| 摘要 |
A steel material which is suitable for hot press working or hot three-dimensional bending and direct quench and which can be used to manufacture a high-strength formed article with sufficient quench hardening even by short time heating at a low temperature has a chemical composition comprising, in mass percent, C: 0.05 - 0.35%, Si: at most 0.5%, Mn: 0.5 - 2.5%, P: at most 0.03%, S: at most 0.01%, sol. Al: at most 0.1%, N: at most 0.01%, and optionally at least one element selected from the group consisting of B: 0.0001 - 0.005 %, Ti: 0.01 - 0.1 %, Cr: 0.18 - 0.5 %, Nb: 0.03 - 0.1 %, Ni: 0.18 - 1.0%, and Mo: 0.03 - 0.5 % and has a steel structure in which the spheroidization ratio of carbides is 0.60 - 0.90. |
