(Non-heat-trested hot-forging steels excellent in tensile strength, fatigue strength and machinability), excellent in tensile strength, fatigue strength and machinability.

摘要

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.10 to 0.35% of C, 0.15 to 2.00% of Si, 0.40 to 2.00% of Mn, 0.40 to 0.10% of S, 0.0005 to 0.05% of Al, 0.003 to 0.05% And V: 0.30 to 0.70%, and further comprising a specific amount of at least one of Cr, Mo, Nb, Pb and Ca, is subjected to hot forging and cooled to room temperature, And the structure ratio f of the knitted structure is 1.4 + 0.4 F 1.4C with respect to the carbon content C (%). According to the present invention, it is possible to produce a non-tempered steel for hot forging which has high tensile strength and high fatigue strength and machinability, which is very industrially effective.