Abstract
The correlation between microstructural evolution and low cycle fatigue behavior of SA508-IV steel were investigated. The fatigue tests of specimens with different tempering times were performed under the strain amplitudes of ±0.45% and ±0.6% at 300 °C, respectively. The experimental results showed that the more and more islands which were martensite/austenite islands (M/A islands) in granular bainite decomposed into carbides and bainitic ferrite matrix with the increase of the tempering time. The fatigue life decreased with increasing the strain amplitude under the same tempering time. However, the fatigue life increased with the increase of the tempering time under the same strain amplitude. After 30 min tempering, the crack initiation preferentially occurred near the M/A islands. However, the crack initiation occurred at the trigeminal grain boundary with the tempering time increasing to 15 h and 45 h. Moreover, the decomposition products of M/A islands – carbides were beneficial to increase the fatigue life of SA508-IV steel due to its resistance against crack propagation.
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