Thermal fatigue testing of die casting die steels

Thermal fatigue is a form of surface failure produced by repeated thermal stresses and is the main cause of die retirement in the die casting industry. A general review of the fundamental and practical aspects of thermal fatigue as encountered in the dies, based on earlier published work, is given and preliminary experiments in an effort to set up a suitable method of testing to study this phenomenon are then described. In the present technique developed to create the thermal conditions experienced by a die steel in aluminum die casting, a small portion of one face of a cylindrical test-piece is intermittantly [sic] heated by H.F. induction whilst the main body of the test-piece is kept at a lower temperature by means of a copper jig. Air under pressure is used as a cooling medium during the cooling part of the cycle. Thermal fatigue resistance of various die steels and prospective die materials for aluminum die casting is determined on the basis of number of cycles for crack initiation, propagation, frequency and severity of cracking supported by graphs and series of photographs. Photographic evidence presented gives a detailed look into the mechanism of thermal fatigue. Present investigations reveal that 18% nickel maraging steel is the most suitable steel for aluminum die casting dies, followed by H-21, H-13 and H-11 respectively --Abstract, page ii