Effect of Neutron Irradiation on Types 316 and 321 and Sandvik 12R72 Stainless Steels

Specimens of Types 316 and 321 and Sandvik 12R72 stainless steels were irradiated in Experimental Breeder Reactor-II (EBR-II) to a fluence of 3.8 × 10₂₂ neutrons (n)/cm₂ (E > 0.1 MeV) at 500 and 600°C. Three different specimen configurations were used: small sheet tension specimens, small right circular cylinders for immersion-density measurements, and thin foils for transmission electron microscopy (TEM). The majority of the specimens were Type 316 stainless steel with differing metallurgical histories that can be classified as either cold rolled or solution annealed and aged. Specimens of the other alloys were in either a solution-annealed or solution-annealed and aged condition. Immersion density and TEM results showed that cold rolling prior to irradiation reduces the amount of swelling observed. For specimens in the annealed condition and irradiated at 500°C, there was essentially no difference in swelling for the three alloys. After irradiation at 600°C, however, TEM of a foil specimen of Type 321 stainless steel revealed very few voids with essentially no swelling. Irradiation-induced precipitates, whose size, type, and density varied with alloy, irradiation temperature, and previous treatment, were present in all alloys. The dislocation structure of the cold-worked specimens was essentially unchanged after the 500° irradiation but was significantly altered during the 600°C irradiation. Results of tension tests showed an increase in the yield strength and a decrease in the total elongation for specimens irradiated in an annealed condition, whereas specimens irradiated in the cold-rolled condition showed the reverse effect.