The role of retained austenite in hydrogen embrittlement of supermartensitic stainless steel

• Two typical supermartensitic stainless steels used in offshore pipelines were tested.
• The test objective was to investigate the relationship between hydrogen embrittlement and the content of retained austenite.
• The amount of retained austenite was found to have a significant effect on embrittlement.
• Strain induced phase transformation from austenite to martensite is believed to enhance hydrogen embrittlement.

Retained austenite may play a role in the hydrogen embrittlement process because austenite has much higher hydrogen solubility than martensite has. The effect of the retained austenite on hydrogen cracking was investigated by tensile testing of standard round bar specimens that had been heat treated in order to achieve different levels of retained austenite. A significant effect of the retained austenite was observed. Samples with high amounts of retained austenite experienced a much higher reduction in ductility after hydrogen charging than samples with low amounts of retained austenite. In order to explain this effect, the hydrogen solubility of samples containing different levels of austenite and precipitates was measured. This was achieved by charging the samples to saturation in an electrolyte and performing hydrogen analysis.