HYDROGEN EMBRITTLEMENT SUSCEPTIBILITY OF GALVANIZED 4135 STEEL IN CEMENT ENVIRONMENT

Hydrogen embrittlement (HE) in SAE 4135 steel in a simulated cement so lution was studied in terms of environmental susceptibility and metall urgical influences. Slow strain rate testing (SSRT) showed that the st eel is susceptible to hydrogen embrittlement when its potential is les s noble than -1.0 V (SCE) for all three tempering temperatures studied , i.e. 480, 580 and 650-degrees-C. At a given cathodic potential, the degree of embrittlement decreased with increasing tempering temperatur e, accompanied by a change in fracture mode from a mostly intergranula r fracture (i.e. along the prior austenite grain boundary) to a predom inantly transgranular type with the crack path following the interface of martensitic laths. The likelihood for hydrogen evolution in a cure d Portland cement was highlighted with measurement of the corrosion po tential in simulated solutions with and without aeration. The corrosio n behaviour was found to be similar in wet cement where the free corro sion potential of galvanized steel stabilized at a level well below th e hydrogen line under de-aerated conditions.