High-strength steel sheet and method of manufacturing high-strength steel sheet

Abstract

A steel sheet contains, by mass %, 0.03% to 0.35% C, 0.01% to 0.50% Si, 3.6% to 8.0% Mn, 0.01% to 1.0% Al, 0.10% or less P, and 0.010% or less S, the remainder being Fe and inevitable impurities. The steel sheet is continuously annealed, heated at a heating rate of 7° C./s or more in a temperature range corresponding to an annealing furnace inside temperature of 450° C. to A° C. (where 500≦A≦600), the maximum end-point temperature of the steel sheet in an annealing furnace is 600° C. to 700° C., the transit time of the steel sheet in a temperature range corresponding to a steel sheet temperature of 600° C. to 700° C. is 30 seconds to 10 minutes, and the concentration of hydrogen in an atmosphere is 20% by volume or more in a heating step.

1 - 4 . (canceled) 
     
     
         5 . A method of manufacturing a high-strength steel sheet, comprising continuously annealing a steel sheet containing, by mass %, 0.03% to 0.35% C, 0.01% to 0.50% Si, 3.6% to 8.0% Mn, 0.01% to 1.0% Al, 0.10% or less P, and 0.010% or less S, the remainder being Fe and inevitable impurities, wherein in a heating step, the steel sheet is heated at a heating rate of 7° C./s or more in a temperature range corresponding to an annealing furnace inside temperature of 450° C. to A° C. (where 500≦A≦600), a maximum end-point temperature of the steel sheet in an annealing furnace is 600° C. to 700° C., transit time of the steel sheet in a temperature range corresponding to a steel sheet temperature of 600° C. to 700° C. is 30 seconds to 10 minutes, and concentration of hydrogen in an atmosphere is 20% by volume or more. 
     
     
         6 . The method according to  claim 5 , wherein the steel sheet further contains, by mass %, one or more selected from among 0.001% to 0.005% B, 0.005% to 0.05% Nb, 0.005% to 0.05% Ti, 0.001% to 1.0% Cr, 0.05% to 1.0% Mo, 0.05% to 1.0% Cu, 0.05% to 1.0% Ni, 0.001% to 0.20% Sn, 0.001% to 0.20% Sb, 0.001% to 0.10% Ta, 0.001% to 0.10% W, and 0.001% to 0.10% V as a component composition. 
     
     
         7 . The method according to  claim 5 , further comprising performing electrolytic pickling in an aqueous solution containing sulfuric acid after the continuous annealing is performed. 
     
     
         8 . A high-strength steel sheet manufactured by the method according to  claim 5 , wherein the amount of an oxide of one or more selected from among Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, Ni, Sn, Sb, Ta, W, and V per side is less than 0.030 g/m 2  in total, the oxide being formed in a surface portion of the steel sheet that is within 100 μm from a surface of the steel sheet. 
     
     
         9 . The method according to  claim 6 , further comprising performing electrolytic pickling in an aqueous solution containing sulfuric acid after the continuous annealing is performed. 
     
     
         10 . A high-strength steel sheet manufactured by the method according to  claim 6 , wherein the amount of an oxide of one or more selected from among Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, Ni, Sn, Sb, Ta, W, and V per side is less than 0.030 g/m 2  in total, the oxide being formed in a surface portion of the steel sheet that is within 100 μm from a surface of the steel sheet. 
     
     
         11 . A high-strength steel sheet manufactured by the method according to  claim 7 , wherein the amount of an oxide of one or more selected from among Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, Ni, Sn, Sb, Ta, W, and V per side is less than 0.030 g/m 2  in total, the oxide being formed in a surface portion of the steel sheet that is within 100 μm from a surface of the steel sheet.