Anisotropic hydrogen embrittlement behavior of hot-rolled A572 steel

In the present work, an investigation of the susceptibility to hydrogen embrittlement of a hot rolled ASTM A572 steel with a banded pearlite/ferrite microstructure was conducted, with the objective of elucidating the anisotropic mechanical behavior of the steel when submitted to hydrogen charging. To this end, tensile test samples were prepared with the tensile axis oriented parallel and perpendicular to the rolling direction of 5.0 mm thick sheets. Hydrogen charging was performed by cathodic polarization. Then, ex-situ tensile tests were carried out on both pristine and exposed samples. Using this methodology, it was possible to verify that the ASTM A572 steel is more susceptible to hydrogen embrittlement when the tensile axis is perpendicular to the rolling direction, and that the influence of prior hydrogen charging is significantly higher after necking. By analyzing the microstructure of specimens submitted to interrupted tensile tests, heterogenous strain partitioning between ferrite and pearlite was identified, which led to crack initiation and development along ferrite/pearlite interfaces. It was possible to show that fracture is facilitated when the main crack front is aligned with pearlite bands, resulting in a greater hydrogen-induced ductility loss.