Less hardened steel with heat treatment distortion

摘要

PROBLEM TO BE SOLVED: To provide case hardening steel which causes little heat-treatment strain even when quenched after undergoing surface-hardening treatment such as carburizing and carbo-nitriding (hereinafter referred to as "carburizing and quenching"), and which is therefore useful as a material for a cylindrical gear.;SOLUTION: The case hardening steel contains, by mass, C: 0.05-0.15%, Si: 2.0% or less (excluding 0%), Mn: 0.95-2.2%, P: 0.03% or less (excluding 0%), S: 0.03% or less (excluding 0%), Cr: 0.2-1.8%, Al: 0.3% or less (excluding 0%), N: 0.02% or less (excluding 0%), B: 0.0005-0.0050%, and O: 0.003% or less (excluding 0%), with the balance being iron and inevitable impurities, wherein a martensitic transformation start temperature T (°C) represented by a predetermined relational expression is 400 °C or higher, and wherein a bainite transformation start time t (second) represented by a predetermined relational expression is 15 seconds or more.;COPYRIGHT: (C)2012,JPO&INPIT