To provide steel for machine structural use having stable and superior machinability without containing Pb which is a substance of giving a load to the environment.
The steel having superior machinability for machine structural use includes, by mass%, 0.10-0.60% C, 0.05-2.0% Si, 0.3-2.5% Mn, 0.02-0.25% S, 0.002-0.030% Al, 0.0005-0.01% Ca, 0.0005-0.008% O, 0.02% or less N and the balance Fe with unavoidable impurities, so that the mass ratio Ca/Al of Ca to Al can be 0.1 to 1.0; and includes a complex sulfide that contains an oxide therein or is adjacent to the oxide, in which the area ratio of oxides to the all complex sulfides contained in the steel is 3 to 90% in the cross-section, and which has the ratio of the pieces of the complex oxides to the pieces of the total sulfides per unit area in an amount of 4 to 80%.
TOKOKAGE NORIMASA
HIRAOKA KAZUHIKO
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