Influence of cold work on the in-pile stress rupture strength of 16 chromium--16 nickel--niobium austenitic stainless steels

The in-pile stress rupture strength of 16Cr--16Ni--Nb stainless steel was investigated. Different pretreatments were used, namely solution annealing plus various cold-working levels up to 20 percent. Thermal stability under irradiation and the high-temperature embrittlement of the different material conditions were studied. The specimens were irradiated in the form of electrically heated pressurized tubes at irradiation temperatures ranging from 615 to 7200C. Irradiation time was up to 4800 h, correspondng to a maximum fast neutron fluence (E > 0.1 MeV) of 8.2 x 1025 n/m2. Neutron irradiation caused a marked reduction in stress rupture strength for the solution-annealed and the cold-worked specimens. For the solution-annealed tubes, this reduction was mainly attributed to high-temperature embrittlement; the decrease in rupture strain was less pronounced for the cold-worked tubes. The reduction in stress rupture strength came mainly from an increase in creep rate. As far as stress rupture strength and creep strength at high irradiation temperatures were concerned, the 15% cold-worked 16Cr--16Ni--Nb steel was superior to the other cold-work levels