Effect Of Phosphorous and Silicon On Hot Cracking Susceptibility Of 14Cr-15Ni-2.3 Mo Ti-Modified Fully-Austenitic Stainless Steel

Abstract

Alloy D9, fully-austenitic stainless steel containing 15Cr, 15Ni, 2.3Mo and 0.3Ti [wt. %] is being used as the material for the fuel clad and wrapper in Fast Breeder Reactors (FBRs). An improved version of this alloy containing higher nickel, silicon and phosphorous than present in D9 is being developed, with the objective of enhancing the radiation swelling resistance of this alloy to achieve higher burn-up for the fuel. Fabrication of this alloy involves autogenous welding to seal the fuel pins and fuel bundle containers. In fully-austenitic stainless steels like D9, hot cracking is a major concern during welding, especially in the absence of any residual delta-ferrite in the prior austenitic mode of solidification. In this study, both Varestraint and hot ductility tests were used to evaluate the hot cracking susceptibility of these alloys. The Varestraint test results indicated that these new alloys have a very high hot cracking susceptibility during autogenous welding, as the total crack length and maximum crack length in both the weld and heat-affected zone and also the BTR values were very high, compared to that of alloy D9. Hot ductility (Gleeble) testing was also carried out to determine the temperature range at which the material is prone to hot cracking when subjected to a thermal cycle that simulates actual welding. The Gleeble test results are also unfavourable to the weldability of these alloys since the nil ductility range of these alloys is much higher compared to that of reasonably weldable alloys. This paper discusses the results of the hot cracking behaviour of this fully-austenitic SS material using the Varestraint and hot ductility tests.