Abstract
Tensile testing of two samples of 3·5Ni-Cr-Mo-V steel, differing significantly in carbon and manganese content and hence in strength after heat treatment, has been carried out in a gaseous hydrogen environment. The ductility observed was found to be dependent on both strength level and heat treatment. Treatments that produced 0·2% flow strength levels below about 1700 MN/m2 appeared to induce resistance to embrittlement by gaseous hydrogen, except where heat treatments were carried out in what appeared to be a critical range for temper embrittlement. A tendency towards temper brittleness resulted in a ductility trough around 400°C that was greatly accentuated by testing in hydrogen. This appears to substantiate a cooperative action of temper embrittlement and hydrogen embrittlement. Very different failure modes are associated with the two conditions giving rise to lowstrain, hydrogen-induced failures: quenched or lightly tempered structures give rise to quasi-cleavage, whereas materials tempered between 350° and 450°C show essentially intergranular failure.
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