Volume 6, Issue 7 (July 2009)
Unusual Enhancement of Ductility Observed During Evolution of a “Deformation Wave” in 12Cr18Ni10Ti Stainless Steel Irradiated in BN-350
Whereas most previous irradiation studies conducted at lower neutron exposures in the range 100–400°C have consistently produced strengthening and strongly reduced ductility in stainless steels, it now appears possible that higher exposures may lead to a reversal in ductility loss for some steels. A new radiation-induced phenomenon has been observed in 12Cr18Ni10Ti stainless steel irradiated to 26 and 55 dpa. It involves “a moving wave of plastic deformation” at 20 and 60°C that produces “anomalously” high values of engineering ductility, especially when compared to deformation occurring at lower neutron exposures. Due to the concentrated deformation occurring at the wave front, the wave moves much faster than the mechanically applied strain rate. However, when strained at 120°C the moving wave is not observed, indicating that the phenomenon operates at lower test temperatures. Using the technique of digital optical extensometry, the “true stress–true strain” curves were obtained. It appears that the moving wave of plastic deformation occurs as a result of an increase in the strain hardening rate, dσ/dε(ε). The increase in strain hardening is thought to arise from an irradiation-induced increase in the propensity of the γ→α martensitic transformation.