Patent ID: 9109274
Filing Date: 2015-08-18
Classification: C21D,C22C

Abstract:
1. A steel plate, comprising the following as components in the steel: C: 0.10 to 0.16% provided that the symbol “%” means “% by mass” and hereinafter the same matter is applied to any symbol “%” described in connection with each of the components, Si: 0.2 to 0.5%, Mn: 1 to 1.4%, P: 0.03% or less, S: 0.01% or less, Al: 0.010 to 0.08%, Cr: 0.03 to 0.25%, Mo: 0.25 to 0.4%, Nb: 0.01 to 0.03%, B: 0.0003 to 0.002%, N: 0.006% or less, REMs: 0.0005 to 0.0030%, Zr: 0.0003 to 0.0020%, Fe and one or more inevitable impurities as the component-balance of the steel, wherein the Ceq (IIW) represented by the following equation ranges from 0.40 to 0.45 both inclusive: in which each parenthesis-symbol [ ] means the content by percentage of one of the elements in the parentheses, and grains of one or more oxides that each have a maximum diameter of 2 μm or less are present in a number density of 200/mm martensite microstructure is contained in a proportion of 29% or more by volume, and the microstructure-balance of the steel is bainite microstructure, the steel plate having a plate thickness of 6 mm or more and a tensile strength of 1100 MPa or more.