Temperature effect on hydrogen embrittlement susceptibility of a high strength martensitic steel

This study investigates the effect of temperature on the hydrogen embrittlement (HE) susceptibility of a modified AISI 4130 high strength steel. In situ incremental step loading tests were performed at temperatures of 4 degrees C, 24 degrees C, and 54 degrees C, with specimens immersed in a 3.5% NaCl aqueous solution under cathodic charging, to evaluate the threshold stress for hydrogen induced cracking. The results showed that all tested conditions exhibited susceptibility to hydrogen embrittlement, with the lowest threshold stress observed at room temperature (24 degrees C), which corresponds to the highest HE susceptibility. This behavior is consistent with findings in the literature, where HE is most critical around room temperature. At 54 degrees C, the material showed the lowest HE susceptibility, attributed to the decreased hydrogen trapping capacity of dislocations at higher temperatures. Conversely, at 4 degrees C, the susceptibility was slightly lower than at 24 degrees C, though the difference was not significant. Fracture analysis revealed a mixed-mode failure characterized by both intergranular and quasi-cleavage features, indicating that hydrogen concentration occurs at both prior austenite grain boundaries and martensite block and packet boundaries. Hydrogen quantification tests confirmed that the diffusible hydrogen content increased with temperature. The obtained results indicated that the HE behavior is primarily influenced by a synergistic interaction between hydrogen diffusion and hydrogen transport by dislocations, where the first one increases with increasing temperature while the second one decreases. Additionally, an interesting behavior was observed in the hydrogen induced crack propagation rate, where it was faster as the test temperature increased.