Patent ID: 10329645

Abstract:
A steel for carburizing or carbonitriding use consisting of, by mass %, C: 0.1 to 0.3%, Si: 0.01 to 0.15%, Mn: 0.6 to 1.5%, S: 0.012 to 0.05%, Cr: 0.5 to 2.0%, Al: 0.030 to 0.050%, Ti: 0.0006 to 0.0025%, N: 0.010 to 0.025%, and O: 0.0006 to 0.0012%, and, optionally, at least one selected from Mo≤0.5%, Ni≤1.5% and Cu≤0.4%, and the balance of Fe and impurities. P and Nb are P≤0.025% and Nb≤0.003% respectively. Formulas of [−5.0≤log (Ti×N)≤−4.4] and [−12.5≤log (Al2×O3)≤−11.7] are satisfied. Austenite grain coarsening is prevented even when the steel is heated in the process of carburizing or carbonitriding, and even under various hot forging temperatures. The steel has excellent bending fatigue strength after carburizing or carbonitriding.