Tensile Property Correlations for Highly Irradiated 20 Percent Cold-Worked Type 316 Stainless Steel

Recent experiments on developmental fast-flux test facility (FFTF) cladding (20 percent cold-worked Type 316 stainless steel) have extended the data base to a fast neutron fluence of 8.4 × 10²² neutrons (n)/cm² (E > 0.1 MeV). The specimens were irradiated in the experimental breeder reactor-II (EBR-II) at temperatures ranging from 371 to 816°C, although peak fluence levels were attained on specimens irradiated near 371 and 649°C only. Tension tests were performed at 232°C, near the irradiation temperature, and, in some cases, above the irradiation temperature. Test specimen strain rates ranged from 4 × 10 ^-5/s to 4 × 10^-2/s.

The data generated on cladding irradiated near 371 °C established that the low-temperature strength and ductility are fluence independent beyond about 5 × 10²² n/cm² (E > 0.1 MeV). The strength behavior of the irradiated cladding at 538, 593, and 649 °C is essentially the same as exhibited by thermally aged developmental cladding at the same temperatures and times out of the reactor. Up to a fluence of ∼5 × 10²² n/cm² (E > 0.1 MeV), the 538°C ductility values remain relatively fluence independent after an initial decrease. Higher temperature (593 and 649 °C) ductilities decrease continually with increasing fluence.

Tensile parameter correlations were developed for the prediction of irradiation effects on the tensile properties of 20 percent cold-worked Type 316 stainless steel. These correlations are based on unirradiated tensile property correlations developed using Hart's equation-of-state approach. The basic premise is that the condition of plastic deformation of some materials such as 316 stainless steel can be characterized by a structure parameter (σ*) which describes the material's “hardness.” It is found that irradiation effects can be incorporated into this formulation by parameterizing the changes in σ* with irradiation temperature and fluence. The resulting correlations provide a description of strength and ductility over the temperature range of 371 to 871 °C and strain rates of 10^-5 to 10 ¹/s.