KR100742931B1 - Non-aging type cold rolled steel sheet with high yield ratio and process for producing the same - Google Patents

Abstract

Provided is a cold rolled steel sheet and a method of manufacturing the same, which improve yield strength and in-plane anisotropy by fine MnS precipitates in Ti-based IF steel.

This cold-rolled steel sheet is, in weight%, C: 0.005% or less, Mn: 0.01-0.3%, S: 0.005-0.08%, Al: 0.1% or less, N: 0.004% or less, P: 0.2% or less, B: 0.0001 -0.002%, Ti: 0.005-0.15%, and is composed of the remaining Fe and other unavoidable impurities,

Mn, S, Ti, N. C is the following relationship, 0 1≤ (Mn / 55) / (S ^★ / 32) ≤ 30, 0.8≤ (Ti ^★ / 48) / (C / 12) ≤ 5.0 Satisfied,

(Where S ^★ = S-0.8x (Ti-0.8x (48/14) xN) x (32/48), Ti ^★ = Ti-0.8x ((48/14) xN + (48/32) xS) ]

The average size of MnS precipitates is less than 0.2㎛.

In the present invention, the fine MnS precipitates are distributed in the IF steel to increase the yield ratio while lowering the in-plane anisotropy.

Automotive material, MnS precipitate, in-plane anisotropy, yield strength, room temperature non-aging

Description

Non-aging cold rolled steel sheet with high yield ratio and its manufacturing method {NON-AGING TYPE COLD ROLLED STEEL SHEET WITH HIGH YIELD RATIO AND PROCESS FOR PRODUCING THE SAME}

Japanese Laid-Open Patent Publication No. 57-0413349

Japanese Unexamined Patent Publication No. 10-158783

The present invention relates to a non-aging cold rolled steel sheet used as a material for automobiles, home appliances, and more particularly, to a cold rolled steel sheet improved in yield strength and in-plane anisotropy by fine MnS precipitates in a Ti-based IF steel. It is about.

Cold rolled steel sheets used in automobiles and home appliances require strength and formability as well as non-aging characteristics. Aging is a kind of strain aging that causes hardening as the solid elements (C, N) adhere to dislocations, leading to a defect called stretcher strain.

The non-aging property of the cold rolled steel sheet can be secured by the annealing of the aluminum-kilted steel, but the annealing has the disadvantage that the annealing time is long and the productivity is low and the material deviation is severe for each part.

Therefore, IF steel (Interstitial Free Steel) which adds strong carbon and nitride forming elements such as Ti and Nb and performs continuous annealing is mainly used. IF steels have a non-aging effect by removing some or all of the carbon and nitrogen employed.

The high-strength method of IF steel is the employment strengthening technology by P. Japanese Laid-Open Patent Publication No. 57-0413349 secures strength by adding 0.04 to 0.12% of P in Ti-added IF steel.

In Japanese Unexamined Patent Publication No. Hei 10-158783, while lowering P, high strength is secured by using a solid solution strengthening element of Mn and Si together. This prior art secures press formability and surface characteristics by controlling hot rolling conditions while securing strength by using Mn as a solid solution strengthening element in Ti or Ti-Nb composite systems. This prior art uses a solid solution strengthening element up to 0.5%, Mn is of high quality, the production cost is increased by the addition of a large amount of Mn, in particular, if the content of Mn increases, the plating properties are not good. This prior art makes no mention of the characteristics of in-plane anisotropy and yield strength. Considering the use of Mn as an element for strengthening employment, the characteristics of high yield ratio cannot be obtained.

It is an object of the present invention to provide a cold rolled steel sheet and a method of manufacturing the same, which can lower in-plane anisotropy while enhancing yield strength by fine MnS precipitates.

Cold rolled steel sheet of the present invention for achieving the above object, by weight, C: 0.005% or less, Mn: 0.01-0.3%, S: 0.005-0.08%, Al: 0.1% or less, N: 0.004% or less, P : 0.2% or less, B: 0.0001-0.002%, Ti: 0.005-0.15%, and is composed of the remaining Fe and other unavoidable impurities,

Mn, S, Ti, N. C is the following relationship, 0 1 ≤ (Mn / 55) / (S ^★ / 32) ≤ 30, 0.8 ≤ (Ti ^★ / 48) / (C / 12) ≤ 5.0 Satisfied,

(Where S ^★ = S-0.8x (Ti-0.8x (48/14) xN) x (32/48), Ti ^★ = Ti-0.8x ((48/14) xN + (48/32) xS) ]

 The average size of the MnS precipitates is 0.2 μm or less.

In the present invention, the fine MnS precipitate is preferably ¹ × 10 ⁵ / mm ² or more, more preferably 1 × 10 ⁶ / mm ² or more. Moreover, it is most preferable that said (Mn / 55) / (S ^* / 32) shall be 1-6. The content of Mn is preferably in the range of 0.01-0.12%.

The cold rolled steel sheet of the present invention has the characteristics of a soft cold rolled steel sheet of 280MPa grade and high strength cold rolled steel sheet of 340MPa or more according to the component design.

When the content of P in the above component system is 0.015% or less, a soft cold rolled steel sheet of 280 MPa grade is obtained. The cold rolled steel sheet further contains one or two of the solid solution strengthening elements Si and Cr, or when the P content is 0.015 to 0.2%, high strength characteristics of 340 MPa or more are secured. In the case of high strength steel containing P alone, the content of P is preferably 0.03 to 0.2%. 0.1-0.8% for Si and 0.2-1.2% for Cr are preferred. In the case of containing at least one of Si and Cr, the content of P may be variously designed in the range of 0.2% or less.

If you want to improve the workability in the cold rolled steel sheet of the present invention may further comprise Mo 0.01 ~ 0.2%.

In the method for producing a cold rolled steel sheet, the slab that satisfies the component system of the present invention is reheated to a temperature of 1100 ° C. or higher, and then hot-rolled at a finish rolling temperature of Ar ₃ or higher and cooled at a speed of 300 ° C./min or higher, and 700 ° C. After winding up at the following temperature, it cold-rolls and continuously anneales.

Hereinafter, the present invention will be described in detail.

The present invention is completed on the basis of the research results that the fine grain of MnS precipitate is secured in the Ti-based IF steel to improve the yield strength and lower the in-plane anisotropy index to improve the workability.

In the IF steel, Mn is a solid solution strengthening element and is added in large amounts up to 0.5% to secure strength. Japanese Unexamined Patent Publication No. Hei 10-158783 is added up to 0.5%, and the embodiment is added at 0.15% or more. In this prior art, as a Ti-based IF steel, S is precipitated as TiS, so Mn is precipitated as fine MnS. In order to achieve this, management of all components is necessary, but it is not done so that Mn acts as a solid solution strengthening element.

In the present invention to secure a fine MnS in the IF steel. S preferentially reacts with Ti and Zr to precipitate most of them. Since the IF steel of the present invention is Ti-added IF steel, Ti reacts with C, N, and S. Therefore, it is necessary to manage the general components so that S precipitates as MnS.

According to the present invention, when the grain is refined by the fine MnS precipitate, the solid solution carbon is more present in the grain boundary than in the grain, thereby ensuring room temperature non-aging characteristics. The dissolved carbon remaining in the grain is relatively free to move, so it does not affect the room temperature aging characteristics in combination with the operating potential. In addition, the finely distributed MnS precipitates according to the present invention have a positive effect on the increase in yield strength and the strength-ductility balance characteristics due to precipitation strengthening, and in-plane anisotropy and plastic anisotropy. For this purpose, if the MnS precipitates should be finely distributed, this may affect the content of Mn and S, their component ratio conditions, and the cooling rate after the hot rolling.

Cold rolled steel sheet of the present invention has a high yield strength can reduce the thickness of the steel sheet has a light weight effect. In addition, the in-plane anisotropy has the advantage of less wrinkles generated during processing and less ear generation after processing. The cold rolled steel sheet of the present invention and a manufacturing method thereof will be described in detail below.

First, C, Mn, S, Al, P, N, B, and Ti, which are basic components, will be described.

The content of carbon (C) is preferably 0.005% or less.

When the carbon content exceeds 0.005%, a large amount of expensive Ti must be added to remove the solid solution carbon which greatly degrades aging and plastic anisotropy. In this case, the manufacturing cost rises and the recrystallization temperature increases. Therefore, the annealing temperature should be increased, otherwise the crystal grains of the annealing plate become fine and the ductility is greatly lowered, and the plating property is also lowered during plating. More preferable content of carbon (C) is 0.003% or less. Preferably, the lower limit of the content of carbon (C) is made 0.0005%. If the content of carbon (C) is less than 0.0005%, the grains of the hot rolled sheet are coarse to lower the strength and to increase the in-plane anisotropy.

The content of manganese (Mn) is preferably 0.01-0.3%.

Manganese is known as MnS to prevent hot shortness caused by solid sulfur by precipitating sulfur in solid state in steel. From this technical point of view, it is common to add a high content of manganese. However, in the present invention, when the sulfur content is appropriate while lowering the content of manganese, MnS precipitates very finely, thereby improving the properties of plastic anisotropy and in-plane anisotropy by grain refinement and improving the yield strength characteristics by precipitation strengthening. Based on the research results, the content of manganese should be less than 0.3%. In order to secure these characteristics, the content of manganese should be 0.01% or more. If the content is less than 0.01%, red brittleness may occur due to the large amount of sulfur remaining in the solid state, and the content of manganese exceeds 0.3%. In the case of, the content of manganese is high and coarse MnS precipitates are formed, making it difficult to secure strength. More preferably, the content of Mn is 0.01-0.12%.

The content of sulfur (S) is preferably 0.005-0.08%.

Sulfur (S) reacts with Mn to form fine MnS precipitates. When the content of S is less than 0.005%, not only the amount of precipitates precipitated is small but also the number of precipitates precipitated is very small. If the content of sulfur is more than 0.08%, the content of the solid solution of sulfur is so high that the ductility and formability is greatly lowered, there is a fear of red brittleness.

The content of aluminum (Al) is preferably 0.1% or less.

Aluminum is an element added as a deoxidizer, but it is added to precipitate nitrogen in the steel to completely prevent aging by solid nitrogen. If the aluminum content is more than 0.1%, the amount of aluminum present in the solid solution state is high, thereby reducing the ductility. Preferred Al content is 0.01-0.1%.

The content of nitrogen (N) is preferably 0.004% or less.

Nitrogen is an element that is inevitably added during steelmaking, and is preferably managed at 0.004% or less.

The content of phosphorus (P) is preferably 0.2% or less.

Phosphorus is an element having a high solid solution strengthening effect and a small decrease in r value, and guarantees high strength in steels for controlling precipitates according to the present invention. In steel grades requiring strength of 280 Mpa, the content of P should be less than 0.015%. For high strength steel of 340Mpa or higher, it is recommended to set it as 0.016 ~ 0.2%. If the content of P is more than 0.2%, it is preferable that the ductility is lowered to limit the upper limit to 0.2%. In the present invention, when Si and Cr are added, various strength designs are possible while the content of P is in the range of 0.2% or less.

The content of boron (B) is preferably 0.0001 to 0.002%.

Boron is added to prevent secondary processing brittleness. For this purpose, the boron content is preferably 0.0001% or more. If the boron content exceeds 0.002%, deep drawing may be greatly degraded.

The content of titanium (Ti) is to be 0.005 ~ 0.15%.

Titanium is added for the purpose of securing inaging and improving moldability. Titanium is a strong carbide-generating element and is added to steel to precipitate TiC precipitates to precipitate insoluble solids. If the addition amount of titanium is less than 0.005%, the precipitation amount of TiC precipitate is too small, and there is little effect of improving the processability of the soil because of less development of the texture. If Ti exceeds 0.15%, the TiC precipitates are too large to reduce the grain refining efficiency, resulting in an increase in in-plane anisotropy, lowering the yield strength and greatly degrading the plating properties.

In the present invention, the content of Mn, S, Ti, N, C in order to secure the MnS precipitate is managed as follows. In the following relationship, each component is used in weight%.

[Relationship 1]

1≤ (Mn / 55) / (S ^★ / 32) ≤30

 [Relationship 2]

S ^★ = S-0.8x (Ti-0.8x (48/14) xN) x (32/48)

In relation 1, S ^★ is the content of S remaining without reacting with Ti and reacting with Mn. S ^★ is determined by relation 2. In order to secure a fine MnS precipitate, the value of the relational expression 1 is preferably 1 or more. If the value of relation 1 is greater than 30, coarse MnS precipitates are distributed, which is not preferable. In order to stably secure MnS of 0.2 µm or less, the value of relation 1 is more preferably 1-20, 1-9, and most preferably 1-6.

In the present invention, carbon is precipitated as TiC. Therefore, the room temperature aging characteristics are affected by the conditions of the solid solution carbon not precipitated by TiC. In consideration of this, it is most preferable that Ti and C satisfy the following conditions.

[Relationship 3]

0.8≤ (Ti ^★ / 48) / (C / 12) ≤5.0,

[Relationship 4]

Ti ^★ = Ti-0.8x ((48/14) xN + (48/32) xS)

Equation 3 is to secure room temperature non-aging characteristics by precipitating TiC to remove carbon in solid solution. In relation 3, Ti ^* is the content of Ti reacting with N and S in the total Ti content and remaining with C. Ti ^* is determined by the relation 4

If the value of the relation 3 is less than 0.8, it is difficult to secure the room temperature non-aging characteristics, and if the value of the relation 3 exceeds 5, the amount of Ti remaining in the solid solution state in the steel is high, the ductility is lowered.

In the component system of the present invention, the finer the distribution, the more advantageous. Preferably, the average size of the MnS precipitate is 0.2 μm or less. According to the results of the present invention, especially when the average size of the precipitate is more than 0.2㎛, the strength is low, the in-plane anisotropy index is not good.

Furthermore, although the precipitate of 0.2 micrometer or less is distributed in a large amount in the component system of this invention, the distribution number is not specifically limited. Preferably, the number of distribution of precipitates is at least 1 × 10 ⁵ , more preferably at least 1 × 10 ⁶ per mm ² . The larger the distribution number of precipitates, the higher the plastic anisotropy index and the lower in-plane anisotropy index are. In general, when the plastic anisotropy index increases, the in-plane anisotropy index rises and there is a limit to increasing the plastic anisotropy index in terms of processability. .

In the present invention, when applied to a high-strength steel sheet of 340 MPa grade or more, one or two or more solid solution strengthening elements such as P, that is, P, Si, and Cr may be added. As described above with respect to P, redundant descriptions are omitted.

The content of silicon (Si) is preferably 0.1-0.8%.

Si is an element having a high solid solution strengthening effect and a low drop in elongation, which ensures high strength in steels for controlling precipitates according to the present invention. When the content of Si is more than 0.1% to secure the strength, in the case of more than 0.8% ductility is reduced.

The content of chromium (Cr) is preferably 0.2 to 1.2%.

Cr is an element that lowers the secondary brittleness temperature and decreases the aging index by Cr carbide while having a high solid-solution strengthening effect, and assures high strength in steels for controlling precipitates according to the present invention and also lowers in-plane anisotropy index. The Cr content is more than 0.2% to secure the strength, in the case of more than 1.2% ductility is reduced.

In the cold rolled steel sheet of the present invention, molybdenum (Mo) may be further added.

The content of molybdenum (Mo) is preferably 0.01 to 0.2%.

Mo is added as an element to increase the plastic anisotropy index, the content of the plastic anisotropy index is increased when the content is more than 0.01%, if the content exceeds 0.2%, the plastic anisotropy index is no longer increased and there is a risk of causing hot brittleness.

The cold rolled steel sheet obtained according to the present invention satisfies 58% or more of yield ratio (yield strength / tensile strength) while sufficient workability (ductility, plastic anisotropy index).

[Manufacturing method of cold rolled steel sheet]

The present invention is characterized in that an average size of MnS precipitates in a cold rolled sheet is hot and cold rolled to satisfy the above-described stress. The average size of MnS precipitates in cold rolled plates is influenced by the component design and manufacturing processes such as reheating temperature and coiling temperature, but especially by the cooling rate after hot rolling.

[Hot Rolling Condition]

In the present invention, the steel that satisfies the above-mentioned emphasis is reheated and hot rolled. The reheating temperature is preferably 1100 ° C or more. This is because when the reheating temperature is lower than 1100 ° C., the coarse precipitates generated during continuous casting remain completely insoluble due to the low reheating temperature, so that many coarse precipitates remain even after hot rolling.

Hot rolling is preferably carried out under the conditions of the finish rolling temperature higher than the Ar ₃ transformation temperature. This is because when the finish rolling temperature is lower than the Ar ₃ transformation temperature, not only the workability is reduced by the formation of the rolled grain but also the strength is lowered.

It is preferable that the cooling rate before winding after hot rolling shall be 300 degreeC / min or more. Even if the component ratio is controlled to obtain a fine precipitate according to the present invention, if the cooling rate is less than 300 ° C / min, the average size of the precipitate may exceed 0.2 ㎛. In other words, as the cooling rate increases, a large number of nuclei are generated and the precipitate becomes fine. The faster the cooling rate, the finer the precipitate is, so it is not necessary to limit the upper limit of the cooling rate.However, even if the cooling rate is faster than 1000 ° C / min, the finer effect of the precipitate is no longer increased, so the cooling rate is 300 to 1000 ° C / min. This is more preferable.

[Coiling condition]

Winding is performed after hot rolling as above, but the winding temperature is preferably 700 ° C or lower. If the coiling temperature exceeds 700 ℃, precipitates grow too coarse, making it difficult to secure strength.

[Cold rolling condition]

Cold rolling is preferably performed at a reduction ratio of 50 to 90%. If the cold reduction rate is less than 50%, the amount of nucleation of the annealing recrystallization is small, so that grains grow too large during annealing, resulting in a decrease in strength and formability due to coarsening of the annealing recrystallization grains. If the cold reduction ratio is more than 90%, the moldability is improved, but the nucleation amount is too high, so the annealing recrystallized grain is too fine to decrease the ductility.

[Continuous Annealing]

Continuous annealing temperature plays an important role in determining the material of the product. In this invention, it is preferable to carry out in the temperature range of 700-900 degreeC. If the continuous annealing temperature is less than 700 ° C., recrystallization is not completed and the target ductility value cannot be secured. If the annealing temperature is more than 900 ° C., the strength decreases due to coarsening of the recrystallized grains. The continuous annealing time keeps the recrystallization complete. If it is about 10 seconds or more, the recrystallization is completed. Preferably the continuous annealing time is in the range of 10 seconds to 30 minutes,

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

Example 1

The steel slabs of Table 1 were reheated, hot rolled to finish, cooled to 400 ° C./min, wound up at 650 ° C., and then cold rolled and continuously annealed at a reduction rate of 75%. The finish rolling temperature of not less than Ar ₃ transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 830 ℃ to 10 ℃ / second.

The obtained annealing plate was processed into a standard specimen according to ASTM E-8 standard to investigate the mechanical properties. The specimen was measured for yield strength, tensile strength, elongation, plastic anisotropy index (r _m value), in-plane anisotropy index (Δr value) and aging evaluation index using a tensile tester (INSTRON, Model 6025). Where r _m = (r ₀ + 2r ₄₅ + r ₉₀ ) / 4, △ r = (r ₀ -2r ₄₅ + r ₉₀ ) / 2, and the aging evaluation index is 100 ° C for 1.0% skin pass-rolled specimen after annealing X 2hr. Yield point elongation rate measured after heat treatment.

sample Chemical composition (% by weight) C Mn P S Al Ti B N Etc A1 0.0009 0.11 0.008 0.022 0.039 0.035 0.0007 0.0008 A2 0.0013 0.08 0.032 0.031 0.043 0.049 0.0009 0.0021 Si: 0.15 A3 0.0025 0.11 0.058 0.043 0.028 0.067 0.0005 0.0019 Si: 0.33 A4 0.0017 0.09 0.082 0.037 0.047 0.057 0.0011 0.0023 Si: 0.24 Mo: 0.082 A5 0.0016 0.1 0.118 0.052 0.022 0.075 0.0012 0.001 Si: 0.31 Cr: 0.13 A6 0.0035 0.45 0.048 0.009 0.033 0 0.005 0.0024 A7 0.0031 0.13 0.118 0.012 0.038 0.15 0 0.0021 Si: 0.33

sample S ^* (Mn / 55) / (S ^* / 32) (Ti ^★ / 48) / (C / 12) Average size of precipitate (㎛) Number of precipitates (pcs / mm ² ) A1 0.0045 14.211 1.78 0.06 3.3 X 10 ⁵ A2 0.0079 5.8631 1.16 0.06 3.6 X 10 ⁵ A3 0.01 6.3706 1.02 0.05 3.8X10 ⁶ A4 0.01 5.255 0.93 0.05 3.6 X 10 ⁶ A5 0.0135 4.3217 1.54 0.05 3.8X10 ⁶ A6 0.0125 20.927 -1.2 0.26 2.6 X 10 ³ A7 -0.065 -1.165 10.5 0.06 4.5 X 10 ⁵ S ^★ = S-0.8x (Ti-0.8x (48/14) xN) x (32/48) Ti ^★ = Ti-0.8x ((48/14) xN + (48/32) xS)

Sample Number Mechanical properties Remarks Yield strength (MPa) Tensile Strength (MPa) Elongation (%) Plastic Anisotropy Index (r _m ) In-plane anisotropy index (Δr) Aging Evaluation Index (%) 2nd processing brittleness (DBTT- ℃) A1 189 295 49 2.21 0.35 0 -50 Invention steel A2 209 332 45 1.93 0.28 0 -50 Invention steel A3 315 362 41 1.96 0.22 0 -50 Invention steel A4 234 380 36 1.75 0.24 0 -40 Invention steel A5 238 407 38 1.63 0.21 0 -50 Invention steel A6 243 339 44 1.38 0.42 3.6 -40 Comparative steel A7 225 404 38 1.79 0.43 0 -40 Comparative steel

In the present invention, the above embodiment is only one example, and the present invention is not limited thereto. Anything that has substantially the same configuration as the technical idea described in the claims of the present invention and achieves the same operation and effect is included in the technical scope of the present invention.

As described above, the present invention is intended to refine the grains by distributing fine MnS precipitates in the IF steel, thereby lowering the in-plane anisotropy index and increasing yield strength by strengthening MnS precipitation.

Claims (12)

delete By weight%, C: 0.005% or less, Mn: 0.01-0.3%, S: 0.005-0.08%, Al: 0.1% or less, N: 0.004% or less, P: 0.2% or less, B: 0.0001-0.002%, Ti : 0.005-0.15%, and is composed of the remaining Fe and other unavoidable impurities, Mn, S, Ti, N. C is the following relationship, 0 1≤ (Mn / 55) / (S ^★ / 32) ≤ 30, 0.8≤ (Ti ^★ / 48) / (C / 12) ≤ 5.0 Satisfied, (Where S ^★ = S-0.8x (Ti-0.8x (48/14) xN) x (32/48), Ti ^★ = Ti-0.8x ((48/14) xN + (48/32) xS) ] The average size of MnS precipitates is less than 0.2㎛ The precipitate water is 1 X 10 ⁶ / mm ² or more, characterized in that the non-aging cold rolled steel sheet. The high yield ratio non-aging cold rolled steel sheet according to claim 2, wherein the Mn content is 0.01-0.12%. The high yield ratio non-aging cold rolled steel sheet according to claim 2, wherein (Mn / 55) / (S ^★ / 32) is 1-6. The high yield ratio non-aging cold rolled steel sheet according to claim 2, further comprising one or two of Si: 0.1 to 0.8% and Cr: 0.2 to 1.2%. The high yield ratio non-aging cold rolled steel sheet according to claim 2 or 5, wherein Mo is further contained 0.01 to 0.2%. delete By weight%, C: 0.005% or less, Mn: 0.01-0.3%, S: 0.005-0.08%, Al: 0.1% or less, N: 0.004% or less, P: 0.2% or less, B: 0.0001-0.002%, Ti : 0.005-0.15%, and is composed of the remaining Fe and other unavoidable impurities, Mn, S, Ti, N. C is the following relationship, 0 1≤ (Mn / 55) / (S ^★ / 32) ≤ 30, 0.8≤ (Ti ^★ / 48) / (C / 12) ≤ 5.0 Satisfying slabs, (Where S ^★ = S-0.8x (Ti-0.8x (48/14) xN) x (32/48), Ti ^★ = Ti-0.8x ((48/14) xN + (48/32) xS) ] After reheating to 1100 ℃ or higher, hot rolling with the finish rolling temperature above Ar ₃ transformation point, cooling at 300 ℃ / min or higher, winding at temperature below 700 ℃, and cold rolling at 50 ~ 90% reduction rate And, a continuous annealing for 10 seconds to 30 minutes in the temperature range of 700 ~ 900 ℃, MnS precipitates of less than 0.2㎛ average distribution of 1x10 ⁶ / mm ² or more method of producing a high yield ratio non-aging cold rolled steel sheet. The method of claim 8, wherein the Mn content is 0.01-0.12%. The method of claim 8, wherein the (Mn / 55) / (S ^★ / 32) is 1-6. The method of manufacturing a high yield ratio non-aging cold rolled steel sheet according to claim 8, further comprising one or two of Si: 0.1 to 0.8% and Cr: 0.2 to 1.2%. The method for producing a high yield ratio non-aging cold rolled steel sheet according to claim 8 or 11, wherein Mo is further contained 0.01 to 0.2%.