STEEL FOR MACHINE STRUCTURE SUPERIOR IN STRENGTH-ANISOTROPY AND MACHINABILITY, AND COMPONENT FOR MACHINE STRUCTURE

PROBLEM TO BE SOLVED: To provide a steel for a machine structure, which shows adequate machinability (particularly, improvement of the life of a tool) even without containing Pb, and also decreases an anisotropy of strength by securing the strength in a transverse direction, and to provide a component for the machine structure made from such a steel for the machine structure. SOLUTION: The steel for the machine structure has a properly adjusted chemical composition while satisfying the following expression (1); ([Al]+[Ca])/[S]≤0.7, wherein [Al], [Ca] and [S] represent contents (mass%) of Al, Ca and S in the steel, respectively; and when a cross section in a rolling direction of the steel is observed, includes oxide-based inclusions which contain 50% or more Al2O3and occupy 10 area% or less, and sulfide-based inclusions which have a core of a complex oxide that contains 4 to 50% CaO, and occupy 20 area% or more. COPYRIGHT: (C)2009,JPO&INPIT