KR101263793B1 - High heat-resistance cold-rolled steel sheet having excellent formability, corrosion resistance, surface properties for working and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a high heat-resistant cold-rolled steel sheet and a method for manufacturing the same excellent in workability, discoloration resistance and corrosion resistance, by weight C: 0.002 ~ 0.005%, Mn: 0.10 ~ 0.35%, P: 0.003 ~ 0.020%, Al : 0.02 ~ 0.08%, Sn: 0.05 ~ 0.25%, Cu: 0.1 ~ 0.4%, N: 0.002 ~ 0.006%, Nb: 0.02 ~ 0.06%, S: 0.003 ~ 0.010% or less, balance Fe and other unavoidable impurities The high heat resistant cold rolled steel sheet for processing and its manufacturing method which are excellent in workability, discoloration resistance, and corrosion resistance are made into a technical summary. According to the present invention, it can be manufactured at low cost compared to the existing stainless steel sheet, has various processing characteristics of elongation flangeability, bending property and deep drawing (excellent room temperature workability), and age-resistant by solid element precipitation This increases the yield point, which does not cause the yield point not only excellent moldability, but also excellent high temperature strength, prolongs the life of the facility by securing the shape freezing properties of high-temperature applications, excellent discoloration resistance at high temperatures, Cu on the surface of the steel sheet By forming a system sulfide, it is possible to manufacture a high heat resistant cold rolled steel sheet having excellent corrosion resistance.

Cold Rolled Steel, Needle Ferrite, Corrosion Resistance, Heat Resistance, Processability, Discoloration Resistance, Aging Resistance

Description

HIGH HEAT-RESISTANCE COLD-ROLLED STEEL SHEET HAVING EXCELLENT FORMABILITY, CORROSION RESISTANCE, SURFACE PROPERTIES FOR WORKING AND MANUFACTURING METHOD THEREOF}

The present invention relates to a high heat resistant cold rolled steel sheet and a method of manufacturing the same for use in automobiles, home appliances, boilers, and the like, and more specifically, for processing, discoloration resistance, and corrosion resistance, which are manufactured by optimizing steel components and process conditions. 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 for parts of products such as automobile exhaust systems, home communication systems, ovens, boilers, etc., but since it is continuously exposed to high temperature environments of several hundred degrees (° C.) or higher, high heat resistance and corrosion resistance are required. In order to secure such high temperature characteristics and corrosion resistance, aluminum hot-dip steel sheets, stainless steel sheets, etc. have been 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, i.e., sag resistance, high temperature strength and discoloration, may be deteriorated due to a local temperature rise when using a product such as an automobile exhaust system. Sex is required. The sag resistance is a sagging phenomenon in which the steel sheet is repeatedly exposed to high temperature to cause a change 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. As the product shape is deformed or destroyed, it is necessary to satisfy the yield strength of 55MPa or more at a high temperature of around 700 ℃ in order to secure the shape freezing.It prevents the oxidation of the steel sheet at high temperature conditions and secures the adhesion with the plating material during plating. Discoloration resistance, which is a surface property, is required.

In addition, due to the characteristics of repeated high and low temperatures, there is a problem that rust occurs in the outside air and exposed metal parts, and in some cases, a hole is generated, causing corrosion. Therefore, higher corrosion resistance is required to prevent such corrosion. do.

Although stainless steel sheet has been mainly used for heat and corrosion resistance, 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 high grain size of Cr when heated at high temperatures. In combination with C, grain boundary corrosion occurs at the Cr depleted zone, which is caused by chromium carbide precipitation at grain boundaries, resulting in poor corrosion resistance.

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. The gloss of the surface is lost and discolored in a short time, so that the heat resistance is insufficient, so there is a problem in that the application can be limited.

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 Processability is required.

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, U.S. Patent No. 4,675,214 discloses that chromium, silicon, and manganese oxides are reduced on the surface of a stainless steel sheet having corrosion resistance or oxidation resistance under reducing gas atmosphere to clean the surface layer of the steel sheet, and then immersed in a molten aluminum bath to produce plating. Although aluminum plated stainless steel is proposed, a separate facility for reduction is required and the working conditions are complicated, and the formation of an aluminum-iron-based alloy layer is prevented due to the formation of CrN on the surface of the steel sheet, causing a plating failure, and Peeling of an alloy layer tends to occur, and there exists a problem which is difficult to obtain target heat resistance and corrosion resistance.

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, it provides a high-temperature cold-rolled steel sheet for processing and excellent manufacturing process, discoloration resistance and corrosion resistance that can be manufactured at low cost by optimizing the steel components and processing conditions while reducing the addition of expensive alloy elements for use in the required applications. Its purpose is to.

In the present invention, C: 0.002 to 0.005%, Mn: 0.10 to 0.35%, P: 0.003 to 0.020%, Al: 0.02 to 0.08%, Sn: 0.05 to 0.25%, Cu: 0.1 to 0.4%, and N: Provides a high heat resistant cold rolled steel sheet having excellent workability, discoloration resistance and corrosion resistance including 0.002% to 0.006%, Nb: 0.02% to 0.06%, S: 0.003% to 0.010%, 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 Cu / S of said Cu and S is 10-25.

In addition, the Cu-based sulfide is formed on the surface of the cold rolled steel sheet has its characteristics.

Here, Cu-based sulfides do have the characteristics that the Cu ₂ S.

Furthermore, the cold rolled steel sheet is characterized in that it is made of an equiaxed ferrite and acicular ferrite structure.

At this time, the volume fraction of the needle-like ferrite tissue is also characterized in that 5 to 15%.

In addition, the Sn-based oxide layer formed on the surface of the cold-rolled steel sheet is also characterized.

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

In the present invention, C: 0.002 to 0.005%, Mn: 0.10 to 0.35%, P: 0.003 to 0.020%, Al: 0.02 to 0.08%, Sn: 0.05 to 0.25%, Cu: 0.1 to 0.4%, Steel slab containing N: 0.002 ~ 0.006%, Nb: 0.02 ~ 0.06%, S: 0.003 ~ 0.010%, balance Fe and other unavoidable impurities is heated, hot rolled, cold rolled, and then cold rolled Annealing the steel sheet at a temperature of 800 ℃ or more, and provides a manufacturing method of high heat resistant cold rolled steel sheet for processing, excellent in workability, discoloration resistance and corrosion resistance characterized in that the cooling rate of the annealed steel sheet at a cooling rate of 30 ℃ / sec or more. do.

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 by having an atomic ratio Cu / S of Cu to S of 10 to 25.

In addition, the hot rolling is characterized in that the 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 also characterized by being performed at 800 to 900 ° C.

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, which is not only excellent in moldability, but also excellent in high temperature strength, prolonging the life of the equipment by securing the shape freezing property of high temperature applied products, and excellent in discoloration resistance at high temperatures. By forming Cu-based sulfide on the surface of the steel sheet, it is possible to manufacture a high heat resistant cold rolled steel sheet having excellent corrosion resistance.

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

The inventors yielded at least 55 MPa at 700 ° C. while satisfying various processing characteristics such as stretch-flangeability, bendability, deep drawing, and anti-aging properties at low cost. The present invention has been completed by repeating studies and experiments to secure strength and discoloration resistance and corrosion resistance at high temperatures. As a result, the present invention contains a very low carbon content in the steel component and controls the amount of Nb and the atomic ratio of Nb and C to form fine Nb-based carbonized precipitates, and optimizes annealing and cooling conditions to optimize the volume of the needle-like ferrite structure. A fraction is secured, Sn is added to form a Sn-based oxide layer on the surface of the steel sheet, and the Cu-based sulfide is formed on the surface of the steel sheet by controlling the addition amount of Cu and the atomic ratio of Cu and S, so that the heat resistance, corrosion resistance and discoloration resistance It has the characteristics to manufacture high heat resistant cold rolled steel sheet for processing, which is very suitable for products such as automobile exhaust system, home communication, oven and boiler at room temperature.

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

Carbon (C) is an element added for improving the strength of the steel sheet, and in the present invention, carbon is mainly consumed by reaction with Nb to form Nb-based carbide precipitates. As the amount of C added increases, the tensile and yield strength increases, but when excessively added, the workability decreases, so the upper limit is preferably 0.005%. If less than 0.002%, however, sufficient Nb-based carbide precipitates may not be strengthened, and grain size may increase, causing a sharp change in material, so that the C content is limited to 0.002 to 0.005%.

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 economic deterioration and center segregation by addition of a large amount of alloying elements, so an upper limit is preferably 0.35%. However, if less than 0.10% workability is improved, but the target strength is difficult to secure, the Mn content is limited to 0.10 to 0.35%.

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 element that improves the strength and corrosion resistance of steel, and it is preferable to contain 0.003% or more in order to secure these properties. However, if the content exceeds 0.020%, it causes central segregation during casting and lowers workability. The content is limited to 0.003 to 0.020%.

Nitrogen (N) exists in solid solution inside the steel and is effective for reinforcing the material. If it contains less than 0.002%, sufficient rigidity cannot be obtained, and the precipitate formation site is reduced. If the content exceeds 0.006%, Since it causes aging and hardening occurs and deteriorates moldability, N content is limited to 0.002% to 0.006%.

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 necessary to reduce the content as much as possible, so the S content is 0.010%. It limits to the following. However, in order to form a Cu-based sulfide such as Cu ₂ S on the surface of the steel sheet to ensure high corrosion resistance, a content of 0.003% or more is required, so the content of S is limited to 0.003 to 0.010%.

Niobium (Nb) is an effective element for increasing the strength of steel sheet and refining grains, and in the present invention, Nb-based carbide precipitates are combined with solid solution dissolved in steel to improve aging and formability, and thus, Nb-based carbide precipitates are formed. It is preferable to contain at least 0.02% because the strength is increased and the grain growth at a high temperature is suppressed to provide the effect of refining the ferrite particles. However, when the content exceeds 0.06%, the material is cured and the operability of the continuous annealing treatment is increased. The content of Nb is limited to 0.02 to 0.06% because it lowers 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 a Sn-based oxide layer such as Sn ₂ O ₃ on the surface of the steel sheet to form 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, but if the content exceeds 0.25%, the increase in manufacturing cost rather than the contribution to improving the corrosion resistance or discoloration resistance Since it is a factor, the content of Sn is limited to 0.05 to 0.25%.

Copper (Cu) is an important element that is very effective in improving the corrosion resistance of steel, and forms a Cu-based sulfide such as Cu ₂ S on the surface of the steel sheet to suppress corrosion such as rust generation. And, in order to obtain such an effect, it is preferable to contain 0.1% or more, but when the content of Cu exceeds 0.4%, it acts as a cause of cracking due to grain boundary embrittlement in the playing step, so the content of Cu is limited to 0.1 to 0.4%. do.

In the case of Nb and Cu, it is also 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. For this purpose, it is also important to maintain room temperature aging resistance, processability and high temperature characteristics and corrosion resistance simultaneously by maintaining the atomic ratio Nb / C of Nb and C and the Cu / S atomic ratio Cu / S in a certain range.

When the value of Nb / C, which is an atomic ratio of Nb and C, is 0.8 to 2.0, Nb-based carbonized precipitates form solid element C in the steel, thereby ensuring room temperature aging resistance and processability, and appropriately annealing and cooling conditions. By controlling the fine grains of Nb-based carbide precipitates to suppress the grain growth at high temperatures to control the ferrite microstructure can ensure excellent high-temperature characteristics.

However, when the value of Nb / C, which is an atomic ratio of Nb and C, is less than 0.8, there is a problem of deterioration of room temperature aging resistance and processability due to excessive solid solution elements in the steel, and excellent high temperature strength because the amount of Nb-based carbide precipitates is insignificant. It cannot be secured. 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 addition, if the value of Cu / S, which is an atomic ratio of Cu and S, is less than 10, the formation of Cu-based sulfides that contribute to the improvement of corrosion resistance is insufficient, and thus it is difficult to expect the effect of improving corrosion resistance, and if the value of Cu / S exceeds 25, Since the frequency of occurrence of surface defects due to solid solution of Cu increases, the value of Cu / S is limited to 10-25.

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 ferrite (acicular ferrite) tissue, the needle-like ferrite tissue is a kind of bainite grown by nucleation in the mouth of austenite before transformation As it grows by nucleation from fine non-metallic inclusions dispersed in steel, ferrite laths are relatively excellent in ductility and toughness due to the disordered structure in which ferrite laths form a high angle boundary with each other. .

Therefore, the present invention by controlling the conditions of the annealing and cooling process appropriately secures the volume fraction of the needle-like ferrite structure 5-15% to form a high-potential-density type microstructure to suppress abnormal growth of grains at high temperature to increase the high temperature strength By securing it, heat resistance can be improved. If the volume fraction of the acicular ferrite structure is less than 5%, it is difficult to secure the high temperature strength, so that target heat resistance is difficult to be obtained. If the volume fraction of the acicular ferrite structure is more than 15%, the workability is deteriorated by hardening of the material. There is a problem, and the volume fraction of the needle ferrite is limited to 5 to 15%.

Hereinafter, the manufacturing method of the high heat resistant cold rolled sheet steel for processing excellent in workability, discoloration resistance, and corrosion resistance 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 30 ° C./sec or higher on an annealing steel sheet at a temperature of 800 ° C. or higher to provide excellent workability, discoloration resistance, and corrosion resistance. High heat resistant cold rolled steel sheet for processing 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 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 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 ℃. 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 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 undergoes 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. If the annealing temperature is less than 800 ° C., there is a problem that it is difficult to obtain a volume fraction of the acicular ferrite structure present in the microstructure of the target steel sheet, and thus it is 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 lower.

The annealed steel sheet can secure a volume fraction of the target acicular ferrite structure through a cooling process, for which the cooling rate is maintained at 30 ℃ / sec or more. This is because when the cooling rate is less than 30 ° C./sec, it is difficult to obtain a volume fraction of the target acicular ferrite 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 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 of the characteristics shown in Table 3 was measured when the yield point elongation was measured and occurred when the elongation occurred, and not occurred when the elongation did not occur, and the bending resistance test was the surface bending after the steel sheet processing. According to the degree of occurrence, the bending index representing this was divided into 5 stages, and 1 to 2 stages with relatively small bending were good, and 3 to 5 stages where the bending occurred to the extent that visual observation can be judged as bad. .

In addition, the sag resistance test was determined to be defective when the sagging of the steel sheet after measuring the sagging of the steel plate after heating the material of 250mm in length, 30mm in width for 100 hours at 700 ℃ using a heat treatment equipment, The high temperature yield strength test was judged to be bad if the yield strength was less than 55MPa at 700 ° C, and higher than that. The high temperature discoloration resistance test showed that the surface glossiness was lowered by more than 30% after maintaining the steel plate at 500 ° C for 48 hours. It was judged to be defective.

In addition, the corrosion resistance test was determined that the corrosion loss after the salt spray experiment with 5% NaCl for 480 hours is less than 0.05g / cm ² , if it is higher than that, the workability test is a crack that occurs during normal temperature processing It was judged as bad in the case.

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 Cu / S of Cu and S refer to the ratio of the value obtained by dividing the weight percent 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 components and the process conditions satisfy the scope of the present invention did not occur in the yield point elongation and good bending resistance was excellent in aging resistance, Nb-based carbide precipitates The yield strength and sag resistance after heat treatment were satisfactory due to the formation of and the optimization of the volume fraction of the needle-like ferrite structure, and the Sn-based oxide layer was formed on the surface of the steel sheet to provide high temperature discoloration resistance. Systemic sulfides were formed, and thus the corrosion resistance was also good, and processing defects did not occur during processing at room temperature, so the processing at room temperature was also excellent.

On the other hand, although the steel components of Table 1 and the like are the 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 outside the scope of the present invention, are mostly low in volume fraction of acicular ferrite structure. It did not have high temperature characteristics, and the workability and aging resistance including corrosion resistance were also poor in many cases. In particular, in the case of Comparative Materials 2, 4, and 5, in which the annealing or cooling conditions were outside the scope of the present invention, all high temperature properties such as sag resistance, high temperature yield strength, and high temperature discoloration resistance were poor. This is because it is difficult to obtain a volume fraction of the needle-like ferrite structure present in the microstructure in the steel sheet due to lack of control, and thus it is difficult to secure excellent high temperature characteristics.

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 component and the atomic ratio of Table 1 are out of the range of the present invention are low in volume fraction of acicular ferrite structure, and have high temperature and high temperature characteristics. There were many bad cases.

Among them, the comparative material 7 had no yield point stretching phenomenon and good bending resistance, so that the aging resistance and workability were good, but sag resistance, high temperature yield strength and high temperature discoloration resistance and corrosion resistance corresponding to high temperature characteristics were poor. This is because not only the deterioration of the operability at the time of annealing due to the polyaddition of deterioration, the deterioration of the characteristics of the surface of the steel sheet, and the addition of Cu-based sulfides did not form, so that the target corrosion resistance could not be secured. 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. In particular, Comparative materials 8 and 9 had a high Cu / S value, and thus the frequency of occurrence of surface defects was increased by solid solution solid Cu. Comparative Material 10 was poor in corrosion resistance because Cu-based sulfides were not formed due to the absence of Cu. .

As a result, it is possible to optimize the compositional conditions of the steel and the conditions of the manufacturing process (especially annealing and cooling conditions) to form fine Nb-based carbide precipitates, to control the volume fraction of the acicular ferrite structure, and to add Sn to the surface of the steel sheet. By forming a Sn-based oxide and forming Cu-based sulfides by adding Cu, it was possible to produce a high heat-resistant cold rolled steel sheet for processing that satisfies both workability, discoloration resistance, and corrosion resistance at low cost.

The above embodiment is only one example, and the present invention is not limited thereto. 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 (17)

By weight% C: 0.002 ~ 0.005%, Mn: 0.10 ~ 0.35%, P: 0.003 ~ 0.020%, Al: 0.02 ~ 0.08%, Sn: 0.05 ~ 0.25%, Cu: 0.1 ~ 0.4%, N: 0.002 ~ 0.006 %, Nb: 0.02 ~ 0.06%, S: 0.003 ~ 0.010%, balance Fe and other unavoidable impurities, The processability, discoloration resistance and corrosion resistance excellent in processing, characterized in that the value of the atomic ratio Nb / C of the Nb and C is 0.8 ~ 2.0, the value of the atomic ratio Cu / S of the Cu and S is 10-25. Heat-resistant cold rolled steel sheet. delete The method of claim 1, The cold rolled steel sheet is a high heat-resistant cold rolled steel sheet for processing, excellent discoloration resistance and corrosion resistance, characterized in that the Nb-based carbide precipitates are formed. delete The method of claim 1, Cu-based sulfide is formed on the surface of the cold rolled steel sheet for processing, high heat resistance cold rolled steel sheet excellent in workability, discoloration resistance and corrosion resistance. The method of claim 5, The Cu-based sulfide is Cu ₂ S, high heat resistance cold rolled steel sheet for workability, discoloration resistance and corrosion resistance. The method of claim 1, The cold rolled steel sheet is a high heat resistant cold rolled steel sheet for processing, discoloration resistance and corrosion resistance excellent, characterized in that consisting of an equiaxed ferrite and acicular ferrite structure. By weight% C: 0.002 ~ 0.005%, Mn: 0.10 ~ 0.35%, P: 0.003 ~ 0.020%, Al: 0.02 ~ 0.08%, Sn: 0.05 ~ 0.25%, Cu: 0.1 ~ 0.4%, N: 0.002 ~ 0.006 %, Nb: 0.02 ~ 0.06%, S: 0.003 ~ 0.010%, balance Fe and other unavoidable impurities, consisting of equiaxed ferrite and acicular ferrite structure, A high heat-resistant cold rolled steel sheet for processing, excellent discoloration resistance and corrosion resistance, characterized in that the volume fraction of the acicular ferrite structure is 5 ~ 15%. The method according to any one of claims 1, 3 and 5 to 8, A high heat resistant cold rolled steel sheet for processing having excellent workability, discoloration resistance, and corrosion resistance, wherein a Sn-based oxide layer is formed on a surface of the cold rolled steel sheet. By weight% C: 0.002 ~ 0.005%, Mn: 0.10 ~ 0.35%, P: 0.003 ~ 0.020%, Al: 0.02 ~ 0.08%, Sn: 0.05 ~ 0.25%, Cu: 0.1 ~ 0.4%, N: 0.002 ~ 0.006 %, Nb: 0.02 to 0.06%, S: 0.003 to 0.010%, residual Fe and other unavoidable impurities, and for processing, characterized in that the Sn2O3 layer, which is a Sn-based oxide layer, is formed on the surface, and has excellent workability, discoloration resistance and corrosion resistance. High heat resistant cold rolled steel sheet. By weight% C: 0.002 ~ 0.005%, Mn: 0.10 ~ 0.35%, P: 0.003 ~ 0.020%, Al: 0.02 ~ 0.08%, Sn: 0.05 ~ 0.25%, Cu: 0.1 ~ 0.4%, N: 0.002 ~ 0.006 Steel slab containing%, Nb: 0.02 ~ 0.06%, S: 0.003 ~ 0.010%, balance Fe and other unavoidable impurities is heated and hot rolled, cold rolled after winding, and then cold rolled steel sheet Annealed at a temperature, and cooled to a cooling rate of 30 ℃ / sec or more with respect to the annealing steel sheet, The steel slab has a workability, discoloration resistance and corrosion resistance, wherein the atomic ratio Nb / C of Nb and C is 0.8 to 2.0, and the atomic ratio Cu / S of Cu and S is 10 to 25. The manufacturing method of this excellent high heat resistant cold rolled steel sheet for processing. delete delete 12. The method of claim 11, The hot rolling is a method of manufacturing a high heat-resistant cold rolled steel sheet for processing, excellent in workability, discoloration resistance and corrosion resistance characterized in that the finish rolling at 900 ~ 950 ℃. 12. The method of claim 11, The hot rolling is a method of manufacturing a high heat resistant cold rolled steel sheet having excellent workability, discoloration resistance and corrosion resistance comprising the step of cooling the hot rolled hot rolled sheet at a cooling rate of 20 ~ 80 ℃ / sec. 12. The method of claim 11, The winding is carried out at 560 ~ 680 ℃ manufacturing method, high heat resistance cold rolled steel sheet excellent in workability, discoloration resistance and corrosion resistance. 12. The method of claim 11, The annealing treatment is carried out at 800 ~ 900 ° C characterized in that the workability, discoloration resistance and corrosion resistance excellent manufacturing method for high temperature cold rolled steel sheet for processing.