Thermal fatigue of materials for die-casting tooling

Abstract This research is conducted to study the thermal fatigue resistance of different hot-work tool steels; AISI H11 and H13, special tool steel and 18% Ni maraging steel. The maraging steel is surface cladded by GTA welding to study the thermal fatigue resistance of surface layer. An influence of mechanical and microstructural properties on thermal fatigue resistance is evaluated. An innovative apparatus for thermal fatigue testing is developed to study the thermal fatigue resistance. The test specimens are subjected to cyclic heating in bath of molten Aluminum Alloy 226 and cooling in bath of water-based lubricant. They are continuously internally cooled with cold water. The specimens are periodically analyzed after completion of particular number of cycles. The microstructure, hardness profile and the surface cracks developed are analyzed. Temperature transients at different locations of test specimen are measured and used in computation of transient stresses performed by finite elements. The specimens of special geometry are developed using finite element modeling to improve testing efficiency. An optimal set of thermal fatigue testing parameters are developed to establish efficient testing. The influence of thermal loading on tempering of hot work tool steel and on aging of maraging steel claddings during testing is determined. The results showed significant differences in thermal fatigue resistance of tested materials and their heat treatments. The best thermal fatigue resistance achieved special tool steel due to its high thermal stability. The resistance of AISI H11 tool steel is slightly superior to that of maraging steel weld.