Chromium Alloyed Surface Densified PM Gears to Replace Conventional Machined Gears
Surface densification is now a well-known technology for improving the performance of PM components. Chromium-alloyed powder grades have been developed in order to replace expensive alloying elements such as nickel and molybdenum with more cost beneficial chromium. Astaloy™ CrL (Fe-1.5Cr-0.2Mo) is a material with excellent formability in the as-sintered state, high hardenability and high fatigue performance and is therefore selected as a candidate material for surface densified gears in this study. Helical gears for the fifth gear in a manual gearbox have been investigated in this study. The response to surface densification by radial rolling is investigated and compared to the behaviour of Astaloy 85 Mo. The result after case hardening is also compared for the two materials using low pressure carburising for the Astaloy CrL and conventional gas carburising for Astaloy 85 Mo. The implications of these results are discussed in terms of tooth root bending fatigue and service life.