Qiu Feng

The Relationship Between Oxidation and Thermal Fatigue of Martensitic Hot-Work Die Steels

Thermal fatigue behaviors of two forged hot-work die steels subjected to cyclic heating (650xa0°C)–water quenching were investigated. A martensitic hot-work die steel containing 10% Cr (HHD), showing superior oxidation resistance and thermal fatigue resistance to the commercial martensitic hot-work die steel (Uddeholm DIEVAR®), was developed. The maximal crack length in HHD was 35% shorter than that in DIEVAR after 2000 thermal cycles, and the hot yield strength at 650xa0°C of HHD was 14% lower than that of DIEVAR prior to thermal fatigue testing, which is 30% higher after 1500 cycles. It is found that cracks initiated and propagated along the oxide layers in the grain boundaries, suggesting that the oxidation-induced thermal fatigue cracks can significantly reduce the mechanical performance and service life for the hot-work die steel. High-temperature oxidation behavior is crucial for thermal fatigue crack formation, while high-temperature yield strength and ductility play a less important role.