Studies on welding of powder metallurgically manufactured borated stainless steel 304b

Abstract

Borated Stainless Steels (BSS) are widely used in nuclear power plants to control neutron criticality in reactors as control rods, shielding material, spent fuel storage racks and transportation casks. 10B isotope is the key element for enhanced neutron absorption in Borated stainless steel. The solubility of boron is low in austenite matrix resulting in the formation of hard and brittle eutectic phases (Cr, Fe)2B, which will deteriorate mechanical newlineproperties particularly impact and fracture toughness. Two different types of manufacturing techniques are used to manufacture borated stainless steels i.e. Powder metallurgy (Grade A) and Ingot metallurgy technique (Grade B). Grade A materials contain significantly finer, spherical and uniformly distributed borides. Fusion welding of BSS poses challenges such as solidification cracking due to wider solidification range and liquation cracking in the partially melted zone. In this study joining of 6mm thick Powder Metallurgy (P/M) borated stainless steel plates have been welded and investigated using Fusion welding (GTAW, Activated GTAW), High energy density welding (EBW) and Solid state welding process (FSW). It was found that full penetration, crack free welds can be obtained with any of these processes. Welded specimens were subjected to mechanical testing i.e tensile, Impact and newlineHardness surveys across the weld. Microstructural studies were conducted using optical microscopy and scanning electron microscopy to bring out the structure property correlation. Fusion and solid state P/M welds were compared with welds made on plates manufactured through conventional ingot metallurgy (I/M) route. Fusion zone (FZ) microstructure of the fusion and high energy density (FB) welds exhibited austenitic dendrites with eutectic borides in the interdendritic regions. Partially melted zone (PMZ) was observed in all types of fusion welds investigated. GTA and AGTA welds exhibited wider PMZ while high energy density (EB) weld shows narrow PMZ. Nugget zone microstructure of the solid s