Low-strength steel sheet for hot stamping, hot-stamped component, and method for manufacturing hot-stamped component

Abstract

A low-strength steel sheet for hot stamping according to an aspect of the present invention satisfies a predetermined chemical composition, the Ac3 point (° C.) represented by Equation (1) is 890° C. or more, and an area ratio of ferrite at a depth to be ¼ of a steel sheet thickness is 80% or more. Ac3 point (° C.)=910−203×[C]1/2+44.7×[Si]−30×[Mn]+700×[P]+400×[Al]+400×[Ti] . . . (1) In Equation (1), [C], [Si], [Mn], [P], [Al], and [Ti] are values denoting the percentage contents of C, Si, Mn, P, Al, and Ti in terms of % by mass, respectively.

1 . A low-strength steel sheet for hot stamping, the steel sheet comprising, in % by mass:
 C: 0.005% to 0.12%,   Si: 0.50% to 2.0%,   Mn: 0.50% or less (not including 0 0 %),   Al: 0.010% to 1.0%,   P: 0.1000% or less (not including 0 0 %),   S: 0.0100% or less (not including 0 0 %),   N: 0.0100% or less (not including 0 0 %), and   O: 0.0100% or less (not including 0 0 %),   wherein an Ac 3  point (° C.) represented by the following Equation (1) is 890° C. or more, and an area ratio of ferrite at a depth to be ¼ of a steel sheet thickness is 80% or more:
   Ac 3  point (° C.)=910−203×[C] 1/2 +44.7×[Si]−30×[Mn]+700×[P]+400×[Al]+400×[Ti]  (1)
 
   in Equation (1), [C], [Si], [Mn], [P], [Al], and [Ti] are values denoting percentage contents of C, Si, Mn, P, Al, and Ti in terms of % by mass, respectively.   
     
     
         2 . The low-strength steel sheet for hot stamping according to  claim 1 , wherein the steel sheet further comprises at least one selected from the group consisting of Ti: 0.10% or less (not including 0%) and Nb: 0.10% or less (not including 0%). 
     
     
         3 . A steel sheet comprising the low-strength steel sheet for hot stamping according to  claim 1  and a steel sheet having a tensile strength of 1000 MPa or more after a heat treatment. 
     
     
         4 . A method for manufacturing a hot stamped member, the method comprising heating the low-strength steel sheet for hot stamping according to  claim 1  to the Ac 3  point (° C.) or less and performing hot stamping. 
     
     
         5 . A hot stamped member comprising the low-strength steel sheet for hot stamping according to  claim 1 .