Fatigue crack growth rate and fracture toughness of electrochemically hydrogen-charged HFW welds of X52 steel

The paper deals with the testing of fatigue crack growth rate (FCGR) and fracture toughness (FT) of electrochemically hydrogen-charged HFW welds of X52 steel. The FCGR tests revealed a significantly accelerated crack growth rate in the presence of hydrogen, particularly at low ΔK values. This effect gradually decreased at higher ΔK levels, likely due to electrolyte depletion. The fracture surfaces of samples at ΔK = 20 MPa.m 0.5 show ductile striation patterns in samples tested in air; on the other hand, samples tested in hydrogen show mixed fractures with quasi-cleavage facets and indistinct striation patterns. In FT testing, hydrogen caused a notable reduction in the J 0.2 parameter (43 %). The samples tested in air consistently exceeded 200 kJ/m²; hydrogen charged samples mostly fell below this threshold, with one case even dropping under 100 kJ/m². Fractography analysis confirmed a micro-void coalescence mechanism in air and quasi-cleavage facets with localized dimple areas under hydrogen charging.