Microstructure, fatigue life and lead capacity of PM tool steel REX20 for bearing applications

Recently, powder metallurgy (PM) tool steel REX(TM)20 was shown to have ver y high rolling contact fatigue life, comparable to silicon nitride, making it an excellent candidate material for bearings in future space systems. In this paper the authors discuss the metallurgical characteristics, dynamic fatigue properties, static load capacity of REX20 steel and its vacuum-proc essed version called VIM CRU20, focusing on the structure-property relation ship. Having high-carbon martensite matrix with fine distribution of globul ar alloy carbides, REX20 can be easily heat treated to very high hardness ( HRC 66 to 67). Rolling contact fatigue tests using 207-size bearings with R EX20 raceway and silicon nitride balls showed substantial improvement over VIMVAR 52100 steel bearings. Static load capacity, hardness, and compressiv e yield strength of REX20 steel were measured in comparison to other bearin g steels. The static load capacity of REX20 at HRC 66-67 is between 3790 an d 4100 MPa (550 to 595 ksi) mean contact stress.