KR101351948B1 - High strength cold-rolled steel sheet having excellent formability, heat resistance, surface properties for working and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a high-strength cold-rolled steel sheet for processing and a method for producing the same excellent in heat resistance and discoloration resistance, by weight: C: 0.01 to 0.1%, Ti: 0.07 to 0.15%, Co: 0.02 to 0.20%, Sn: 0.05 to 0.25%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08%, N: 0.002 ~ 0.006%, S: 0.015% or less, heat resistance and discoloration including residual Fe and other unavoidable impurities High-strength cold-rolled steel sheet for processing and its manufacturing method excellent in the properties are the technical gist.
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 elongation flangeability, bending property and deep drawing property, which is excellent in room temperature workability, and has increased yield resistance due to solid element precipitation. Not only does the stretching phenomenon occur, not only excellent moldability, but also excellent high temperature strength to ensure the shape freezing properties of high-temperature applications, the equipment life is extended, it is possible to manufacture a high strength cold rolled steel sheet for processing excellent in discoloration resistance at high temperatures.

Description

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

The present invention relates to a high-strength high-temperature cold-rolled steel sheet used in automobiles, home appliances and boilers, and to a method for manufacturing the same. More specifically, the high-strength for processing excellent in heat resistance and discoloration resistance produced by optimizing steel components and process conditions. It relates to a 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, household flues, ovens, boilers, etc. An aluminum hot-dip galvanized steel sheet, a stainless steel sheet, etc. were processed and used.

Here, the high temperature characteristic is one of the characteristics when the processed product is used in a high temperature environment, such as sag resistance, high temperature strength and discoloration resistance, and the product characteristics may be deteriorated by local temperature rise when using a product such as an automobile exhaust system. Therefore, 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, and when the thermal stress is concentrated to a specific place, 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, 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 the grain of Cr is combined with C when heated at high temperatures. There is a problem in that corrosion resistance is inferior due to grain boundary corrosion in the Cr depleted zone formed by chromium carbide precipitation.

In addition, in order to secure oxidation resistance at high temperatures, an aluminum hot dip galvanized steel sheet may be used. However, when the aluminum hot dip galvanized steel 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, the heat-resistant steel sheet is manufactured to accommodate products in a limited space in addition to the above-described high temperature characteristics, such as automobile exhaust system, home communication, oven and boiler, and formed into a complicated shape by various methods to expand or bend after pipework. As a process is required, not only room temperature processability is required, but tensile strength of 350 MPa or more is required at room temperature in order to secure impact resistance characteristics of the use member.

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 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 apply it to a member of, and it is not easy to adjust the amount of the steel component to be 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, high strength cold rolled steel for processing and its manufacturing method which can be manufactured at low cost by optimizing steel components and process conditions while reducing the addition of expensive alloying elements, including medium and low carbon, for use in required applications The purpose is to provide.

In the present invention, C: 0.01-0.1%, Ti: 0.07-0.15%, Co: 0.02-0.20%, Sn: 0.05-0.25%, Mn: 0.3-0.6%, P: 0.03-0.08%, Al: It provides a high strength cold rolled steel sheet for processing having excellent heat resistance and discoloration resistance, including 0.02 to 0.08%, N: 0.002 to 0.006%, S: 0.015% or less, balance Fe and other unavoidable impurities.

At this time, there is also a feature in that the value of the effective addition ratio (Ti × Co) / C of C to Ti and Co is 0.1 to 0.5.

In addition, the cold rolled steel sheet is characterized in that the (Ti, Co) -based carbide composite precipitate is formed.

In addition, the cold-rolled steel sheet is characterized by being composed of equiaxed ferrite and needle-like ferrite.

Furthermore, the volume fraction of the acicular ferrite structure of the cold rolled steel sheet is also characterized by 10 to 20%.

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

Here, the Sn-based oxide layer is also characterized by being a Sn ₂ O ₃ layer.

In addition, the present invention is in the weight% C: 0.01 ~ 0.1%, Ti: 0.07 ~ 0.15%, Co: 0.02 ~ 0.20%, Sn: 0.05 ~ 0.25%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Steel slab containing Al: 0.02 ~ 0.08%, N: 0.002 ~ 0.006%, 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 800 ℃ or more, and provides a high-strength cold rolled steel sheet for processing excellent in heat resistance and discoloration resistance characterized in that the cooling rate of the annealed steel sheet at a cooling rate of 40 ℃ / sec or more.

In this case, the steel slab is also characterized in that the value of the effective addition ratio (Ti × Co) / C of C to Ti and Co is 0.1 to 0.5.

In addition, the hot rolling is characterized in that it comprises the step of finishing rolling at 880 ~ 950 ℃.

In addition, there is also a feature that further comprises the step of cooling the hot rolled hot rolled sheet in the finishing rolling step 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 also characterized by being performed at 800 to 900 ° C.

As described above, according to the present invention, it is possible to manufacture at a lower cost than the conventional stainless steel sheet, and has various processing characteristics of elongation flangeability, bending property, and deep drawing property, so that it is excellent in room temperature processability, and age-resistant by solid element precipitation. Not only does the yield point draw phenomenon increase, 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 high strength cold rolled steel sheet for processing of high heat resistance with excellent discoloration resistance at high temperature Can be prepared.

1 is a photograph comparing the microstructure of Inventive Material 2 and Comparative Material 8.

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 and discoloration resistance at high temperature simultaneously. As a result, the present invention includes a low to medium carbon content in the steel components, increase the content of Mn, P, and control the addition amount and addition ratio of Ti, Co to form a fine (Ti, Co) -based carbon composite complex, Optimizing the annealing and cooling conditions to secure the volume fraction of acicular ferrite structure, and by adding Sn to form Sn-based oxide layer on the surface of steel sheet by heat treatment, heat resistance, corrosion resistance and discoloration at high temperature, aging resistance and workability at room temperature It is excellent in manufacturing high strength, high temperature resistant cold rolled steel sheets suitable for product parts such as automobile exhaust systems, home appliances, boilers, and the like.

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

Carbon (C) is an element added to improve the strength of the steel sheet, and is mainly consumed by the reaction with Ti for forming a (Ti, Co) -based carbide composite precipitate in the present invention. As the amount of C added increases, the tensile and yield strength increases, but when added excessively, the workability decreases, so the upper limit is preferably 0.1%. However, if less than 0.01%, a sufficient (Ti, Co) -based carbonized composite precipitate can not be strengthened and the grain size is increased to cause a sudden change in the material, the content of C is limited to 0.01 ~ 0.1%.

Manganese (Mn) is a solid solution strengthening element, which improves the strength of steel and improves hot workability, but 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 high strength is difficult to secure, the Mn content 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%, the core segregation during casting and workability is reduced, P The content of is limited to 0.03 ~ 0.08%.

Nitrogen (N) is a solid element inside the steel and is effective for reinforcing the material. If it is contained less than 0.002%, sufficient rigidity cannot be obtained and the precipitate formation site is reduced. As a cause of aging and hardening occurs to deteriorate moldability, the content of N is limited to 0.002 ~ 0.006%.

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. . However, in order to ensure the above effect, it is preferable to manage at 0.010% or less.

Titanium (Ti) is an effective element for increasing the strength of steel sheet and refining grains. In the present invention, titanium (Ti, Co) -based carbonized composite precipitates are combined with solid-solution C in steel to improve aging and formability. It is preferable to contain 0.07% or more because the strength is increased by the formation of the Co-based carbonized composite precipitate and the grain growth at a high temperature is suppressed to provide finer particles. However, when the content exceeds 0.15%, The content of Ti is limited to 0.07 to 0.15% because of this hardening, which leads to a decrease in operability of the continuous annealing treatment and deteriorates the surface properties of the steel sheet.

Cobalt (Co) is an element which promotes the formation of precipitates in the steel to increase the strength and improve the corrosion resistance. In order to obtain such an effect, it is preferable that Co is contained in an amount of 0.02% or more. When the content exceeds 0.20% And the addition of a large amount of a higher-priced alloy element than the effect of contributing to the precipitation promotion acts as a factor of raising the production cost, so that the content of Co is limited to 0.02 to 0.20%.

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 0.05% or more in order to obtain such effects, but if the content exceeds 0.25%, it is a factor of increase in manufacturing cost rather than contributing to improvement of corrosion resistance or discoloration resistance. Therefore, the content of Sn is limited to 0.05 ~ 0.25%.

In the case of Ti and Co, it is also important to manage alone, but it is also possible to maintain the effective weight addition ratio (Ti × Co) / C of Ti and Co in a certain range to ensure room temperature aging resistance, processability and high temperature strength simultaneously. It is important.

That is, when the value of (Ti × Co) / C is in the range of 0.1 to 0.5, solid-solution element C is fixed in the steel by the formation of the (Ti, Co) -based carbonized composite precipitate, thereby ensuring room temperature aging resistance and workability. By appropriately controlling the annealing and cooling conditions, fine (Ti, Co) -based carbonized composite precipitates can be formed, and excellent high-temperature characteristics can be obtained by controlling the ferrite microstructure through suppressing grain growth at high temperatures. However, when the value of (Ti × Co) / C is less than 0.1, there is a problem that the room temperature aging resistance and workability may be deteriorated due to excessive elemental solids in the steel, and the amount of the (Ti, Co) -based carbonized composite precipitate is insignificant. It can be difficult to secure very good high temperature strength. In addition, if the value exceeds 0.5, the material may be cured, the temperature of the recrystallization may be increased sharply, and the surface properties may deteriorate and the workability of the post process may be degraded. It is preferable to limit the value of C to 0.1-0.5.

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 as needed to improve the properties of the present cold-rolled steel sheet, alloy elements that are not identified in the embodiment of the present invention is not interpreted to be excluded from the scope of the present invention.

In addition, the cold-rolled steel sheet of the present invention is characterized by consisting of an equiaxed ferrite (polygonal ferrite) and acicular ferrite tissue, the needle-like ferrite tissue is a kind of bainite grown by nucleation in the mouth of austenite before transformation As the nucleation grows from the fine non-metallic inclusions dispersed in the steel, the ferrite laths are relatively superior in ductility or toughness due to the disordered structure in which the ferrite laths form a high angle boundary with each other.

The present invention secures a volume fraction of the needle-like ferrite structure by 10 to 20% by appropriately controlling the conditions of the annealing and cooling process to form a high potential density type microstructure, thereby suppressing abnormal growth of crystal grains at a high temperature. It is possible to further improve heat resistance. When the volume fraction of the acicular ferrite structure is less than 10%, it may be difficult to secure very good high temperature strength, so that it may be difficult to obtain target heat resistance, and when the volume fraction of the acicular ferrite structure exceeds 20%, the material may be hardened. There is a problem that the workability may be deteriorated, and the volume fraction of the needle-like ferrite is limited to 10 to 20%.

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

After reheating the steel slab having the above composition, it is hot rolled, cold rolled after winding, and cooled at a cooling rate of 40 ° C./sec or more on an annealing steel sheet at a temperature of 800 ° C. or higher to provide excellent heat resistance and discoloration resistance. Cold rolled steel sheet can be manufactured.

After reheating the steel slab formed as the above-described component system at a normal temperature, the finish rolling temperature during hot rolling is preferably in the range of 880 to 950 ° C. If the finish rolling temperature is less than 880 ° C., hot rolling is performed at a relatively low temperature region. As this is terminated, the final formed grains may be mixed, resulting in deterioration of workability and rolling property, and when the finish rolling temperature exceeds 950 ° C., uniform hot rolling may not be performed throughout the thickness, resulting in insufficient grain refinement. In this case, the impact toughness may be lowered due to grain coarsening, so the finish rolling temperature is preferably limited to 880 to 950 ° C.

After the hot finish rolling, it is preferable to cool the hot rolled steel sheet in a run-out table at a cooling rate of 20 to 80 ° C./sec. If the cooling rate is less than 20 ° C./sec, it is necessary to promote grain growth. This is because coarse crystal grains are formed, which may be a cause of deterioration in strength and workability. When the cooling rate exceeds 80 ° C / sec, there is a possibility of acting as a cause of variation of materials due to the uneven cooling in the width direction.

After cooling in the runout table, the hot rolled steel sheet is preferably wound at a temperature of 560 ~ 680 ℃. At this time, when the coiling temperature is less than 560 ℃, the material of the hot rolled material is somewhat hardened and the load in the cold rolling process, which is the next process, becomes large, and thus it is difficult to secure the rolling property, and the non-uniformity of the widthwise temperature is increased, resulting in low temperature precipitates. Due to the difference in the production behavior of the material deviation may be caused, the workability may be reduced, there is a problem that the high temperature characteristics may also be deteriorated. In addition, when the coiling temperature exceeds 680 ° C, the structure of the final product may be coarse, and there is a problem that the workability and corrosion resistance may be lowered. Therefore, the coiling temperature is preferably limited to 560 to 680 ° C.

After the wound steel sheet is subjected to pickling treatment and cold rolling to a target thickness, it is preferable to undergo a continuous annealing process at a temperature of 800 ° C. or higher for recrystallization and microstructure control. The annealing temperature of 800 ° C. or more corresponds to a temperature for sufficiently securing the transformation driving force of the needle-like ferrite structure. Here, when the annealing temperature is less than 800 ℃, it is difficult to obtain the volume fraction of the needle-like ferrite structure present in the microstructure of the target steel sheet, and thus there is a problem that it may be difficult to secure very good room temperature and high temperature strength. 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 lower.

The annealed steel sheet can secure the volume fraction of the target acicular ferrite structure through a cooling process, for this purpose to maintain a cooling rate of 40 ℃ / 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 ferrite 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 ferrite structure and the characteristics at room temperature and high temperature were evaluated for each of the prepared cold rolled steel sheets.

 Yield elongation phenomenon is indicated when the yield point elongation is measured and not occurred when elongation has occurred, and not occurred when the elongation has not occurred, and the bending resistance test is performed to the extent that surface bending occurs after steel sheet processing. By dividing the bending index that expresses this into five stages, one to two stages, which are relatively insignificant, are considered good, and three to five stages where the bending phenomenon occurs to the extent that visual observation can be judged as defective.

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 sheet was measured and judged to be defective when the degree of deflection was 5 mm or more. The high temperature yield strength test was judged to be poor when the yield strength was less than 55 MPa at 700 ° C., and to be good when it was more than that. The 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.

The machinability test was judged to be defective when a crack occurred during processing at room temperature.

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 components and the process conditions satisfy the scope of the present invention did not occur in the yield point stretching phenomenon and good bending resistance was excellent in aging resistance, and also at room temperature tensile strength 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 generation of (Ti, Co) -based carbonized composite precipitates and optimization of the volume fraction of acicular ferrite structure, and surface gloss at high temperature. The degree of reduction was less than 30%, and the discoloration resistance was good, and the processing cracks did not occur during processing at room temperature, so the processing at room temperature was also excellent.

On the other hand, while the steel component of Table 1 is an invention steel that satisfies 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 excellent in low volume fraction of acicular ferrite structure. It did not have characteristics (sag resistance, high temperature strength, discoloration resistance), poor tensile strength at room temperature, and poor workability and aging resistance (yielding point stretching phenomenon, bending resistance).

In addition, although the process conditions of Table 2 satisfy the scope of the present invention, as a result of evaluating the characteristics of the comparative material 6 to 10 degrees after the steel components and the like of Table 1 outside the scope of the present invention, the volume fraction of the needle-like ferrite structure was It is difficult to satisfy both the workability and the high temperature characteristics at the same time because the low temperature and high temperature characteristics are often poor.

On the other hand, Figure 1 is a photograph comparing the microstructure of the invention material 2 and the comparative material 8, in the invention material 2 of Figure 1 (a) is a ferrite structure of a shape close to the polygon is an equiaxed ferrite structure, a long stretched shape ferrite Denotes acicular ferrite structure. Although the volume fraction of the needle-like ferrite structure of Inventive Material 2 was 18.3%, both the evaluation of the characteristics of the room temperature and the high temperature were satisfactory, but the comparative material 8 of FIG. 1 (b) consisted only of the equiaxed ferrite structure without the needle-like ferrite structure. It can be seen in Table 3 that the poor aging resistance, sag resistance, discoloration resistance and room temperature tensile strength.

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, Co) -based carbonized composite precipitates and to control the volume fraction of the acicular ferrite structure. By forming a Sn-based oxide such as Sn ₂ O ₃ on the surface of the steel sheet by heat treatment, a high-strength cold rolled steel sheet for processing that satisfies heat resistance and discoloration resistance at low cost can be produced.

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 (13)

By weight% C: 0.01 ~ 0.1%, Ti: 0.07 ~ 0.15%, Co: 0.02 ~ 0.20%, Sn: 0.05 ~ 0.25%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08 High strength cold rolled steel sheet for processing, containing%, N: 0.002 ~ 0.006%, S: 0.015% or less, balance Fe and other unavoidable impurities, and having a Sn ₂ O ₃ layer formed on its surface. The method of claim 1,
High-strength cold rolled steel sheet having excellent heat resistance and discoloration resistance, characterized in that the effective addition ratio (Ti × Co) / C of C to Ti and Co is 0.1 to 0.5. The method of claim 1,
The cold rolled steel sheet is a high strength cold rolled steel sheet for processing excellent in heat resistance and discoloration, characterized in that (Ti, Co) -based carbonized composite precipitates are formed. By weight% C: 0.01 ~ 0.1%, Ti: 0.07 ~ 0.15%, Co: 0.02 ~ 0.20%, Sn: 0.05 ~ 0.25%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08 A high strength cold rolled steel sheet for processing having excellent heat resistance and discoloration resistance, comprising%, N: 0.002% to 0.006%, S: 0.015% or less, balance Fe and other unavoidable impurities, and consisting of an equiaxed ferrite and acicular ferrite structure. 5. The method of claim 4,
A high-strength cold rolled steel sheet having excellent heat resistance and discoloration resistance, wherein the volume fraction of the acicular ferrite structure of the cold rolled steel sheet is 10 to 20%. The method according to claim 4 or 5,
A high strength cold rolled steel sheet for processing having excellent heat resistance and discoloration resistance, characterized in that a Sn-based oxide layer is formed on the surface of the cold rolled steel sheet. The method according to claim 6,
The Sn-based oxide layer is a high-strength cold rolled steel sheet having excellent heat resistance and discoloration resistance, characterized in that the Sn ₂ O ₃ layer. By weight% C: 0.01 ~ 0.1%, Ti: 0.07 ~ 0.15%, Co: 0.02 ~ 0.20%, Sn: 0.05 ~ 0.25%, Mn: 0.3 ~ 0.6%, P: 0.03 ~ 0.08%, Al: 0.02 ~ 0.08 %, N: 0.002 ~ 0.006%, S: 0.015% or less, steel slab containing remainder Fe and other unavoidable impurities are heated and hot rolled, cold rolled after winding, and then cold rolled steel sheet at a temperature above 800 ° C. Annealed at and cooled to a cooling rate of 40 ℃ / sec or more with respect to the annealed steel sheet, the surface of the cooled steel sheet is Sn ₂ O ₃ layer formed of Sn-based oxide layer, characterized in that excellent heat and discoloration resistance Manufacturing method of high strength cold rolled steel sheet for processing. 9. The method of claim 8,
The steel slab is a method of manufacturing a high strength cold rolled steel sheet for processing excellent in heat resistance and discoloration, characterized in that the value of the effective addition ratio (Ti × Co) / C of C to Ti and Co is 0.1 to 0.5. 10. The method according to claim 8 or 9,
The hot rolling is a manufacturing method of high strength cold rolled steel sheet for processing excellent in heat resistance and discoloration, characterized in that it comprises the step of finishing rolling at 880 ~ 950 ℃. The method of claim 10,
The method of manufacturing a high strength cold rolled steel sheet having excellent heat resistance and discoloration resistance, further comprising the step of cooling the hot rolled hot rolled sheet in the finishing rolling step at a cooling rate of 20 to 80 ° C./sec. 10. The method according to claim 8 or 9,
Said winding is performed at 560-680 degreeC, The manufacturing method of the high strength cold rolled steel sheet for processing excellent in heat resistance and discoloration resistance characterized by the above-mentioned. 10. The method according to claim 8 or 9,
The annealing treatment is carried out at 800 ~ 900 ℃ the manufacturing method of high strength cold rolled steel sheet for processing excellent in heat resistance and discoloration resistance.

Images