ROLLED STEEL BAR OR WIRE FOR HOT FORGING

摘要

Provided is a rolled steel bar or wire for hot forging, having excellent bending fatigue strength, surface fatigue strength, abrasion resistance, and machinability even after hot forging. This rolled steel bar or wire for hot forging has a chemical composition containing C, Si, Mn, S, Cr, Mo (optional), Al, and N, with the remainder comprising Fe and impurities. The chemical composition furthermore has 1.60 to 2.10 of fn1 as defined by the formula (1). The structure of the rolled steel bar or wire for hot forging comprises a ferrite-pearlite structure, a ferrite-pearlite-bainite structure, or a ferrite-bainite structure. Upon examination of 15 fields of view randomly selected in a cross-section so that each field of view has an area of 62,500 µm2, the maximum/minimum average ferrite particle diameter is 2.0 or less. fn1 = Cr + 2 × Mo (1). The corresponding element content (mass%) is substituted for each element symbol in the formula (1).