NON-HEAT TREATED STEEL FOR HOT FORGING AND STEEL FOR HOT ROLLING EXCELLENT IN FRACTURE SPLITTABILITY AND MACHINABILITY, AND HOT FORGING NON-HEAT TREATED STEEL PART

摘要

The object is to produce a hot-forging microalloyed steel and a hot-rolled steel material each having excellent fracture splittability and machinability and a hot-forging microalloyed steel part without deteriorating processability and mechanical properties and without the need of adding Pb or the like. Disclosed is a hot-forging microalloyed steel comprising more than 0.35 mass% and not more than 0.60 mass% of C, 0.50 to 2.50 mass% of Si, 0.20 to 2.00 mass% of Mn, 0.010 to 0.150 mass% of P, 0.040 to 0.150 mass% of S, 0.10 to 0.50 mass% of V, 0.0005 to 0.0050 mass% of Zr, 0.0005 to 0.0050 mass% of Ca, 0.0020 to 0.0200 mass% of N, and less than 0.010 mass% of Al, with the remainder being substantially Fe and unavoidable impurities.