Heat Fatigue Behavior of 4Cr5MoSiV1 and 8407S Steels

{With the self-restricting test method, heat fatigue behavior of 4Cr5MoSiV1 steel and 8407 steel is investigated under the same heat treatment condition. The crack morphology and fracture surface is also analyzed. Heat fatigue cracks of both steels initiate at the time between 100 to 200 cycles. The initiating cracks of 8407S steel are smaller and more equable than that in 4Cr5MoSiV1 steel. When the annealing temperature is below 610°C, the heat fatigue behavior of 4Cr5MoSiV1 steel is better than that of 8407S steel. However, as the annealing temperature exceeds 610°C, the behavior of the latter seems superior. Also analyzed is the mechanism of heat fatigue, which reveals the main factor affecting heat fatigue resistance is the thermal stability and strength or hardness of steels.}