Improvement of creep properties in a helium injected austenitic stainless steel

The effect of helium on creep properties was studied in AISI Type 316 austenitic steels after two kinds of treatment, namely, cold rolling and grain-boundary strengthening. Helium was injected into the specimens using a cyclotron, and the creep-rupture tests were performed at 6500C in air. In the cold-rolled specimens, the creep-rupture strengths increased with cold working. The loss of ductility due to the helium injection was minimum at about 10 percent of cold rolling. In the grain-boundary strengthened treatment, serrated grain boundaries were produced by the two step solution treatment. The specimens with serrated grain boundaries had good creep-rupture strength in both the presence or absence of helium. However, a specimen with extreme grain growth during the two step solution treatment had low creep ductility and severe helium embrittlement. A specimen which had serrated grain boundaries without extreme grain growth had excellent creep properties in both helium uninjected and injected cases