STEEL MATERIAL FOR MACHINE STRUCTURAL USE EXCELLENT IN MACHINABILITY AND FATIGUE CHARACTERISTIC

摘要

PROBLEM TO BE SOLVED: To provide a steel material for machine structural use, which does not includes free-cutting elements such as Pb but ensures a machinability equivalent to or higher than that of a conventional Pb-added free-cutting steel and is excellent in fatigue characteristics after quenching.;SOLUTION: The steel material for machine structural use is obtained by subjecting a steel material having a graphite phase to a quenching treatment, wherein the structure after the quenching treatment is a mixture of a martensite parent phase and a graphite phase and/or a graphite vacancy and that a martensite phase having a higher C concentration compared to that in the martensite parent phase is formed around the graphite phase or the graphite vacancy.;COPYRIGHT: (C)2008,JPO&INPIT