Effect of Welding Parameters on the Hydrogen Embrittlement of Cathodic Hydrogen-Charged Friction Stir Welded High Carbon Steel Joints

The hydrogen embrittlement behavior in terms of hydrogen-induced surface blistering and hydrogen-induced internal cracking of the friction stir welded high carbon steel plates was evaluated by the cathodic hydrogen charging method. The welding processes were performed at different revolutionary pitches of 0.83, 0.5, and 0.25 mm/rev and therefore, the stir zones of the welds had various microstructures accordingly. After hydrogen charging for 4 hours, the base metal showed large quantities of irreversible dome-shaped blisters on the sample surface. On the contrary, the blisters were hardly observed in the stir zone regardless of the welding parameters and only a small number of microcracks were formed. Compared with the base metal, the stir zones produced at 0.83 mm/rev and 0.5 mm/rev had less ductility reduction after hydrogen charging for the same time. It revealed that the stir zones showed higher resistance to hydrogen embrittlement than the base metal. However, the specimen welded at 0.25 mm/rev showed premature failure after hydrogen charging as a result of the formation of cracks in the twin martensite structure beneath the specimen surface.