Reduction of hydrogen embrittlement in an ultra-high-strength steel by laser surface annealing

This paper shows that laser beam irradiation improves the resistance to hyd rogen embrittlement (HE) in an ultra-high-strength maraging steel. Localize d laser irradiation of a peak-aged steel plate resulted in the formation of a soft surface layer called the laser-annealed zone (LAZ). A composite reg ion (CR) was formed when both the top and bottom surfaces of a peak-aged sp ecimen were laser-annealed (LA) to leave an interior layer of untransformed base metal (BM) sandwiched between the two LAZs. Slow strain rate tensile tests showed that LA specimens had lower strength and ductility than the pe ak-aged specimens when tested in air, but in a H2S solution, the soft LAZs showed less susceptibility to HE than the BM. The fatigue crack growth rate s (FCGRs) in the CR were lower than those in the BM regardless of testing e nvironment and stress ratio (R). The retarded crack growth in the CR was at tributed to the combination of residual compressive stresses and the soft m icrostructures in the LAZs. The tensile fracture appearance of LA specimens tested in a H2S solution exhibited intergranular fracture in the BM. Fract ographs of the fatigue specimens tested in gaseous hydrogen revealed transg ranular fracture in the LAZs and mainly quasi-cleavage fracture in the BM.