The effect of heat treatment on the toughness, hardness and microstructureof low carbon white cast irons

The effect of destabilisation and subcritical heat treatment on the impact toughness, hardness, and the amount and mechanical stability of retained au stenite in a low carbon white cast iron have been investigated. The experim ental results show that the impact energy constantly increases when the des tabilisation temperature is raised from 950 degreesC to 1200 degreesC. Alth ough the hardness decreases, the heat-treated hardness is still greater tha n the as-cast state. After destabilisation treatment at 1130 degreesC, temp ering at 200 to 250 degreesC for 3 hours leads to the highest impact toughn ess, and secondary hardening was observed when tempering over 400 degreesC. The amount of retained austenite increased with the increase in the destab ilisation temperature, and the treatment significantly improves the mechani cal stability of the retained austenite compared with the as-cast state. Te mpering below 400 degreesC does not affect the amount of retained austenite and its mechanical stability. But the amount of retained austenite is dram atically reduced when tempered above 400 degreesC. The relationship between the mechanical properties and the microstructure changes was discussed. (C ) 2001 Kluwer Academic Publishers.