Method of manufacturing twinning induced plasticity type ultra-high strength steel sheet

Abstract

The present invention features a method of manufacturing a TWIP type ultra-high strength steel sheet, which can improve the yield strength, tensile strength and elongation rate of the TWIP type ultra-high strength steel sheet by appropriately adjusting the amounts of carbon (C), silicon (Si), manganese (Mn), aluminum (Al), molybdenum (Mo), phosphorus (P) and sulfur (S).

1 . A method of manufacturing a TWIP type ultra-high strength 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), and residual iron (Fe) and other inevitable impurities in four passes or more;   recovering the cold-rolled steel sheet at a temperature of 200˜220° C. after the third pass of the cold rolling; and   annealing the recovered steel sheet.   
   
   
       2 . The method of manufacturing a TWIP type ultra-high strength steel sheet according to  claim 1 , wherein the recovering of the cold-rolled steel sheet is conducted for 5˜6 minutes. 
   
   
       3 . The method of manufacturing a TWIP type ultra-high strength steel sheet according to  claim 1 , wherein the annealing of the recovered steel sheet is conducted at a temperature of 700˜850° C. for 5˜6 minutes. 
   
   
       4 . A method of manufacturing a TWIP type ultra-high strength 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), and residual iron (Fe) and other inevitable impurities in four passes or more; and   recovering the cold-rolled steel sheet.   
   
   
       5 . The method of manufacturing a TWIP type ultra-high strength steel sheet of  claim 4 , wherein the cold-rolled steel sheet is recovered at a temperature of 200˜220° C.. 
   
   
       6 . The method of manufacturing a TWIP type ultra-high strength steel sheet of  claim 5 , wherein the cold-rolled steel sheet is recovered after the third pass of the cold rolling. 
   
   
       7 . The method of manufacturing a TWIP type ultra-high strength steel sheet according to  claim 6 , wherein the recovering of the cold-rolled steel sheet is conducted for 5˜6 minutes. 
   
   
       8 . The method of manufacturing a TWIP type ultra-high strength steel sheet of  claim 4 , further comprising annealing the recovered steel sheet. 
   
   
       9 . The method of manufacturing a TWIP type ultra-high strength steel sheet according to  claim 8 , wherein the annealing of the recovered steel sheet is conducted at a temperature of 700˜850° C.. 
   
   
       10 . The method of manufacturing a TWIP type ultra-high strength steel sheet according to  claim 8 , wherein the annealing of the recovered steel sheet is conducted for 5˜6 minutes.