Tougher valve seats use two hard particles but no cobalt

Development of powder metallurgy T42 high speed steel for structural applications

“…Simultaneously, Hitachi and Nissan introduced a development for high performance exhaust VSI based on HSS (Kawata et al, 1998). More recently, a new cobaltfree material has been presented, consisting of a Fe-3.5Mo matrix (wt%) with a dispersion of two types of hard particles (Fe-Cr-C and Fe-Mo-Si) (Fujiki et al, 2005). In line with these developments, there are now several commercial solutions trying to encompass a good wear resistance at service temperature with microstructural stability, good machinability, low cost and a robust processing (Kawata and Maki, 2006).…”