KR20090068871A - High strength steel sheet having excellent yield strength and low temperature toughness and manufacturing method thereof - Google Patents

Abstract

A high-strength steel plate having excellent yield strength and low temperature toughness, and the manufacturing method thereof are provided to supply a high-strength steel plate having excellent yield strength and low temperature toughness with low expenses by optimizing and controlling component systems and deposits, and controlling hot rolling conditions. A high-strength steel plate having excellent yield strength and low temperature toughness comprises 0.03~0.1 weight percent C, 0.01~0.5 weight percent Si, 1.2~2.0 weight percent Mn, less than 0.02 weight percent S, 0.01~0.1 weight percent Nb, 0.01~0.1 weight percent Ti, less than 0.01 weight percent N, 0.1~0.5 weight percent Mo, 0.1~0.5 weight percent Ni, 0.01~0.1 weight percent V, 0.1~0.5 weight percent Cr, other inevitable impurities and Fe, wherein the Ti, Nb, C and N satisfy the relations as follows: 0.13<= (Ti*/48+Nb*/93)/(C/12) <= 0.25, 0.13<= (Ti*/48+Nb*/93)/(C/12) <= 0.25, 0.24 <= (V/51)/(C*/12) <= 1.6, 0.24 <= (V/51)/(C*/12) <= 1.6, 6<= (Mo/96)/(P/31) <= 30, 6<= (Mo/96)/(P/31) <= 30, and Ti* = Ti - 0.7*(48/14)N, Nb* = Nb-0.7*(93/14)N, C* = C - 0.7*[(Nb-0.7*(93/14)N) + (Ti-0.7*(48/14)N)]. A manufacturing method of a high-strength steel plate comprises the steps of re-heating the high-strength steel plate at 1100~1350°C, going through recystallization and non-recrystallization hot rolling processes within the range of 950~1100°C, going through a hot rolling process for finishing in the reduction ratio of more than 60% at 780~880°C, going through a water cooling process at a velocity of 10~50°C/sec on a run-out table, and winding at 400~600°C.

Description

High Strength Steel Sheet having Excellent Yield Strength and Low Temperature Toughness and Manufacturing Method Thereof}

The present invention relates to a high-strength tough tough hot rolled steel used in construction, pipelines and offshore structures, and to a method for manufacturing the same. More specifically, a composite addition of Nb, V, Mo, and Ti, and appropriately control the hot rolling process By improving the yield strength by the microstructure and precipitation of (Ti, Nb) C, NbC, VC, and the like, the present invention relates to a hot-rolled API steel and a method for manufacturing the same, which simultaneously improve low-temperature toughness by inhibiting P segregation using Mo.

When using steel pipes for oil or gas transportation, the transportation pressure is increased to increase the transportation efficiency. Recently, the transportation pressure has reached 120 atm. In order to withstand such transport pressure, the thickness of the pipe must be sufficiently thick, but as the thickness of the steel increases, the amount of rolling reduction during rolling is insufficient, and the ferrite grains may be coarse because it is difficult to secure a sufficient cooling rate in the central portion of the steel. Therefore, there exists a problem that strength and low-temperature toughness fall.

In order to solve this problem, conventionally, a technique of properly controlling the ratio of Ti and N in the component system to prevent initial austenite grain growth during slab heating to obtain fine ferrite to secure strength and low temperature toughness at the same time has appeared. Furnace is difficult to secure sufficient strength in the thick material of 18mm or more, and also can not prevent the diffusion of P remaining in the slab to the grain boundary may promote grain boundary brittleness after the hot-rolled steel winding.

Therefore, in order to secure the strength and toughness of the thick material at the same time, it is important to prevent coarsening of the structure and to secure additional strength and toughness by fully utilizing the precipitates and alloying elements.

The present invention is to solve the above problems and to optimize the hot rolling conditions in order to ensure sufficient strength even in hot rolled steel having a thickness of 18mm or more and to adjust the ratio of Ti, Nb, V, C, Mo and P in the component system to the API specification. The present invention provides a method for producing a steel material for thick high-strength hot rolled line pipe having a suitable yield strength.

In the present invention, by weight%, C: 0.03-0.1%, Si: 0.01-0.5%, Mn: 1.2-2.0%, S: 0.02% or less, Nb: 0.01-0.1%, Ti: 0.01-0.1%, N: 0.01% or less, Mo: 0.1-0.5%, Ni: 0.1-0.5%, V: 0.01-0.1%, Cr: 0.1-0.5%, and other unavoidable impurities and the balance Fe, the Ti, Nb, C, N Between and.

0.13 ≦ (Ti * / 48 + Nb * / 93) / (C / 12) ≦ 0.25;

0.24 ≦ (V / 51) / (C * / 12) ≦ 1.6; And

6 ≦ (Mo / 96) / (P / 31) ≦ 30;

(Wherein Ti * = Ti-0.7 * (48/14) N, Nb * = Nb-0.7 * (93/14) N, C * = C-0.7 * [(Nb-0.7 * (93/14) N ) + (Ti-0.7 * (48/14) N)])

It provides a high strength steel sheet characterized by satisfying the relationship.

Furthermore, the present invention is a reheating step of reheating to 1100 ~ 1350 ℃ for steel slab having the above-described component system, recrystallized and unrecrystallized rolling in the range of 950 ~ 1100 ℃, a reduction ratio of 60% or more at 780 ~ 880 ℃ It provides a method of producing a high strength steel sheet comprising a step of hot rolling to finish, a step of water cooling at a rate of 10 ~ 50 ℃ / sec on the run-out table and the winding step of winding at 400 ~ 600 ℃.

In the case of optimizing and controlling the component system and the precipitate as in the present invention and adjusting the hot rolling conditions, it is possible to provide a high strength steel sheet having excellent yield strength and low temperature toughness at a low cost.

The present inventors secured the strength of the thick material without the formation of low temperature transformation tissue such as bainite, and analyzed the method of improving the low temperature toughness, and well controlled the ratio of Ti, Nb, V and C to maximize the formation of precipitates. In addition, it was confirmed that toughness can be increased by suppressing the grain boundary segregation of P, which promotes grain boundary fracture at low temperature, using Mo.

In addition, when using such alloying elements, the precipitation rate and aspect of the precipitates are different depending on the rolling temperature and rolling reduction, so that it is also necessary to optimize the ratio of each component. The present invention has been completed to secure the strength and low temperature toughness of the above thick hot rolled material simultaneously.

Hereinafter, the present invention will be described in more detail.

The basic configuration of the present invention is as follows.

1. Refine the ferrite of steel by control rolling and secure the strength in the material after using precipitate.

2. Component-based composition satisfying 0.13 ≦ (Ti * / 48 + Nb * / 93) / (C / 12) ≦ 0.5, 0.24 ≦ (V / 51) / (C * / 12) ≦ 3.

Provided that Ti * = Ti-0.7 * (48/14) N, Nb * = Nb-0.7 * (93/14) N and

C * = C-0.7 * [(Nb-0.7 * (93/14) N) + (Ti-0.7 * (48/14) N)] is satisfied and the average size of precipitates is 0.2㎛ or less (Ti, Nb) C, NbC, VC precipitates are formed to secure the yield strength of thick materials

3. Securing low temperature toughness by suppressing grain boundary segregation of P by controlling Mo satisfying 6≤ (Mo / 96) / (P / 31) ≤30

In the case of a thick material having a thickness of 18 mm or more, as in the present invention steel, it is necessary to refine the final ferrite in order to secure the yield strength and to secure the strength by using a precipitate. In this case, Ashby-Orowan expressed the yield strength (σy) of the steel as shown in the following formula (1) by modifying the Hall-Petch equation.

^{σy = σi + KD -1/2 + (} 10.8f 1/2 /X)(ln(X/6.125*10 -4)) ------ (1)

Where σ i is friction stress, K is strength factor, D is grain size, f is precipitate fraction, and X is precipitate size.

According to Equation (1), the yield strength of the steel increases as the grain size decreases, the amount of precipitates increases and the size of precipitates decreases. As the final thickness of the steel becomes thicker, the total rolling reduction decreases. Therefore, in order to refine the ferrite structure, it is necessary to secure a certain amount of unrecrystallized reverse rolling reduction. lost. It is also important to use appropriate precipitates to counteract the ferrite coarsening effect of reduced rolling reduction.

Precipitates affecting the yield strength of steel are mainly precipitated in the temperature range where ferrite is formed, so the formation temperature of each precipitate is determined by thermodynamic equilibrium. In general, the precipitation temperature of TiC precipitate is the highest, and the precipitation temperature decreases in the order of NbC and VC. In addition, when Ti and Nb are added together, the composite precipitate of the (Ti, Nb) C type and NbC are simultaneously precipitated, and V is likely to exist as a single precipitate due to the relatively low precipitation temperature. Therefore, in order to secure the strength by fully utilizing the added Ti, Nb, and V, it is required to adjust the amounts of Ti, Nb, and C so that V can be precipitated even after (Ti, Nb) C and NbC are precipitated. .

In addition, P is a representative element that, together with Sb, Sn and As, segregates at grain boundaries and weakens the bonds between grains, thereby causing temper brittleness. In particular, if the coil is maintained between 370 ~ 600 ℃ during rolling or slow cooling, P is diffused to the grain boundary, the low-temperature toughness degradation phenomenon that the impact energy is reduced.

However, when Mo is added together, it forms a Fe-Mo-P compound to prevent P from segregating at the grain boundary, thereby preventing grain embrittlement due to P segregation. However, when Mo is added to 0.5% or more, the hardenability of the steel is too high to form a low-temperature transformation phase to reduce the impact toughness, so care must be taken in adding Mo.

EMBODIMENT OF THE INVENTION Hereinafter, the component system which comprises this invention is demonstrated in detail. (Hereinafter by weight)

Content of carbon (C): 0.03 ~ 0.1%

C is the most economical and effective element for reinforcing steel, but the weldability, formability and toughness are reduced by the addition of a large amount, and in the present invention, C is limited to 0.03-0.10%. When the amount of C added is less than 0.03%, it is not economical because other alloy elements must be added in a relatively large amount to obtain the same strength, and when it is added in excess of 0.10%, weldability, formability and toughness may be reduced.

Silicon (Si) content: 0.01 ~ 0.5%

Si is also needed to deoxidize molten steel and serves as a solid solution strengthening element, so an amount of 0.01 to 0.50% is required. If the added amount is less than 0.01%, it is difficult to obtain clean steel because it does not sufficiently deoxidize the molten steel.If it is added more than 0.5%, the red scale is formed by Si during hot rolling, and the surface shape of the steel sheet becomes very bad and the ductility is also reduced. Because it is not desirable.

Manganese (Mn) content: 1.2 to 2.0%

Mn is an effective element to solidify the steel to be added more than 1.2% can exhibit high strength with an increase in the hardenability. However, if the content exceeds 2.0%, the upper limit is set to 2.0% because segregation is greatly developed at the center of thickness during casting of the slab in the steelmaking process and the weldability of the final product is deteriorated.

Sulfur (S) content: 0.02% or less

S is also an impurity element present in the steel and forms a non-metallic inclusion by combining with Mn and the like, and thus it is desirable to reduce it as much as possible because it greatly impairs the toughness and strength of the steel. Therefore, the upper limit is set to 0.02%.

Niobium (Nb) content: 0.01 ~ 0.1%

Nb is a very useful element for refining grains and at the same time, it should be added at least 0.01% because of the dynamics that greatly improve the strength of the steel, but if it exceeds 0.1%, excessive Nb carbonitride is precipitated, which is detrimental to the toughness of the steel. Therefore, limit to 0.01 ~ 0.1%.

Ti content: 0.01 ~ 0.1%

Ti is an element useful for miniaturizing crystal grains. It exists as TiN in steel and has the effect of inhibiting the growth of grains during heating for hot rolling. Also, Ti remaining after being reacted with nitrogen is dissolved in carbon to bond with carbon to precipitate TiC. Is formed and the formation of TiC is very fine, greatly improving the strength of the steel. Therefore, in order to obtain the effect of inhibiting austenite grain growth due to TiN precipitation and increasing the strength due to TiC formation, at least 0.01% of Ti should be added, but if more than 0.1% is added, the steel sheet is welded and melted to the melting point when manufacturing the steel pipe. As the TiN is re-used, the toughness of the weld heat affected zone deteriorates, so the upper limit of Ti addition is made 0.1%.

Nitrogen (N) content: 0.01% or less

The reason for component limitation of N is attributable to the above Ti addition. In general, N is dissolved in the steel and precipitates to increase the strength of the steel, which is much greater than carbon. On the other hand, however, the more nitrogen is present in the steel, the toughness can be greatly reduced, and it is a general trend to reduce the nitrogen content as much as possible. However, in the present invention, a proper amount of nitrogen is present to react with Ti to form TiN, thereby imparting a role of inhibiting grain growth during reheating. However, when a part of Ti is left without reacting with N, the upper limit is made 0.01% because the strength of the steel may be reduced by reacting with carbon in a subsequent step.

Molybdenum content: 0.1 ~ 0.5%

Mo is very effective in increasing the strength of the material, and serves to lower the yield ratio by promoting the formation of acicular ferrite, a low temperature metamorphic tissue. In addition, cementite and carbide are integrated to exhibit deteriorated impact characteristics and to suppress formation of pearlite tissues that contribute to lowering the yield strength after piping, thereby reducing good impact toughness and lowering yield strength after piping. To this end, Mo is added 0.1% or more, but Mo is an expensive element, and the upper limit is limited to 0.5% in order to prevent welding low temperature cracking, and to prevent the low-temperature transformation phase is generated in the base material to reduce the toughness.

Nickel (Ni) content: 0.1 ~ 0.5%

Ni is an austenite stabilizing element that suppresses the formation of pearlite, and is an element that facilitates the formation of acicular ferrite, which is a low-temperature metamorphic structure, and is added in an amount of 0.1% or more. Limited to 0.5% or less.

Vanadium (V) content: 0.01 ~ 0.1%

V has a similar effect to Nb. Particularly, when V is added together with Nb, a remarkable effect is generated, and since the strength of the steel according to the present invention is further increased, 0.01% or more should be added. However, when the content is excessively greater than 0.1%, excessive V carbonitride This precipitate is detrimental to the toughness of the steel, and is limited to 0.01 to 0.1% in view of the toughness of the weld heat affected zone and consequently on-site weldability.

Content of chromium (Cr): 0.1 ~ 0.5%

Cr generally increases the hardenability of the steel during direct quenching. In addition, this generally improves corrosion resistance and hydrogen cracking resistance, and like Mo, it is possible to suppress the formation of pearlite structure and obtain good impact toughness. To this end, Cr should be added at least 0.1%, but it is preferable to limit the content to 0.5% or less since excessive tendency may cause cooling cracks after spot welding and deteriorate the steel and its HAZ toughness.

The relationship between the important component systems among the components constituting the present invention is as follows.

[Relationship 1]

0.13≤ (Ti * / 48 + Nb * / 93) / (C / 12) ≤ 0.25

[Relationship 2]

Ti * = Ti-0.7 * (48/14) N

[Relationship 3]

Nb * = Nb-0.7 * (93/14) N

The relationship 1 is to secure a fine (Ti, Nb) C precipitate. In relation 1, Ti * and Nb * is a content of reacting with N and remaining with C in the total content of Ti and Nb. Ti * and Nb * are determined by the relations 2 and 3 above. In order to secure a fine (Ti, Nb) C precipitate, it is preferable that the value of the relational formula 1 satisfies 0.13 to 0.25. When the value of the relation 1 is 0.13 or more, effective (Ti, Nb) C and NbC precipitates are precipitated. On the other hand, in case of more than 0.25, (Ti, Nb) C and NbC precipitates are coarse, which is not good for securing strength, and the amount of C which can be combined with V to make VC is reduced, so that sufficient strength cannot be obtained. .

[Relationship 4]

0.24 ≤ (V / 51) / (C * / 12) ≤ 1.6

[Relationship 5]

C * = C-0.7 * [(Nb-0.7 * (93/14) N) + (Ti-0.7 * (48/14) N)]

The relation 4 is to secure a fine VC precipitate. In relation 4, C * is the amount of C that reacts with TI, Nb and remains with V in the total C content. C * is determined by relation 5 above. When the value of the relation 4 is less than 0.24, it is difficult to secure sufficient VC precipitates, and when the value of the relation 4 exceeds 1.6, VC precipitates become coarse or, like Ti and Nb precipitates, the number of precipitates decreases, which is not good for securing strength.

[Relationship 6]

6≤ (Mo / 96) / (P / 31) ≤30

The relation 6 is for preventing the grain boundary segregation of P. If the value of relation 6 is less than 6, the effect of P grain boundary segregation due to the formation of Fe-Mo-P compound is not sufficient. If the value of relation 5 is 30 or more, impact energy decreases due to the formation of low temperature transformation with increasing hardenability. .

In the component system of the present invention, the finer the distribution, the more advantageous. Preferably, the average size of the precipitate is 0.2 μm or less. Furthermore, although the precipitate of 0.2 micrometer or less is largely distributed in the component system of this invention, the distribution number is not specifically limited. Preferably, the distribution number of precipitates is preferably ⁵ × ^{10 9} or more per mm 2.

Hereinafter, the manufacturing method of manufacturing the steel material of this invention is demonstrated.

The present invention is characterized by satisfying the average size of (Ti, Nb) C, NbC, VC precipitates in the hot rolled plate by hot rolling a steel satisfying the above-mentioned composition to 0.2 μm or less. The average size of (Ti, Nb) C, NbC, VC in hot rolled plate is influenced by the design process such as reheating temperature, winding temperature, etc., especially in the cooling rate after hot rolling.

The temperature of reheating the slabs is important in the present invention. If the reheating temperature is set to 1100 ° C. or lower than the temperature at which the additional alloy elements precipitated during the reworking process are sufficiently reusable, precipitates such as (Ti, Nb) C and NbC are reduced in the process after hot rolling. Accordingly, by maintaining the reheating temperature at 1100 ° C. or higher, it is possible to promote the reusability of the precipitate and maintain the austenite grain size of an appropriate size, thereby obtaining a uniform microstructure in the longitudinal direction of the coil while improving the strength level of the material. At this time, if the reheating zone temperature is too high, the strength decreases due to abnormal grain growth of the austenite grains, so the upper limit of the reheating zone temperature is preferably 1350 ° C.

The heated slab is preferably recrystallized and unrecrystallized rolling in the range of 950 ~ 1100 ℃ and rolling finish hot rolling 60% or more at 780 ~ 880 ℃. This is because if the rolling finish temperature is too high, the final structure is coarse to obtain the desired strength, and if too low, the finishing mill equipment load problem occurs.

After the hot rolling is finished, water cooling is performed on the run-out table at a rate of 10 to 50 ° C./sec to form fine ferrites and precipitates, thereby securing sufficient strength. Even if the component ratio is controlled to obtain fine precipitates according to the present invention, if the cooling rate is less than 10 ° C / sec, the average size of the precipitates may exceed 0.2 μm. In other words, as the cooling rate increases, a large number of nuclei are generated and the precipitate becomes fine. As the cooling rate increases, the size of the precipitate becomes finer, so it is not necessary to limit the upper limit of the cooling rate.However, even if the cooling rate is faster than 50 ° C / sec, the precipitate refinement effect does not increase any more. Is more preferable.

The coiling temperature is appropriately in the 400-600 ℃ temperature range, if higher than 600 ℃ microstructure is formed of coarse ferrite and pearlite, precipitates grow too coarse, it is difficult to secure the strength.

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

Inventive steel having a chemical composition as shown in Table 1 was produced as a slab by the continuous casting method, and then hot-rolled at a reduction ratio of 60% or more under the conditions of Table 3 to prepare a plate.

Steel grade C Si Mn S Nb Ni Mo Ti N V Cr Comparative Steel 1 0.071 0.25 1.82 0.0011 0.057 0.22 0.19 0.021 0.0033 0.055 0.20 Comparative Steel 2 0.076 0.24 1.80 0.0012 0.055 0.21 0.17 0.022 0.0029 0.054 0.19 Comparative Steel 3 0.068 0.23 1.83 0.009 0.068 0.23 0.30 0.019 0.0038 0.058 0.15 Inventive Steel 1 0.072 0.25 1.85 0.0012 0.072 0.25 0.22 0.022 0.0034 0.057 0.20 Inventive Steel 2 0.052 0.24 1.78 0.0010 0.052 0.23 0.28 0.021 0.0036 0.049 0.13 Inventive Steel 3 0.063 0.22 1.79 0.0011 0.071 0.22 0.31 0.020 0.0031 0.048 0.13

Steel grade Ti * Nb * (Ti * / 48 + Nb * / 93) / (C / 12) C * (V / 51) / (C * / 12) (Mo / 93) / (P / 31) Number of precipitates below 20nm (pcs / mm ² ) Average size of precipitates (㎛) Comparative Steel 1 0.013 0.042 0.12 0.033 0.22 5.4 4.6 X ^{10 9} 0.04 Comparative Steel 2 0.015 0.042 0.12 0.036 0.19 5.6 4.2 X ^{10 9} 0.04 Comparative Steel 3 0.010 0.050 0.13 0.026 0.29 11.4 5.2 X ^{10 9} 0.05 Inventive Steel 1 0.014 0.056 0.15 0.023 0.32 7.1 6.9X10 ⁹ 0.03 Inventive Steel 2 0.012 0.048 0.18 0.010 0.66 10.9 7.3 X ^{10 9} 0.04 Inventive Steel 3 0.013 0.057 0.17 0.015 0.42 13.3 7.8X10 ⁹ 0.04 Ti * = Ti-0.7 * (48/14) N Nb * = Nb-0.7 * (93/14) NC * = C-0.7 * [(Nb-0.7 * (93/14) N) + (Ti-0.7 * (48/14) N)]

In order to understand the mechanical properties of the steel from the hot-rolled sheets as described above, the tensile test piece was taken at 30 degrees clockwise with respect to the rolling direction, which is in the circumferential direction of the pipe when spiral pipe is connected. In the corresponding direction. Tensile test pieces were used for API 5L standard test pieces, and the tensile test was conducted at a cross head speed of 10 mm / min.

Yield strength and tensile strength of the invention and the comparative material can be found in Table 3 below. As shown in Table 3 below, the yield strength and tensile strength of the inventive steels are similar to those of the comparative steel, but it can be seen that a significant difference appears in the low temperature impact toughness.

division Reheating Temperature (℃) Finish rolling temperature (℃) Winding temperature (℃) Cooling rate (℃ / s) Thickness (mm) Yield strength (MPa) Tensile Strength (MPa) Impact Energy (J) @ -20 ℃ Comparative Steel 1 1085 763 505 17 18 542 717 200 Comparative Steel 2 1142 782 521 18 18 551 745 180 Comparative Steel 3 1172 783 493 19 18 583 773 230 Inventive Steel 1 1230 767 525 22 18 582 787 260 Inventive Steel 2 1202 762 578 17 18 568 751 290 Inventive Steel 3 1260 783 575 21 18 601 781 300

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 and achieves the same effect as the technical idea described in the claims of the present invention is included in the technical scope of the present invention.

Claims (6)

By weight%, C: 0.03-0.1%, Si: 0.01-0.5%, Mn: 1.2-2.0%, S: 0.02% or less, Nb: 0.01-0.1%, Ti: 0.01-0.1%, N: 0.01% or less , Mo: 0.1-0.5%, Ni: 0.1-0.5%, V: 0.01-0.1%, Cr: 0.1-0.5%, and other unavoidable impurities and balance Fe, Between Ti, Nb, C, N and V. 0.13 ≦ (Ti * / 48 + Nb * / 93) / (C / 12) ≦ 0.25; 0.24 ≦ (V / 51) / (C * / 12) ≦ 1.6; And 6 ≦ (Mo / 96) / (P / 31) ≦ 30; (Wherein Ti * = Ti-0.7 * (48/14) N, Nb * = Nb-0.7 * (93/14) N, C * = C-0.7 * [(Nb-0.7 * (93/14) N ) + (Ti-0.7 * (48/14) N)]) High strength steel sheet, characterized in that to satisfy the relationship. The high strength steel sheet according to claim 1, wherein the high strength steel sheet includes one or two or more precipitates selected from the group consisting of (Ti, Nb) C, NbC, and VC. The high strength steel sheet according to claim 2, wherein the average size of the precipitate is 0.2 µm or less. 4. The high strength steel sheet according to claim 2 or 3, wherein the number of distribution of precipitates is 5 × ^{10 9} or more per mm 2. By weight%, C: 0.03-0.1%, Si: 0.01-0.5%, Mn: 1.2-2.0%, S: 0.02% or less, Nb: 0.01-0.1%, Ti: 0.01-0.1%, N: 0.01% or less , Mo: 0.1-0.5%, Ni: 0.1-0.5%, V: 0.01-0.1%, Cr: 0.1-0.5%, and other unavoidable impurities and balance Fe, Between Ti, Nb, C, N and V. 0.13 ≦ (Ti * / 48 + Nb * / 93) / (C / 12) ≦ 0.25; 0.24 ≦ (V / 51) / (C * / 12) ≦ 1.6; And 6 ≦ (Mo / 96) / (P / 31) ≦ 30; (Wherein Ti * = Ti-0.7 * (48/14) N, Nb * = Nb-0.7 * (93/14) N, C * = C-0.7 * [(Nb-0.7 * (93/14) N ) + (Ti-0.7 * (48/14) N)]) For steel slabs that satisfy the relationship of Reheating step to reheat to 1100 ~ 1350 ℃; Recrystallized and unrecrystallized rolling in the range of 950 ~ 1100 ℃; Finishing hot rolling at a reduction ratio of 60% or more at 780 to 880 ° C; Water cooling on a run-out table at a rate of 10-50 ° C./sec; And Winding step of winding at 400-600 ° C; Method for producing a high strength steel sheet comprising a. The method of manufacturing a high strength steel sheet according to claim 5, wherein the high strength steel sheet includes one or two or more precipitates selected from the group consisting of (Ti, Nb) C, NbC, and VC.