Hot embrittlement and effect of grain size on hot ductility of martensitic heat-resistant steels

The hot ductility of martensitic heat-resistant steels was studied by tensile tests in temperature range from 600 °C to 1150 °C. A significant hot embrittlement was observed at 700-900 °C. The tensile specimens fracture in dimple mode at low and high temperature, while intergranular fracture appears at the hot embrittlement temperature. The microvoids mainly form interior grains at low temperature, while mainly form at grain boundaries at high temperature. The intergranular cracks forming at high temperature, which leads to the hot embrittlement, is attributed to the grain boundaries sliding. Furthermore, fining grains can markedly improve ductility at high temperature, while has little effect at low temperature. Fining grains improves ductility by controlling the propagation of intergranular cracks and improving dynamic recrystallization at high temperature.