Homogenisation of austenite during non-equilibrium heating in hypereutectoid steels

The homogenisation (Stage III) of austenite during non-equilibrium heating of hypereutectoid steels has been characterised for the first time through dilatometric strain measurements and electron microscopic techniques. It has been found that the homogenisation temperature (A(ch)) is significantly higher than the cementite dissolution temperature (A(cm)). Though there is a complete conversion of low-temperature constituents to austenite above the A(cm), a significant segregation of carbon in the austenite is observed below the A(ch). Performing heat treatment with an incomplete austenitisation between the A(cm) and the A(ch) temperature can affect the subsequent on-cooling phase transformations. It is proposed that the A(ch) temperature should be used as the full austenitisation temperature in hypereutectoid steels.