KR101263794B1 - High strength and heat-resistance 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, high-temperature cold rolled steel sheet having excellent workability, heat resistance, and discoloration resistance, and a method for manufacturing the same, wherein the weight ratio is C: 0.002 to 0.005%, Sn: 0.05 to 0.25%, and B: 0.001 to 0.003%. , Zr: 0.03 ~ 0.08%, N: 0.002 ~ 0.006%, Mn: 0.4 ~ 0.8%, Al: 0.02 ~ 0.08%, P: 0.03 ~ 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities The high-temperature high-temperature cold-rolled steel sheet for processing and its manufacturing method which are excellent in heat resistance, workability, and discoloration resistance are made into a 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 such as extension flangeability, bending property, and deep drawing property, and thus has excellent room temperature workability, It is not only excellent in moldability due to the increase in aging resistance and no yield point elongation, but also has high r-bar value, so it can be applied to high processing materials. It is possible to produce a high strength, high temperature resistant cold rolled steel sheet having excellent resistance to discoloration at high temperatures.

Cold Rolled Steel, Needle Ferrite, Heat Resistance, Processability, Discoloration Resistance, High Strength, Aging Resistance

Description

High-strength, high-temperature cold-rolled steel sheet for processing, and its manufacturing method having excellent workability, heat resistance, and discoloration resistance, and a method for manufacturing the same.

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 particularly, the present invention provides excellent workability, heat resistance, and discoloration resistance by optimizing steel components and process conditions. It relates to a high strength, high heat resistant cold rolled steel sheet and a method of manufacturing the same.

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

The high temperature property is one of the characteristics when the processed product is used in a high temperature environment. The high temperature property, 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.

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

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

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

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

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

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

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. High-strength, high-temperature, cold-rolled steel sheet and its manufacture for high processability, heat resistance, and discoloration resistance that can be manufactured at low cost by optimizing steel components and processing conditions while reducing the addition of expensive alloy elements for use in demanding applications. The purpose is to provide a method.

In the present invention, C: 0.002 to 0.005%, Sn: 0.05 to 0.25%, B: 0.001 to 0.003%, Zr: 0.03 to 0.08%, N: 0.002 to 0.006%, Mn: 0.4 to 0.8%, Al: Provides a high strength, high temperature cold rolled steel sheet for processing with high heat resistance, workability and discoloration resistance, including 0.02 to 0.08%, P: 0.03 to 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities.

At this time, the characteristic of the atomic ratio Zr / C of Zr and C is 0.03 to 1.2.

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

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

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

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

Here, the volume fraction of the acicular ferrite structure of the cold rolled steel sheet is also characterized by 5 to 15%.

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

At this time, the Sn-based oxide layer is also characterized in that the Sn ₂ O ₃ layer.

In addition, the present invention is in the weight% C: 0.002 ~ 0.005%, Sn: 0.05 ~ 0.25%, B: 0.001 ~ 0.003%, Zr: 0.03 ~ 0.08%, N: 0.002 ~ 0.006%, Mn: 0.4 ~ 0.8%, Steel slab containing Al: 0.02 ~ 0.08%, P: 0.03 ~ 0.08%, S: 0.015% or less, remainder Fe and other unavoidable impurities is heated, hot rolled, cold rolled, and then cold rolled steel sheet Annealing treatment at a temperature of 800 ℃ or more, and a high strength cold-rolled steel sheet for processing high strength, excellent in workability, heat resistance and discoloration resistance characterized in that the cooling rate of 30 ℃ / sec or more with respect to the annealed steel sheet to provide.

At this time, the characteristic of the atomic ratio Zr / C of Zr and C is 0.03 to 1.2.

Moreover, the characteristic is that the value of the atomic ratio B / N of said B and N is 0.5-1.5.

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, so it is not only excellent in formability, but also has high r-bar value, so it can be applied to high processing materials. The service life is extended, and high strength, high temperature resistant cold rolled steel sheet having high discoloration resistance at high temperature can be manufactured.

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 small amount of ultra low carbon, increases the content of Mn and P in the steel components, and controls the amount of Zr, C, B, and N added and their atomic ratios to control fine Zr-based carbonized precipitates and B-based nitride precipitates. By optimizing the annealing and cooling conditions to secure the volume fraction of the needle-like ferrite structure, and by adding Sn to form a Sn ₂ O ₃ layer on the surface of the steel sheet by heat treatment, heat resistance, corrosion resistance and discoloration resistance at high temperature It has the characteristics of manufacturing high strength cold-rolled steel sheet for processing of high strength suitable for product parts such as automobile exhaust system, home appliance, boiler, etc. because of its excellent aging resistance and workability.

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 Zr in the present invention to form 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%. However, if the content is less than 0.002%, sufficient strengthening effect of carbonized precipitates of Zr-based materials cannot be obtained, and the grain size is increased to cause a sudden change in material, so the content of C 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 0.8%. However, if less than 0.4%, the workability is improved, but it is difficult to secure the target high strength, Mn content is limited to 0.4 ~ 0.8%.

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) 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%.

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

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

Zirconium (Zr) combines with solid solution elements in the steel to form carbonized precipitates to promote the development of aging resistance and {111} texture, improving workability such as drawing, and improving the strength of steel sheet by forming carbonized precipitates. It is preferable to contain 0.03% or more because it provides an effect of miniaturizing ferrite particles by increasing grain restraint at high temperature, but when the content exceeds 0.08%, the material is hardened and the workability of the continuous annealing treatment is reduced, and the steel sheet Since it deteriorates the surface properties of the Zr content is limited to 0.03 ~ 0.08%.

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 Zr 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 also important to ensure the room temperature aging resistance, processability and high temperature strength at the same time by maintaining the value of the atomic ratio Zr / C of Zr and C and the value of the atomic ratio B / N of B and N in a certain range.

That is, when the value of Zr / C is 0.03 ~ 1.20, Zr-based carbonized precipitates are formed to solidify solid elements in steel to secure room temperature aging resistance and processability, and fine Zr-based carbonization by appropriately controlling the annealing and cooling conditions. By forming a precipitate to suppress grain growth at high temperature to control the ferrite microstructure, it is possible to secure excellent high temperature characteristics.

However, when the value of Zr / C is less than 0.03, there is a problem of deterioration of room temperature aging resistance and workability due to excessive solid solution elements in the steel, and the precipitation amount of Zr-based carbide precipitates is insignificant, so that excellent high temperature strength cannot be secured. In addition, when the value exceeds 1.20, 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 Zr / C is 0.03 to 1.20. It is limited to.

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 maintain the value of B / N, which is an atomic ratio of B and N, at 0.5 to 1.5. When the B / N value is less than 0.5, there is a problem that the room temperature resistance is degraded due to excessive solid solution in steel, the grain suppression effect is insufficient at high temperature, and when the B / N value exceeds 1.5, the ductility is lowered and the workability is decreased. , The value of B / N is limited to 0.5 to 1.5.

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

On the other hand, the cold-rolled steel sheet of the present invention is characterized by consisting of an equiaxed ferrite (polygonal ferrite) and acicular ferrite (acicular ferrite) structure, the needle-like ferrite tissue is a kind of bainite that grows nucleated in the mouth of austenite before transformation As the nucleation grows from the fine non-metallic inclusions dispersed in the steel, when the transformation is completed, the ferrite laths are relatively superior in ductility or toughness due to the disordered structure of forming high grain boundaries.

The present invention secures the volume fraction of the needle-like ferrite structure by 5-15% by appropriately controlling the conditions of the annealing and cooling process to form a high-potential-density type microstructure, thereby inhibiting abnormal growth of grains at high temperature to secure high temperature strength. By doing so, 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-like ferrite structure is limited to 5-15%.

Hereinafter, the manufacturing method of the high strength high temperature cold rolled steel sheet for processing which is 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 to 30 ° C./sec or more on an annealing steel sheet at a temperature of 800 ° C. or higher, thereby providing excellent workability, heat resistance, and discoloration resistance. It is possible to manufacture a high strength, high heat resistant cold rolled steel sheet.

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

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

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

After the wound steel sheet is subjected to pickling treatment and cold rolling to a target thickness, the steel sheet 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., the volume fraction of the needle-like ferrite structure present in the microstructure of the target steel sheet cannot be obtained, which makes it difficult to secure excellent 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 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 point elongation is generated when the yield point elongation is measured, and when no extension occurs, it is indicated as not occurring. The bending resistance test is classified according to the degree of surface bending 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 steel sheet was measured and judged to be bad when the deflection degree was 5 mm or more. The high temperature yield strength test was determined 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.

In addition, high r-bar value is required for drawing processing due to the recent increase in molding amount and complexity of the shape. Thus, a standard specimen according to ASTM E-8 standard is processed, and the processed specimen is manufactured by Instron Corporation. Using the tensile tester model 6025, the plastic strain ratio (rankford value; r value) was obtained for each rolling direction, and based on this, the value of r-bar, which is an index of formability, was calculated by the following equation.

r-bar = (r ₀ + 2r ₄₅ + r ₉₀ ) / 4

In the above formula, r ₀ , r ₄₅ and r ₉₀ are the r values in the rolling direction, the rolling direction 45 ° direction, and the rolling direction 90 ° direction, respectively.

In Table 1, the values of Zr / C and B / N are atomic ratios, and the ratios of values obtained by dividing the weight percent of each component by their atomic weights respectively.

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 the formation of Zr-based carbide and B-nitride precipitates and optimization of the volume fraction of acicular ferrite structure. As the degree of reduction of the figure was less than 30%, the discoloration resistance was good, and it was confirmed that the r-bar values, the evaluation indexes of moldability, were all high values of 1.8 or more, and could be applied to high processing materials.

On the other hand, the steel component of Table 1, etc., is an invention steel that satisfies the scope of the present invention, but 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 high in low fraction of acicular ferrite structure. It did not have characteristics (sag resistance, high temperature strength, discoloration resistance), tensile strength at room temperature was lower than 350MPa, and workability (r-bar value) and aging resistance (yielding point stretching, bending resistance) were also poor. Many.

In addition, although the process conditions of Table 2 satisfy the scope of the present invention, the steel component of Table 1 and the like after evaluation of the manufacturing properties of the comparative material 6 to 10 degrees outside the scope of the present invention, the fraction of the needle-like ferrite structure is low , The room temperature and high temperature characteristics were often poor. Among them, Comparative Material 6 had no yield point stretching phenomenon and good bending resistance and workability (r-bar value), but sag resistance, high temperature strength and discoloration resistance corresponding to high temperature characteristics were poor. This is because grain growth was not sufficiently suppressed at high temperatures by addition. In addition, Comparative Materials 7 to 10 have a high amount of solid carbon in steel, and thus have poor workability and aging resistance, and do not form Zr- or B-based precipitates due to no addition of Zr or B-components. Was not suitable.

In addition, although the volume fraction (%) and r-bar value of the needle-like ferrite tissue of the invention and the comparative material are shown in the graph of FIG. 1, as described above, the invention materials 1 to 5 are all included within the scope of the invention, and the room temperature and Although all of the high temperature characteristics were good, Comparative Materials 1 to 10 were often out of the scope of the invention. However, some comparative materials (Comparative Materials 5 and 6) had good r-bar values of 1.8 or more, whereas acicular ferrites were good. It was confirmed that the volume fraction of the tissue was very low to satisfy both the processability and the high temperature characteristics at the same time.

Eventually, the compositional conditions of the steel and the conditions of the manufacturing process (particularly annealing and cooling conditions) can be optimized to form fine Zr-based carbide and B-nitride precipitates and to control the volume fraction of the needle-like ferrite structure. by by a thermal treatment to form a Sn-based oxide, such as Sn ₂ O ₃ on the surface of the steel sheet, it can be expensive and shared a high strength to satisfy the processability, heat resistance and discoloration resistance at a low cost at the same time to produce a heat-resistant cold-rolled steel sheet.

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.

1 is a graph showing the volume fraction (%) and r-bar value of the needle-like ferrite structure of the invention and the comparative material.

Claims (16)

By weight% C: 0.002 ~ 0.005%, Sn: 0.05 ~ 0.25%, B: 0.001 ~ 0.003%, Zr: 0.03 ~ 0.08%, N: 0.002 ~ 0.006%, Mn: 0.4 ~ 0.8%, Al: 0.02 ~ 0.08 %, P: 0.03 ~ 0.08%, S: 0.015% or less, including balance Fe and other unavoidable impurities, The value of the atomic ratio Zr / C of the Zr and C is 0.03 to 1.2, and the value of the atomic ratio B / N of the B and N is 0.5 to 1.5, which is excellent in workability, heat resistance and discoloration resistance. High heat resistant cold rolled steel sheet for processing. delete The method of claim 1, The cold rolled steel sheet is a high heat resistant cold rolled steel sheet for processing having high workability, heat resistance and discoloration resistance, characterized in that Zr-based carbide precipitates are formed. delete The method of claim 1, The cold rolled steel sheet is a high heat resistant cold rolled steel sheet for processing of high strength, heat resistance and discoloration resistance, characterized in that the B-based nitride precipitates are formed. The method of claim 1, The cold rolled steel sheet is a high-strength cold-rolled steel sheet for processing of high strength, excellent in workability, heat resistance and discoloration, characterized in that consisting of an isometric ferrite and acicular ferrite structure. By weight% C: 0.002 ~ 0.005%, Sn: 0.05 ~ 0.25%, B: 0.001 ~ 0.003%, Zr: 0.03 ~ 0.08%, N: 0.002 ~ 0.006%, Mn: 0.4 ~ 0.8%, Al: 0.02 ~ 0.08 %, P: 0.03 ~ 0.08%, S: 0.015% or less, including residual Fe and other unavoidable impurities, consisting of equiaxed ferrite and acicular ferrite structure, The high-temperature cold-rolled steel sheet for processing high strength excellent in workability, heat resistance and discoloration, 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 7, A high heat resistant cold rolled steel sheet for processing having high strength and heat resistance and discoloration 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%, Sn: 0.05 ~ 0.25%, B: 0.001 ~ 0.003%, Zr: 0.03 ~ 0.08%, N: 0.002 ~ 0.006%, Mn: 0.4 ~ 0.8%, Al: 0.02 ~ 0.08 %, P: 0.03 ~ 0.08%, S: 0.015% or less, including the remaining Fe and other unavoidable impurities, the Sn2O3 layer, which is a Sn-based oxide layer, is formed on the surface and has excellent workability, heat resistance and discoloration resistance. High heat resistant cold rolled steel sheet for processing. By weight% C: 0.002 ~ 0.005%, Sn: 0.05 ~ 0.25%, B: 0.001 ~ 0.003%, Zr: 0.03 ~ 0.08%, N: 0.002 ~ 0.006%, Mn: 0.4 ~ 0.8%, Al: 0.02 ~ 0.08 Steel slab containing%, P: 0.03 ~ 0.08%, S: 0.015% or less, balance Fe and other unavoidable impurities is heated and hot rolled, cold rolled after winding, and then cold rolled steel plate Annealed at and cooled to a cooling rate of 30 ℃ / sec or more with respect to the annealing steel sheet, The value of the atomic ratio Zr / C of the Zr and C is 0.03 to 1.2, and the value of the atomic ratio B / N of the B and N is 0.5 to 1.5, which is excellent in workability, heat resistance and discoloration resistance. Manufacturing method of high heat resistant cold rolled steel sheet for processing. delete delete The method of claim 10, The hot rolling is a method of manufacturing a high strength cold-rolled steel sheet for processing of high strength, excellent workability, heat resistance and discoloration, characterized in that the finish rolling at 900 ~ 950 ℃. The method of claim 10, The hot rolling is a method of manufacturing a high strength high temperature cold rolled steel sheet for processing, heat resistance and discoloration resistance, characterized in that it comprises the step of cooling the hot rolled hot rolled sheet at a cooling rate of 20 ~ 80 ℃ / sec. The method of claim 10, The winding is carried out at 560 ~ 680 ℃ manufacturing method of high strength cold-rolled steel sheet for processing of high strength excellent in workability, heat resistance and discoloration resistance. The method of claim 10, The annealing treatment is carried out at 800 ~ 900 ℃, characterized in that the workability, heat resistance and discoloration resistance excellent high strength cold-rolled steel sheet for processing.

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