Manganese diffusion coating of steels

Abstract

Manganese diffusion coatings have been developed on various carbon steels by a pack-cementation process using low-cost ferromanganese cement. The microstructures of the coatings are related to the steel composition and the manganizing treatment; in all cases, these consist of a martensitic layer directly in contact with the substrate and a superimposed γ-(FeMn) austenitic layer. For high-carbon steels, carbide layers are also formed at the external surface. The corrosion resistance is improved when the surface of the steel is enriched with manganese. However, the most interesting features of this treatment are the resulting tribological properties. The γ-(FeMn) layer is soft after manganizing but work-hardens deeply in a manner similar to Hadfield steels. After an initial period, the friction and wear behaviour is better than that of the untreated steels due to the rapid formation of a thick oxide layer on the wear track. Mechanical applications such as bearings and friction parts can be envisaged for this surface treatment