KR20110072791A - Austenitic steel sheet with high ductility and high resistance of delayed fracture and manufacturing method the same - Google Patents

Abstract

PURPOSE: An austenitic steel sheet with excellent ductility and delayed fracture resistance and a manufacturing method thereof are provided to lighten a vehicle body by using the steel sheet for the components of a vehicle. CONSTITUTION: An austenitic steel sheet with excellent ductility and delayed fracture resistance comprises carbon 0.3~1.0 weight%, silicon 0.3~2.5 weight%, manganese 10~18 weight%, titanium 0.01~0.3 weight%, boron 0.0005~0.01 weight%, nitrogen less than 0.04 weight%, phosphorus less than 0.1 weight%, sulfur less than 0.2 weight%, iron, and inevitable impurities. The tensile strength of the austenitic steel sheet is more than 780MPa. The elongation of the austenitic steel sheet is more than 30%.

Description

Austenitic Steel Sheet with High Ductility and High Resistance of Delayed Fracture and Manufacturing Method The Same}

The present invention relates to a high strength steel sheet and a method for manufacturing the same, and more particularly, to an austenitic high strength steel sheet having excellent strength and ductility and having improved delayed fracture resistance.

In recent years, the use of high strength steel sheets has been greatly demanded in order to improve fuel efficiency, reduce exhaust gas, and prevent shock absorption or damage to a vehicle body when vehicle body weight is reduced.

The high strength steel sheet for automobiles currently used is steel plate with tensile strength of 780 MPa or more. However, as the strength is improved, the elongation decreases rapidly, which makes it difficult to process complex automotive parts, and the processing process is long even when processing the same parts. There is this.

Therefore, a steel sheet excellent in elongation while securing a tensile strength of 780 MPa or more is required. Steel sheets using metamorphic structures have been proposed for steel sheets having these characteristics. Among these steel sheets, abnormal steels (dual phase steels) or soft steels, which disperse hard martensite in soft ferrite matrix and simultaneously secure elongation and strength, have been proposed. A typical example is the modified organic plastic steel (TRIP steel), which further improves elongation as the residual austenite is transformed into martensite during processing by dispersing residual austenite instead of martensite in the ferrite matrix.

However, these abnormal tissue steels and metamorphic organic plastic steels have limitations in improving elongation compared to tensile strength. Especially, in the case of complicated body parts requiring elongation of 25% or less at tensile strength of 780 MPa or more, it is difficult to form. have. In addition, these steels are basically a ferritic steel sheet, which exhibits a dispersion strengthening effect using a second phase to improve strength. On the contrary, when a large amount of the second phase is dispersed, an elongation is lowered because ferrites having excellent ductility are reduced. There is. As described above, the ferrite-based high strength steel sheet cannot avoid the phenomenon that the elongation rapidly decreases when the strength is increased.

In order to fundamentally solve this problem of strength-elongation of high strength steel sheets for automobiles, it is the only way to use austenitic steel grades instead of ferritic steel grades. Austenite mainly utilizes solid solution strengthening by adding carbon, nitrogen, or manganese or precipitation strengthening by precipitation to increase strength. However, austenite is deformed by forming twins inside austenite during processing, and twin deformation has a very small advantage of decreasing elongation due to solid solution strengthening or precipitation strengthening. Therefore, in order to increase the strength while minimizing the elongation deterioration it is necessary to manufacture austenitic steel sheet.

Recently, high manganese steels containing a large amount of manganese have been developed as austenitic high strength steel sheets for automobiles. Such techniques include Japanese Laid-Open Patent Publication No. 1992-259325, WO 02/101109, etc. These techniques have a very high manganese content of 15% or more, which leads to an increase in the input price of ferroalloy and at the same time in manganese. Phosphorus contained in the steel increases the content of phosphorus in steel increases the risk of cracking during casting and has the disadvantage of increasing hydrogen embrittlement.

Another technique is EP 1 878 811 A1, which also suggests a method for manufacturing high ductility high strength steels using C- (15-26%) Mn-Ti-Nb-Mo-Cr systems. There is a problem due to the manganese content, in addition to Nb, Mo and the like has a problem of reducing the delayed fracture (Delayed Fracture) by hydrogen embrittlement.

Another technique is Korean Laid-Open Patent Publication No. 2008-0130399. In addition to a large amount of manganese, aluminum nitride (AlN) is formed at the grain boundary during solidification or slab heating according to the addition of a large amount of aluminum. There is a problem that causes cracking or edge cracking of the steel sheet.

An object of the present invention is to provide an austenitic high strength steel sheet having excellent ductility and delayed fracture properties satisfying a tensile strength of 780 MPa or more, an elongation of 30% or more, and a stacking defect energy of 30 mJ / m 2 or more, and a method of manufacturing the same.

In one embodiment, the present invention provides, in weight percent, carbon (C): 0.3-1.0%, silicon (Si): 0.3-2.5%, manganese (Mn): 10-18%, aluminum (Al): 1.0-4.0 %, Titanium (Ti): 0.01-0.3%, boron (B): 0.0005-0.01%, nitrogen (N): 0.04% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, balance An austenitic high strength steel sheet containing iron (Fe) and other unavoidable impurities and satisfying 60C + Mn + 2Ni + 9Al + 3Si ≧ 50% by weight is provided.

The steel sheet is by weight, nickel (Ni): 0.05 to 2.0%, chromium (Cr): 0.01 to 2.0%, niobium (Nb): 0.01 to 0.10% and vanadium (V): 0.01 to 0.5% or It may further comprise two or more.

The lamination defect energy of the steel sheet is preferably 30 mJ / m 2 or more.

The tensile strength of the steel sheet is preferably 780 MPa or more, and the elongation is 30% or more.

The steel sheet is preferably one of a hot rolled steel sheet, a cold rolled steel sheet, a hot dip steel sheet and an electroplated steel sheet.

As another embodiment of the present invention, in weight%, carbon (C): 0.3-1.0%, silicon (Si): 0.3-2.5%, manganese (Mn): 10-18%, aluminum (Al): 1.0-4.0 %, Titanium (Ti): 0.01-0.3%, boron (B): 0.0005-0.01%, nitrogen (N): 0.04% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, balance Heating a slab containing iron (Fe) and other unavoidable impurities and satisfying 60C + Mn + 2Ni + 9Al + 3Si ≧ 50% by weight to 1050-1250 ° C .; Finishing rolling the heated slab at 850˜950 ° C .; And winding the rolled steel sheet at 700 ° C. or less.

The steel sheet is by weight, nickel (Ni): 0.05 to 2.0%, chromium (Cr): 0.01 to 2.0%, niobium (Nb): 0.01 to 0.10% and vanadium (V): 0.01 to 0.5% or It may further comprise two or more.

The method may further include cold rolling and annealing the wound steel sheet, and may further include electroplating the cold rolled steel sheet after the annealing. In addition, after cold rolling, the method may include continuously annealing at a recrystallization temperature or higher and performing hot dip plating.

The present invention can provide a high strength steel sheet having a tensile strength of 780 MPa or more excellent in formability and impact characteristics, and a method of manufacturing the same, and can be applied to various steel sheets for automobile parts to improve vehicle body weight reduction and crash safety.

In order to secure a complete austenite phase at room temperature, the present invention is characterized in that the austenitic forming elements carbon, manganese, nickel and ferrite forming elements aluminum and silicon (60) are 60C + Mn + 2Ni + 9Al + 3Si ≥ 50% by weight. Suggest to satisfy, and control the stacking defect energy to be more than 30mJ / ㎡ to form an appropriate amount of twins and dislocations when the steel sheet is deformed.

 The present invention can enhance the precipitation strengthening effect by forming fine precipitates in austenite by adding carbonitride forming elements such as titanium, vanadium, niobium, etc. in addition to solid solution strengthening by carbon or silicon in order to increase the strength. In addition, in order to prevent deterioration of delayed fracture characteristics due to deterioration of martensite due to desorption of surface elements such as decarburization and demanganese in steel sheet manufacturing process, the austenite structure is lowered. Add. Finally, in case of delayed fracture after casting process and deformation, phosphorus content is lowered and boron is added to prevent deterioration of grain boundary fracture strength.

Hereinafter, the component system of the steel sheet of the present invention will be described.

Carbon (C): 0.3-1.0 wt%

Carbon is a useful element for stabilizing austenite and increasing stacking fault energy. When the content of carbon is less than 0.3% by weight, it is difficult to form stable austenite at room temperature, and because martensite is formed during deformation, the strength is increased but the ductility is low. On the other hand, when the content exceeds 1.0% by weight, carbides are easily formed in the heat treatment process to generate a large amount of sites serving as starting points of hydrogen embrittlement cracks, resulting in deterioration in delayed fracture characteristics and excessive increase in stacking defect energy. Therefore, rather than forming twins during deformation, deformation behavior is caused by slip deformation, resulting in reduced strength and low elongation.

Silicon (Si): 0.3 ~ 2.5 wt%

Silicon makes grains finer, improves strength by solid solution strengthening, and lowers the formation temperature of martensite, making it easier to obtain austenite at room temperature. In addition, since the stacking defect energy is increased, and the diffusion rate of carbon in steel, such as aluminum, is reduced, dynamic strain aging is suppressed, and precipitation of carbides is suppressed during heat treatment, thereby improving delayed fracture resistance. In addition, by improving the corrosion resistance of the high manganese steel has the effect of suppressing over-acid pickling in the pickling process. This effect is insignificant when the content of silicon is less than 0.3% by weight. However, when the content exceeds 2.5% by weight, the lamination defect energy is excessively increased, the elongation is lowered, silicon oxide is formed on the surface of the steel sheet, which lowers the plating property, and the silicon oxide is also formed in the welded portion, which is weldable. Is lowered.

Manganese (Mn): 10-18 wt%

Manganese is an essential element for stably securing austenite structure and is useful for increasing stacking defect energy. When the content of manganese is less than 10% by weight, martensite is formed to increase strength but rapidly decrease in ductility, and lamination defect energy is lowered to partially form austenite as epsilon-martensite. On the other hand, if the content exceeds 18%, the manufacturing cost increases due to a large amount of manganese, the slab cracks due to the increase in the phosphorus content in the steel, and the internal grain boundary oxidation occurs excessively when the slab is reheated, Defects due to oxides occur and surface properties are inferior during plating.

Aluminum (Al): 1.0-4.0 wt%

Aluminum is generally added for deoxidation of steel. In the present invention, aluminum is added to secure workability and to improve austenite stabilization and delayed fracture resistance. The workability of high manganese steel is closely related to the stacking defect energy. When the stacking defect energy of an appropriate range or less is obtained, epsilon martensite is generated, resulting in poor workability and delayed fracture resistance. On the other hand, when the lamination defect energy is excessive, twin deformation does not occur and thus the strength is lowered and the workability is lowered. Aluminum is an element that can effectively increase the stacking defect energy, and in the present invention, the stacking defect energy due to the lowering of the manganese content can be compensated for. When the content of aluminum is less than 1.0% by weight, such an effect is insignificant, and when the content of manganese is low, it is difficult to satisfy the relation 1, and it is difficult to secure the austenite single phase structure. On the other hand, when the content is more than 4.0% by weight, the ferrite structure is easily formed, the structure having a regular grid is formed, the ductility is rapidly reduced, the surface quality of hot rolled or plated steel sheet is sharply worsened.

Titanium (Ti): 0.01 ~ 0.3 wt%

Titanium is an effective element in combination with carbon and nitrogen to form carbonitrides to suppress grain growth and to refine grain size. In addition, by forming a TiN precipitate in the casting structure during continuous casting to reduce the dissolved nitrogen, it is possible to significantly reduce the occurrence of cracking during slab cracking and hot rolling rough rolling by precipitation of grain boundary AlN, BN. In addition, phosphorus causing grain boundary segregation can be precipitated with FeTiP. This effect is insignificant when the content of titanium is less than 0.01% by weight. On the other hand, if the content exceeds 0.3% by weight, problems such as clogging of the nozzle in the continuous casting process, and there is a problem of increasing the manufacturing cost because titanium is an expensive metal.

Boron (B): 0.0005 to 0.01 weight%

Boron is effective in suppressing grain boundary segregation and preventing hydrogen embrittlement caused by the reaction of hydrogen and phosphorus by competing at the boundary between phosphorus and grain boundary or twinning interface.Boron is segregated at grain boundary to improve processability by increasing grain strength. It is a useful element. This effect is negligible when the boron content is less than 0.0005% by weight. On the other hand, when the content is greater than 0.01% by weight, a large amount of BN is formed, causing slab cracking and surface defects.

Nitrogen (P): 0.04 wt% or less

Nitrogen is an element that stabilizes austenite and reacts with aluminum or titanium during solidification to precipitate fine nitrides, which affects the quality of the slabs and the cracking of hot rolled sheets. However, when the nitrogen content exceeds 0.04% by weight, the nitride is excessively precipitated, which may lower the hot workability and elongation.

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

However, since phosphorus and sulfur are generally mentioned impurities, the following briefly describes them.

Phosphorus (P): 0.1 wt% or less

Phosphorus is an impurity inevitably contained by manganese in the production of high manganese steel, and it is preferable to control it as low as possible because it is included in the steel to cause grain boundary segregation. In theory, the phosphorus content is advantageously limited to 0%, but inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the phosphorus content is preferably limited to 0.1% by weight.

Sulfur (S): 0.02% by weight or less

Sulfur is an inevitable impurity, and reacts with manganese to form MnS, resulting in defects such as flange cracks, and reducing hole expandability. In theory, the sulfur content is advantageously limited to 0%, but inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, and the upper limit of the sulfur content in the present invention is preferably limited to 0.02% by weight.

60C + Mn + 2Ni + 9Al + 3Si≥50 wt%

In the present invention, when the value of 60C + Mn + 2Ni + 9Al + 3Si is less than 50% by weight, austenite cannot be stabilized and thus austenite single phase structure cannot be obtained. Instead of lowering the content of manganese a little, instead of actively using aluminum and silicon as an alternative component, a content relational expression is proposed. When aluminum and silicon are added, carbon can contribute to stabilizing austenite by suppressing iron carbide formation in steel.

In addition, the steel of the present invention may further improve the effects of the present invention when one or more elements of nickel (Ni), chromium (Cr), niobium (Ni), and vanadium (V) described below are additionally added. Can be.

Nickel (Ni): 0.05-2.0 wt%

Nickel is an effective element for improving austenite stabilization, elongation and high temperature ductility. This effect is insignificant when the nickel content is less than 0.05% by weight. On the other hand, when the content exceeds 2.0% by weight, the improvement of the effect is not large compared to the cost increase.

Chromium (Cr): 0.01-2.0 wt%

Chromium reacts with external oxygen in the hot rolling or annealing process to form a chromium-based oxide film having a thickness of about 20 to 50 μm on the surface of the steel sheet to prevent leaching of manganese, silicon, etc. contained in the steel into the surface layer, thereby stabilizing the surface structure. It is an element that contributes to and improves the plating surface properties. This effect is insignificant when the content of chromium is less than 0.01% by weight. On the other hand, when the content is more than 2.0% by weight chromium carbide is formed, the workability and delayed fracture characteristics are reduced.

Niobium (Nb): 0.01 to 0.10 wt%

Niobium is a useful element for bonding carbides with carbon to form carbides to increase the strength of steels and to refine grains. This effect is insignificant when the content of niobium is less than 0.01% by weight. On the other hand, when the content exceeds 0.10% by weight, segregation at grain boundaries may cause grain embrittlement or excessively coarsened precipitated phase, which may cause a problem of increasing rolling load by delaying recrystallization during hot rolling.

Vanadium (V): 0.01 to 0.5% by weight

Vanadium is an element that forms carbonitrides by combining with carbon and nitrogen, such as titanium, and thus forms a fine precipitated phase at low temperature, and thus has a high precipitation strengthening effect and is useful for securing austenite. This effect is insignificant when the content of vanadium is less than 0.01% by weight. On the other hand, when the content exceeds 0.5% by weight, the precipitated phase is excessively coarsened to lower the grain growth effect and hot brittleness occurs.

As a steel sheet having the above-described component system, it is necessary to limit the microstructure of the steel sheet to preferable conditions for becoming a steel sheet having excellent surface cracking resistance and excellent strength and toughness. The microstructure of the steel sheet of the present invention is austenite single phase, the austenite is twinned to form austenite during processing, the deformation proceeds, twin strain deformation is very small decrease in elongation due to solid solution strengthening or precipitation strengthening. When ferrite is included, it is difficult to improve both strength and ductility.

The present invention can control the carbon, manganese, aluminum and silicon content as described above to ensure the stacking defect energy of more than 30mJ / ㎡, and to ensure the ductility due to dislocations and twins during deformation.

In addition, the tensile strength of the steel sheet of the present invention is 780MPa or more, the elongation is 30% or more, excellent strength and ductility, excellent delayed fracture characteristics, excellent wettability of molten zinc and electroplating adhesion is provided. can do.

The most preferred method derived by the present inventors for producing the steel sheet which satisfies the object of the present invention as described above will be described below.

In the manufacturing method of the present invention, a slab satisfying the above-described component system is roughly heated and homogenized, and then manufactured into a hot rolled steel sheet through hot rolling and winding, and the hot rolled steel sheet is cold rolled and annealed to a cold rolled steel sheet. It provides a method of manufacturing. Furthermore, it provides a method of manufacturing the cold rolled steel sheet by electro galvanized or alloyed hot dip galvanized steel sheet. Hereinafter, detailed conditions of each step will be described.

Slab heating: 1050 ~ 1250 ℃

If the slab is heated at less than 1050 ° C., it is difficult to secure the temperature during finish rolling, which increases the rolling load and does not complete recrystallization, thereby degrading mechanical properties. On the other hand, if it exceeds 1250 ℃ liquid film may be formed at the columnar grain boundary of the slab cracks during hot rolling.

Hot Rolled: 850 ~ 950 ℃

The reheated slab as described above is subjected to finish rolling at 850 ~ 950 ℃. If the finish rolling temperature is less than 850 ° C, recrystallization is not completed and grains become coarse. On the other hand, if it exceeds 950 ℃ surface oxidation may occur during rolling.

Winding stage: below 700 ℃

If the coiling temperature exceeds 700 ℃, a large amount of thick oxide film and internal oxidation occurs on the surface of the hot-rolled steel sheet, so that it is not easy to remove the oxide layer during pickling, and the internal oxide layer remaining after pickling may develop due to surface defects in subsequent processes. Can be.

After winding, the cooled hot rolled steel sheet is subjected to cold rolling and continuous annealing treatment after pickling. The annealing temperature should be carried out above the recrystallization temperature. If the annealing temperature is too low, it is difficult to secure sufficient processability because the rolling structure is unrecrystallized and a large amount of dislocation remains. The steel of the present invention is an austenitic steel in which no phase transformation occurs in the annealing process, and in order to secure workability, it is preferable to limit the annealing temperature above the recrystallization temperature.

The cold rolled steel sheet manufactured by the above manufacturing conditions may be manufactured by galvanized steel sheet to improve corrosion resistance, and the present invention may be manufactured by an electrogalvanized steel sheet by electroplating or a hot dip galvanized steel sheet by melt plating. . In order to manufacture the galvanized steel sheet, the annealed cold rolled steel sheet can be electroplated in a conventional method and conditions using a hydrochloric acid bath or a sulfuric acid bath. In addition, hot-dip galvanizing may be annealed under the same conditions as the above continuous annealing, and then a hot-dip galvanized steel sheet may be manufactured in a hot-dip zinc bath, or an alloyed hot-dip plating treatment may be performed to heat the plating layer to produce an alloyed hot-dip galvanized steel sheet. .

Hereinafter, the present invention will be described in detail through examples.

(Example)

A steel slab satisfying the component system shown in Table 1 below was heated to 1200 ° C., maintained for 1 hour, subjected to finish hot rolling at 900 ° C., and wound up at 600 ° C. to prepare a hot rolled steel sheet. The tensile strength and elongation of the hot rolled steel sheet were measured and shown in Table 2 below.

The hot rolled steel sheet was cold rolled at a reduction ratio of 50%, and annealed at 800 ° C. to produce a cold rolled steel sheet. The tensile strength and elongation of the cold rolled steel sheet were measured and shown in Table 2 below. In addition, the delayed fracture resistance for the cold rolled steel sheet by measuring the number of days the cup breaks by immersing in a water tank after the cup molding with a drawing ratio of 1.8, and after 60 days is good (○), less than 60 days is judged to be poor (×) It is shown in Table 2 below.

In addition, the cold-rolled steel sheet was evaluated for hot-dip galvanizing after the hot dip galvanizing, and the wet-plating wetness was evaluated. The adhesion of the zinc-plated layer after the electro-galvanizing was measured and shown in Table 2 below. In addition, the microstructure and the lamination defect energy of the hot rolled steel sheet and cold rolled steel sheet were measured and the results are shown in Table 2 below.

division C Mn Al Si P S Cr Ni N B Ti Nb V Comparative Steel 1 0.1 12.0 2.8 0.5 0.011 0.003 - - 0.006 - - - - Comparative Steel 2 0.15 12.0 2.0 2.0 0.010 0.003 - - 0.007 - - - - Comparative Steel 3 0.20 12.0 2.5 0.5 0.011 0.002 - - 0.006 - - - - Comparative Steel 4 0.41 13.9 0.1 0.5 0.015 0.002 - - 0.006 - - - - Comparative Steel 5 0.40 11.2 1.2 0.05 0.010 0.003 - - 0.007 - - - - Inventive Steel 1 0.39 11.9 2.1 2.0 0.010 0.002 - - 0.006 0.001 0.10 - - Inventive Steel 2 0.71 10.9 2.0 1.6 0.015 0.003 0.10 - 0.007 0.001 0.09 - - Invention Steel 3 0.58 12.4 1.8 1.0 0.012 0.002 0.20 - 0.007 0.001 0.09 - - Inventive Steel 4 0.60 12.5 1.6 1.0 0.010 0.002 0.50 0.37 0.007 0.002 0.10 - 0.24 Inventive Steel 5 0.65 14.3 2.0 0.5 0.021 0.002 0.02 0.30 0.008 0.001 0.10 - - Inventive Steel 6 0.54 14.1 2.4 0.5 0.021 0.002 0.50 0.02 0.008 0.002 0.09 0.05 0.25

(Each unit is in weight percent)

division Hot rolled steel
The tensile strength
(MPa) Hot rolled steel
Elongation
(%) Cold rolled steel sheet
The tensile strength
(MPa) Cold rolled steel sheet
Elongation
(%) delay
Destruction
characteristic Melting
Plated
Wettability Electricity
Plated
Adhesion group Lamination
flaw
energy Comparative Steel 1 1292 14 1312 10 × ○ ○ A + M 24.8 Comparative Steel 2 1364 21 1410 18 × ○ ○ A + M 24.0 Comparative Steel 3 1118 29 1225 21 × ○ ○ A + F 26.0 Comparative Steel 4 904 20 927 21 × ○ ○ A + M 15.2 Comparative Steel 5 848 19 880 23 × ○ ○ A + M 22.1 Inventive Steel 1 1130 36 1253 40 ○ ○ ○ M 33.4 Inventive Steel 2 1050 40 1216 45 ○ ○ ○ M 43.2 Invention Steel 3 895 52 954 60 ○ ○ ○ M 35.4 Inventive Steel 4 949 42 1079 48 ○ ○ ○ M 34.5 Inventive Steel 5 917 49 996 52 ○ ○ ○ M 38.9 Inventive Steel 6 882 49 958 40 ○ ○ ○ M 38.0

(A: austenite, M: martensite, F: ferrite)

As shown in Tables 1 and 2, Comparative Steels 1 to 5 are steel grades out of the component system of the present invention. As a result, the elongation is lower than that of the inventive steel, and the inferior delayed fracture property is inferior. In the microstructure, martensite or ferrite structure except austenite was observed, and the lamination defect energy was measured to be less than 30 mJ / m 2. This result is due to a hard structure such as martensite, the elongation is lowered, and due to the low lamination defect energy, the transformation of austenite into epsilon martensite or martensite occurs in the austenite during tensile deformation or cup forming. This is because cracks due to hydrogen embrittlement occur at the interface by releasing hydrogen to the interface of the tissue.

On the contrary, invented steels 1 to 6 added a large amount of C, Al, Si instead of low Mn to secure austenite stability, and when the lamination defect energy was deformed to 30 mJ / m 2 or more, no martensite transformation occurred, Since continuous deformation by twinning is possible, high elongation is obtained and delayed fracture is improved by suppressing explosive hydrogen release such as martensite transformation. In addition, the invention steel and the comparative steel had a low Si / Mn ratio of 0.2 or less, so that the wettability of the molten zinc and the adhesion of the electro zinc plating were good. Therefore, in the case of the present invention, it can be seen that the tensile strength of 780 MPa or more, high elongation of 30% or more, as well as excellent delayed fracture resistance and good hot dip galvanizing and electro zinc plating properties.

Claims (11)

By weight%, carbon (C): 0.3-1.0%, silicon (Si): 0.3-2.5%, manganese (Mn): 10-18%, aluminum (Al): 1.0-4.0%, titanium (Ti): 0.01 -0.3%, boron (B): 0.0005-0.01%, nitrogen (N): 0.04% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, residual iron (Fe) and other unavoidable impurities Austenitic high strength steel sheet comprising a, satisfying 60C + Mn + 2 Ni + 9 Al + 3 Si ≥ 50% by weight. The method of claim 1, wherein the steel sheet is weight percent, nickel (Ni): 0.05 to 2.0%, chromium (Cr): 0.01 to 2.0%, niobium (Nb): 0.01 to 0.10% and vanadium (V): 0.01 to Austenitic high strength steel sheet further comprising 0.5%, one or two or more. The austenitic high strength steel sheet according to claim 1, wherein the stacking defect energy of the steel sheet is 30 mJ / m 2 or more. The austenitic high strength steel sheet according to claim 1, wherein the tensile strength of the steel sheet is 780 MPa or more. The austenitic high strength steel sheet according to claim 1, wherein the elongation of the steel sheet is 30% or more. The austenitic high strength steel sheet according to claim 1, wherein the steel sheet is one of a hot rolled steel sheet, a cold rolled steel sheet, a hot dip steel sheet, and an electroplated steel sheet. By weight%, carbon (C): 0.3-1.0%, silicon (Si): 0.3-2.5%, manganese (Mn): 10-18%, aluminum (Al): 1.0-4.0%, titanium (Ti): 0.01 -0.3%, boron (B): 0.0005-0.01%, nitrogen (N): 0.04% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, residual iron (Fe) and other unavoidable impurities A slab comprising 60 C + Mn + 2Ni + 9Al + 3Si ≧ 50% by weight to 1050˜1250 ° C .; Finishing rolling the heated slab at 850˜950 ° C .; And Method for producing a high austenitic steel sheet comprising the step of winding the rolled steel sheet at 700 ℃ or less. The method according to claim 7, wherein the steel sheet is by weight, nickel (Ni): 0.05 to 2.0%, chromium (Cr): 0.01 to 2.0%, niobium (Nb): 0.01 to 0.10% and vanadium (V): 0.01 to A method for producing an austenitic high strength steel sheet further comprising one or two or more of 0.5%. The method of claim 7, wherein the manufacturing method further comprises cold rolling and annealing the wound steel sheet. The method of claim 9, wherein the manufacturing method further comprises the step of electroplating the cold rolled steel sheet after annealing. 10. The method of claim 9, wherein the manufacturing method includes a step of continuous annealing at a recrystallization temperature or higher after the cold rolling of the steel sheet, and a step of hot dip plating.