Secondary hardening in an Cr-Mo-V steel: Effect of thermal cycle tempering

Secondary hardening by precipitation of alloy carbides during tempering in an experimental Cr-Mo-V alloy steel was studied under continuous and isothermal conditions. Measurements of microhardness and nanohardness analysed the hardening behaviour during stage IV as a function of time, temperature, and heating rate. Scanning electron microscopy and scanning probe evidenced the carbides precipitated during stage IV. It was observed that hardening is a function of not only tempering temperature and time but also of the heating rate according to the Hollomon–Jaffe parameter. The parameter increases as the heating rate increases due to the effect on the temperature, showing a clear softening. The hardening behaviour, evaluated with the Hollomon–Jaffe parameter, was very similar regardless of the test, micro- or nanoindentation.