Void swelling resistance of phosphorus-modified austenitic stainless steels during HFIR irradiation at 300–500°C to 57 dpa

Abstract

The austenitic stainless steel prime candidate alloy (PCA) is a Ti-modified alloy (14Cr16Ni) developed for void swelling resistance at 400–600°C by the US Fusion Reactor Materials (FMR) program. During irradiation in the High Flux Isotope Reactor (HFIR) to 34 and 57 dpa (70–75 appm He/dpa) at 300–600°C, th e PCA (and the closely related D9 type alloy) has been shown to be highly susceptible to void swelling at 500°C. Generally such alloys show good void swelling resistance to higher doses during irradiation in fast-breeder reactors (FBRs, 0.5–1 appm He/dpa) in the 20–25% cold-worked (CW) condition. New multiply-stabilized, phosphorus-modified PCA alloys have been developed, with specific amounts and combinations of minor alloy elements added for improved MC formation and stability characteristics during irradiation. After HFIR irradiation at 300–500°C to 34–57 dpa, the multiply-stabilized, phosphorus-modified PCA and phosphorus-modified D9 alloy showed better swelling resistance (by density-change measurements) than similar alloys without phosphorus, particularly at 500°C. Microstructural studies after 34 dpa at 500°C showed that void swelling resistance in the multiply-stabilized, phosphorus-modified PCA alloys was directly related to the formation of ultrafine dispersions of MC precipitates during HFIR irradiation.