Abstract
A stress coupled hydrogen diffusion finite element model has been developed to simulate incremental step load (ISL) test. It is further integrated with a cohesive zone model (CZM) based on a stiffness-separation law. The influence of hydrogen on the cohesive law has been implemented through a newly proposed approach rooted in the hydrogen enhanced decohesion (HEDE) mechanism. Finally, this coupled model has been utilized to assess hydrogen embrittlement (HE) susceptibility of materials through the prediction of crack initiation time. The crack initiation time decreases with the increase of initial hydrogen concentration in a quench and tempered 36NiCrMo4 (4340) steel showing a ductile-brittle transition behavior. Similar observations were done from ISL experiments. In addition to initial hydrogen concentration, the influence of yield strength, fracture toughness and hydrogen diffusivity on material susceptibility was also studied. Three different materials-iron, niobium, 304 stainless steel in addition to 36NiCrMo4 (4340) steel were selected for the study. Iron shows better resistance to HE failure owing to its low yield strength and high fracture toughness while 304 austenitic stainless steel reveals least susceptibility to hydrogen induced cracking. This is largely attributed to the lower diffusivity of hydrogen in 304 stainless steel.
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