KR101286172B1 - High strength and heat-resistance cold-rolled steel sheet having excellent formability, heat resistance for working and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a high-strength, high-temperature cold rolled steel sheet having excellent workability and heat resistance, and a method for manufacturing the same, in weight% of C: 0.002 to 0.010%, Mn: 0.3 to 0.6%, P: 0.03 to 0.08%, and Al: 0.02. ~ 0.08%, B: 0.001 ~ 0.003%, W: 0.05 ~ 0.30%, N: 0.002 ~ 0.010%, Nb: 0.02 ~ 0.08%, S: 0.015% or less, processability and heat resistance including residual Fe and other unavoidable impurities The excellent high strength high heat resistant cold rolled steel sheet and its manufacturing method are made into a technical summary. According to the present invention, it can be manufactured at a lower cost than the conventional stainless steel sheet, and has various processing characteristics such as extension flange, bending property, and deep drawing property, and thus has excellent room temperature processability, and anti-aging property due to precipitation of solid elements. It is possible to produce high strength cold-rolled steel sheet for high-strength processing, which increases the life of the facility by securing the shape freezing property of the high-temperature applied product because it has excellent moldability due to the increase in yield point stretching.

Cold Rolled Steel Sheet, Needle Bainite, Heat Resistance, Processability, High Strength, Aging Resistance

Description

High-strength, high-temperature cold-rolled steel sheet for processing and its manufacturing method excellent in workability and heat resistance {HIGH STRENGTH AND HEAT-RESISTANCE COLD-ROLLED STEEL SHEET HAVING EXCELLENT FORMABILITY, HEAT RESISTANCE FOR WORKING AND MANUFACTURING METHOD THEREOF}

The present invention relates to a high strength, high temperature resistant cold rolled steel sheet used in automobiles, home appliances and boilers, and to a method of manufacturing the same. It relates to a heat resistant cold rolled steel sheet and a method of manufacturing the same.

In the past, cast iron was generally used in parts of products such as automobile exhaust systems, home communication systems, ovens, boilers, etc., but high heat resistance is required because it is continuously exposed to a high temperature environment of several hundred degrees (° C.) or higher. In order to secure an aluminum hot-dip galvanized steel sheet, stainless steel sheet, etc. were processed and used.

The high temperature property is one of the characteristics when the processed product is used in a high temperature environment. The high temperature property, that is, sag resistance and high temperature strength, is required because the product property may be deteriorated by a local temperature rise when using a product such as an automobile exhaust system. . The sag resistance is a phenomenon in which the steel sheet is repeatedly exposed to high temperature and sagging due to changes in the material. When such a phenomenon occurs, it is difficult to maintain the shape of the molded part, and when the thermal stress is concentrated to a specific place, the high temperature strength decreases. Since the product shape is deformed or destroyed, it is necessary to satisfy the yield strength of 55MPa or more at a high temperature of about 700 ° C to secure the shape freezing property.

Stainless steel sheet has been mainly used for such heat-resistance, but stainless steel sheet is not only expensive to manufacture due to the addition of expensive alloy elements such as Cr and Ni, but also has a high Cr and There is a problem in that corrosion resistance (corrosion resistance) is lowered because grain boundary corrosion occurs in the Cr depleted zone region formed by the precipitation of chromium carbide at the grain boundary by bonding.

Also, in order to secure oxidation resistance at high temperature, an aluminum hot dip galvanized steel sheet may be used. When the aluminum hot dip galvanized sheet is heated to a high temperature of 400 ° C. or higher, an alloy layer of an interface is grown due to the interdiffusion reaction between Fe and Al. There is a problem in that the application can be applied because it loses the gloss of the surface in a short time and the color change is insufficient heat resistance.

In addition, products such as automobile exhaust system, home communication, oven, boiler, etc. are manufactured to be accommodated in a limited space, and formed into a complex shape by various methods, so that the processing process to expand or bend after piping is required, in addition to the above high temperature characteristics Not only workability is required, but tensile strength of 350 MPa or more is required at room temperature in order to secure impact characteristics of the use member.

Thus, Japanese Laid-Open Patent Publication No. 9-176816 attempts to improve heat resistance and workability by heat-treating a steel sheet after adjusting aluminum content of Al and solid solution N in steel, but the steel sheet is used at a temperature of 550 ° C. or higher. It is difficult to be applied to a member of, and it is not easy to adjust the amount of the steel component to be added, which may cause workability deterioration and processing defects due to aging.

In addition, Japanese Patent Application Laid-open No. Hei 8-319548 attempts to manufacture a hot-dip aluminum plated steel sheet having excellent high temperature strength by forming a coating layer on the surface of the steel sheet, but suggests a method of improving the plating conditions rather than improving the properties of the steel sheet. Not only is the adjustment difficult when the ingredients are changed, but also there is a problem that it is difficult to obtain target heat resistance.

In addition, Japanese Laid-Open Patent Publication No. Hei 9-111396 intends to manufacture a high strength steel sheet having excellent impact resistance characteristics composed of two-phase structure of ferrite and martensite, but there is a problem in that moldability is not good due to insufficient stretching.

The present inventors have repeatedly conducted research and experiments to solve the above problems and propose the present invention based on the results, and the present invention simultaneously exhibits high temperature and room temperature characteristics such as automobile exhaust system, household communication, oven and boiler, etc. The present invention provides a high-strength cold-rolled steel sheet for processing and heat-resistance with excellent workability and heat resistance that can be manufactured at low cost by optimizing steel components and processing conditions while reducing the addition of expensive alloying elements for use in demanding applications. There is this.

In the present invention, C: 0.002 to 0.010%, Mn: 0.3 to 0.6%, P: 0.03 to 0.08%, Al: 0.02 to 0.08%, B: 0.001 to 0.003%, W: 0.05 to 0.30%, and N: Provides a high strength, high temperature cold rolled steel sheet for processing having excellent workability and heat resistance including 0.002 to 0.010%, Nb: 0.02 to 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities.

At this time, the characteristic of the atomic ratio Nb / C of Nb and C is 0.8-2.0, too.

In addition, the cold rolled steel sheet is characterized in that the Nb-based carbide precipitates are formed.

In addition, the characteristic is that the value of the atomic ratio B / N of the B and N is 0.5 ~ 1.5.

In addition, the cold rolled steel sheet is characterized in that the B-based nitride precipitates are formed.

Further, the cold rolled steel sheet is also characterized by being made of an equiaxed ferrite and acicular bainite structure.

At this time, the volume fraction of the needle-shaped bainite structure of the cold rolled steel sheet is also characterized by 10 to 25%.

In addition, the present invention is in the weight% C: 0.002 ~ 0.010%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08%, B: 0.001 ~ 0.003%, W: 0.05 ~ 0.30%, Steel slab containing N: 0.002 ~ 0.010%, Nb: 0.02 ~ 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities is heated, hot rolled, cold rolled, and then cold rolled steel sheet The annealing treatment at a temperature of 830 ℃ or more, and provides a high-temperature high-temperature cold rolled steel sheet for workability and heat resistance excellent in the processability and heat resistance characterized in that the cooling rate of 40 ℃ / sec or more with respect to the annealed steel sheet.

At this time, the steel slab is characterized in that the value of the atomic ratio Nb / C of the Nb and C is 0.8 ~ 2.0.

In addition, the steel slab is characterized in that the value of the atomic ratio B / N of the B and N is 0.5 ~ 1.5.

In addition, the hot rolling is also characterized by finish rolling at 900 ~ 950 ℃.

In addition, the hot rolling is characterized in that it comprises the step of cooling the hot rolled hot rolled plate at a cooling rate of 20 ~ 80 ℃ / sec.

Furthermore, the said winding is also characterized by what is performed at 560-680 degreeC.

In addition, the annealing treatment is characterized in that it is performed at 830 ~ 900 ℃.

As described above, according to the present invention, it can be manufactured at a lower cost than the conventional stainless steel sheet, and has various processing characteristics of extension flangeability, bending property, and deep drawing property, and thus has excellent room temperature processability, As the precipitation resistance increases the aging resistance, there is no yield point elongation, so it is not only excellent in moldability but also excellent in high temperature strength, so that high-temperature cold-rolled steel sheet for high-strength processing can be manufactured to secure the shape freezing property of high-temperature applications. Can be.

Hereinafter, the cold rolled steel sheet of the present invention will be described in detail.

The present inventors have satisfied various processing characteristics such as stretch-flangeability, bendability, deep drawing, etc., anti-aging properties, and corrosion resistance at low cost and 55 MPa at 700 ° C. The present invention was completed by repeating the research and experiment to secure the yield strength and the tensile strength of 350MPa or more at room temperature. As a result, the present invention includes a very low carbon content, increase the content of Mn, P in the steel components, control the atomic ratio of Nb and C and B and N to form a fine Nb-based carbonized precipitate and B-based nitride precipitates By optimizing the annealing and cooling conditions to secure the volume fraction of acicular bainite structure, it has excellent heat resistance and corrosion resistance at high temperature, aging resistance and processability at room temperature, and is suitable for products such as automobile exhaust system, home communication, oven and boiler. It is characterized by the manufacture of high strength, high temperature resistant cold rolled steel sheets.

First, the reasons for limiting components of the present invention will be described.

Carbon (C) is an element added to improve the strength of room temperature and high temperature of the steel sheet and is mainly consumed by the reaction with Nb in the present invention to form precipitates. As the amount of C added increases, the tensile and yield strength increases, but when added excessively, it causes aging and the workability decreases, so the upper limit is preferably 0.010%. However, if the content is less than 0.002%, sufficient Nb-based carbide precipitates may not be obtained, and the grain size may increase, causing a sudden change in the material. Therefore, the C content is limited to 0.002 to 0.010%.

Manganese (Mn) is a solid solution strengthening element that increases the strength of steel and improves hot workability, but is an element that inhibits ductility and workability by MnS formation. Therefore, when Mn is added excessively, ductility falls and it becomes a factor of economical deterioration and center segregation by adding a large amount of alloying elements, and therefore an upper limit is preferably 0.6%. However, if less than 0.3% workability is improved, but the target strength is difficult to secure, the content of Mn is limited to 0.3 ~ 0.6%.

Aluminum (Al) is an element added for deoxidation of molten steel and is preferably contained in an amount of 0.02% or more because it is combined with solid solution elements in steel to improve aging characteristics. However, excessive addition of more than 0.08% increases the amount of inclusions in the steel, causing surface defects and lowering the workability, Al content is limited to 0.02 ~ 0.08%.

Phosphorus (P) is an important element to improve the strength and corrosion resistance of the steel, it is preferable to contain 0.03% or more in order to secure these properties, but if the content exceeds 0.08%, it causes the center segregation during casting and workability is reduced, The content of P is limited to 0.03 to 0.08%.

Nitrogen (N) exists in solid solution inside the steel and is effective for strengthening the material. If it contains less than 0.002%, sufficient stiffness cannot be obtained, and the precipitate formation site is reduced. Since it causes aging and hardening occurs and deteriorates moldability, N content is limited to 0.002% to 0.010%.

Boron (B) is dissolved in the steel to increase the strength and toughness, and to improve the aging resistance and workability by forming boron-based nitride precipitates such as BN, effective in suppressing grain growth at high temperature. It is preferable to add more than 0.001%, but if the content exceeds 0.003%, material variation is caused, and retardation of recrystallization at a high temperature is a factor that degrades workability, so the content of B is limited to 0.001 to 0.003%.

Sulfur (S) combines with Mn in the steel to form non-metallic inclusions that serve as the starting point of corrosion and causes red shortness, so it is desirable to reduce the content as much as possible, so the content of S is limited to 0.015% or less. .

Niobium (Nb) is an effective element for increasing the strength of steel sheet and refining grains. In the present invention, niobium (Nb) is combined with C in solid solution in steel to form Nb-based carbonized precipitates to improve aging and formability and increase strength. It is preferable to contain 0.02% or more because it suppresses grain growth and provides finer particles. However, when the content exceeds 0.08%, the material hardens, and the operability decreases during continuous annealing, and the surface characteristics of the steel sheet are reduced. Since it deteriorates, the content of Nb is limited to 0.02 to 0.08%.

Tungsten (W) is an effective element to enhance the precipitation precipitation and high temperature strength in steel. To achieve this effect, tungsten (W) needs to be added at least 0.05%. However, when the content of W exceeds 0.30%, it is more expensive than the contribution to the promotion of precipitation. Since it becomes a rising factor of the manufacturing cost according to the addition of alloying elements, the content of W is limited to 0.05 ~ 0.30%.

In the case of Nb and B, it is also important to manage alone, but in order to secure the high temperature and room temperature characteristics targeted by the present invention, the effects of precipitate formation and solid solution elements in the steel should be considered. To this end, it is important to maintain room temperature aging resistance, processability and high temperature strength simultaneously by maintaining the atomic ratio Nb / C of Nb and C and the atomic ratio B / N of B and N in a certain range.

When the atomic ratio Nb / C of Nb and C is 0.8 to 2.0, Nb-based carbonized precipitates form solid element solids C in the steel to ensure room temperature aging resistance and processability, and to properly control annealing and cooling conditions. By suppressing grain growth at high temperatures through the formation of fine Nb-based carbide precipitates, it is possible to secure excellent high temperature characteristics by controlling the microstructure.

However, when the value of Nb / C is less than 0.8, there is a problem of deterioration of room temperature aging resistance and workability due to excessive solid solution elements in the steel, and excellent high temperature strength cannot be secured because the amount of Nb-based carbide precipitates is insignificant. In addition, when the value exceeds 2.0, the material hardens, the temperature of the recrystallization is rapidly increased, the surface properties deteriorate and the workability of the post-process is lowered. Therefore, the value of Nb / C is 0.8 to 2.0. It is limited to.

In order to optimize the aging resistance at room temperature, the workability, and the effect of inhibiting grain growth at high temperature, it is necessary to keep the values of the atomic ratio B / N of B and N at 0.5 to 1.5. When the B / N value is less than 0.5, there is a problem that the room temperature resistance is degraded due to excessive solid solution in steel, the grain suppression effect is insufficient at high temperature, and when the B / N value exceeds 1.5, the ductility is lowered and the workability is decreased. , The value of B / N is limited to 0.5 to 1.5.

The cold rolled steel sheet of the present invention comprises the above components and consists of the remainder Fe and other unavoidable impurities. And alloy elements may be further added to improve the properties of the present cold-rolled steel, if necessary, it is not interpreted to be excluded from the scope of the present invention because the alloy element is not added in the embodiment of the present invention.

On the other hand, the cold-rolled steel sheet of the present invention is characterized by consisting of an equiaxed ferrite (polygonal ferrite) and acicular bainite structure, the acicular bainite is a plate-like ferrite structure having a carbide therein and has a high dislocation density. , Toughness is excellent.

The present invention, by appropriately controlling the conditions of the annealing and cooling process to secure a volume fraction of the needle-like bainite tissue 10 to 25% to form a high-potential-density type microstructure to suppress abnormal growth of crystal grains at high temperature to room temperature and high temperature Strength can be improved. However, when the volume fraction of the acicular bainite structure is less than 10%, it is difficult to secure room temperature and high temperature strength, so that it is difficult to obtain excellent heat resistance. When the volume fraction of the acicular bainite structure is more than 25%, it is hardened by material hardening. There is a problem that workability deteriorates, and the volume fraction of acicular bainite is limited to 10 to 25%.

Hereinafter, the manufacturing method of the high-strength high temperature resistant cold rolled steel sheet excellent in heat resistance and workability of this invention is demonstrated in detail.

After reheating the steel slab having the above composition, hot rolling, cold rolling after winding, and cooling the steel sheet annealed at a temperature of 830 ° C. or higher at a cooling rate of 40 ° C./sec or higher to achieve high strength and high workability. Heat-resistant cold rolled steel sheet can be produced.

After reheating the steel slab formed as the above-described component system at a normal temperature, the finish rolling temperature during hot rolling is 900 to 950 ° C., and when the finish rolling temperature is less than 900 ° C., the hot rolling is completed in a relatively low temperature region. Due to the occurrence of hybridization of the finally formed crystal grains, the workability and rolling properties are lowered, and if the finish rolling temperature exceeds 950 ° C, uniform hot rolling is not performed throughout the thickness, resulting in insufficient grain refinement, resulting in grain coarsening. Since impact toughness falls, finish rolling temperature is restrict | limited to 900-950 degreeC.

After the hot finish rolling, the annually rolled steel sheet is cooled at a run-out table at a cooling rate of 20 to 80 ° C./sec. If the cooling rate is less than 20 ° C./sec, the grain growth is promoted. This is because coarse grains are formed, which may be a cause of deterioration in strength and workability, and when the cooling rate exceeds 80 ° C / sec, it acts as a cause of variation in materials due to widthwise cooling unevenness.

After cooling in the runout table, the hot rolled steel sheet is wound at a temperature of 560 ~ 680 ℃. If the coiling temperature is less than 560 ℃, the material of the hot rolled material is somewhat hardened to increase the load in the cold rolling process, which is the next process, and thus it is difficult to secure rolling property, and the nonuniformity of the widthwise temperature increases, resulting in a difference in the production behavior of low temperature precipitates. Due to this material variation is caused workability is lowered, there is a problem that the high temperature characteristics are deteriorated. In addition, when the coiling temperature exceeds 680 ℃, there is a problem that the structure of the final product is produced coarse, deterioration of workability and corrosion resistance, the coiling temperature is limited to 560 ~ 680 ℃.

After the wound steel sheet is subjected to pickling treatment and cold rolling to a target thickness, the steel sheet is subjected to continuous annealing at high temperature for recrystallization and microstructure control. At this time, in order to sufficiently secure the transformation driving force of the needle-shaped bainite structure, the annealing temperature is preferably 830 ° C or higher. If the annealing temperature is lower than 830 ° C, the volume fraction of the needle-shaped bainite present in the microstructure of the target steel sheet can be obtained. This is because it is difficult to secure excellent high temperature characteristics. However, since annealing at too high temperature may increase the surface defects of the steel sheet, the annealing temperature is preferably managed at 900 ° C. or lower.

The annealed steel sheet can secure a volume fraction of the target acicular bainite structure through a cooling process, for which the cooling rate is maintained at 40 ° C / sec or more. This is because when the cooling rate is less than 40 ° C / sec, it is difficult to obtain the volume fraction of the target acicular bainite structure due to slow cooling.

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

[Example]

Invented steels 1 and 2 and Comparative steels 1 to 5 prepared by melting the composition shown in Table 1 below under the process conditions as shown in Table 2 to produce cold rolled steel invention materials 1 to 5 and Comparative materials 1 to 10 After that, the volume fraction of the acicular bainite structure and the characteristics at room temperature and high temperature were evaluated for each of the prepared cold rolled steel sheets.

 Yield elongation phenomenon of the characteristics described in Table 3 is expressed as occurrence when the elongation is generated by measuring the yield point elongation, and not occurred when the elongation is not generated, and the bending resistance test is performed after the steel sheet processing. The degree of bending was divided according to the degree of occurrence, and the bending index representing this was divided into five stages, and 1 to 2 stages with relatively small bending were good, and 3 to 5 stages where the bending occurred as bad as possible for visual observation. Determined.

In addition, the room temperature tensile strength test was determined to be good if the tensile strength of 350MPa or more at room temperature, less than that, the sag resistance test after heating the material of 250mm in length, 30mm in width using a heat treatment equipment for 100 hours at 700 ℃ Sagging of the steel plate was measured and it was judged to be bad when the deflection degree was 5 mm or more and less than 5 mm. The high temperature yield strength test was good when the yield strength was 55 MPa or more at 700 ° C., and less than that. It was. In addition, the workability test was judged to be defective when a work crack occurred during normal temperature processing.

At this time, in Table 1, the value of the atomic ratio Nb / C of Nb and C and the value of the atomic ratio B / N of B and N refer to the ratio of the value obtained by dividing the weight percentage of each element by its atomic weight.

Table 1 Components of Inventive and Comparative Steels

[Table 2] Condition of Manufacturing Process by Steel Plate

[Table 3] Evaluation of properties by steel plate

As shown in Table 3, Inventive Materials 1 to 5 in which the steel component and the process conditions satisfy the scope of the present invention did not occur in the yield point stretching phenomenon, good bending resistance and excellent aging resistance, tensile strength is also room temperature The yield strength was satisfactory at 350 MPa or more at, and the yield strength at high temperature and the sag resistance after heat treatment (sag resistance) were also good due to the formation of Nb-based carbide and B-nitride precipitates and optimization of the volume fraction of acicular bainite structure. There was no work cracking at the time, so the workability at room temperature was also excellent.

On the other hand, although the steel components of Table 1 and the like are invention steels satisfying the scope of the present invention, Comparative Materials 1 to 5 in which some of the process conditions of Table 2 are out of the scope of the present invention are mostly low in volume fraction of acicular bainite structure. It did not have excellent high temperature strength, and it was often poor workability and aging resistance as well as room temperature tensile strength.

In addition, although the process conditions of Table 2 satisfy the scope of the present invention, Comparative Materials 6 to 10 in which the steel components of Table 1 and the like are outside the scope of the present invention were often poor in workability and aging resistance, Due to the low volume fraction, most of the high temperature properties were poor, and because W was not added and the contents of Mn and P were low, the tensile strength of the room temperature was often lowered.

Among them, Comparative Material 7 had no yield point stretching phenomenon, good bending resistance, excellent aging resistance and workability, and good tensile strength of 350 MPa or more, but poor sag resistance and high temperature yield strength. This is because when the annealing is performed due to the polyaddition and no addition of W, the operability deteriorates and the surface properties of the steel sheet are deteriorated, so that the target high temperature characteristics cannot be obtained. In addition, Comparative Materials 8 to 10 had a high amount of solid solution carbon in steel, which was poor in workability and aging resistance, and had a low Nb / C value, which resulted in insignificant amounts of Nb-based carbide precipitates and low volume fraction of acicular ferrite structure. It was poor.

Eventually, the compositional conditions of the steel and the conditions of the manufacturing process (especially annealing and cooling conditions) can be optimized to form fine Nb-based carbide and B-nitride precipitates, and the volume fraction of the needle-shaped bainite structure can be controlled. By employing a certain amount of steel and increasing the content of Mn and P, it was possible to manufacture a high-temperature cold-rolled steel sheet for processing that satisfies workability, heat resistance and high strength at low cost.

The present invention is not limited to the above-described embodiments. Anything having substantially the same constitution as the technical idea described in the claims of the present invention and achieving the same operational effect is included in the technical scope of the present invention.

Claims (14)

By weight% C: 0.002 ~ 0.010%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08%, B: 0.001 ~ 0.003%, W: 0.05 ~ 0.30%, N: 0.002 ~ 0.010 %, Nb: 0.02 ~ 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities, A high strength cold-rolled steel sheet for processing of high strength, excellent in workability and heat resistance, consisting of an equiaxed ferrite and acicular bainite structure, and having a volume fraction of acicular bainite structure of 10 to 25%. The method of claim 1, The high heat resistance cold rolled steel sheet for processing having high workability and heat resistance, wherein the atomic ratio Nb / C of Nb and C is 0.8 to 2.0. The method of claim 1, The cold rolled steel sheet is a high heat resistant cold rolled steel sheet for processing of high strength and excellent heat resistance, characterized in that the Nb-based carbide precipitates are formed. The method of claim 1, The high-temperature cold-rolled steel sheet for processing of high strength and excellent heat resistance, characterized in that the value of the atomic ratio B / N of the B and N is 0.5 ~ 1.5. The method of claim 1, The cold rolled steel sheet is a high heat resistant cold rolled steel sheet for processing of high strength and excellent heat resistance, characterized in that the B-based nitride precipitates are formed. delete delete By weight% C: 0.002 ~ 0.010%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08%, B: 0.001 ~ 0.003%, W: 0.05 ~ 0.30%, N: 0.002 ~ 0.010 %, Nb: 0.02 to 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities, and the atomic ratio Nb / C of Nb and C is 0.8-2.0 and the atomic ratio B / N of B and N After heating the steel slab with N value of 0.5 ~ 1.5, finish rolling at 900 ~ 950 ℃ and cooling the rolled hot rolled sheet at a cooling rate of 20 ~ 80 ℃ / sec, and cold rolling after winding at 560 ~ 680 ℃ The cold rolled steel sheet was then annealed at a temperature of 830 to 900 ° C., and cooled to a cooling rate of 40 ° C./sec or more for the annealed steel sheet to form an equiaxed ferrite and acicular bainite structure and to form acicular bainite. A method for producing a high strength, high temperature cold rolled steel sheet for processing having high workability and heat resistance, which adjusts the volume fraction of the tissue to 10-25%. delete delete delete delete delete delete