Embrittlement of laser surface-annealed 17-4 PH stainless steel

Abstract

Stress corrosion cracking and fatigue crack growth behavior were determined in 17-4 PH stainless steel under various metallurgical conditions, including the H900 (482°C/1 h), H1025 (552°C/4 h) aging and laser surface annealing treatments. Peak-aged (H900) specimens locally irradiated by laser beam consisted of a portion of composite region (CR), in which comprised of soft laser-annealed (LA) zones on the outer surfaces and the hard base metal in between. Slow extension rate tensile tests were performed at room temperature in a saturated H2S solution to evaluate the hydrogen embrittlement susceptibility of various specimens. H900 specimens show an obvious improvement in impact toughness after irradiating by laser. Regardless of testing environments, H900 specimens exhibited better tensile properties than the other specimens. Experimental results also indicated that H900 specimens had the highest fatigue crack growth rates among the specimens, particularly at low stress intensity factor range. The retardation of crack growth in the region ahead of the CR in the LA specimens was rather pronounced. For compact tension specimens tested in gaseous hydrogen, enhanced crack growth was correlated with quasi-cleavage fracture in contrast to transgranular fatigue fracture in air.