Thermal Fatigue Behavior Of Niobium Microalloyed H13 Steel

AISIH13 hot work tool steel is widely used for hot forging, hot-extrusion and die-casting because of its high temperature strength, impact toughness, heat checking resistance and wear resistance etc. The thermally induced surface damage, i.e., thermal fatigue, is believed to be controlled by the magnitude of the imposed cyclic strain. The thermal fatigue on the surface of hot working die, which is responsible to the initiation of the cracks, is reported to result in more than 80% of the failure of dies.In this paper, aimed to suppress the crack generation and improve the heat checking resistance, niobium is added into the H13 steel. The mechanical properties, the resistance to temper softening, thermal stability, the cyclic softening and the thermal fatigue life prediction for H13 steel with and without niobium are investigated. The coarsening kinetics of M23C6 carbide in H13 steel during thermal fatigue is also studied. And the main results are summarized as follows:1. The influence of the niobium on the microstructure and the type, size and distribution of carbides in AISI H13 steel have been investigated by means of Thermo-calc software and TEM&EDS. It is shown that austenitic grains of H13 steel containing niobium are smaller than those without niobium. Experimental results indicate that the 0.07 pct niobium in H13 steel is sufficient to suppress grain growth at the austenitizing temperature up to 1120℃. After microalloyed by 0.07pct niobium, the carbides become smaller and its distribution become much more dispersive in the...