Patent ID: 6309475
Filing Date: 2001-10-30
Classification: C21D,C23C,Y10S

Abstract:
A method for producing a rolling element which has a surface layer mainly composed of martensite, residual austenite, carbide such as cementite having an average grain size of 3 .mu.m or less and no .alpha.-Fe phase (ferrite) and which has an inner structure of an (.alpha.+.gamma.)-Fe two phase region, said method comprisingcooling steel material from the austenitic range to form an (.alpha.+.gamma.)-Fe two phase inner structure,forming a rolling element by plastic working said steel material at a temperature in the range of 800-1300.degree. C.,applying one or more types of heat treatment selected from carburization, carbonitriding and nitriding to said rolling element,cooling said rolling element, thenapplying a reheating hardening process to said rolling element, said steel material containing: at least 1.0 to 4.5 wt % Si and Al in total; 0.35 wt % or less C; and balance Fe and unavoidable impurities, wherein said Al and Si function to reduce deformation resistance in said plastic working for forming the steel material into a rolling element by widening the range of heating temperature for an .alpha.-Fe phase region or (.alpha.+.gamma.)-Fe two phase region to at least 800.degree. C. to 1,300.degree. C., and to prevent precipitation of coarse cementite in the rolling surface of the rolling element, even if carbon potential is 1.2 wt % or more in the carburization and/or carbonitriding heat treatment which is carried out for the purpose of increasing the strength of the rolling element.