High-strength twip steel sheet and method of manufacturing the same

Abstract

The present invention features a high-strength and light TWIP steel sheet which can be used to manufacture vehicle body parts, and a method of manufacturing the same.

1 . A method of manufacturing a high-strength TWIP steel sheet, comprising:
 cold-rolling a hot-rolled steel sheet having a composition including 0.15˜0.30 wt % of carbon (C), 0.01˜0.03 wt % of silicon (Si), 15˜25 wt % of manganese (Mn), 1.2˜3.0 wt % of aluminum (Al), 0.020 wt % or less of phosphorus (P), 0.001˜0.002 wt % of sulfur (S), 4.0˜5.0 wt % of titanium (Ti), and residual iron and inevitable impurities; and   continuously annealing the cold-rolled steel sheet.   
     
     
         2 . The method according to  claim 1 , wherein the hot-rolled steel sheet is obtained by preparing a powdered titanium-manganese (Ti—Mn) alloy, melting the titanium-manganese (Ti—Mn) alloy in a converter together with another composition and then continuously casting them to form a slab, hot-rolling the slab from 1100˜1300° C. to 850˜950° C., and then cooling the hot-rolled slab. 
     
     
         3 . The method according to  claim 2 , wherein the hot-rolled slab is air-cooled from 850˜950° C. to 650˜750° C. at a cooling rate of 35˜45° C./sec. 
     
     
         4 . A high-strength TWIP steel sheet having a composition, the composition comprising:
 0.15˜0.30 wt % of carbon (C);   0.01˜0.03 wt % of silicon (Si);   15˜25 wt % of manganese (Mn);   1.2˜3.0 wt % of aluminum (Al);   0.020 wt % or less of phosphorus (P);   0.001˜0.002 wt % of sulfur (S);   4.0˜5.0 wt % of titanium (Ti); and   residual iron and inevitable impurities.   
     
     
         5 . The high-strength TWIP steel sheet according to  claim 4 , wherein the composition is formed into the TWIP steel sheet having a yield strength of 550 MPa or more by preparing a powdered titanium-manganese (Ti—Mn) alloy, melting the titanium-manganese (Ti—Mn) alloy in a converter together with another composition and then continuously casting them to form a slab, hot-rolling the slab to recrystallize, cold-rolling the hot-rolled slab, and then annealing the cold-rolled slab. 
     
     
         6 . The high-strength TWIP steel sheet according to  claim 5 , wherein, in the hot rolling, the continuous-cast slab is hot-rolled from 1100˜1300° C. to 850˜950° C.; and then the hot-rolled slab is air-cooled from 850˜950° C. to 650˜750° C. at a cooling rate of 35˜45° C./sec. 
     
     
         7 . A method of manufacturing a high-strength TWIP steel sheet, comprising:
 cold-rolling a hot-rolled steel sheet having a composition comprising carbon (C), silicon (Si), manganese (Mn), aluminum (Al), phosphorus (P), sulfur (S), titanium (Ti), and residual iron and inevitable impurities; and   annealing the cold-rolled steel sheet.   
     
     
         8 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 0.15˜0.30 wt % of carbon (C). 
     
     
         9 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 0.01˜0.03 wt % of silicon (Si). 
     
     
         10 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 15˜25 wt % of manganese (Mn). 
     
     
         11 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 1.2˜3.0 wt % of aluminum (Al). 
     
     
         12 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 0.020 wt % or less of phosphorus (P). 
     
     
         13 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 0.001˜0.002 wt % of sulfur (S). 
     
     
         14 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition comprising 4.0˜5.0 wt % of titanium (Ti). 
     
     
         15 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein the hot-rolled steel sheet has a composition further comprising residual iron and inevitable impurities. 
     
     
         16 . The method of manufacturing a high-strength TWIP steel sheet of  claim 7 , wherein annealing the cold-rolled steel sheet is performed continuously. 
     
     
         17 . A high-strength TWIP steel sheet having a composition, the composition comprising:
 carbon (C);   silicon (Si);   manganese (Mn);   aluminum (Al).;   phosphorus (P);   sulfur (S);   titanium (Ti); and   residual iron and inevitable impurities.