Comparative Study on Thermal Fatigue Behavior of Two Hot Work Die Steels

The thermal fatigue behavior of 5CrNiMoV and 5CrNiMoVNb steel was compared. The results show that length of the main thermal fatigue crack for 5CrNiMoV and 5CrNiMoVNb steel are, respectively, 184.47 and 104.06 mu m after 2000 thermal fatigue cycles. The fatigue crack initiation and propagation rate in 5CrNiMoVNb steel are significantly lower than that in 5CrNiMoV steel. Besides, a mixed way of transgranular and intergranular crack propagation occurs in 5CrNiMoV steel, while only transgranular propagation occurs in 5CrNiMoVNb steel. Due to high content of small carbide particles and the strong inhibitory effect on dislocation movement and microstructure coarsening, 5CrNiMoVNb steel has better microstructure stability, hardness and toughness. Based on the simplified thermal fatigue life model, it indicates that the thermal fatigue life is dependent on the stresses corresponding to the limit temperatures of their cycles. Therefore, the 5CrNiMoVNb steel with higher room temperature and high temperature stress shows longer thermal fatigue life.