Hydrogen embrittlement behavior of high strength rail steels: A comparison between pearlitic and bainitic microstructures

The present study was attempted to evaluate the hydrogen embrittlement (HE) behavior of two high strength rail steels with pearlitic and bainitic microstructures by using slow strain rate test (SSRT) with notched round bar specimens. The results show that the bainitic rail steel with a mixed microstructure of bainite, tempered martensite and M/A constituents exhibits superior mechanical properties in comparison with the pearlitic rail steel. The results of SSRT revealed that the bainitic rail steel is more susceptible to HE than the pearlitic rail steel, which is ascribed mainly to the higher strength level and the microstructural characteristics of the bainitic rail steel. The attempt of re-tempering treatment of the as-received bainitic rail steel exhibits no notable improvement in the resistance to HE at no expense of strength. It is thus suggested that further efforts concerning obtaining low susceptibility to HE besides obtaining excellent combination of strength and toughness should be conducted to guarantee the safety service of the bainitic steel rails.