microstructure evaluation of high alloy steel under thermal loading conditions

Abstract

This project evaluated the material used to repair the damaged hot forging dies in terms of microstructure and hardness. The work has also compared the microstructure and hardness levels of the material under various heat treatment conditions and compared that to the parent, i.e. nonheat-treated material. It has been observed that the hardness and grain structure alongside precipitation within the material varied according to the heat treatment profile and time duration. In the current project, the temperatures ranged between 600-800oC with heat treatment durations between 10-100 hours. In total, 8 samples have been characterised in the current project under various testing conditions. It has been revealed that the higher the temperature, the lower the hardness of the steel. This is due to the formation of austenite at higher temperatures. Moreover, the lower the temperature, the higher the hardness of the tested steel. This is due to the formation of pearlite which contains cementite which is hard and brittle. In terms of the hold time, the longer the time, the larger the grains and the lower the strength. On the contrary, the shorter the hold time, the smaller the grains and hence the stronger the material. The hold time at a certain temperature can lead to phase transformation from austenite to pearlite (the amount of pearlite increases with increasing the time).