Steel for cold forging and method of making

摘要

An improved steel for cold forging for machine structural use, particularly, case hardening steel, contents of Al, N and Nb are selected to satisfy a specific corelation therebetween, and the amounts of O and S are controlled. The steel is resistant to cracking at the cold forging, and growth of austenite crystals to coarse grains during carburizing or carbonitriding is prevented. Disclosed are preferable structure of the steel and rolling conditions to obtain the structure, and conditions for continuous casting of the steel.