NON-HEAT-TREATED HOT-FORGING STEEL EXCELLENT IN TENSILE STRENGTH, FATIGUE STRENGTH AND MACHINABILITY.

摘要

A non-heat-treated ferritic-bainitic steel to be used as hot-forged, wherein the following relation holds between the bainitic structure fraction f and the carbon content C(%): 1.4C + 0.4 /= f /= 1.4C in the metal structure after hot forging a steel material containing the following elements on the weight basis: C: 0.10 SIMILAR 0.35 %; Si: 0.15 SIMILAR 2.00 %; Mn: 0.40 SIMILAR 2.00 %; S: 0.03 SIMILAR 0.10 %; Al: 0.0005 SIMILAR 0.05 %; Ti: 0.003 SIMILAR 0.05 %; N: 0.0020 SIMILAR 0.0070 %; V: 0.30 SIMILAR 0.70 % and further containing at least one of Cr, Mo, Nb, Pb and Ca in a specified amount and cooling the forged steel to room temperature. It is possible to produce a non-heat-treated hot-forging steel having high tensile strength, fatigue strength and machinability.