Cyclic behavior and fatigue resistance of AISI H11 and AISI H13 tool steels

The present experimental work investigates the isothermal low cycle fatigue resistance of two well-known tool steels, AISI H11 and AISI H13, at four different temperatures: ambient, 200 degrees C, 350 degrees C and 550 degrees C. The characterization of the steels included tensile and creep tests too. The tensile, the creep and the cyclic properties are in fact often employed to assess the thermal fatigue of a material. The fatigue tests up to 350 degrees C resulted in similar strain-cycles to fracture curves, whereas the ones performed at 550 degrees C were significantly different. A deep analysis was hence carried out to distinguish the contribution of the fatigue, of the creep and of the oxidation. It was found that at 550 degrees C fatigue and oxidation are the main driving mechanisms. Finally, the fracture surfaces were observed both by stereo and scanning electron microscopes. Multiple crack nucleation was observed, especially for the tests at high temperature.