Thermal fatigue in hot‐working tools

Abstract

Hot‐working, in general, is one of the fundaments of the industrialised society and the hot‐work tool, which gives the part its basic shape, is one of the most essential elements. Most hot‐working tools are subjected to extreme temperature variations, which give rise to stresses and strains and may eventually lead to thermal fatigue. Two hot forming applications have been studied, hot forging and die casting. Tools from these applications were examined to determine damage, material response, thermal fatigue crack initiation and propagation. Surface strain measurements during thermal fatigue testing were performed on the tool material to evaluate the surface mechanical strain levels during typical thermal cycling. Isothermal fatigue testing was also performed to determine the stress–strain response in the temperature interval 200–600°C. It was found that thermal fatigue crack initiation occurs within 1% of the tools life in both applications.