Method of manufacturing hot-press-formed steel member

Abstract

To establish a method for obtaining a hot-press-formed steel member, which exhibits high strength, high tensile elongation (ductility) and high bendability, thereby having excellent deformation characteristics at the time of collision crush (crashworthiness), and which is capable of ensuring excellent delayed fracture resistance. A method for producing a hot-press-formed steel member by heating a steel sheet, which has a chemical component composition containing 0.10% (% by mass, and hereinafter the same shall apply) to 0.30% (inclusive) of C, 1.0% to 2.5% (inclusive) of Si, 1.0% to 3.0% (inclusive) of Si and Al in total and 1.5% to 3.0% (inclusive) of Mn, with the balance consisting of iron and unavoidable impurities, and hot press forming the steel sheet one or more times. The method for producing a hot-press-formed steel member is characterized in that: the heating temperature is set to not less than the Ac3 transformation point; the starting temperature of the hot pressing is set to not more than the heating temperature but not less than the Ms point; and the average cooling rate from (the Ms point−150)° C. to 40° C. is set to 5° C./s or less.

1 - 8 . (canceled) 
     
     
         9 . A hot-press-formed steel member produced by a method comprising,
 heating a steel sheet having a chemical composition satisfying   C: 0.10 to 0.30% by mass,   Si: 1.0 to 2.5% by mass,   Si+Al: 1.0 to 3.0% by mass in total, and   Mn: 1.5 to 3.0% by mass,   the remainder consisting of iron and inevitable impurities, and   hot press forming the steel sheet one or more times,   wherein the heating temperature is an Ac 3  transformation point or higher,   start temperature of the hot press forming is the heating temperature or lower and a Ms point or higher, and   an average cooling rate from (Ms point−150)° C. to 40° C. is 5° C./sec or less,   wherein the hot-press-formed steel member being characterized by having a steel microstructure that contains 2 vol % or more of retained austenite.   
     
     
         10 . A steel sheet to be hot press formed for use in a method of a hot-pressed-formed steel member, the steel sheet by satisfying
 C: 0.10 to 0.30% by mass,   Si: 1.0 to 2.5% by mass,   Si+Al: 1.50 to 3.0% by mass in total, and   Mn: 1.5 to 3.0% by mass,   the remainder consisting of iron and inevitable impurities,   wherein the method comprises:   heating the steel sheet, and   hot press forming the steel sheet one or more times,   wherein the heating temperature is an Ac 3  transformation point or higher,   start temperature of the hot press forming is the heating temperature or lower and a Ms point or higher, and   an average cooling rate from (Ms point−150)° C. to 40° C. is 5° C./sec or less.   
     
     
         11 . The steel sheet according to  claim 10 , further containing 1% or less and greater than 0% of Cr. 
     
     
         12 . The steel sheet according to  claim 10 , further containing 0.10% or less and greater than 0% of Ti. 
     
     
         13 . The steel sheet according to  claim 10 , further containing 0.005% or less and greater than 0% of B. 
     
     
         14 . The steel sheet according to  claim 10 , further containing 0.5% or less and greater than 0% in total of Ni and/or Cu. 
     
     
         15 . The steel sheet according to  claim 10 , further containing 1% or less and greater than 0% of Mo. 
     
     
         16 . The steel sheet according to  claim 10 , further containing 0.05% or less and greater than 0% of Nb. 
     
     
         17 . An automotive steel component, the steel component being produced by performing working on the hot-press-formed steel member according to  claim 9 .