Fatigue properties of a low alloy 42SiCr steel heat treated by quenching and partitioning process

AbstractIn connection with increasing needs of different branches of industry for steels with excellent mechanical properties, like high strength combined with high ductility on one hand and low or at least moderate costs on the other hand, an experimental low alloy 42SiCr steel has been developed. If a conventional heat treatment is applied to this material, a very high strength can be reached, however with an unacceptable low ductility. Well balanced properties, i.e. strength about 2000 MPa and ductility more than 10 – 15%, can be achieved by an application of advanced heat treatment methods like Q-P (quenching and partitioning) process, consisting in quenching at intervals between martensite start and martensite finish temperatures resulting in stabilization of untransformed austenite by partitioning carbon. In service, numerous engineering components are exposed to variable, fatigue loading, whereas resistance to fatigue is usually particularly affected by different heat treatment methods or parameters and fatigue damage mechanisms have strong connections to material type, strength and microstructure. The aim of this study was to investigate fatigue properties of the 42SiCr steel treated using the Q-P process. Results of fatigue experiments are presented with respect to the basic material state and after traditional heat treatment – quenching and tempering. Fatigue damage initiation mechanisms, analysed particularly from fracture surfaces, and connections between fatigue properties and microstructure are discussed