Sintered Steels Prealloyed with Manganese – Chances and Risks
Paper in proceedings, 2010
Manganese as an alloying element in sintered steels offers technical and commercial advantages; so far it has been used however only tentatively and added mainly through admixing. Here it is shown that also prealloying can be a viable route since the adverse effect of Mn on the compressibility is markedly less than commonly assumed, and the compacts shrink during sintering, in contrast to expansion with the mixed variants. Sintering of Mn prealloyed steel compacts is similar to the route used for Cr-Mo prealloyed grades, the main reduction stage being carbothermic reduction at T>1000°C, although in reducing atmospheres part of the surface oxides can be removed at T < 500°C. Generally, sintering at T>1200°C is recommended to ensure sufficient oxygen removal. The main problem with Mn, the tendency to Mn loss at the surfaces by evaporation during sintering must be considered also here, but it is alleviated by prealloying compared to admixing, due to the lower initial activity of Mn in prealloyed materials.