KR20090103619A - High-strength steel sheet, and method for producing the same - Google Patents

Abstract

The present invention relates to a high strength steel sheet and a method of manufacturing the same. % By weight Carbon (C): 0.05-0.12%, Silicon (Si): 0.001-0.01%, Manganese (Mn): 2.0-3.0%, Sulfur (S): 0.003% or less, Phosphorus (P): 0.01% or less Aluminum (Al): 0.2-1.0%, Chromium (Cr): 0.1-0.5%, Copper (Cu): 0.1-0.3%, Vanadium (V): 0.02-0.1%, Nitrogen (N): 0.007% or less, 80-90% of ferrite containing residual iron (Fe) and other unavoidable impurities and having a grain size of 5-20 µm is formed, and 10% -20% of a phase containing martensite is formed as the second phase. Accordingly, there is an effect that can produce a high strength steel sheet that can satisfy the tensile strength and high elongation of 700 MPa or more even at a relatively low cost.

Description

High strength steel sheet and its manufacturing method {High-strength steel sheet, and method for producing the same}

The present invention relates to a high-strength steel sheet and a method of manufacturing the same, and more particularly, to adjust the component ratio of each component element and to control the fraction of ferrite and martensite so as to have excellent workability and weldability, high tensile strength and excellent elongation. It relates to a high strength steel sheet and a method of manufacturing the same.

As the competition intensifies, the automobile industry is increasing the demand for quality and diversification of automobile quality, and is striving to increase the rigidity of the body and improve fuel efficiency in order to satisfy the stricter regulations on safety and environmental regulations. .

Recently, the research interests of the steel industry and the automotive industry are focused on environmental pollution, high strength, and light weight, and as the automobile design is complicated and the needs of consumers are diversified, the automotive industry demands steel having high strength and excellent workability and formability. .

In particular, in the case of cold-rolled steel sheet used as an outer plate material of the automobile, various characteristics such as dent resistance, shape freezing and press workability are required. Among them, various studies are being conducted to secure excellent press formability and high strength at the same time.

For example, two-phase steel (DP, Dual Phase) using a composite structure of martensite and ferrite, and TRPS (TRIans, Induction Plasticity) steel based on three-phase structure of ferrite, bainite and residual austenite have. Both steels have strength and ductility superior to their class.

Among them, dual phase steel (DP) is characterized by rolling the slab from the furnace in the austenite section and transforming austenite to martensite by lowering the end temperature of cooling from the martensite transformation in the cooling process. It is a river. The biphasic tissue steel increases in strength as the proportion of martensite increases and in ductility as the proportion of ferrite increases. These two-phase tissue steels are mainly applied to members, bumpers, etc., because they have superior ductility and stretching processability and excellent absorption of impact energy, compared to precipitation-reinforced steels. However, in the case of the dual phase steel (DP, Dual Phase) 80kg / mm ² In order to obtain the above strength, it is necessary to increase the martensite ratio.

The strained organic plastic (TRIP) steel forms austenite in the rolling process and then controls the cooling rate and the cooling end temperature during the cooling process to partially retain the austenite at room temperature, and the residual austenite becomes martensite during plastic deformation. It is a steel that increases ductility by relieving stress concentration by transforming. The strained organic plastic (TRIP) steel is used as a high strength steel having excellent properties at the same time strength and ductility. However, the strained organic plastic steel has a better elongation than the conventional two-phase steel, but has a disadvantage in that yield strength is increased and shape freezing is lowered.

In addition, complex phases (CP) strengths based on martensite or bainite and complex microstructures are being developed, and these are usually used for bumper reinforcement, such as ultra-high strength steels having strengths of more than 1000 MPa.

In addition, the use environment of the automobile is increasingly severe due to factors such as use of deicing salt, pollution, acid rain, etc., and the life of the automobile is prolonged.

Therefore, the demand for high strength and excellent workability, formability and corrosion resistance than the general cold-rolled steel sheet is increasing, for this purpose, the high-strength hot-dip galvanized steel sheet having excellent elongation and resistance ratio is to be developed.

In particular, the development of the above-described strained organic plastic (TRIP) steel involves many factors, both thermodynamically and metallicly, which requires a lot of research time and investment. Therefore, in order to satisfy the required characteristics of the automobile, an early study should be made.

As a prior art to improve this, Japanese Patent Laid-Open No. 8-134591 discloses a high strength alloyed hot dip galvanized steel sheet having a resistance ratio and excellent press workability. However, this has a disadvantage of low elongation.

In Japanese Patent JP-A-55-100934, box annealing is carried out in the ferrite-austenite coexistence area, the manganese content is increased to increase the austenite phase in the continuous annealing process, and a gas jet cooling method is used to form a two-phase structure. A method of lowering the yield strength is presented. However, this method is subjected to box annealing for a long time in a relatively high two-phase region, there is a problem that the steel sheets adhere to each other by thermal expansion of the coiled steel sheet. In addition, it is difficult to produce steel sheets of high r-value (plastic deformation ratio: index indicating moldability) and low yield strength because of economically inexpensive box annealing.

Japanese Patent JP-B-35900 proposes a method for obtaining high r-value and low yield strength. However, this method requires a cooling rate of 100 ° C / s or more, so the gas jet cooling method is difficult to implement.

US Patent US2003 / 012944A1 proposes a method for securing high r-value and tensile strength of 780MPa by controlling vanadium content. However, vanadium is a expensive element, so there is a disadvantage in that it is a burden of the manufacturing cost. In addition, there is a problem in the weldability because of the high content of silicon.

The present invention is to solve the conventional problems as described above, the object of the present invention after forming austenite in the rolling process to form a ferrite, martensite by controlling the cooling rate and cooling temperature in the cooling process and the like The present invention provides a high-strength steel sheet having excellent press workability, which has excellent plating property, weldability, and excellent elongation with strength while reducing the amount of alloying elements added, compared to the conventional one.

Another object of the present invention is to balance strength and ductility by properly combining the fractions of ferrite and martensite.

The present invention is to solve the conventional problems as described above, the present invention by weight% carbon (C): 0.05 ~ 0.12%, silicon (Si): 0.001 ~ 0.01%, manganese (Mn): 2.0 ~ 3.0 %, Sulfur (S): 0.003% or less, phosphorus (P): 0.01% or less, aluminum (Al): 0.2-1.0%, chromium (Cr): 0.1-0.5%, copper (Cu): 0.1-0.3%, Vanadium (V): 0.02 to 0.1%, Nitrogen (N): 0.007% or less, including 80% to 90% of ferrite containing residual iron (Fe) and other unavoidable impurities, and having a grain size of 5 to 20 µm. As two phases, 10 to 20% of the phases containing martensite are formed.

The content of carbon, silicon, manganese, phosphorus and sulfur is in the range satisfying Pcm: C + Si / 30 + Mn / 20 + 2P + 4S ≤ 0.27.

% By weight Carbon (C): 0.05-0.12%, Silicon (Si): 0.001-0.01%, Manganese (Mn): 2.0-3.0%, Sulfur (S): 0.003% or less, Phosphorus (P): 0.01% or less Aluminum (Al): 0.2-1.0%, Chromium (Cr): 0.1-0.5%, Copper (Cu): 0.1-0.3%, Vanadium (V): 0.02-0.1%, Nitrogen (N): 0.007% or less, Steel slab having an alloy composition of balance iron (Fe) and other unavoidable impurities is homogenized at 1200 ~ 1300 ℃, hot rolled at Ar3 ~ Ar3 + 50, wound up at 500 ~ 570 ℃, and cold reduction rate 50% After cold rolling and annealing, hot dip galvanizing or alloying hot dip galvanizing is performed.

As a final step of the continuous annealing, it is maintained for 5 to 120 seconds in the temperature range Ar1 ~ Ar3.

In the galvanizing process, after the annealing, the steel sheet is quenched to 495 ° C. or lower at a cooling rate of 5 to 50 ° C./s, and further cooled to 250 to 300 ° C. at a cooling rate of 5 to 50 ° C./s or more.

In the galvanizing process, after the annealing, the steel plate is quenched to 495 ° C. or lower at a cooling rate of 5 to 50 ° C./s, and is re-heated to an area of 500 to 550 ° C., followed by alloying, and then to 5 ° C. to 250 ° C. to 350 ° C. Cool at a cooling rate of more than / s.

According to the present invention, based on the component system satisfying Pcm: C + Si / 30 + Mn / 20 + 2P + 4S ≤0.27, the carbon, silicon content, which is the main constituent of the steel, is reduced, and the manganese and copper contents are increased to obtain the desired tensile strength. It was intended to secure excellent elongation.

In addition, by reducing the silicon content that inhibits the plating properties, instead of increasing the content of aluminum to improve the plating properties and elongation. At the same time, relatively inexpensive chromium was added instead of expensive molybdenum added to improve the hardenability, thereby preventing bainite or pearlite transformation.

In addition, chromium and vanadium were added in combination to improve elongation, and a small amount of boron was added to reduce grain refinement and material deviation to balance strength and ductility.

As a result, a two-phase tissue steel having a grain boundary size of 5 to 20 µm in which 80 to 90% is formed, and a second phase including martensite is formed to be 10 to 20%, is obtained at a relatively low cost. There is an effect of producing a high strength steel sheet that can satisfy the tensile strength and high elongation of MPa or more.

According to the present invention, through the process of component control and heat treatment of the alloying element is formed two-phase tissue steel 80 to 90% of the grain size of 5 ~ 20㎛ grain formed and 10 to 20% of the phase containing martensite as a second phase Since it can be obtained, there is an effect that can produce a high strength steel sheet that can satisfy the tensile strength and high elongation of 700 MPa or more even at a relatively low cost.

Hereinafter, a preferred embodiment of the high strength steel sheet according to the present invention and a manufacturing method thereof will be described in detail.

High-strength steel sheet of the present invention by weight% carbon (C): 0.05 ~ 0.12%, silicon (Si): 0.001 ~ 0.01%, manganese (Mn): 2.0 ~ 3.0%, sulfur (S): 0.003% or less, phosphorus ( P): 0.01% or less, aluminum (Al): 0.2-1.0%, chromium (Cr): 0.1-0.5%, copper (Cu): 0.1-0.3%, vanadium (V): 0.02-0.1%, nitrogen (N ): 0.007% or less, consisting of residual iron (Fe) and other unavoidable impurities.

After heating the steel slab having such a composition at a heating furnace at 1200 ° C. or higher, hot rolling at a condition of hot finishing temperature of Ar 3 or higher and Ar 3 + 50 or lower, winding at 500 to 570 ° C., and then pickling the hot rolled steel sheet. Cold rolling should be carried out with a rolling reduction of at least 50%.

After the cold rolled steel sheet is maintained for 5 to 120 seconds in the region of Ar1 or more and Ar3 or less, it is quenched to a temperature of 500 ° C or less at a rate of 5 ° C / s. Next, the hot dip galvanizing process is performed and reheated to a temperature range of 450 to 550 ° C. to alloy the hot dip galvanized film, followed by quenching to 300 ° C. at a cooling rate of 5 ° C./s or more, for example, a hot dip galvanized steel sheet. ).

In the present invention, to reduce the content of carbon, silicon, the main components of the steel for excellent weldability, instead of increasing the content of manganese, copper to secure the tensile strength and elongation.

In addition, the silicon content is minimized, and instead, the content of aluminum is increased to improve the plating property and elongation, and at the same time, inexpensive molybdenum is added instead of expensive chromium to prevent bainite or pearlite transformation.

In addition, chromium and vanadium are added in combination to improve elongation, and a small amount of boron is added to reduce grain refinement and material variation.

In particular, the present invention is to manufacture the microstructure of the steel is composed of two phases including ferrite and martensite by controlling the cooling rate and the cooling end temperature in the cooling process after the heat treatment and the alloy composition described above.

In steel sheet, ductility increases as the fraction of martensite increases in the overall structure, and ductility increases as the fraction of ferrite increases.If the martensite fraction is too large for strength, the fraction of ferrite decreases and the ductility decreases. . Therefore, the steel sheet is formed such that the ferrite having an average grain size of 5-20 μm in the cooling process is 80-90%, and the second phase including martensite is formed in 10-20%.

In addition, the carbon, silicon, manganese, phosphorus, sulfur content in the alloy design satisfies the range of Pcm: C + Si / 30 + Mn / 20 + 2P + 4S ≤ 0.27.

Hereinafter, the components of the present invention high strength steel sheet and the efficacy of each component will be described.

Carbon (C): 0.05-0.12 wt%

Carbon is an indispensable element for reinforcing steel sheet. In addition, when a small amount is added, carbon is added at 0.05% or more to secure the strength of the material because it is difficult to secure martensite fraction due to transformation of austenite into ferrite. However, if it exceeds 0.12%, spot weldability will fall, and the upper limit is limited to 0.12%.

Silicon (Si): 0.001 to 0.01 wt%

Silicon is a ferrite stabilizing element that is dissolved in ferrite and contributes to strength, and is usually added as a deoxidizer. Silicon promotes austenite-ferrite transformation on cooling in composite tissue steels, increasing the ferrite fraction.

When the silicon content is less than 0.001%, the strength of the ferrite decreases as well as the carbide inhibiting effect is reduced, so it is preferable to add more than 0.001%. However, excessive addition may cause surface defects due to plating property and red scale, so the upper limit thereof is 0.01%.

Manganese (Mn): 2.0-3.0 wt%

Manganese is an austenite stabilizing element that increases strength through the effect of strengthening solid solution and improving hardenability. In the present invention, instead of reducing the carbon content for spot weldability and material stabilization, it is added to improve the insufficient strength.

In view of these considerations, it is preferable to add manganese as much as 2.0% or more. However, when excessively added, weldability and plating property are degraded, hydrogen organic brittleness is generated by inclusion formation, and segregation portion (Mns) is formed at the center of the steel sheet during hot rolling, so the upper limit is preferably limited to 3.0 wt% or less. .

Sulfur (S): 0.003wt% or less

Sulfur inhibits toughness and weldability, increases MnS non-metallic inclusions, causes cracking during processing of the steel, and increases coarse inclusions when excessively added, thereby causing fatigue properties. In the present invention, since a large amount of manganese is added, sulfur is preferably added to the minimum, but sulfur is inevitably included in the concept of impurities, so the upper limit thereof is limited to 0.003 wt%.

Phosphorus (P): 0.01 wt% or less

Phosphorus is an element useful for securing the strength of the material. However, when added in a large amount, not only the workability decreases but also the weldability decreases, so the upper limit thereof is limited to 0.01%.

Aluminum (Al): 0.2 ~ 1.0wt%

Aluminum is an element mainly used as a deoxidizer, and combines with nitrogen in steel to form AlN to refine the structure and remove oxygen in steel, thereby preventing cracks in slab manufacturing.

In the present invention, since aluminum is added to compensate for this by reducing the content of silicon having an effect of improving elongation, 0.2wt% or more should be added. However, when the addition is excessive, the deoxidation effect is excessive and the grains are coarsened, so the strength is lowered. Therefore, the upper limit is preferably limited to 1.0 wt%.

Chromium (Cr): 0.1-0.5 wt%

Chromium is a ferrite-forming element, which delays the transformation of austenite into pearlite or bainite and improves its strength by causing austenite to be transformed into martensite at room temperature after abnormal reverse annealing. If the amount of chromium is less than 0.1wt%, it is difficult to obtain sufficient strength, and when it is added more than 0.5wt%, there is a problem that the balance of strength and ductility is broken, so the upper limit is limited to 0.5wt% or less.

Copper (Cu): 0.1 ~ 0.3wt%

Copper has the effect of improving strength, but there is a problem that can cause hot brittleness, so it should be added in an appropriate amount, and if it contains more than 0.3%, expensive nickel must be added in a 1: 1 ratio, so it is desirable to limit it to 0.1 ~ 0.3wt%. Do.

Vanadium (V): 0.02 to 0.1 wt%

Vanadium is added as a strengthening element. Vanadium helps to transform austenite into martensite, and when added together with chromium, synergistic effects can be achieved to achieve proper strength and elongation. Therefore, it is important to add vanadium so that it can be well matched with the chromium content.

Vanadium carbide can be dissolved at a relatively low temperature and is easily dissolved upon slab reheating. If the amount of vanadium is less than 0.02%, the amount of finely dispersed complex carbide is insufficient and the amount of vanadium is more than 0.1 wt%. The carbides are coarsened to lower the strength, so the upper and lower values are limited to 0.1 wt%.

Boron (B): 0.003% or less

Boron increases the hardenability of the steel and diffuses into grain boundaries during heat treatment, thereby delaying the pearlite transformation of austenite and the ferrite reverse transformation of martensite. However, it is preferable to limit the upper limit to 0.003 wt% or less since the elongation decreases due to the increase of the solid solution boron, and the boron may diffuse on the surface and degrade the plating property.

Nitrogen (N): 0.007% or less

Nitrogen (N) increases austenite formation when the trace amount is added, and increases the strength by forming aluminum nitride (AlN) or titanium nitride (TiN), it is advantageous to keep the addition amount as low as possible. In particular, nitrogen is preferably limited to the range of 0.007 wt% or less because it reduces elongation at the time of excessive addition and inhibits workability. Nitrogen is a concept of impurities inevitably added here, so it does not matter.

The present invention contains the components of the steel sheet, and the rest are substantially iron (Fe) and unavoidable elements, and the element is included according to the situation of raw materials, materials, manufacturing facilities, etc., allowing fine incorporation of inevitable impurities of less than 0.01%. do.

The slab having the composition as described above is obtained as a slab through the ingot or continuous casting process after obtaining the molten steel through the steelmaking process, and here it is manufactured in the form of steel sheet through hot rolling, cold rolling, annealing, the surface of the steel sheet After the hot dip galvanizing process is carried out.

-Furnace process;

The slab of the present invention is re-heated at 1200 ° C. or higher and maintained for 1 to 2 hours to homogenize to re-use segregated components during casting. If the reheating temperature is low, the segregated components are not reusable. If the reheating temperature is excessively high, the austenite grain size increases and the ferrite grains are coarsened, so the reheating temperature is preferably set at 1200 to 1300 ° C. Of course, the reheat temperature holding time can be adjusted according to the slab thickness.

In addition, it is preferable to maintain the homogenization treatment time for a long time because it is not economically useful, and if short, uniformity of the material may be insufficient and product quality may be degraded.

- hot / cold rolling process;

The homogenized slab in the furnace is hot rolled at Ar3 ~ Ar3 + 50 ℃ to produce single-phase hot rolled coil. The coiling temperature is finished in the coiling temperature (CT) of 500 ~ 700 ℃, preferably 550 ~ 650 ℃ in order to facilitate cold rolling, the furnace is cold-treated to room temperature, and then the picked hot rolled steel sheet is pickled and 50% Cold rolling is performed at the above reduction ratio.

Here, when the finish hot rolling temperature is less than Ar3, excessive dislocations are introduced into the ferrite during rolling to form coarse grains on the surface during cooling or winding, and when Ar3 + 50 ° C, the ferrite grain size increases and the strength decreases, thus Ar3 Limit to Ar3 + 50 ° C.

In addition, when the coiling temperature is less than 500 ° C, a second phase having high strength is generated in the hot rolled steel sheet to increase the strength of the hot rolled sheet, and the shape of the steel sheet worsens after hot rolling, and thus cold rolling is difficult. Since coarse pearlite is formed in the annealing process, re-dissolution does not occur well, so that an annealing steel sheet having a uniform structure cannot be obtained.

A continuous annealing process;

In order to control the fraction of martensite and ferrite, the cold rolled steel sheet is maintained for 5 ~ 120 seconds in the region above Ar1 temperature and below Ar3 temperature to control the fraction of martensite and ferrite. It is quenched to ~ 250 ℃ and annealed continuously.

During this process, it is important to cool the austenite phase produced in the two-phase region at a sufficient cooling rate to prevent transformation into pearlite or bainite. If the temperature is kept below 5 seconds in the region above Ar1 temperature or below Ar3 temperature, the austenite phase is not sufficiently formed during heating, so that an appropriate amount of martensite fraction cannot be obtained, and when it exceeds 120 seconds, the productivity decreases. It is preferable to hold for ˜120 seconds.

A hot dip galvanizing process and an alloying hot dip galvanizing process may be further performed.

- hot-dip galvanizing process;

The continuously annealed steel sheet is quenched to 495 ° C. at a cooling rate of 5 to 50 ° C./s and plated, and further cooled to 250 to 300 ° C. at a cooling rate of 5 to 50 ° C./s or more.

An alloying hot dip galvanizing process;

The continuously annealed steel plate was quenched to 495 ° C. or lower at a cooling rate of 5 to 50 ° C./s, plated, reheated to 500 to 550 ° C., and alloyed, and then cooled to 5 ° C./s to 250 to 350 ° C. Cool to.

Hereinafter, the above-described high strength steel sheet and a method of manufacturing the same will be described by comparing with a comparative example through an invention example.

Table 1 shows the component ratio of the invention example and comparative example of this invention.

division Chemical composition (wt%) Remarks C Si Mn P (max) S (max) Al Cr Mo Cu B (ppm) Nb V N One 0.10 0.10 2.2 0.01 0.003 0.04 - 0.1 - - 0.02 - 0.006 Comparative example 2 0.10 0.10 2.0 0.01 0.003 0.04 - 0.1 - - 0.02 - 0.006 Comparative example 3 0.10 0.10 2.5 0.01 0.003 0.04 - 0.1 - - 0.02 - 0.006 Comparative example 4 0.08 0.10 2.2 0.01 0.003 0.04 - 0.1 - - 0.02 - 0.006 Comparative example 5 0.12 0.10 2.2 0.01 0.003 0.04 - 0.1 - - 0.02 - 0.006 Comparative example 6 0.15 0.10 2.2 0.01 0.003 0.04 - 0.1 - - 0.02 - 0.006 Comparative example 7 0.10 0.10 2.2 0.01 0.003 0.04 - 0.2 - - 0.02 - 0.006 Comparative example 8 0.10 0.10 2.2 0.01 0.003 0.04 - 0.1 - 10 0.01 - 0.006 Comparative example 9 0.10 0.10 2.2 0.01 0.003 0.04 - 0.1 0.1 - 0.02 - 0.006 Comparative example 10 0.10 0.01 2.2 0.01 0.003 0.06 - - 0.1 - - 0.05 0.006 Inventive Example 11 0.10 0.01 2.2 0.01 0.003 0.06 0.5 - 0.1 10 - 0.02 0.006 Inventive Example 12 0.10 0.01 2.2 0.01 0.002 0.06 0.3 - 0.1 10 - 0.05 0.006 Inventive Example

Table 2 shows the results of measuring the mechanical properties of the steel produced by the invention examples and comparative examples of Table 1.

division Manufacture conditions  YS (MPa) TS (MPa) El (%) Yield Ratio (%) Remarks CT AT One 580 790 554.7 777.1 15.2 71.4 Comparative example 2 580 790 493.4 718.3 17.7 68.7 Comparative example 3 580 790 620.3 884.5 14.6 70.1 Comparative example 4 580 790 527.7 774.2 13.1 68.2 Comparative example 5 580 790 581.1 788.4 17.5 79.7 Comparative example 6 580 790 600.7 780.1 17.9 77.0 Comparative example 7 580 790 605.2 882.5 13.8 68.6 Comparative example 8 580 790 512.1 770.8 17.6 66.4 Comparative example 9 580 790 536.1 804.6 18.2 66.6 Comparative example 10 580 790 417.5 703.8 27.1 59.3 Inventive Example 11 580 790 508.6 805.3 22.5 63.1 Inventive Example 12 580 790 503.0 802.9 22.8 62.6 Inventive Example

[CT: coiling temperature, AT: annealing temperature, TS (MPa): tensile strength, YS (MPa): yield strength, EL (%): elongation]

Table 2 shows that the slab with the alloy design of Table 1 was heated at 1250 ° C. for 1 hour, hot rolled at 900 ° C. for finishing for 1 hour, cooled to 580 ° C. for 1 hour, and further cold-rolled, cold-rolled and alloyed molten zinc. After the steel sheet is manufactured by plating, strength, elongation, and the like are tested using the specimen of the steel sheet. Here, the hot rolled steel sheet is pickled in the usual manner, cold rolled and continuously annealed, and cold rolling is performed at a rolling reduction of 50%.

Looking at Tables 1 and 2, it can be seen that the high elongation and low yield strength are obtained by the increase of the aluminum content and the addition of copper, boron, and vanadium, and the areas are not so obtained. It can be seen that even with the addition of chromium, high elongation and low yield ratio can be realized, so that the desired strength and elongation can be obtained at a relatively low cost.

Therefore, it can be seen that a high-strength steel sheet which can be used as a 700 MPa-grade automotive steel sheet having excellent elongation at a lower cost than the related art.

Within the scope of the basic technical idea of the present invention, many other modifications are possible to those skilled in the art, and the scope of the present invention should be interpreted based on the appended claims. will be.

Claims (6)

% By weight Carbon (C): 0.05-0.12%, Silicon (Si): 0.001-0.01%, Manganese (Mn): 2.0-3.0%, Sulfur (S): 0.003% or less, Phosphorus (P): 0.01% or less Aluminum (Al): 0.2-1.0%, Chromium (Cr): 0.1-0.5%, Copper (Cu): 0.1-0.3%, Vanadium (V): 0.02-0.1%, Nitrogen (N): 0.007% or less, Balance iron (Fe) and other unavoidable impurities, A high strength steel sheet in which ferrite having a grain boundary size of 5 to 20 µm is formed at 80 to 90%, and a phase containing martensite is formed at 10 to 20% as a second phase. The method of claim 1, The high strength steel sheet, characterized in that the content of carbon, silicon, manganese, phosphorus, sulfur is in the range satisfying Pcm: C + Si / 30 + Mn / 20 + 2P + 4S ≤ 0.27. % By weight Carbon (C): 0.05-0.12%, Silicon (Si): 0.001-0.01%, Manganese (Mn): 2.0-3.0%, Sulfur (S): 0.003% or less, Phosphorus (P): 0.01% or less Aluminum (Al): 0.2-1.0%, Chromium (Cr): 0.1-0.5%, Copper (Cu): 0.1-0.3%, Vanadium (V): 0.02-0.1%, Nitrogen (N): 0.007% or less, Steel slab with alloy composition of balance iron (Fe) and other unavoidable impurities Homogenizing treatment at 1200 ~ 1300 ℃, hot rolling finished at Ar3 point ~ Ar3 + 50, winding at 500 ~ 570 ℃, cold rolling at 50% of cold rolling rate and continuous annealing, followed by hot dip galvanizing or alloyed hot dip galvanizing Process for producing a high strength steel sheet, characterized in that the step of performing. The method of claim 3, wherein Method for producing a high strength steel sheet, characterized in that the last step of the continuous annealing is maintained for 5 to 120 seconds in the temperature range Ar1 ~ Ar3 point. The method of claim 3, wherein In the galvanizing process, after the continuous annealing, the steel sheet is quenched to 495 ° C. or lower at a cooling rate of 5 to 50 ° C./s, and further cooled to 250 to 300 ° C. at a cooling rate of 5 to 50 ° C./s or more. Method for producing a high strength steel sheet characterized by. The method of claim 3, wherein In the galvanizing process, after the continuous annealing, the steel sheet is quenched to 495 ° C. or lower at a cooling rate of 5 to 50 ° C./s, and plated and reheated to 500 to 550 ° C., followed by alloying to 5 to 250 to 350 ° C. Method for producing a high strength steel sheet, characterized by cooling at a cooling rate of more than ℃ / s.