Effect of Structural Orientation on the Susceptibility of Commercial Duplex Stainless Steels to Hydrogen Embrittlement

Slow tensile straining, over a range of strain rates, of specimens machined from two commercial duplex stainless steel pipes has identified the important factors influencing their degree of embrittlement by hydrogen. Despite their very different microstructures, both materials suffered a significant loss in ductility after thermally charging with hydrogen. However, a difference in behavior between the two steels becomes apparent when uncharged specimens are tested in hydrogen below two bar pressure. The steel having a strongly banded distribution of austenite exhibited behavior that was very dependent on orientation and this is ascribed to the barrier-to-crack propagation presented by the austenite stringers. Behavior generally seems to be dominated by the ferrite matrix, but the possible role of ϵ-martensite, where the ferrite is not so highly embrittled, is also discussed.