WO2018004297A1 - High strength steel plate having excellent low yield ratio characteristics and low temperature toughness and method for manufacturing same - Google Patents

Abstract

One aspect of the present invention relates to a high strength steel plate having excellent low yield ratio characteristics and low temperature toughness, comprising, by weight %: C: 0.03 to 0.08%; Si: 0.05 to 0.3%; Mn: 1.0 to 2.0%; Al: 0.005 to 0.04%; Nb: 0.005 to 0.04%; Ti: 0.001 to 0.02%; Cu: 0.05 to 0.4%; Ni: 0.6 to 2.0%; Mo: 0.08 to 0.3%; N: 0.002 to 0.006%; P: 0.01% or less; S: 0.003% or less; and the remainder being Fe and unavoidable impurities, in which a microstructure contains, by area fraction, 80 to 92% of ferrite, 8 to 20% of a martensite/austenite mixed structure (MA), wherein the MA has an average size measured as a circle-equivalent diameter of 3 ㎛ or less.

Description

High strength steel sheet with excellent resistivity ratio and low temperature toughness and manufacturing method

The present invention relates to a high-strength steel sheet excellent in resistivity ratio and low temperature toughness and a method of manufacturing the same.

In order to be applicable not only to shipbuilding and marine structural steel fields but also to industrial fields requiring molding and seismic characteristics, it is necessary to develop steels having not only cryogenic toughness but also resistance yield ratio characteristics.

Steels with resistance yield ratio not only have excellent formability by increasing the difference between yield strength and tensile strength, but also delay the plastic deformation time until fracture can occur and absorb energy in this process to prevent collapse by external force. can do. In addition, even if there is a deformation, it is possible to repair before collapse, thereby preventing damage to property and life due to damage to the structure.

In order to secure the resistance ratio, the technology of two phase organization of steel was developed. Specifically, the first phase is soft ferrite, and the remaining second phase is martensite, pearlite, or bainite, thereby implementing a resistance ratio.

However, the impact toughness due to the hard two phase and the carbon content is increased for the second phase, so that the toughness of the weld is degraded, thereby causing brittle fracture of the structure at low temperature.

Accordingly, Patent Literature 1 has been developed as a technique for securing both resistance ratio and low temperature impact toughness.

In Patent Document 1, the microstructure includes 2-10 vol% of MA (martensite / austenite mixed structure) and 90 vol% or more of cyclic ferrite, thereby ensuring resistance ratio and excellent low temperature toughness.

According to Patent Document 1, it is possible to implement a yield ratio of about 0.8 but there is an insufficient problem to secure the seismic characteristics can not implement a sufficient resistance yield ratio.

Therefore, there is a demand for development of a high strength steel sheet having excellent resistance yield ratio characteristics and low temperature toughness and a method of manufacturing the same, which can ensure a lower yield ratio.

(Prior art document)

(Patent Document 1) Korean Unexamined Patent Publication No. 2013-0076577

One aspect of the present invention is to provide a high-strength steel sheet excellent in resistance ratio ratio characteristics and low temperature toughness and a method of manufacturing the same.

In addition, the subject of this invention is not limited to the content mentioned above. The problem of the present invention will be understood from the general contents of the present specification, those skilled in the art will have no difficulty understanding the additional problem of the present invention.

One aspect of the present invention is by weight, C: 0.03-0.08%, Si: 0.05-0.3%, Mn: 1.0-2.0%, Al: 0.005-0.04%, Nb: 0.005-0.04%, Ti: 0.001-0.02 %, Cu: 0.05-0.4%, Ni: 0.6-2.0%, Mo: 0.08-0.3%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, including remaining Fe and unavoidable impurities ,

The microstructure includes 80 to 92% of ferrite and 8 to 20% of MA (martensite / austenite mixed structure) as an area fraction, and the MA has a resistivity ratio characteristic of 3 μm or less in average size measured in equivalent diameter and It relates to a high strength steel sheet excellent in low temperature toughness.

In addition, another aspect of the present invention is by weight, C: 0.03-0.08%, Si: 0.05-0.3%, Mn: 1.0-2.0%, Al: 0.005-0.04%, Nb: 0.005-0.04%, Ti: 0.001 to 0.02%, Cu: 0.05 to 0.4%, Ni: 0.6 to 2.0%, Mo: 0.08 to 0.3%, N: 0.002 to 0.006%, P: 0.01% or less, S: 0.003% or less, remaining Fe and unavoidable impurities Heating the slab including 1050 to 1200 ° C;

Hot rolling the heated slab to a finish rolling end temperature of 760 to 850 ° C. to obtain a hot rolled steel sheet;

Cooling the hot rolled steel sheet to 450 ° C. or less at a cooling rate of 5 ° C./s or more; And

After the cooled hot-rolled steel sheet heated to a temperature range of 850 ~ 960 ℃, the normalizing heat treatment step of maintaining for [1.3t + (10 ~ 30)]; It is about a method.

(T is a value measured in mm of the thickness of the hot rolled steel sheet.)

In addition, the solution of the said subject does not enumerate all the characteristics of this invention. Various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

According to the present invention, excellent resistance ratio ratio and low temperature toughness can be ensured, and in particular, a low resistance ratio of 0.65 or less can be secured, thereby ensuring excellent seismic characteristics as well as formability.

Accordingly, the present invention can be applied not only to shipbuilding and marine structural steel fields but also to industrial fields requiring molding and seismic characteristics.

1 is a photograph taken with an optical microscope (OM) of the microstructure of Test No. 1 of the invention example.

2 is a photograph taken with a scanning electron microscope (SEM) of the microstructure of Test No. 1 as an example of the invention.

3 is a photograph taken by using an optical microscope (OM) of the microstructure of Test No. 12 as a comparative example.

Hereinafter, preferred embodiments of the present invention will be described. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

The present inventors are able to secure a yield ratio of about 0.8 in the prior art, but it is possible to secure a certain degree of moldability, but it is not possible to implement a sufficient resistance ratio, recognizing that there is an insufficient problem of securing seismic characteristics, and solved this. In order to study deeply.

As a result, the larger the difference between the hardness of the base material and the second phase to achieve a resistance ratio ratio, the more uniform the distribution of MA, the more advantageous, and in the case of Patent Document 1, the base material lacks the hardness difference from the MA as an ecuous ferrite, MA It was found that the phase was formed at grain boundaries and the MA size was coarse to achieve sufficient resistance ratio.

Therefore, the microstructure of the base material is made of ferrite, and the fine MA phase is uniformly distributed in the ferrite grain boundary and the inside of the grain, so that a resistivity ratio of 0.65 or less can be secured. It was confirmed that the control to include, and came to complete the present invention.

Hereinafter, a high strength steel sheet having excellent resistance ratio ratio characteristics and low temperature toughness according to an aspect of the present invention will be described in detail.

High-strength steel sheet having excellent resistance ratio and low temperature toughness according to an aspect of the present invention is a weight%, C: 0.03 ~ 0.08%, Si: 0.05 ~ 0.3%, Mn: 1.0 ~ 2.0%, Al: 0.005 ~ 0.04%, Nb: 0.005 to 0.04%, Ti: 0.001 to 0.02%, Cu: 0.05 to 0.4%, Ni: 0.6 to 2.0%, Mo: 0.08 to 0.3%, N: 0.002 to 0.006%, P: 0.01% or less, S: 0.003% or less, including the remaining Fe and inevitable impurities,

The microstructure includes 80 to 92% of ferrite and 8 to 20% of MA (martensite / austenite mixed structure) in an area fraction, and the MA has an average size of 3 μm or less measured in a circular equivalent diameter.

First, an alloy composition of a high strength steel sheet having excellent resistance ratio and low temperature toughness according to an aspect of the present invention will be described in detail. Hereinafter, the unit of each element content is weight%.

C: 0.03-0.08%

In the present invention, C is an element that causes solid solution strengthening and exists as carbonitride by Nb to secure tensile strength.

When the C content is less than 0.03%, the above effects are insufficient. On the other hand, when the C content is more than 0.08%, the MA is coarsened and pearlite is formed to deteriorate the impact characteristics at low temperatures, and it is difficult to sufficiently secure bainite.

Si: 0.05-0.3%

Si serves to deoxidize molten steel by assisting Al, and is added to secure yield strength and tensile strength.

When the Si content is less than 0.05%, the above effects are insufficient. On the other hand, when the Si content is more than 0.3%, the impact property may be degraded by coarsening of the MA, and the welding property may be degraded.

Mn: 1.0-2.0%

Mn contributes greatly to the strength increasing effect by solid solution strengthening and is an element that helps to form bainite.

When the Mn content is less than 1.0%, the above effects are insufficient. On the other hand, excessive addition may cause a decrease in toughness due to the formation of MnS inclusions and segregation of the central portion, so the upper limit is 2.0%.

Al: 0.005-0.04%

Al needs to be added 0.005% or more as a major deoxidizer of steel. However, when added in excess of 0.04%, the effect is saturated and may cause low temperature toughness by increasing the fraction and size of Al ₂ O ₃ inclusions.

Nb: 0.005-0.04%

Nb is an element that suppresses recrystallization during rolling or cooling by precipitation of solid solution or carbonitride, thereby making the structure fine and increasing the strength. When the Nb content is less than 0.005%, the above effects are insufficient. On the other hand, when the Nb content is more than 0.04%, there is a problem that can lower the toughness of the base metal and the toughness after welding.

Ti: 0.001-0.02%

Ti combines with oxygen or nitrogen to form precipitates, thereby inhibiting coarsening of tissues and contributing to miniaturization and improving toughness.

When the Ti content is less than 0.001%, the above effects are insufficient. On the other hand, when the Ti content is more than 0.02%, precipitates are formed coarsely and may cause destruction.

Cu: 0.05 ~ 0.4%

Cu is a component that does not significantly reduce the impact characteristics, and thus improves strength by solid solution and precipitation. In order to sufficiently improve the strength, it should be contained in 0.05% or more, but when the Cu content is more than 0.4%, surface cracks of the steel sheet due to Cu thermal shock may occur.

Ni: 0.6 ~ 2.0%

Ni is an element that can improve strength and toughness at the same time as the increase in content is not great, and is an element that helps to form bainite by decreasing the Ar3 temperature.

When the Ni content is less than 0.6%, the above effects are insufficient. On the other hand, when the Ni content is more than 2.0%, the manufacturing cost may increase and the weldability may deteriorate.

Mo: 0.08 ~ 0.3%

Mo is an austenite stabilizing element that affects the amount of MA and plays a large role in improving the strength. It is also an element that prevents a drop in strength during heat treatment and helps to form bainite.

When the Mo content is less than 0.08%, the above effects are insufficient. On the other hand, when the Mo content is more than 0.3%, there is a problem that the manufacturing cost increases and the base material toughness and post-weld toughness may be reduced.

N: 0.002-0.006%

N is an element that forms a precipitate with Ti, Nb, Al and the like to make the austenite structure fine when the slab is heated to help improve strength and toughness.

When the N content is less than 0.002%, the above effects are insufficient. On the other hand, when the N content is more than 0.006%, it causes surface cracking at high temperatures, forms precipitates, and the remaining N may exist in an atomic state to reduce toughness.

P: 0.01% or less

P may cause grain boundary segregation as impurities and cause the steel to be withdrawn. Therefore, it is important to control the upper limit and it is preferable to control it to 0.01% or less.

S: 0.003% or less

S, as an impurity, mainly combines with Mn to form MnS inclusions, which are factors that inhibit low-temperature toughness. Therefore, it is important to control the upper limit, and in order to secure low temperature toughness, it is preferable to control S to 0.003% or less.

The remaining component of the present invention is iron (Fe). However, in the conventional manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.

Hereinafter, the microstructure of the high strength steel sheet excellent in the resistance ratio ratio characteristics and low temperature toughness according to an aspect of the present invention will be described in detail.

The microstructure of the high strength steel sheet having excellent resistivity ratio properties and low temperature toughness according to an aspect of the present invention includes 80 to 92% of ferrite and 8 to 20% of MA in an area fraction, and the average of the MAs is measured by the equivalent diameter. The size is 3 micrometers or less. Hereinafter, the fraction of microstructure means an area fraction unless otherwise specified.

Ferrite is to ensure basic toughness and strength, preferably 80% or more. In addition, in order to ensure sufficient MA, the upper limit is preferably 92%. Furthermore, it is preferable that the ferrite does not contain an acicular ferrite. This is because the epoxy ferrite has a small hardness difference from the MA, and thus a sufficient resistance ratio cannot be secured.

If the MA is less than 8%, it is difficult to secure a resistance ratio of 0.65 or less. If the MA is more than 20%, the impact toughness may be lowered and the elongation may be reduced. In addition, when the average size measured by the equivalent circular diameter of MA is more than 3㎛, MA is mainly formed in the grain boundary, it is difficult to ensure a uniform distribution and resistance ratio of MA.

Other unavoidable phases may be included in addition to the above-described ferrite and MA, but are not excluded. For example, pearlite of 1 area% or less may be included.

In this case, in order to ensure excellent resistance ratio characteristics and low temperature toughness, when the 100 μm straight line is drawn on the steel sheet of the present invention, as well as the MA fraction and size, it is preferable that 5 to 13 MAs are disposed on the straight line. .

That is, a plurality of straight lines are drawn up and down or left and right on a microstructure photograph having a size of 100 μm × 100 μm, and at this time, 5 to 13 MAs may be present on each line. This is because MA, which mainly causes breakage, is present in the grain boundary, and when the above conditions are satisfied, the MA is evenly distributed in the grain boundary and inside the grain, which is advantageous in securing a resistance ratio.

In addition, the ratio of the MA present in the ferrite grains and the MA present in the grain boundary may be 1: 3 to 1:10. The ratio refers to the ratio of the number of MA, because by satisfying the ratio can be uniformly distributed so that the MA present in the ferrite grains becomes 0.5 to 5 area%.

In addition, the ferrite may have an average size of 20 μm or less as measured by a circle equivalent diameter. If the average size of the ferrite is more than 20㎛ it may be difficult to secure sufficient toughness and strength.

On the other hand, the steel sheet according to the present invention is normalized heat treatment, the microstructure of the steel sheet before the normalizing heat treatment may be 50 ~ 90 area% of bainite.

Since the microstructure of the steel sheet before the heat treatment is bainite with carbides present therein, it is possible to distribute MA evenly in the grain boundary and inside the grain after heat treatment. Therefore, the microstructure of the steel sheet before the heat treatment is preferably 50 to 90 area%. Do.

In addition, the steel sheet according to the present invention has a yield ratio of 0.5 to 0.65, the low temperature impact characteristics at -40 ℃ may be 100J or more. Yield ratio is 0.65 or less to increase the difference between yield strength and tensile strength, not only excellent formability, but also delay the time of plastic deformation until fracture can occur and absorb energy in this process to prevent collapse by external force can do.

Therefore, it can be preferably applied not only to the field of shipbuilding and marine structural steel but also to the industrial field requiring molding and seismic characteristics.

At this time, the yield strength of the steel sheet is 350 ~ 400MPa, tensile strength may be 600MPa or more.

Hereinafter, another aspect of the present invention will be described in detail a method for producing a high strength steel sheet having excellent resistance ratio characteristics and low temperature toughness.

Another aspect of the present invention provides a method for producing a high strength steel sheet having excellent resistance ratio and low temperature toughness, comprising: heating a slab having the above-described alloy composition to 1050 to 1200 ° C; Hot rolling the heated slab to a finish rolling end temperature of 760 to 850 ° C. to obtain a hot rolled steel sheet; Cooling the hot rolled steel sheet to 450 ° C. or less at a cooling rate of 5 ° C./s or more; And a normalizing heat treatment step of heating the cooled hot-rolled steel sheet to a temperature range of 850 to 960 ° C., and then maintaining it for [1.3t + (10 to 30)] minutes. The t is a value measured in mm of the hot rolled steel sheet.

Slab heating stage

The slab having the alloy composition described above is heated to 1050-1200 ° C.

If the heating temperature is more than 1200 ℃ austenite grains may be coarsened to lower the toughness, if less than 1050 ℃ Ti, Nb, etc. are not sufficiently dissolved, the strength may be reduced.

Hot rolling stage

The heated slab is hot rolled to a finish rolling end temperature of 760 to 850 ° C. to obtain a hot rolled steel sheet.

In general, the rolling temperature of the heat-treated steel is about 850 ~ 1000 ℃ general rolling is applied. However, in the present invention, it is important to form the initial tissue as bainite. Therefore, a controlled rolling process for finishing rolling at low temperature is needed instead of general rolling showing ferrite-pearlite structure.

Re-crystallization rolling during hot rolling is necessary to refine the austenite grain size, and it is advantageous in terms of physical properties as the rolling reduction per pass increases.

Unrecrystallized rolling must be completed at a temperature of at least Ar3 of the steel and is at least about 760 ° C. More specifically, the finish rolling end temperature may be defined at 760 to 850 ° C. If the finish rolling finish temperature is higher than 850 ℃, it is difficult to suppress the ferrite-pearlite transformation, if it is less than 760 ℃ may lead to non-uniformity of the microstructure in the thickness direction, to reduce the reduction in the amount of reduction due to the load load of the rolling roll May not be able to form microstructures.

By finishing the finish rolling in the temperature range of 760 to 850 ° C, ferrite-pearlite transformation is suppressed and bainite structure is realized through cooling. The initial structure of bainite is for uniform MA distribution after heat treatment. In the ferrite-pearlite structure, MAs are mainly formed at grain boundaries, while in bainite structures, MAs are formed at both grain boundaries and inside grains.

Cooling stage

The hot rolled steel sheet is cooled to 450 ° C. or less at a cooling rate of 5 ° C./s or more.

Accelerated cooling after hot rolling is very important for the implementation of the target structure of the inventive steel. Bainite should be implemented to form fine and uniform MA. Cooling finish temperature and cooling rate are important factors for bainite formation.

If the cooling finish temperature is higher than 450 ℃, the grain size may become coarse, and coarse carbide may cause coarse MA to be formed after heat treatment, which may lead to a decrease in toughness and more than 50 area% of bainite. Difficult to secure

If the cooling rate is less than 5 ℃ / s fine structure of the needle-like ferrite or ferrite + pearlite is formed in a large amount may cause a decrease in strength, and after the heat treatment, coarse ferrite + pearlite or second phase rather than the abnormal structure of ferrite + MA There may be a sudden drop in quantity, it is difficult to secure more than 50 area% bainite.

Normalizing  Heat treatment step

After heating the cooled hot-rolled steel sheet to a temperature range of 850 ~ 960 ℃, it is maintained for [1.3t + (10 ~ 30)] minutes. The t is a value measured in mm of the hot rolled steel sheet.

If the normalizing temperature is less than 850 ° C or the holding time is less than (1.3t + 10) minutes, it is difficult to re-use cementite and pearlite in pearlite, bainite and MA. The remaining hardened phase will remain coarse.

On the other hand, when the normalizing temperature is higher than 960 ° C or the holding time is longer than (1.3t + 30) minutes, all carbides in the bainite grains move to the grain boundary or the coarsening of carbides occurs, resulting in the final MA size and uniform distribution. Cannot be formed. In addition, grain growth may occur, resulting in a decrease in strength and deterioration of impact.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only for illustrating the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

After preparing molten steel having the component composition shown in Table 1, the slab was manufactured using continuous casting. The slabs were rolled, cooled, and normalized to heat treatment under the conditions shown in Table 2 to prepare steel sheets.

Table 3 below describes the bainite fraction and mechanical properties of the steel sheet before normalizing heat treatment.

Table 4 below describes the MA fraction of the steel sheet after the normalizing heat treatment, the average MA size, the number of MAs over 100 μm, and the mechanical properties thereof. In the case of the invention, it was ferrite except for MA, and the average grain size of the ferrite was not described separately as 20 µm or less.

The average MA size is the average size measured by the diameter of the equivalent circle, and the number of MAs on a 100 μm line is obtained by drawing 10 straight lines up and down or left and right on a 100 μm × 100 μm microstructure photograph. The average number was described after measuring the number.

Specifically, the effects of rolling temperature, cooling end temperature, and heat treatment time were investigated. And Table 3 shows the MA fraction, yield ratio and mechanical properties of the steel sheet prepared by the components A ~ H, manufacturing conditions 1 to 12.

The unit of each element content in Table 1 is weight%. Invention steels A to D are steel sheets satisfying the component range defined by the present invention, and comparative steels E to H are steel sheets which do not satisfy the component range defined by the present invention. Comparative steel E is higher than C content, comparative steel F is lower than Mo content, comparative steel G is lower than Mn content, and comparative steel H is lower than Ni content.

Inventive examples satisfying both the alloy composition and the manufacturing conditions presented in the present invention can ensure the yield ratio below 0.65, it can be confirmed that the impact toughness of -40 ℃ 100J or more excellent.

In case of Test Nos. 6, 7, 9, and 10, which are comparative examples, the alloy composition presented in the present invention was satisfied, but it did not satisfy the manufacturing conditions, did not secure sufficient yield ratio, and the impact toughness of -40 ° C was less than 100J. You can see that it's feverish.

In the case of the test Nos. 11 to 14, which are comparative examples, the manufacturing conditions presented in the present invention were satisfied, but the alloy composition did not satisfy the sufficient yield ratio, and the test Nos. 11 and 14 had an impact toughness of -40 ° C less than 100J. You can see that you are enthusiastic.

Looking at the invention example of Table 4 it can be seen that the MA fraction is higher than the comparative example. As can be seen in Table 3, by securing a high bainite fraction before the normalized heat treatment, carbides in the grains of the initial bainite structure, the grains at the grain boundary are transformed into fine MA.

Looking at the microstructure of the test No. 1 of the invention example, Figures 1 and 2, it can be seen that a fine and uniform MA is formed.

On the other hand, when the microstructure of the test No. 12 of the comparative example is taken, it can be seen that the carbide and pearlite appear in two main phases, and thus, the fraction of MA is low, and the formed MA is in the form of a polygon and mainly exists in grain boundaries.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (9)

By weight%, C: 0.03-0.08%, Si: 0.05-0.3%, Mn: 1.0-2.0%, Al: 0.005-0.04%, Nb: 0.005-0.04%, Ti: 0.001-0.02%, Cu: 0.05- 0.4%, Ni: 0.6-2.0%, Mo: 0.08-0.3%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, including the remaining Fe and inevitable impurities, The microstructure includes 80 to 92% of ferrite and 8 to 20% of MA (martensite / austenite mixed structure) as an area fraction, and the MA has a resistance ratio ratio of 3 μm or less measured on a circular equivalent diameter, and High strength steel sheet with excellent low temperature toughness. The method of claim 1, A high strength steel sheet having excellent resistivity ratio and low temperature toughness, wherein 5 to 13 MAs extending over the straight line exist when a 100 µm straight line is drawn on the steel sheet. The method of claim 1, A high strength steel sheet having excellent resistance ratio and low temperature toughness, wherein the ratio of MA present in the ferrite grains and MA present in the grain boundary is 1: 3 to 1:10. The method of claim 1, The ferrite is a high strength steel sheet having excellent resistance ratio and low temperature toughness, characterized in that the average size measured by the equivalent diameter of 20㎛ or less. The method of claim 1, The steel sheet is normalized heat treatment, The microstructure of the steel sheet before the normalizing heat treatment is characterized in that the bainite is 50 ~ 90 area%, high strength steel sheet having excellent resistance to wear properties and low temperature toughness. The method of claim 1, The steel sheet has a high yield strength and low temperature toughness, characterized in that the yield ratio is 0.5 ~ 0.65, the low temperature impact characteristics at -40 ℃ 100J or more. The method of claim 1, Yield strength of the steel sheet is 350 ~ 400MPa, tensile strength is 600MPa or more characterized in that the high strength steel sheet excellent in the resistance yield ratio characteristics and low temperature toughness. By weight%, C: 0.03-0.08%, Si: 0.05-0.3%, Mn: 1.0-2.0%, Al: 0.005-0.04%, Nb: 0.005-0.04%, Ti: 0.001-0.02%, Cu: 0.05- Slab containing 0.4%, Ni: 0.6 ~ 2.0%, Mo: 0.08 ~ 0.3%, N: 0.002 ~ 0.006%, P: 0.01% or less, S: 0.003% or less, remaining Fe and unavoidable impurities Heating to; Hot rolling the heated slab to a finish rolling end temperature of 760 to 850 ° C. to obtain a hot rolled steel sheet; Cooling the hot rolled steel sheet to 450 ° C. or less at a cooling rate of 5 ° C./s or more; And After the cooled hot-rolled steel sheet heated to a temperature range of 850 ~ 960 ℃, the normalizing heat treatment step of maintaining for [1.3t + (10 ~ 30)]; Way. (T is a value measured in mm of the thickness of the hot rolled steel sheet.) The method of claim 8, The microstructure of the cooled hot-rolled steel sheet is 50 to 90 area% bainite, characterized in that the high-strength steel sheet excellent resistance resistance properties and low temperature toughness.

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