Effect of Neutron Irradiation on the Microstructure and Properties of Titanium-Stabilized Type 316 Stainless Steels

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Abstract
The effects of titanium additions up to 0.6 wt% on the irradiation-induced swelling and changes in creep-rupture properties were investigated. Samples were irradiated in the Experimental Breeder Reactor II at temperatures in the range from 450 to 700°C to a maximum neutron fluence of 7.8 × 1026 n/m2 (>0.1 MeV). In annealed material, the irradiation-induced swelling exhibited a minimum in the range 0.2 to 0.4 wt% titanium. The minimum in swelling was directly attributable to a minimum in the concentration of voids. Samples irradiated in the 20% cold-worked condition exhibited slight densification at 3.0 × 1026 n/m2 (>0.1 MeV) at both 500 and 600°C. A small density decrease (0.23%) occurred during irradiation to 6.6 × 1026 n/m2 (>0.1 MeV). Postirradiation creep-rupture ductility was a maximum for alloys containing 0.23 and 0.33 wt% titanium. The observed swelling behavior in the annealed material is thought to be associated with changing amounts of titanium and carbon in solution in the austenite as the total titanium concentration is increased. The improved ductility is attributable to a decreased tendency for grain boundary crack formation and appears to be associated with removal of sulfur and possibly other impurities from solution in the austenite.