While the increase in hardness is achieved through martensite formation with normal hardening, with austempering it is an isothermal micro-structural transformation in the bainite stage, which occurs at a fixed temperature.
The component is first austenitised, this means heat treatment takes place at temperatures of 800 – 1,050°C regardless of the material. This process also occurs with conventional hardening. However, the subsequent quenching process is then captured in the austenitisation temperature, in other words above the martensite formation temperature. In general a salt bath with a temperature of approx. 300 – 400°C is selected for this.
Brief summary of the process:
Bainite structures will occur as the end-product of this process. These structures display specific characteristics compared with structures occurring with conventional hardening.