KR100815799B1 - High yield ratio cold rolled steel with excellent weatherability - Google Patents

Abstract

A high yield ratio type cold-rolled steel sheet with excellent weather resistance and a manufacturing method thereof are provided to secure a cold-rolled steel sheet having excellent weather resistance and formability while maintaining a high strength of at least 80 kg/cm^2 and a high yield ratio. A high yield ratio type weather resistant cold-rolled steel sheet has a composition comprising, by weight percent, 0.08 to 0.20% of carbon(C), 0.1 to 0.5% of silicon(Si), 0.9 to 2.0% of manganese(Mn), 0.02% or less of phosphorous(P), 0.01% or less of sulfur(S), 0.02 to 0.07% of aluminum(Al), 0.03 to 0.06% of niobium(Nb), 0.05 to 0.30% of nickel(Ni), 0.2 to 0.5% of copper(Cu), 0.3 to 0.6% of chromium(Cr), 0.001 to 0.004% of boron(B), and 0.02 to 0.08% of cobalt(Co) with the balance of Fe and other inevitable impurities. The cold-rolled steel sheet has a tensile strength of 80 kg/mm^2 or more.

Description

Cold-Rolled Steel Sheet With High Yield Ratio and Excellent Weather Resistance}

Japanese Laid-Open Patent Publication No. 7-207408

Japanese Patent Application Laid-Open No. 11-21622

Japanese Patent Application Laid-open No. Hei 6-104858

     The present invention relates to a high strength weather resistant cold rolled steel sheet used in construction, railroad cars, containers, and the like, and more particularly, to a high strength weather resistant cold rolled steel sheet having a high yield ratio and a method of manufacturing the same.

Conventionally, materials such as stainless steel or aluminum have been used for the purpose of reducing the weight and extending the service life of a container or a railway vehicle. Characteristics required for such products include bendability, weldability and durability. In addition, in the case of transport structures, it is often necessary to suppress the deformation due to impact because the cargo is often impacted when loading and loading the cargo. For this purpose, it is recommended to apply a material having a high yield ratio.

Yield-ratio is defined as the ratio of the tensile strength to the yield strength of the material values obtained through the tensile test, and the higher yield ratio at the same tensile strength level means that the yield strength of the material is higher. In other words, the steel having a high yield ratio increases the ability to suppress the deformation by increasing the resistance to deformation even when subjected to high impact strength, which is a material property of the elastic region. When used in a container or the like, it is desirable to secure a yield ratio of 80% or more. In particular, a container or the like has been required to use steel having excellent weatherability because it must withstand various climatic conditions of the ocean or the land depending on the transport conditions.

For example, in the past, weather resistant rolled steel, SPA-C (Industrial Standards KS-D3542 and JIS-G3125), has been used, but these steels have a low tensile strength of 50 kg / mm ² and thus have their own products when making larger products. Increasing transportation costs due to weight has been a limiting factor. In addition, although there are high-strength cold-rolled steel having a tensile strength of 60 ~ 80kg / mm ² grade for the structural member of the vehicle, even in the case of these materials, there is a problem in that it does not exhibit the desired weather resistance as the emphasis on strength characteristics.

In recent years, in the container industry, in order to cope with cost reduction and environmental problems, attempts have been made to significantly reduce the weight of containers and to produce larger containers, thereby greatly increasing the efficiency of transportation. In particular, there is a demand for steel sheets having weather resistance and high strength of 80 kg / mm ² or more, and techniques related to the manufacturing method of these materials have been proposed.

For example, in Japanese Patent Laid-Open No. 7-207408, C 0.008% or less, Si 0.5-2.5%, Mn 0.1-3.5%, P 0.03-0.20%, S 0.01% or less, Cu 0.05-2.0%, Al 0.005- Steels containing 0.1% and N 0.008% or less, Cr 0.05-6.0%, Ni 0.05-2.0% and Mo 0.05-3.0%, B 0.0003-0.002% are heated at 1100-1300 ° C and the rolling ends at 800-950 ° C. A method for producing a hot rolled steel strip, characterized in that the winding to 400 ~ 700 ℃. However, in this technology, only a few embodiments show that the tensile strength is 60-70kg / mm ² and in most cases, the tensile strength is 50kg / mm ² , so that it is impossible to secure the 80kg / mm ² tensile strength. . In addition, there is a problem in that weldability is deteriorated and manufacturing cost is increased by adding a large amount of hardenability improving elements such as Cr and Mo among the component components.

As another example, Japanese Patent Laid-Open No. 11-21622 discloses C 0.15% or less, Si 0.7% or less, Mn 0.2-1.5%, P 0.03-0.15%, S 0.02% or less, Cu 0.4% or less, Al 0.01- or less. Steels containing 0.1% and less than 0.1% Cr, 0.4 to 4.0% Ni and 0.1 to 1.5% Mo are heated to 1050-1300 ° C, hot rolled at 40% or more at 950 ° C or more, and then rolling finished at 900-750 ° C. And air cooling is proposed. However, even at this time, most of the tensile strength is 50kg / mm ² grade, only a few showed the tensile characteristics of 60kg / mm ² grade, this technique can be said to be mainly applied to 50kg / mm grade ² steel sheet. In addition, although the effect of improving the corrosion resistance in the seawater atmosphere by adding a large amount of P to 0.03 ~ 0.15% is mentioned, the addition of a large amount of P causes a central segregation of the cold rolled material, such that the workability of the steel sheet is drastically deteriorated there was.

In addition, Japanese Patent Laid-Open No. 6-104858 discloses C 0.02 to 0.12%, Si 0.5% or less, Mn 0.1 to 2.0%, P 0.07 to 0.15%, S 0.02% or less, Cu 0.25 to 0.55% or less, Al 0.01 to Steels containing 0.05% and Cr 0.3-1.25%, N ₂ 0.006% or less, Ti 0.06-0.20% are controlled in the range 12.1X _{ti, eff} (%) / Mn (%)> 1.0 and reheated at 1180 ° C. or higher, After hot rolling at 880 ~ 950 ℃, it provides the technology of winding below 650 ℃. This technique adds Ti content in conjunction with the amount of Mn added as a precipitate control element. However, embodiments of this technique also have a tensile strength of 60 kg / mm ² , which is lower than the 80 kg / mm ² target targeted in the present invention.

Thus, in the present invention to solve the above problems, it is to ensure the weather resistance and high yield ratio characteristics having a high strength characteristics of 80kg / mm ² or more.

 High yield ratio weather resistant cold rolled steel sheet of the present invention for achieving the above object,

By weight%, carbon (C) 0.08 to 0.20%, silicon (Si) 0.1 to 0.5%, manganese (Mn) 0.9 to 2.0%, phosphorus (P) 0.02% or less, sulfur (S) 0.01% or less, aluminum (Al ) 0.02 to 0.07%, niobium (Nb) 0.03 to 0.06%, nickel (Ni) 0.05 to 0.30%, copper (Cu) 0.2 to 0.5%, chromium (Cr) 0.3 to 0.6%, boron (B) 0.001 to 0.004% , Cobalt (Co) 0.02 ~ 0.08% and will be composed of the remaining Fe and other unavoidable impurities.

The tensile strength of the cold rolled steel sheet is preferably 80kg / mm ² or more.

In addition, the cold rolled steel sheet manufacturing method of the present invention, in weight%, 0.08 to 0.20% carbon (C), 0.1 to 0.5% silicon (Si), 0.9 to 2.0% manganese (Mn), 0.02% or less of phosphorus (P), Sulfur (S) 0.01% or less, Aluminum (Al) 0.02-0.07%, Niobium (Nb) 0.03-0.06%, Nickel (Ni) 0.05-0.30%, Copper (Cu) 0.2-0.5%, Chromium (Cr) 0.3- Finish rolling temperature condition of 850 ~ 950 ℃ by reheating the steel containing 0.6%, boron (B) 0.001 ~ 0.004%, cobalt (Co) 0.02 ~ 0.08% and consisting of remaining Fe and other unavoidable impurities to 1150 ~ 1300 ℃ It is composed of hot rolling and cooling at a cooling rate of 20-40 ° C. per second, wound up at a temperature of 500-650 ° C., followed by cold rolling, followed by continuous annealing at 500 ° C. or higher and A ₁ transformation point.

Hereinafter, the present invention will be described in detail.

MEANS TO SOLVE THE PROBLEM The present inventors completed this invention by repeating research and experiment to satisfy | fill weatherability with various processing characteristics, and to ensure the characteristic of high yield ratio with the characteristic of high strength. The present invention is to control the addition amount of Cr, B, Nb, etc. in the weathering component system of Cu-Co to secure a high yield ratio with high strength characteristics.

The carbon (C) is preferably 0.08-0.20% by weight (hereinafter, simply expressed as%).

C is an element added to improve the strength of the steel sheet, and the tensile strength and yield strength increase as the amount added increases. However, the upper limit is preferably 0.20% because excessive workability decreases the workability of the material. On the other hand, when the amount of C is less than 0.08%, there is a problem in that sufficient precipitation strengthening effect cannot be obtained.

Silicon (Si) is preferably 0.1-0.5%.

Si not only provides molten steel deoxidation and solid solution strengthening effect, but also forms a dense oxide of Fe ₂ SiO ₄ together with Fe in the surface layer of the steel at high temperature to improve corrosion resistance. Addition is preferred. Therefore, Si should be added to improve weather resistance, but if excessively added, there is a problem that the weldability is lowered and the plating property is degraded. Therefore, it is preferable to add Si at 0.5% or less.

As for manganese (Mn), 0.9-2.0% is preferable.

Mn is an element that is effective for strengthening by solid solution and is an important element for increasing the strength of steel and improving hot workability, but is also an element that inhibits the ductility and workability of a material due to MnS formation. If the content of Mn is small, it is advantageous for workability but there is a problem in strength. Therefore, it is preferable to add 0.9% or more to secure the target strength. On the other hand, when Mn is excessively added, the upper limit is preferably 2.0% because there is a problem of deterioration in economics and weldability due to the addition of a large amount of expensive alloying elements.

Phosphorus (P) is preferably 0.02% or less.

Since P plays a role of improving the corrosion resistance of the steel, it is preferable to add a large amount in terms of corrosion resistance. However, since P is the element causing the largest segregation of the core during casting, a large amount of P decreases weldability and toughness. Therefore, the content is preferably limited to 0.02% or less.

Sulfur (S) is preferably 0.01% or less.

Although S is known as an element effective in improving corrosion resistance, it is preferable to reduce the content as much as possible because it combines with Mn in steel to form a nonmetallic inclusion serving as a corrosion start point. Therefore, the amount of S is limited to 0.01% or less, more preferably 0.005% or less.

As for aluminum (Al), 0.02-0.07% is preferable.

Al is generally an element which is effective in improving deoxidation and corrosion resistance of molten steel, but when it is added excessively, there is a problem of decreasing workability by increasing the amount of inclusions in the steel, so the content is preferably set at 0.02 to 0.07%.

Niobium (Nb) is preferably 0.03-0.06%.

Nb is not only an effect of delaying the recrystallization of ferrite, but also an element showing the effect of increasing the strength of the steel sheet by being precipitated in combination with C, N _2, etc. in steel, and the addition of 0.03% or more is preferable for securing the target strength. On the other hand, when Nb is added in an amount of more than 0.06%, it may cause a rise in manufacturing cost and a decrease in hot rolling workability.

Nickel (Ni) is preferably 0.05-0.3%.

Ni is generally an element that improves corrosion resistance as well as preventing casting cracks generated during casting in Cu-added steel. In order to exert such effects, addition of 0.05% or more is preferable. However, when the Ni content exceeds 0.3%, not only the corrosion resistance is deteriorated but also the cost is increased due to the excessive use of expensive alloy elements.

Copper (Cu) is preferably 0.2-0.5%.

Cu is an element which forms a stable rust layer in a corrosive atmosphere and improves corrosion resistance, and in order to ensure target corrosion resistance, addition of 0.2% or more is preferable. However, when the added amount of Cu exceeds 0.5%, not only does it cause grain boundary cracking during the play, but also there is a fear that the surface state of the hot rolled steel sheet is roughened.

Chromium (Cr) is preferably 0.3-0.6%.

Cr is an element that plays a role of forming a stable rust layer, such as Cu, is preferably 0.3% or more in order to secure corrosion resistance and obtain strength. In addition, when the amount of Cr is more than 0.6%, it not only acts as a factor causing hole corrosion but also rapidly increases the manufacturing cost.

The boron (B) is preferably 0.001-0.004%.

B is an element that not only improves the hardenability of the steel but also delays the recrystallization of the ferrite phase, and in order to obtain a target level of strength in the low temperature region, addition of 0.001% or more is preferable. On the other hand, if the B content exceeds 0.004%, the hardenability is increased by promoting the formation of a hard phase such as bainite in the hot rolling process by the increase of the hardenability.

Cobalt (Co) is preferably 0.02-0.08%.

Co is an element that reacts with Cu, Cr, etc., added to secure corrosion resistance in steel, and promotes formation of a surface layer corrosion inhibiting product. In order to obtain such an effect, at least 0.02% or more is preferable. However, when the amount of Co added is more than 0.08%, it will act as an increase factor of the manufacturing cost rather than the effect of improving the corrosion resistance.

The steel of the present invention is composed of the above-mentioned components and inevitable impurities and the remaining Fe. If necessary, an alloying element may be added to the weathering steel to add a property improvement, and an alloying element not disclosed in the embodiment of the present invention is added and is not interpreted as being excluded from the scope of the present invention.

The cold rolled steel sheet of the present invention has high yield ratio and high yield ratio. According to one embodiment of the present invention, the tensile strength may be 80 kg / mm ² or more, and for example, has a tensile strength of about 80 to 110 kg / mm ² . The yield ratio should be 80% or more, for example, approximately 85-94%. In addition, the ductility has a property of 10% or more.

These characteristics are obtained by low temperature annealing of the present invention described below while satisfying the above component system. Due to low temperature annealing, all of the rolled deformation grains do not recover and some of them exist in the microstructure. The microstructure of the present invention may be ferrite or a hybrid structure of ferrite and perlite, but is not limited thereto.

Hereinafter, the manufacturing method of the cold rolled steel sheet of this invention is demonstrated.

It will be described in detail through an embodiment a method for producing a steel composition as described above. Steel with the above chemical composition is reheated at 1150 ~ 1300 ℃, finish hot rolling at 850 ~ 950 ℃, cooled at 20 ~ 40 ℃ / sec cooling rate and wound up at 500 ~ 650 ℃, then cold rolled and heat treated 500 ~ A ₁ Tensile strength excellent in weatherability by continuous annealing at the temperature below transformation point 80kg / mm ² The present invention relates to a method for producing a high yield ratio cold rolled steel sheet.

If the reheating temperature is less than 1150 ° C., the breakage of the solidified structure formed during casting is insufficient, so that the center segregation is well developed, resulting in the mixing of the finally formed crystal grains and the workability and impact toughness are significantly reduced. In addition, if the reheating temperature exceeds 1300 ℃, the formation of scale by oxidation is promoted, and the slab thickness decreases and the impact toughness decreases due to the coarsening of grains when reheating. The management range is limited to 1150-1300 degreeC.

If the finish hot rolling temperature is higher than 950 ° C, uniform hot rolling is not performed throughout the thickness, resulting in insufficient grain refinement, resulting in a drop in impact toughness due to grain coarsening. On the contrary, as the hot rolling is finished in the low temperature region at the finishing hot rolling temperature of 850 ° C, it is preferable to limit the finishing hot rolling temperature to 850 ° C to 950 ° C as the hybridization of crystal grains proceeds rapidly, resulting in deterioration of corrosion resistance and workability.

After hot rolling as described above, the cooling is preferably 20-40 ° C. That is, if the cooling rate in the run-out-table (ROT) after finishing hot rolling is less than 20 ° C per second, coarse grains are formed by promoting grain growth, which is a factor of lowering strength. It is preferable to set it as 20 degreeC per second. On the other hand, if the cooling rate exceeds 40 ℃ per second to form a hard second phase, such as bainite to significantly reduce the cold rollability, the cooling rate is preferably set to 20 ~ 40 ℃ per second.

Cooling and winding as described above, the winding temperature is preferably 500-650 ℃. If the hot rolled coil temperature exceeds 650 ° C., a sufficient precipitation effect is not obtained, thereby making it difficult to secure a stable target strength of 80 kg / mm ² . On the other hand, at winding temperatures of less than 500 ° C, a hard phase is generated during cooling and holding, and thus rolling properties cannot be secured as the roll force of the rolling mill rises in the cold rolling process. It is preferable to limit to 500-650 degreeC.

The hot rolled material is subjected to rolling under normal cold rolling conditions and subjected to a continuous annealing process. At this time, it is necessary to properly manage the annealing temperature in order to secure the target material properties. If the annealing temperature is lower than 500 ° C. in the continuous annealing process, the deformation grains during cold rolling remain as it is, and thus the ductility drops sharply. On the other hand, at the annealing temperature above the A ₁ transformation point, the martensite phase is formed by transformation during cooling after annealing, and the yield strength is lowered. As the yield ratio is lowered below 60%, resistance to deformation cannot be secured, so the upper limit of the annealing temperature is it is preferred that the a ₁ transformation point. In the present invention, it is possible to leave some part of the rolling strain on the cold rolled steel sheet by low temperature annealing.

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

Example 1

For steels prepared as shown in Table 1, after evaluation and weather resistance test for standardized corrosion resistance index (CI) values were performed, the evaluation results are shown in [Table 2]. The weather resistance test is the result of a salt spray test (SST) for 480 hours in a 5% salt solution (NaCl solution) at 30 ℃. Here, the corrosion resistance index (CI) is a weather-related evaluation index specified in ASTM G101, and the higher this value, the better the weather resistance of the steel, which is mainly calculated based on alloying elements and is defined as follows.

Corrosion Resistance Index (CI) = 26.01 (% Cu) + 3.88 (% Ni) + 1.2 (% Cr) + 1.49 (% Si) + 17.28 (% P)-7.29 (% Cu) (% Ni)-9.10 (% Ni) (% P)-33.39 (% Cu) ²

Steel grade Chemical composition (% by weight) C Si Mn P S Al Nb Co Ni Cu Cr B Inventive Steel 1 0.12 0.28 1.45 0.010 0.002 0.035 0.044 0.04 0.14 0.35 0.64 0.0028 Inventive Steel 2 0.14 0.46 1.26 0.012 0.003 0.032 0.051 0.06 0.15 0.36 0.54 0.0019 Comparative Steel 1 0.05 0.25 2.54 0.012 0.006 0.033 0.024 0.04 0.213 0.45 0.96 -0.0030 Comparative Steel 2 0.13 0.65 1.44 0.094 0.005 0.042 - - 0.46 0.75 1.05 0.0025 Comparative Steel 3 0.12 0.05 0.56 0.064 0.004 0.034 0.041 - 0.15 0.36 - 0.0015 Comparative Steel 4 0.13 0.21 1.34 0.009 0.024 0.051 - - 0.12 0.31 0.76 -

River bell Corrosion Resistance Index (CI) Corrosion degree (weight loss, gr / cm ² ) Weatherability Assessment Inventive Steel 1 6.544475 0.0288 Good Inventive Steel 2 6.748976 0.0278 Good Comparative Steel 1 6.779319 0.0295 Good Comparative Steel 2 3.454711 0.0601 Defective Comparative Steel 3 6.317656 0.0491 Defective Comparative Steel 4 6.419325 0.0338 Defective

As shown in Table 2, the comparative steel (2) had a low corrosion resistance index and a large corrosion loss, making it difficult to apply in terms of weather resistance. The comparative steel (3) and the comparative steel (4) had slightly higher CI values, but the salt spray test was performed. Corrosion loss by showed 0.030 g / cm <^2> or more, and the weather resistance fell. On the other hand, the inventive steels (1), (2) and comparative steels (1) showed excellent weather resistance in terms of corrosion loss and corrosion resistance index.

Example 2

In Table 1 of Example 1, using the invention steel (1), (2) and comparative steels (1) to (4), by working under the same conditions as Table 3 to produce a cold-rolled steel sheet mechanical for each material Table 4 shows the results of evaluating the properties and processing characteristics.

division Used steel grade Reheating Temperature (℃) Hot rolled finish temperature (℃) Cooling rate (℃ / s) Winding temperature (℃) Annealing Temperature (℃) Invention 1 Inventive Steel 1 1220 870 25 620 640 Invention 2 1260 910 25 620 660 Invention 3 Inventive Steel 2 1200 860 30 560 550 Invention 4 1250 880 30 560 650 Comparative Material 1 Inventive Steel 1 1080 700 25 450 650 Comparative Material 2 1220 870 25 620 800 Comparative Material 3 1220 870 60 500 650 Comparative Material 4 Inventive Steel 2 1250 880 25 620 450 Comparative Material 5 1250 880 25 620 780 Comparative Material 6 Comparative Steel 1 1250 940 30 560 780 Comparative Material7 1250 920 25 560 650 Comparative Material 8 Comparative Steel 2 1230 910 30 620 650 Comparative Material 9 Comparative Steel 3 1190 860 25 600 650 Comparative Material 10 Comparative Steel 4 1220 870 20 620 650 Comparative Material 11 1220 890 25 620 850

division Yield strength (kgf / mm ² ) Tensile Strength (kgf / mm ² ) Elongation (%) Yield Ratio (%) Bandability Machinability Invention 1 84.9 90.4 11 93.9 Good Invention 2 82.1 92.4 13 88.9 Good Invention 3 86.3 101.0 10 85.4 Good Invention 4 83.8 95.2 12 88.0 Good Comparative Material 1 96.4 106.1 3 90.9 Crack occurrence Comparative Material 2 46.5 82.1 19 56.6 Good Comparative Material 3 92.2 104.1 2 88.6 Crack occurrence Comparative Material 4 98.2 99.1 One 99.1 Crack occurrence Comparative Material 5 56.3 82.9 8 67.9 Crack occurrence Comparative Material 6 55.9 86.8 17 64.4 Good Comparative Material7 101.0 104.7 4 96.5 Crack occurrence Comparative Material 8 79.2 81.0 2 97.8 Crack occurrence Comparative Material 9 79.8 82.2 2 97.1 Crack occurrence Comparative Material 10 84.6 85.3 2 99.2 Crack occurrence Comparative Material 11 46.5 72.5 24 64.1 Good

As shown in Table 4, in the case of the inventive materials (1) to (4) in which the chemical composition and the manufacturing conditions satisfy the scope of the present invention, the tensile strength is not less than 80kgf / mm ² , the yield ratio is not less than 80%, the ductility is not less than 10% It was possible to secure the high yield ratio type weather resistant steel having high strength because no cracking occurred during bending.

On the other hand, the comparative materials (1) to (5) which satisfy the chemical composition range of the inventive steel but whose manufacturing conditions are out of the range of the invention failed to obtain the target properties. That is, in the case of the comparative material 2 and the comparative material 5 having higher annealing temperature than the present invention, the tensile strength criterion was satisfied, but as the annealing temperature was high, the yield strength was increased by the second phase generated by the transformation in the cooling step. Yield ratio was lowered to 70% or less. That is, there was a problem in that the deformation resistance was not obtained because the yield ratio of 80% or more could not be obtained.

Comparative material (4) having an annealing temperature lower than the range of the invention was not able to secure ductility and bending workability as most of the deformation grains produced during cold rolling remain. In addition, even in the case of the comparative material (1) in which the hot rolling finish temperature and the coiling temperature were out of the scope of the present invention and the comparative material (3) in which the cooling rate was higher than the invention range, the ductility was less than 5%, so that proper workability could not be secured.

Although Mn and Cr deviated from the composition of the present invention, it was difficult to secure ductility and workability when the manufacturing conditions were made into the present invention range for the comparative steel (1), which had relatively excellent weather resistance (Comparative Material 7). In addition, if the annealing temperature was increased to ensure ductility and workability, yield strength was lowered due to the formation of composite tissues, resulting in a yield ratio of more than 80%.

In the case where the manufacturing conditions change test was carried out for the comparative steels (2) to (3), in which the chemical composition was outside the composition range of the steel of the present invention and the weather resistance could not be secured (Comparative Materials 8 to 11), as shown in Table 4, It was found that the proper range of the material could not be set.

 As described above, according to the present invention, it is possible to provide a steel sheet with high added value such as applications requiring impact resistance, as well as securing weather resistance and mechanical properties at the same time and obtaining a high yield ratio. In addition, as the continuous annealing operation is performed in a relatively low temperature region, energy saving and annealing workability improvement effects can be obtained at the same time.

Claims (3)

By weight%, carbon (C) 0.08 to 0.20%, silicon (Si) 0.1 to 0.5%, manganese (Mn) 0.9 to 2.0%, phosphorus (P) 0.02% or less, sulfur (S) 0.01% or less, aluminum (Al ) 0.02 to 0.07%, niobium (Nb) 0.03 to 0.06%, nickel (Ni) 0.05 to 0.30%, copper (Cu) 0.2 to 0.5%, chromium (Cr) 0.3 to 0.6%, boron (B) 0.001 to 0.004% , Cobalt (Co) 0.02 ~ 0.08% high yield ratio weather resistant cold rolled steel sheet composed of the remaining Fe and other unavoidable impurities. The method of claim 1, The tensile strength of the cold rolled steel sheet is a high yield ratio type weather resistant cold rolled steel, characterized in that more than 80kg / mm ² . By weight%, carbon (C) 0.08 to 0.20%, silicon (Si) 0.1 to 0.5%, manganese (Mn) 0.9 to 2.0%, phosphorus (P) 0.02% or less, sulfur (S) 0.01% or less, aluminum (Al ) 0.02 to 0.07%, niobium (Nb) 0.03 to 0.06%, nickel (Ni) 0.05 to 0.30%, copper (Cu) 0.2 to 0.5%, chromium (Cr) 0.3 to 0.6%, boron (B) 0.001 to 0.004% , Cobalt (Co) 0.02 ~ 0.08%, steel reconstituted with the remaining Fe and other unavoidable impurities, reheated to 1150 ~ 1300 ℃, hot rolled to 850 ~ 950 ℃ finishing rolling temperature and cooled 20 ~ 40 ℃ per second A method of producing a high yield ratio cold rolled steel sheet, which is cooled at a rate and wound at a temperature of 500 to 650 ° C., followed by cold rolling, followed by continuous annealing at a temperature of 500 ° C. or higher to less than A ₁ transformation point.