| 摘要 |
PROBLEM TO BE SOLVED: To provide a workpiece made of a superhigh strength steel which is composed of a TRIP type martensitic steel having a host phase structure of martensite and having high tensile strength. SOLUTION: The workpiece made of a superhigh strength steel has a composition comprising 0.1 to 0.4% C,≤2.5% (excluding 0%) Si, 0.5 to 2% Mn,≤0.05% Al, one or more kinds selected from Nb, Ti and V by 0.01 to 0.3% in total,≤2.0% Cr,≤0.5% Mo,≤1.0% Ni, Cr, Mo and Ni by≤2.0% in total, and≤0.005% (excluding 0%) B, and in which a value (Ceq*) obtained by dividing the C content from a carbon equivalent is 0.3 to 0.6%, and the balance Fe with inevitable impurities, and has a metallic structure composed of martensite as a host phase structure of≥85%, and a second phase structure composed of retained austenite of 1 to 15% and polygonal ferrite and granular bainitic ferrite of≤5% in total. COPYRIGHT: (C)2011,JPO&INPIT |
