CASE HARDENING STEEL HAVING EXCELLENT CRYSTAL GRAIN COARSENING RESISTANCE AND COLD WORKABILITY, AND METHOD FOR PRODUCING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a case hardening steel which exhibits excellent crystal grain coarsening resistance even when subjected to carburizing at a temperature higher than that in the conventional example so as to be case-hardened such as carburized and carbonitrided in a shorter period of time as the stock for rod-shaped machine parts such as a pulley for a CVT requiring carburizing depth and excellent workability and which also has excellent cold workability.;SOLUTION: The case hardening steel having excellent crystal grain coarsening resistance and cold workability is composed of a rolled steel in which the contents of C, Si, Mn or the like are specified, and further, the contents of N, Al and Ti are specified. The case hardening steel is characterized in that carbides and/or carbonitrides satisfying inequality (1): (Ti)/(Nb)≥0.05 are present in an amount of ≥2.0×10⁷ pieces/mm² in the cross-section, and further, the maximum value of the standard deviation in the Vickers hardness in the cross-section is ≤10. Alternatively, the steel has a metallic structure where the area ratio of (ferrite+pearlite) is ≥80%.;COPYRIGHT: (C)2007,JPO&INPIT