Fatigue property of SA508-ІV steel with different microstructures for a
novel nuclear reactor pressure vessels
Abstract
The effect of different microstructures (granular bainite and
martensite) on the low cycle fatigue (LCF) behavior of SA508-IV steel
was investigated. The LCF tests were performed with the strain
amplitudes of ±0.45% and ±0.6% at 300 °C, respectively. The
experimental results showed that the stress concentration between M/A
islands and bainitic ferrite matrix was prone to facilitate cracks
initiation, which would cause more crack initiation points in granular
bainite during the fatigue. The fraction of the high-angle grain
boundaries (HAGBs) of granular bainite and martensite were 32.01% and
42.34%, respectively. The HAGBs could effectively hinder crack
propagation. In addition, the separation of fatigue striations in the
martensite structure was narrow compared to granular bainite structure
under the same conditions, suggesting the crack propagation rate of
martensite was slower. Finally, the fatigue live of martensite was much
longer at the same strain amplitude, which was attributed to less crack
initiation, more HAGBs, more fine carbides and less crack propagation
rate.