Influence of temperature and microstructure on the fatigue behaviour in the threshold regime for a super duplex stainless steel

The fatigue crack propagation behaviour of a super duplex stainless steel in the near threshold regime at -50 degrees C, 20 degrees C (RT) and 150 degrees C has been studied. The fatigue threshold values of the stress intensity factor range and the effective threshold value of this material are higher at -50 degrees C and 150 degrees C than at RT. The closure threshold value is also smaller at RT than at -50 degrees C, but comparable with that at 150 degrees C. The material aged at 475 degrees C for 3 hours shows similar effective threshold value, but a smaller closure threshold value. Crack propagation mismatch at the interface of the two phases and brittle to ductile fracture transition in the material at -50 degrees C or in the aged material at RT were observed, and possible mechanisms were discussed.