STEEL SHEET SUITABLE AS IMPACT ABSORBING MEMBER AND METHOD FOR MANUFACTURING SAME

摘要

The steel sheet of the present invention being suitable as a raw material for an automobile impact absorbing member having high impact absorbing energy and not being resistant to cracking even when crushed has a chemical composition containing by mass% 0.08 0.30% C 1.5 3.5% Mn 0.50 3.0% Si + Al 0.10% or less P 0.010% or less S 0.010% or less N and also in some cases one or more species selected from 0.5% or less Cr 0.5% or less Mo 0.010% or less B less than 0.04% Ti less than 0.030% Nb less than 0.5% V 0.010% or less Ca 0.010% or less Mg 0.050% or less REM and 0.050% or less Bi. The steel sheet has a microstructure containing by area% more than 50% bainite 3 30% martensite and 3 15% residual austenite the remainder comprising ferrite having an average particle diameter of less than 5 µm. The steel sheet also has mechanical characteristics in which the product of the uniform elongation and the hole expansion ratio is at least 300% and the 5% effective flow stress is at least 900 MPa.