Failure assessment in a h10 hot die forging tool related to thermal fatigue

A failure analysis has been performed to investigate the root cause for the rejection of the H10 (DIN 1.2365) hot work tool steel of the Hatebur forging machine. The punch is subjected to intensive thermal shocks, cyclically variable loads and high pressure at high temperatures. Although several surface defects are found related to different degradation phenomena, the higher thermal expansion occurred at the surface, compared with the inner part of the die, makes thermal fatigue the main failure responsible. In fact, thermal conductivity of an alloy will depend upon temperature and microstructure and therefore time and of course chemical composition. Damage analysis including dimensional control, surface analysis and metallographic analysis is completed by ThermoCalc and JMatPro calculations done for the standard 1.2365 tool steel. These are very useful tools to know in advance which are the stability ranges of the phases present (at equilibrium and nonequilibrium conditions), the elements in solid solution, the nature of the carbides, CCT curves and some other features for a better understanding of the failure analysis of the described system.