High-strength and high-ductility steel sheet and method of manufacturing the same

Abstract

A high-strength and high-ductility steel sheet having a composition including, by weight, 1.0 to 1.4% C, 5.0 to 9.0% Mn, 2.0 to 8.0% Cr and the balance Fe, and unavoidable impurities. The steel sheet has an austenite structure formed at room temperature, and stacking fault energy is effectively controlled by the addition of Cr and N 2 . Mechanical twins are formed during the plastic deformation of the steel, thereby leading to high levels of work hardening, tensile strength and workability.

What is claimed is: 
     
         1 . A high-strength and high-ductility steel sheet having a composition comprising, by weight, 0.8 to 1.4% carbon, 5.0 to 10.0% manganese, 2.0 to 8.0% chromium and the balance iron, and unavoidable impurities. 
     
     
         2 . The steel sheet according to  claim 1 , comprising twinning-induced plasticity steel. 
     
     
         3 . The steel sheet according to  claim 1 , excluding chromium carbides. 
     
     
         4 . The steel sheet according to  claim 1 , comprising a hot-rolled steel sheet heat-treated at a temperature of 1100° C. or higher. 
     
     
         5 . The steel sheet according to  claim 4 , wherein the hot-rolled steel is manufactured by heating the steel sheet at a temperature of 1100° C. or higher, hot-rolling the heated steel sheet at a temperature of 900° C. or higher, and subsequently cooling the hot-rolled steel sheet by air cooling or forced cooling. 
     
     
         6 . The steel sheet according to  claim 4 , comprising a cold-rolled annealed steel manufactured by cold-rolling the hot-rolled steel. 
     
     
         7 . The steel sheet according to  claim 6 , wherein the cold-rolled annealed steel is manufactured by cold-rolling the cooled steel sheet with a thickness reduction ratio of 30% or greater at room temperature, annealing the cold-rolled steel sheet at a temperature of 800° C. or higher, and subsequently cooling the annealed steel sheet by air cooling or forced cooling. 
     
     
         8 . The steel sheet according to  claim 1 , wherein a value obtained by multiplying a tensile strength with a total elongation is 30,000 MPa % or greater. 
     
     
         9 . The steel sheet according to  claim 1 , wherein an amount of the chromium ranges from 4.0 to 7.0% by weight. 
     
     
         10 . The steel sheet according to  claim 1 , wherein the composition further comprises, by weight, 0.1 to 2.0% aluminum. 
     
     
         11 . A method of manufacturing a high-strength and high-ductility steel sheet, the method comprising:
 preparing a steel sheet having a composition comprising, by weight, 0.8 to 1.4% carbon, 5.0 to 10.0% manganese, 2.0 to 8.0% chromium and the balance iron, and unavoidable impurities;   heating the steel sheet at a temperature of 1100° C. or higher;   hot-rolling the heated steel sheet at a temperature of 900° C. or higher; and   cooling the hot-rolled steel sheet by air cooling or forced cooling.   
     
     
         12 . The method according to  claim 11 , further comprising:
 cold-rolling the cooled steel sheet with a thickness reduction ratio of 30% or greater at room temperature;   annealing the cold-rolled steel sheet at a temperature of 800° C. or higher; and   cooling the annealed steel sheet by air cooling or forced cooling.   
     
     
         13 . The method according to  claim 11 , wherein an amount of the chromium ranges, by weight, 4.0 to 7.0%. 
     
     
         14 . The method according to  claim 11 , wherein the composition further comprises, by weight, 0.1 to 2.0% aluminum.