Self-welding susceptibility of cold worked alloy D9 and 316LN austenitic steels in flowing sodium

Abstract

Specimens of 20% cold worked alloy D9 and 316LN were tested for self-welding susceptibility in flowing sodium at 823 K. A contact stress of 24·5 MPa was maintained during the test, and tests were carried out for two different durations of 3 and 4·5 months for each. It was found that susceptibility to self-welding in flowing sodium is higher for cold worked alloy D9 than for cold worked 316LN. This is in contrast with no self-welding reported for annealed alloy D9 and high susceptibility to self-welding reported for annealed austenitic stainless steels like 316LN, 321 and 304. Dynamic recrystallisation of the cold worked structure at the location of self-welding, which does not occur for cold worked 316LN steel, is the reason attributed to the high susceptibility of cold worked alloy D9 to self-welding. It appears that carburisation of cold worked alloy surface, which leads to the formation of coarse TiC precipitates at the surfaces, assists dynamic recrystallisation.