FREE MACHINING STEEL FOR USE IN MACHINE STRUCTURE OF EXCELLENT MECHANICAL CHARACTERISTICS

摘要

Free machining steel for use in machine structures capableof stably and reliably providing excellent machinability (chipdisposability and tool life) and mechanical characteristics(transverse direction toughness) comparable, in a Pb free state,with existent Pb-added steels the machining steel beingmanufactured so as to contain 0.0005 to 0.02 mass% of Mg andprovide a distribution index F1 for the sulfide particles definedby the following equation (1) of 0.4 to 0.65 or a distributionindex for the sulfide particles defined by the following equation(2) of 1 to 2.5:Fl = X1/ (A/n) 1/2 ............... (1), orF2 = .sigma. /X2 ............... ( 2 )as described in the specification.