KR20120127860A - High strength cold-rolled steel sheet having excellent formability, heat resistance, surface properties for working and manufacturing nethod thereof - Google Patents

Abstract

The present invention relates to a high-strength cold rolled steel sheet excellent in workability, heat resistance and discoloration resistance, and a method for manufacturing the same, 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%, Sn: 0.05 ~ 0.25%, N: 0.002 ~ 0.010%, Ti: 0.04 ~ 0.10%, S: 0.015% or less, balance Fe and other unavoidable The high-strength cold-rolled steel sheet excellent in workability, heat resistance, and discoloration resistance including impurities, and a manufacturing method thereof are considered as technical gist.
According to the present invention, it can be manufactured at low cost compared to the existing stainless steel sheet, and has various processing characteristics such as extension flange, bending property, and deep drawing property, which is excellent in room temperature processability, and resistance to aging due to precipitation of solid elements. Not only does it increase yield point, so it is not only excellent in formability, but also excellent in high temperature strength, and extends equipment life by securing shape freezing property of high temperature applied products, and can produce high strength cold rolled steel sheet having excellent discoloration resistance at high temperature. have.

Description

High strength cold rolled steel sheet with excellent workability, heat resistance, and discoloration resistance and manufacturing method thereof

The present invention relates to a high strength cold rolled steel sheet used in automobiles, home appliances, boilers, and the like, and more particularly, to a high strength cold rolled steel sheet having excellent workability, heat resistance, and discoloration resistance prepared by optimizing steel components and process conditions. It relates to a manufacturing method.

Cast iron is generally used for parts of products such as automobile exhaust systems, household flues, ovens and boilers, but aluminum is melted to secure such high temperature characteristics because it is continuously exposed to high temperatures of several hundred degrees (° C.) and requires high heat resistance. Plated steel sheet, stainless steel sheet, etc. were processed and used.

     Here, the high temperature property is one of the characteristics when the processed product is used in a high temperature environment, and includes sag resistance, high temperature strength, and discoloration resistance, and the product property may be degraded due to local temperature rise when using a product such as an automobile exhaust system. High temperature characteristics are required. The sag resistance is a phenomenon in which the steel sheet is repeatedly exposed to high temperature, causing a change in material and sagging. When such a phenomenon occurs, it is difficult to maintain the shape of the molded part. Since the product shape is deformed or destroyed due to deterioration, it is necessary to satisfy the yield strength of 55 MPa or more at a high temperature of about 700 ° C. in order to secure the shape freezing property. Discoloration resistance, which is a surface property for securing, is required.

     Conventionally, stainless steel sheet has been mainly used for heat resistance. However, stainless steel sheet is not only expensive to manufacture due to the addition of expensive alloying elements such as Cr and Ni, but also has a grain boundary of Cr and C when heated at high temperature. By combining, grain boundary corrosion occurs in the Cr depleted zone, which is caused by the precipitation of chromium carbide (chromium carbide) at the grain boundary, resulting in poor corrosion resistance.

     In addition, in order to secure oxidation resistance at high temperature, an aluminum hot dip galvanized steel sheet may be used, but when the aluminum hot dip galvanized steel sheet is heated to a high temperature of 400 ° C. or higher, an alloy layer at an interface due to the interdiffusion reaction between Fe and Al is grown. 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, in addition to the high temperature characteristics described above, heat-resistant steel sheet is manufactured so that products such as automobile exhaust system, home communication, oven and boiler, etc. are accommodated in a limited space, and formed into a complicated shape by various methods to expand or bend after piping. In addition to the high temperature characteristics, a room temperature processability is also required because a process is required.

     In order to solve this problem, Japanese Patent Laid-Open No. Hei 8-319548 intends 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 improving the plating conditions rather than improving the characteristics of the steel sheet. Since the present invention is not only difficult to adjust when the plating layer is changed, there is a problem that it is difficult to obtain target heat resistance.

In addition, Japanese Patent Application Laid-open No. Hei 9-176816 intends 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 added.

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.

In order to solve the above problems, the present inventors have repeatedly conducted research and experiments and propose the present invention based on the results, and the present invention has high temperature characteristics and room temperature processability, such as automobile exhaust system, home communication, oven and boiler. At the same time, the object of the present invention is to provide a high-strength cold rolled steel sheet having excellent workability and corrosion 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.

In order to achieve the above object, the present invention provides a weight% of 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%, and W: 0.05. ~ 0.30%, Sn: 0.05 ~ 0.25%, N: 0.002 ~ 0.010%, Ti: 0.04 ~ 0.10%, S: 0.015% or less, high strength with excellent workability, heat resistance and discoloration resistance including residual Fe and other unavoidable impurities Provide cold rolled steel sheet.

     At this time, there is also a feature that the value of the effective atomic ratio Ti / C of C to Ti is 1.8 to 2.7. In addition, the cold rolled steel sheet is also characterized in that the Ti-based carbide precipitates are formed.

     In addition, there is a feature in that the value of the atomic ratio B / N of B and N is 0.2 to 1.5. In addition, the cold rolled steel sheet is characterized in that the B-based nitride precipitates are formed.

     In addition, the cold rolled steel sheet is characterized in that it is made of an equiaxed ferrite and acicular bainite structure. Here, the volume fraction of the acicular bainite is also characterized by 10 to 25%.

     The Sn-based oxide layer is also formed on the surface of the cold rolled steel sheet.

Furthermore, the Sn-based oxide layer is Sn ₂ O ₃ Containing The layer also has its characteristics.

   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 Sn: 0.05 ~ 0.25%, N: 0.002 ~ 0.010%, Ti: 0.04 ~ 0.10%, S: 0.015% or less, balance Fe and other unavoidable impurities is heated, hot rolled, cold rolled after winding The cold rolled steel sheet is then annealed at a temperature of 830 ° C. or higher, and cooled to a cooling rate of 40 ° C./sec or more with respect to the annealed steel sheet, wherein the high strength cold rolled steel sheet has excellent workability, heat resistance, and discoloration resistance. It provides a manufacturing method.

At this time, the steel slab is characterized in that the value of the effective atomic ratio Ti / C of C to Ti is 1.8 ~ 2.7. In addition, the steel slab is characterized in that the value of the atomic ratio B / N of the B and N is 0.2 to 1.5.

In addition, the hot rolling is characterized in that it comprises the step of finishing rolling at 900 ~ 940 ℃.

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

      The winding is also characterized by being performed at 560 to 680 ° C.

Furthermore, the annealing treatment is also characterized by being performed at 830 to 900 占 폚.

As described above, according to the present invention, it can be manufactured at a lower cost than the conventional stainless steel sheet, and satisfies various processing characteristics of extension flangeability, bending property, and deep drawing property, and thus has excellent room temperature workability, and solid solution element. As the precipitation resistance increases the aging resistance, there is no yield point stretching phenomenon, and it is excellent in formability. Also, it has excellent high temperature strength and ensures the shape freezing property of high temperature applied products, thus prolonging the life of the equipment and high discoloration resistance at high temperature. Cold rolled steel sheet can be manufactured.

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

The inventors have realized various processing characteristics such as stretch-flangeability, bendability, deep drawing, etc., anti-aging properties, and corrosion resistance at low cost and 55 MPa at low cost. 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 and discoloration resistance at high temperature simultaneously. 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 Ti and C and the atomic ratio of B and N to fine Ti-based carbonized precipitate and B-based nitride precipitate By optimizing the annealing and cooling conditions to secure the volume fraction of acicular bainite tissue, and it has excellent heat resistance, corrosion resistance and discoloration resistance at high temperature, aging resistance and processability at room temperature, It is characterized by the production of high strength cold rolled steel sheet suitable as a product member such as a boiler.

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

     Carbon (C) is an element added to improve the room temperature and high temperature strength of the steel sheet, and is mainly consumed by the reaction with Ti in the present invention to form a carbide precipitate. As the amount of C added increases, the tensile and yield strength increases, but when added excessively, it causes aging and the workability is lowered, so the upper limit is preferably 0.010%. If less than 0.002%, however, sufficient Ti-based carbide precipitates may not be obtained, and the grain size may increase, causing a sudden change in material, so that the C content is limited to 0.002 to 0.01%.

     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 that improves the strength and corrosion resistance of steel, and it is preferable to contain 0.03% or more to secure these properties. However, if the content exceeds 0.08%, it causes central segregation during casting and lowers workability. The content of is limited to 0.03 ~ 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%.

     Sulfur (S) combines with Mn in the steel to form non-metallic inclusions that act as corrosion initiation points 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. . However, in order to ensure the said effect reliably, it is preferable to manage at 0.010% or less.

     Boron (B) is dissolved in steel to increase strength and toughness, improve aging resistance and workability by forming boron nitride precipitates, and are effective for suppressing grain growth at high temperatures. It is preferable to be added, but if the content exceeds 0.003%, a material deviation is caused and the recrystallization is significantly delayed at a high temperature, thereby degrading workability, so the content of B is limited to 0.001 to 0.003%.

     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%.

     Titanium (Ti) is an effective element for increasing the strength of steel sheet and refining grains, and in the present invention, Ti-based carbide precipitates are combined with solid solution C in steel to improve aging and formability, and thus, TiC-based carbide composite precipitates It is preferable to contain 0.04% or more because the strength is increased by formation and the effect of suppressing grain growth at high temperature to refine the ferrite particles, but when the content exceeds 0.10%, the material is cured and the operation of continuous annealing treatment is performed. Ti content is limited to 0.04 ~ 0.10% because it brings about deterioration and deteriorates the surface properties of the steel sheet.

Tin (Sn) is an element that exists in a solid state inside the steel to improve high temperature characteristics and corrosion resistance, and is heated and oxidized by heat treatment to form Sn-based oxides such as Sn ₂ O ₃ on the surface of the steel sheet, thereby forming an alloying layer on the surface of the steel sheet. It is preferable to add more than 0.05% to achieve this effect, but to suppress the formation and to improve the corrosion resistance and discoloration resistance at high temperature, but if the content exceeds 0.25%, the production cost rather than the contribution to the improvement of corrosion resistance or discoloration resistance Since the cause of the increase, the Sn content is limited to 0.05 ~ 0.25%.

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

     That is, when the effective atomic ratio value of Ti / C is 1.8 to 2.7, solid solution element C is fixed in the steel due to the formation of Ti-based carbide precipitates, thereby ensuring room temperature aging resistance and processability, and appropriately controlling the annealing and cooling conditions. By controlling the ferrite microstructure by inhibiting grain growth at high temperatures through the formation of fine Ti precipitates, it is possible to secure excellent high temperature characteristics. However, when the value of Ti / C is less than 1.8, there is a problem of deterioration of room temperature aging resistance and workability due to excessive solid solution elements in the steel, and an excellent high temperature strength cannot be secured because the amount of carbide precipitates such as TiC is insignificant. In addition, when the value exceeds 2.7, the material hardens, the temperature of recrystallization is rapidly increased, the surface properties deteriorate and the workability of the post-process is lowered. Therefore, the Ti / C effective atomic ratio value is 1.8. It is limited to 2.7.

     In addition, in order to optimize the aging resistance at room temperature, the workability, and the effect of suppressing grain growth at high temperature, it is necessary to keep the values of the atomic ratio B / N of B and N at 0.4 to 1.2. If the B / N value is less than 0.2, there is a problem in that the room temperature aging resistance is deteriorated due to excessive solid solution in steel, and the grain restraining effect is insufficient at high temperature, and when the B / N value exceeds 1.5, the ductility decreases and the workability decreases. , B / N value is limited to 0.2-1.5.

     The cold rolled steel sheet of the present invention comprises the above components and consists of the balance 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 by the addition of alloying elements not identified 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 equiaxed ferrite (polygonal ferrite) and bainite (bainite) structure, the needle-like bainite tissue is nucleated and grown in the mouth of austenite before transformation Because the nucleation is generated from the fine non-metallic inclusions dispersed in the growth, when the transformation is completed, the ferrite laths are relatively ductile or toughness due to the disordered structure forming a high angle boundary with each other.

Accordingly, the present invention, by appropriately controlling the conditions of the annealing and cooling process to secure a volume fraction of the needle-like bainite structure 10 to 25% to form a high-potential-density type microstructure to suppress abnormal growth of crystal grains at high temperature to high temperature strength By ensuring the heat resistance can be improved. When the volume fraction of the acicular ferrite structure is less than 10%, it is difficult to secure the high temperature strength, so that the target heat resistance is difficult to be obtained. When the volume fraction of the acicular bainite structure is more than 25%, the workability is deteriorated by hardening of the material. There is a problem, and the volume fraction of acicular bainite is limited to 10 to 25%.

     Hereinafter, the manufacturing method of the high strength 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 obtain a high strength cold rolled steel sheet having excellent workability and heat resistance. It can manufacture.

     After reheating the steel slab formed like the above-described component system at a normal temperature, the finish rolling temperature during hot rolling is 900 to 940 ° C. If the finish rolling temperature is less than 900 ° C, the hot rolling is completed in a relatively low temperature region. When the final formed grains are mixed and workability and rolling property are lowered, and when the finish rolling temperature exceeds 940 ° C, uniform hot rolling is not performed throughout the thickness, resulting in insufficient grain refinement, which is caused by grain coarsening. Since impact toughness falls, it is preferable to limit finish rolling temperature to 900-940 degreeC.

     After the hot finish rolling, the hot 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 crystal grains are formed, which is a factor of deterioration of strength and workability, and when the cooling rate exceeds 80 ° C / sec, it acts as a cause of variation of materials due to non-uniform width cooling.

     After cooling in the runout table, the hot rolled steel sheet is wound at a temperature of 560 ~ 680 ℃. When the coiling temperature is less than 560 ℃, the material of the hot rolled material is somewhat hardened, so that the load in the cold rolling process, which is the next process, becomes large, making it difficult to secure rolling property, and the nonuniformity of the width direction 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 ° C, there is a problem that the structure of the final product is coarsened and the workability and corrosion resistance are lowered. Therefore, the coiling temperature is preferably limited to 560 to 680 ° C.

     The wound steel sheet is subjected to a pickling process and cold rolling to a target thickness, and then subjected to a continuous annealing process at a temperature of 830 ° C. or higher for recrystallization and microstructure control. The annealing temperature of 830 ° C. or more corresponds to a temperature for sufficiently securing the transformation driving force of the needle-shaped bainite structure. If the annealing temperature is less than 830 ° C., the volume fraction of the acicular bainite structure present in the microstructure of the target steel sheet cannot be obtained, which makes it difficult to secure excellent high temperature characteristics. However, since the surface defects of the steel sheet may increase during high temperature annealing, the annealing temperature is preferably managed at 900 ° C. or less.

The annealing 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. If 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.

Invented steels 1 and 2 and Comparative steels 1 to 5 prepared by melting with 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. Table 1 below shows the components of the inventive steel and the comparative steel, and Table 2 shows the conditions of the steel sheet manufacturing process. In this case, the atomic ratio Ti / C of Ti and C and the atomic ratio B / of B and N in Table 1 The value of N is the ratio of the weight percentage of each element divided by its atomic weight, respectively.

Yield elongation phenomenon of the characteristics shown in Table 3 was indicated as occurring when the elongation was generated by measuring the yield point elongation through the tensile test, and not occurring when the elongation did not occur. After the steel sheet was processed, it was divided according to the degree of surface bending, and the bending index representing this was divided into five stages, and 1 to 2 stages with relatively small bending were satisfactory. Was determined to be defective.

In addition, the tensile strength test at room temperature 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 sheet was measured and judged to be defective when the degree of deflection was 5 mm or more, and the high temperature yield strength test was judged to be poor when the yield strength was less than 55 MPa at 700 ° C., and more than that. The high temperature discoloration test was judged to be poor when the surface glossiness was lowered by 30% or more after maintaining the steel sheet at a temperature of 500 ° C. for 48 hours. In addition, the workability test was judged to be defective when a work crack occurred during normal temperature processing. Table 3 shows the results of the evaluation of the characteristics of each steel sheet.

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 had no yield point stretching phenomenon and good bending resistance with excellent aging resistance, and tensile strength was also normal temperature. It was good at more than 350MPa, and the yield strength at high temperature and sag resistance after heat treatment (sag resistance) were good due to the formation of Ti-based carbide and B-nitride precipitates and optimization of the volume fraction of acicular bainite structure. The high temperature discoloration resistance was also good due to the formation of Sn-based oxide layer.

     On the other hand, although the steel component of Table 1, etc. is an invention steel which satisfy | fills the scope of this invention, Comparative materials 1-5 which some of the process conditions of Table 2 are out of the scope of this invention mostly have the volume fraction of acicular bainite structure. As a result, they did not have excellent high temperature properties (sag resistance, high temperature yield strength, high temperature discoloration resistance), and 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 fall outside the scope of the present invention, when the post-production characteristics were evaluated, the workability and the aging resistance were poor. In general, high temperature characteristics were poor due to the low volume fraction of acicular bainite structure, and the tensile strength of room temperature was lowered due to the low content of Mn and P without addition of W, and high temperature discoloration resistance due to no addition of Sn. This defect was difficult to satisfy both the room temperature and the high temperature characteristics at the same time. 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, high temperature yield strength and high temperature discoloration resistance. This is due to the excessive addition of Ti and the addition of W, resulting in poor operating performance, deterioration of the surface properties of the steel sheet, and the inability to achieve the desired high temperature properties. Because In addition, the comparative materials 8 to 10 have a high amount of solid carbon in steel, which is not only poor in workability and aging resistance, but also low in Ti / C, so that the amount of Ti-based precipitates is insignificant and the volume fraction of acicular bainite structure is very low. This was bad.

     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 Ti-based carbide precipitates and B-based nitride precipitates, and the volume fraction of the acicular bainite structure can be controlled. The high strength cold rolled steel sheet was added to increase the content of Mn and P in a certain amount of steel and satisfactorily workability, heat resistance, and discoloration resistance at low cost.

     The above embodiment is only one example, and the present invention is not limited thereto. Any thing that has substantially the same structure and the same effect as the technical idea described in the claim of the present invention is included in the technical scope of this invention.

Claims (16)

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%, Sn: 0.05 ~ 0.25 High strength cold rolled steel with excellent workability, heat resistance and discoloration, including%, N: 0.002 ~ 0.010%, Ti: 0.04 ~ 0.10%, S: 0.015% or less, balance Fe and other unavoidable impurities. The method of claim 1,
A high strength cold rolled steel sheet having excellent workability, heat resistance, and discoloration resistance, wherein the atomic ratio Ti / C of Ti and C is 1.8 to 2.7. The method of claim 1,
The cold rolled steel sheet is a high strength cold rolled steel sheet excellent in workability and heat resistance, characterized in that the Ti-based carbide precipitates are formed. The method of claim 1,
A high strength cold rolled steel sheet having excellent workability, heat resistance and discoloration resistance, wherein the atomic ratio B / N of the B and N is 0.2 to 1.5. The method of claim 1,
The cold rolled steel sheet is a high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration, characterized in that the B-based nitride precipitate is formed. The method according to any one of claims 1 to 5,
The cold rolled steel sheet is a high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration, characterized in that it is made of an equiaxed ferrite and acicular bainite structure. The method according to claim 6,
The high volume cold rolled steel sheet having excellent workability, heat resistance, and discoloration, wherein the volume fraction of the acicular bainite structure of the cold rolled steel sheet is 10 to 25%. The method according to any one of claims 1 to 5,
A high strength cold rolled steel sheet having excellent workability, heat resistance, and discoloration resistance, wherein a Sn-based oxide layer is formed on a surface of the cold rolled steel sheet. 9. The method of claim 8,
The Sn-based oxide layer is a high strength cold rolled steel sheet excellent in workability, heat resistance, and discoloration, characterized in that the layer containing Sn ₂ O ₃ 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%, Sn: 0.05 ~ 0.25 Steel slab containing%, N: 0.002 ~ 0.010%, Ti: 0.04 ~ 0.10%, S: 0.015% or less, balance Fe and other unavoidable impurities is heated and hot rolled, cold rolled and then cold rolled Process for annealing at a temperature of 830 ℃ or more, and cooling the annealed steel sheet at a cooling rate of 40 ℃ / sec or more of the high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration resistance. The method of claim 10,
The steel slab is a method of producing a high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration, characterized in that the value of the Ti / C atomic ratio Ti / C of 1.8 ~ 2.7. The method of claim 10,
The steel slab is a method of producing a high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration, characterized in that the value of the B / N atomic ratio B / N of 0.2 ~ 1.5. The method according to any one of claims 10 to 12,
The hot rolling is a manufacturing method of high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration, characterized in that it comprises the step of finishing rolling at 900 ~ 940 ℃. The method according to any one of claims 10 to 12,
The hot rolling is a method of manufacturing a high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration, further comprising the step of cooling the hot rolled hot rolled sheet at a cooling rate of 20 ~ 80 ℃ / sec. The method according to any one of claims 10 to 12,
The winding is carried out at 560 ~ 680 ℃ manufacturing method of high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration resistance. The method according to any one of claims 10 to 12,
The annealing treatment is carried out at 830 ~ 900 ℃ method for producing high strength cold rolled steel sheet excellent in workability, heat resistance and discoloration resistance.