Abstract: The bars were widely used in many areas such as high speed road, high railway and bridge engineering. In this paper, the effect of microstructure on hydrogen embrittlement susceptibility of two strength grade of bainitic bars was investigated by electrochemical hydrogen charging tests and slow strain rate tensile tests, scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and electron back scatter diffraction patterns (EBSD). The results showed that microstructure had strong impact on hydrogen embrittlement susceptibility. Due to the appropriate alloying and microstructural designs, the strength of PSB1080 bars was much higher than that of PSB830 bars. However, it is surprising that the hydrogen embrittlement susceptibility of the PSB1080 bars was lower. The uneven distribution of hydrogen in PSB830 was mainly caused by the heterogeneous distribution of microstructure. The reason of higher hydrogen embrittlement susceptibility of PSB830 was that the martensite with high dislocation density was regard as the reversible hydrogen trap, therefore, a lot of hydrogen atoms were absorbed in the specimens. During tensile test, the hydrogen atoms were easy to diffuse and enrich. On contrary, the martensite and bainite with better coordinated deformation capability were uniform distribution in the PSB1080. The filmy retained austenite, which was located between laths, was seen as an irreversible hydrogen trap, so the diffusion and enrichment of hydrogen atom was hindered. At the same time, the filmy retained austenite also had high mechanical stability and chemical stability. Therefore, the hydrogen embrittlement susceptibility of PSB1080 bars was lower than PSB830 bars.
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2019, Vol. 33 
