Patent ID: 10358708

Abstract:
A steel plate has a chemical composition containing, by mass %, C: 0.03% or more and 0.08% or less, Si: 0.01% or more and 1.0% or less, Mn: 1.2% or more and 3.0% or less, P: 0.015% or less, S: 0.005% or less, Al: 0.08% or less, Nb: 0.005% or more and 0.07% or less, Ti: 0.005% or more and 0.025% or less, N: 0.010% or less, O: 0.005% or less and the balance being Fe and inevitable impurities, a structure being a dual-phase structure consisting of a bainite phase and island martensite, wherein the area fraction of the island martensite is 3% to 15%, the equivalent circle diameter of the island martensite is 3.0 μm or less, and the remainder of the structure is a bainite phase.