsening of the recrystallized grains. Therefore, it is preferable that annealing temperature is 800-900 degreeC.

The annealing of the cold-rolled steel sheet is preferably carried out so that the recrystallization is completed. In this case, the annealing time is preferably limited to 10 seconds to 30 minutes.

Hereinafter, the present invention will be described in more detail with reference to Examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

To prepare a steel slab having the composition shown in Table 1, after reheating the steel slab to 1200 ℃ hot-rolled and rolled to 700 ℃, cold-rolled at 70%, followed by continuous annealing at 850 ℃ cold rolling Steel sheet was prepared.

The cold-rolled steel sheet produced by the above method was measured for tensile strength and elongation, and the microstructure was observed. The results are shown in Table 2 below. In Table 2 below, the tensile strength is 180 to 250 MPa, the elongation (%) is 50% or more, and TS × El is 10,000 Mpa% or more, when all three are satisfied, ○, when any one of the three is satisfied (Triangle | delta) and when none were satisfied, it described with x.

division C Mn P S Si Al Nb Cu Cr Mo N Ni Inventive Steel 1 0.0005 0.15 0.0067 0.0021 0.0040 0.037 0.04 0.018 0.014 - 0.0021 - Invention river 2 0.0006 0.14 0.0057 0.0034 0.0068 0.029 0.04 0.013 0.017 - 0.0032 - Invention steel 3 0.0015 0.18 0.0076 0.0051 0.0039 0.045 0.05 0.026 0.021 - 0.0023 - Inventive Steel 4 0.0010 0.07 0.0079 0.0029 0.0038 0.027 0.10 0.017 0.029 - 0.0019 - Invention steel 5 0.0010 0.10 0.0061 0.0076 0.0051 0.021 0.10 0.014 0.011 - 0.0032 - Invention steel 6 0.0011 0.08 0.0054 0.0079 0.0062 0.032 0.11 0.022 - 0.001 0.0025 - Invention steel 7 0.0014 0.19 0.0045 0.0067 0.0047 0.039 0.14 0.019 - 0.002 0.0028 - Inventive Steel 8 0.0012 0.11 0.0034 0.0054 0.0042 0.049 0.12 0.015 - 0.003 0.0026 - Invention river 9 0.0014 0.13 0.0032 0.0072 0.0042 0.026 0.13 0.011 - 0.004 0.0023 - Invented Steel 10 0.0011 0.06 0.0039 0.0067 0.0039 0.029 0.11 0.018 - 0.005 0.0028 0.012 Invention steel 11 0.0009 0.09 0.0042 0.0061 0.0053 0.031 0.09 0.029 - - 0.0018 0.029 Invention steel 12 0.0008 0.14 0.0049 0.0057 0.0051 0.029 0.08 0.015 - - 0.0025 0.021 Invention steel 13 0.0005 0.11 0.0059 0.0054 0.0048 0.032 0.04 0.026 - - 0.0034 0.017 Invented Steel 14 0.0009 0.06 0.0067 0.0045 0.0037 0.023 0.08 0.022 - - 0.0032 0.021 Invented Steel 15 0.0007 0.05 0.0072 0.0061 0.0035 0.027 0.06 0.026 - - 0.0022 - Comparative Example 1 0.0003 0.09 0.0088 0.0059 0.0038 0.033 - - - - 0.0022 - Comparative Example 2 0.0004 0.10 0.0091 0.0067 0.0040 0.035 - - - - 0.0024 - Comparative Example 3 0.0003 0.05 0.0076 0.0061 0.0062 0.028 - - - - 0.0025 - Comparative Example 4 0.0019 0.14 0.0061 0.0079 0.0058 0.029 - - - - 0.0034 - Comparative Example 5 0.0020 0.13 0.0098 0.0061 0.0062 0.033 - - - - 0.0021 - Comparative Example 6 0.0024 0.15 0.0112 0.0072 0.0038 0.039 - - - - 0.0028 - Comparative Example 7 0.0018 0.14 0.0097 0.0061 0.0048 0.029 - - - - 0.0039 - Comparative Example 8 0.0016 0.05 0.0102 0.0054 0.0049 0.034 - - - - 0.0019 - Comparative Example 9 0.0002 0.09 0.0097 0.0045 0.0038 0.023 - - - - 0.0023 - Comparative Example 10 0.0019 0.09 0.0087 0.0062 0.0052 0.021 - - - - 0.0026 - Comparative Example 11 0.0021 0.10 0.0051 0.0057 0.0053 0.026 - - - - 0.0032 - Comparative Example 12 0.0022 0.15 0.0106 0.0076 0.0051 0.024 - - - - 0.0032 - Comparative Example 13 0.0018 0.13 0.0078 0.0076 0.0049 0.028 - - - - 0.0029 - Comparative Example 14 0.0019 0.05 0.0099 0.0077 0.0062 0.037 - - - - 0.0039 - Comparative Example 15 0.0004 0.05 0.0061 0.0079 0.0038 0.034 - - - - 0.0026 -

division TS (Mpa) El (%) TS X El (Mpa%) Grain size (average) ≤10㎛ grain area percentage (%) Aspect ratio≤2.0
Share(%) TS, El, TS × El evaluation Inventive Steel 1 185 55 10175 10.4 33 93 ○ Invention river 2 229 54 12366 10.5 31 84 ○ Invention steel 3 239 51 12189 7.8 59 79 ○ Inventive Steel 4 197 55 10835 7.9 58 86 ○ Invention steel 5 195 54 10530 8.8 57 76 ○ Invention steel 6 231 51 11781 10.2 37 92 ○ Invention steel 7 246 52 12792 8.1 57 91 ○ Inventive Steel 8 212 53 11236 8.9 55 90 ○ Invention river 9 249 51 12699 8.2 56 84 ○ Invented Steel 10 230 52 11960 7.1 53 88 ○ Invention steel 11 211 54 11394 9.9 44 89 ○ Invention steel 12 199 55 10945 8.9 42 86 ○ Invention steel 13 187 56 10472 10.9 31 95 ○ Invented Steel 14 207 53 10971 8.4 54 80 ○ Invented Steel 15 194 54 10476 7.4 39 75 ○ Comparative Example 1 161 58 9338 11.8 34 69 △ Comparative Example 2 176 56 9856 11.8 44 61 △ Comparative Example 3 167 58 9686 11.2 27 65 △ Comparative Example 4 157 54 8478 6.8 63 69 △ Comparative Example 5 182 53 9646 6.7 62 68 △ Comparative Example 6 177 43 7611 6.5 64 63 × Comparative Example 7 165 47 7755 6.9 61 59 × Comparative Example 8 179 48 8592 5.8 60 57 × Comparative Example 9 177 56 9912 11.5 57 74 △ Comparative Example 10 175 55 9625 6.1 68 68 △ Comparative Example 11 165 59 9735 6.4 61 66 △ Comparative Example 12 174 57 9918 6.9 62 75 △ Comparative Example 13 177 49 8673 5.2 62 65 × Comparative Example 14 178 49 8722 6.4 63 61 × Comparative Example 15 179 49 8771 11.4 45 68 ×

Claims (8)

By weight%, C: 0.0005 to 0.0015%, Si: 0.003 to 0.007%, Mn: 0.05 to 0.2%, Al: 0.02 to 0.05%, Nb: 0.04 to 0.14%, N: 0.001 to 0.005%, P: 0.008% Or less, S: 0.008% or less, the remainder includes Fe and unavoidable impurities,
The average grain size of the microstructure grains is 7-11 μm, the occupancy area of the grains having a particle size of 10 μm or less is 30-60% of the total grain area ratio, and the number of precipitates having an aspect ratio of 2.0 or less is the total number of precipitates. Cold rolled steel with excellent workability of more than 75%.
The method of claim 1,
The cold rolled steel sheet is Cu: 0.01 ~ 0.03%, Cr: 0.01 ~ 0.03%, Mo: 0.001 ~ 0.005%, Ni: 0.001 ~ 0.03% The cold rolled steel sheet excellent workability further comprising one or more selected from the group consisting of.
3. The method according to claim 1 or 2,
The microstructure of the cold rolled steel sheet is a cold rolled steel sheet excellent in workability is ferrite.
3. The method according to claim 1 or 2,
Cold rolled steel with excellent workability, with TS × El of 10,000 MPa% or more.
By weight%, C: 0.0005 to 0.0015%, Si: 0.003 to 0.007%, Mn: 0.05 to 0.2%, Al: 0.02 to 0.05%, Nb: 0.04 to 0.14%, N: 0.001 to 0.005%, P: 0.008% S: 0.008% or less Re-heating the steel slab containing Fe and unavoidable impurities to 1100 ° C. or more;
Hot rolling the reheated steel slab and finishing hot rolling at a temperature of Ar3 or higher to produce a hot rolled steel sheet;
Winding the hot rolled steel sheet at a temperature of 650˜750 ° C .;
Manufacturing a cold rolled steel sheet by cold rolling the hot rolled steel sheet at a reduction ratio of 50 to 90% after the winding; And
Process for producing a cold rolled steel sheet having excellent workability comprising the step of annealing the cold rolled steel sheet at a temperature of 800 ~ 900 ℃.
6. The method of claim 5,
The steel slab is made of a cold rolled steel sheet having excellent workability further comprising at least one selected from the group consisting of Cu: 0.01 to 0.03%, Cr: 0.01 to 0.03%, Mo: 0.001 to 0.005%, and Ni: 0.001 to 0.03%. Way.
The method according to claim 5 or 6,
The annealing is carried out by a continuous annealing method, a method of producing a cold rolled steel sheet excellent in workability for 10 seconds to 30 minutes. The method of claim 3, wherein
Cold rolled steel with excellent workability, with TS × El of 10,000 MPa% or more.