The influence of microstructure and mechanical properties on the machinability of martensitic and bainitic prehardened mould steels

The machinability of two prehardened mould steels, one continuously-cooled and one quenched and tempered, is compared in terms of cutting temperature, cutting force and tool life. Both materials have a hardness of similar to 40 HRC which is a typical hardness for prehardened mould steels. The results of machinability tests are related to mechanical properties and microstructural features, and the material removal rate is estimated for the materials. The continuously-cooled steel with bainitic structure shows higher machinability and possesses superior impact toughness and ductility compared to the quenched and tempered steel with martensitic structure. These properties are very important for plastic mould steels. The continuously-cooled bainitic steel also has the advantage of not requiring any costly quenching and tempering processes in connection with its production.