Vacuum heat treatment of sintered Mn steels: influence of martensite content on impact properties

The influence of the martensite content on the impact properties of three through hardened Mn steels was investigated. When the maximum amount of martensite is 50%, impact properties are influenced by the martensite content through its effect on microhardness, according to the typical behaviour of a porous material having a tough microstructure. For higher amounts of martensite (up to 100%) a transition towards a brittle behaviour is observed. In this case, carbon content has a prevailing effect over the martensite content in determining the brittleness of materials. Steels with a medium low carbon content must be used to obtain a hardened but still deformable microstructure by through hardening and, when allowed by the actual cooling conditions, by sinterhardening.