HYDROGEN EMBRITTLEMENT SUSCEPTIBILITY OF GALVANIZED 4135 STEEL IN CEMENT ENVIRONMENT

Hydrogen embrittlement (HE) in SAE 4135 steel in a simulated cement solution was studied in terms of environmental susceptibility and metallurgical influences. Slow strain rate testing (SSRT) showed that the steel is susceptible to hydrogen embrittlement when its potential is less 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 temperature, accompanied by a change in fracture mode from a mostly intergranular fracture (i.e. along the prior austenite grain boundary) to a predominantly transgranular type with the crack path following the interface of martensitic laths. The likelihood for hydrogen evolution in a cured Portland cement was highlighted with measurement of the corrosion potential in simulated solutions with and without aeration. The corrosion behaviour was found to be similar in wet cement where the free corrosion potential of galvanized steel stabilized at a level well below the hydrogen line under de-aerated conditions.