HIGH STRENGTH HOT FORGED NON-HEAT TREATED STEEL HAVING EXCELLENT FATIGUE LIMIT RATIO AND TOUGHNESS

摘要

PPROBLEM TO BE SOLVED: To provide a high strength hot forged non-heat treated steel having excellent fatigue limit ratio and toughness even as-hot forged. PSOLUTION: (1) The high strength hot forged non-heat treated steel has a composition comprising 0.10 to 0.50% C, 0.05 to 2% Si, 0.3 to 3% Mn, 0.005 to 0.1% Al, 0.05% P, 0.5% S, 0.003% O, 0.02% N, at least Nb and/or Ti among Nb, Ti and V, and in which V may be comprised, where, in the case Nb is comprised, 0.2% Nb is satisfied, in the case Ti is comprised, 0.20% Ti, 0.010% N and Ti/N3.4 are all satisfied, and, in the case V is comprised, 0.6% V is satisfied, and the balance Fe with inevitable impurities. (2) Prescribed MP1 and MP2 obtained in accordance with prescribed procedures satisfy MP1510SP-4/SPand MP2/MP10.05. PCOPYRIGHT: (C)2008,JPO&INPIT