Temperature profiles and conditions for thermal fatigue cracking in brass die casting dies

In this study, the temperature variations in the surface layer of a hot work tool steel was experimentally evaluated during actual brass die casting. A special method was developed to measure the temperature in the surface layer of the mould at different depths. Untreated, borided, and physical vapour deposition (PVD) coated (CrN) tools were included. Temperature profiles in the surface layer of the mould were recorded and details of the thermal cycling were obtained. Starting with a tool of room temperature, the tool temperature range averages during the initial 20 casting events. Simultaneously, within a surface layer of about 2 mm thickness, the maximum stress is reduced to a constant level. Based on the temperature profiles, the maximum surface temperature of the mould and the thickness of the tool surface layer within which fatigue damage can occur were estimated to about 826 °C and 1.5 mm, respectively. This limited thickness results from the decrease in temperature range and, consequently, stress from the tool surface and inwards. Finally, no notable influence of the investigated surface engineering on the thermal conditions was found.