ROLLED STEEL BAR OR WIRE FOR HOT FORGING

摘要

A rolled steel bar or wire for hot forging capable of achieving at a high level both bending/surface-fatigue strength and machinability of components is provided. The rolled steel bar or wire for hot forging comprises, in % by mass, 0.1-0.25% C, 0.01-0.10% Si, 0.4-1.0% Mn, 0.003-0.05% S, 1.60-2.00% Cr, 0.10 % max. (including 0%) Mo, 0.025-0.05% Al, and 0.010-0.025% N. In formula (1), fn1 fulfills 1.82?fn1?2.10. P, Ti, and O in impurities are contained in the amounts of P at 0.025% max, Ti at 0.003% max, and O (oxygen) at 0.002% max. When 15 fields of view randomly selected in a cross-section so that each field of view has an area of 62,500 µm2 are examined, the maximum/minimum average ferrite particle diameter is 2.0 or less. fn1=Cr+2×Mo ... (1).