Production manner null of the case hardening steel where the carburization quench distortion

摘要

PURPOSE:To produce, with certainty, a case hardening steel reduced in carburizing and hardening strain and excellent in dimensional accuracy by carrying out surface hardening treatment by using a steel stock in which the variance of the measured values of hardness in a cross section in the vicinity of the inflection point in a Jominy test is regulated to a specific value or below. CONSTITUTION:A case hardening steel is obtained by means of surface hardening treatment at high temp., such as carbonitriding treatment, At this time, a Jominy test is carried out on a test piece, and hardness (HV) is measured with respect to plural points in a cross section in the vicinity of the inflection point on the resulting Jominy curve. Then, the above surface hardening treatment is carried out by using a steel stock in which the variance of the above measured values is regulated to =10. By using the above steel stock free from nonuniformity of structure, a case hardening steel member reduced in carburizing and hardening strain and excellent in dimensional accuracy can be stably obtained.