Ultra high strength twip steel sheet and manufacturing method thereof

Abstract

Disclosed herein is an ultra high strength TWIP steel sheet having an austenite matrix texture, comprising 0.15˜0.30 wt % of carbon, 0.01˜0.03 wt % of silicon, 15˜25 wt % of manganese, 1.2˜3.0 wt % of aluminum, 0.020 wt % or less of phosphorus, 0.001˜0.002 wt % of sulfur, and residual iron and other inevitable impurities, wherein the TWIP steel sheet is cold-rolled at a reduction ratio of 35˜40% per pass under a condition of 180˜220 Mpa in front and rear tension, and thus has an average plastic strain ratio of 1.2 or more. The ultra high strength TWIP steel sheet has an improved average plastic strain ratio and excellent formability because it has a developed Goss orientation.

1 . An ultra high strength TWIP steel sheet having an austenite matrix, comprising 0.15˜0.30 wt % of carbon, 0.01˜0.03 wt % of silicon, 15˜25 wt % of manganese, 1.2˜3.0 wt % of aluminum, 0.020 wt % or less of phosphorus, 0.001˜0.002 wt % of sulfur, and residual iron and other inevitable impurities, wherein the TWIP steel sheet is cold-rolled at a reduction ratio of 35˜40% per pass under a condition of 180˜220 Mpa in front and rear tension, and thus has an average plastic strain ratio of 1.2 or more. 
   
   
       2 . A method of manufacturing an ultra high strength TWIP steel sheet having an improved average plastic strain ratio, comprising:
 cold-rolling a hot-rolled steel sheet having an austenite matrix and comprising 15˜25 wt % of manganese at a reduction ratio of 35˜40% per pass under a condition of 180˜220 Mpa in front and rear tension; and   annealing the cold-rolled steel sheet at a temperature of 850˜900° C.   
   
   
       3 . The method of manufacturing an ultra high strength TWIP steel sheet according to  claim 2 , wherein the hot-rolled steel sheet comprises 0.15˜0.30 wt % of carbon, 0.01˜0.03 wt % of silicon, 15˜25 wt % of manganese, 1.2˜3.0 wt % of aluminum, 0.020 wt % or less of phosphorus, 0.001˜0.002 wt % of sulfur, and residual iron and other inevitable impurities 
   
   
       4 . The method of manufacturing an ultra high strength TWIP steel sheet according to  claim 2 , wherein the hot-rolled steel sheet is obtained by hot-rolling a continuously-cast slab at a temperature of 1300˜1100° C. and then cooling the hot-rolled slab at a cooling rate of 60° C./sec or less. 
   
   
       5 . An ultra high strength TWIP steel sheet having an austenite matrix, comprising 0.15˜0.30 wt % of carbon, 0.01˜0.03 wt % of silicon, 15˜25 wt % of manganese, 1.2˜3.0 wt % of aluminum, 0.020 wt % or less of phosphorus, 0.001˜0.002 wt % of sulfur, and residual iron and other inevitable impurities, wherein the TWIP steel sheet is cold-rolled at a reduction ratio of 35˜40% per pass under a condition of 180˜220 Mpa in front and rear tension. 
   
   
       6 . The ultra high strength TWIP steel sheet of  claim 5 , wherein the sheet has an average plastic strain ratio of 1.2 or more. 
   
   
       7 . A method of manufacturing an ultra high strength TWIP steel sheet having an improved average plastic strain ratio, comprising:
 cold-rolling a hot-rolled steel sheet having an austenite matrix and comprising 15˜25 wt % of manganese at a reduction ratio of 35˜40% per pass under a condition of 180˜220 Mpa in front and rear tension; and   annealing the cold-rolled steel sheet.   
   
   
       8 . The method of  claim 7 , wherein the annealing is carried out at a temperature of 850˜900° C.