Recent Progress in Hydrogen Embrittlement of Welded Joints of High‐Strength Low‐Alloy Steel: Focusing on Microstructure

Hydrogen embrittlement (HE) occurs as a result of hydrogen atom ingress and causes a significant decrease in plasticity and strength, making it a crucial failure mode in high‐strength low‐alloy steels. The microstructure plays a vital role in HE fracture behavior because of the various hydrogen trappings. The welding thermal cycle and alloying elements determine the great difference of the microstructure of the welded joint. Thus, this article reviews the current studies investigating the role of the microstructure in determining the HE behavior of the welded joints, thereby aiming to reveal the fracture process and mechanism. Dislocations and inclusions in welded joints reduce HE resistance. Acicular ferrite with a fine interlocking structure can block the prolonging of hydrogen‐induced cracking. The transformation of the retained austenite with a high concentration of hydrogen atoms into martensite accelerates HE fractures. The δ‐ferrite in the welded joint promotes the HE resistance deterioration and hydrogen‐induced cracking. Appropriate coating of the steel surface is an effective approach for preventing HE fractures.