High strength steel sheet and manufacturing method therefor

Abstract

The present invention relates to a high strength steel sheet having a tensile strength of 700 to 1,300 Mpa and an elongation of 12% or more, and having a tempered martensite single phase structure. The steel sheet of the present invention is manufactured through the steps of: rapidly heating a material steel sheet for 3 to 60 seconds to an Ac3 transformation point or higher and maintaining the material steel sheet, the material steel sheet containing 0.08 to 0.30 wt % of C, 0.01 to 2.0 wt % of Si, 0.30 to 3.0 wt % of Mn, 0.05 wt % or less of P and 0.05 wt % or less of S and the remainder being Fe and other unavoidable impurities; rapidly cooling the heated steel sheet to 100° C./s or higher with water or oil; and rapidly tempering to 500° C. to A1 transformation point for 3 to 60 seconds including heating and maintaining time.

1 . A high-strength steel sheet having a tensile strength of 700-1,300 MPa and an elongation of 12% or more and being composed of a tempered martensite single-phase metal structure, the high-strength steel sheet being manufactured by carrying out quenching and tempering on a material steel sheet through high-frequency induction heating or resistance heating, the material steel sheet comprising C: 0.08-0.30 wt %, Si: 0.01-2.0 wt %, Mn: 0.30-3.0 wt %, P: 0.05 wt % or less, S: 0.05 wt %, and the balance Fe and unavoidable impurities. 
     
     
         2 . The high-strength steel sheet of  claim 1 , wherein the steel sheet is manufactured by additionally adding at least any one component of Cr: 0.05-2.0 wt %, Mo: 0.05-2.0 wt %, B: 0.0003-0.0050 wt %, Ti: 0.01-0.20 wt %, and Al: 0.01-0.10 wt %. 
     
     
         3 . The high-strength steel sheet of  claim 1 , wherein the steel sheet has a hot-dip galvanizing layer provided on a surface thereof. 
     
     
         4 . A method for manufacturing a high-strength steel sheet, the method comprising:
 rapidly heating a material steel sheet at the Ac3 transformation point or higher for 3-60 seconds and then holding the heated steel sheet, the material steel sheet comprising C: 0.08-0.30 wt %, Si: 0.01-2.0 wt %, Mn: 0.30-3.0 wt %, P: 0.05 wt % or less, S: 0.05 wt %, and the balance Fe and unavoidable impurities;   rapidly cooling the steel sheet in a heated state at 100° C./s or more using water or oil;   tempering the steel sheet at a temperature of 500° C. to the A1 transformation point for 3-60 seconds, including the time required for heating and holding;   cooling the heated steel sheet using water and air; and   obtaining a high-strength steel sheet having a tensile strength of 700-1,300 MPa and an elongation of 12% or more and being composed of a tempered martensite single-phase metal structure.   
     
     
         5 . The method of  claim 4 , wherein the steel sheet is manufactured by additionally adding at least any one component of Cr: 0.05-2.0 wt %, Mo: 0.05-2.0 wt %, B: 0.0003-0.0050 wt/o, Ti: 0.01-0.20 wt %, and Al: 0.01-0.10 wt %. 
     
     
         6 . The method of  claim 4 , wherein, after the final step, a plating layer forming step for forming a hot-dip galvanizing layer on a surface of the steel sheet is added. 
     
     
         7 . The method of  claim 6 , wherein an alloying thermal treatment step for reheating the steel sheet is added following the plating layer forming step. 
     
     
         8 . The high-strength steel sheet of  claim 2 , wherein the steel sheet has a hot-dip galvanizing layer provided on a surface thereof. 
     
     
         9 . The method of  claim 5 , wherein, after the final step, a plating layer forming step for forming a hot-dip galvanizing layer on a surface of the steel sheet is added. 
     
     
         10 . The method of  claim 9 , wherein an alloying thermal treatment step for reheating the steel sheet is added following the plating layer forming step.