Effect of welding techniques on the microstructure and mechanical properties of reduced activation ferritic-martensitic (RAFM) steel weld joints

Highlights: • 10 mm thick RAFM steel is welded by A-TIG welding process with two passes. • Post Weld Heat Treatment (PWHT) conditions are optimized for A-TIG weld joint. • Harder martensite forms in the A-TIG weld metal. • Strength properties are better for A-TIG weld joint. -- Abstract: Reduced Activation Ferritic-Martensitic steels (RAFM) are chosen as the candidate material for structural components in fusion reactors. Gas Tungsten Arc (GTA) welding is one of the candidate process for fabricating the structural components made of RAFM steel. A variant of GTA welding process called as Activated Tungsten Inert Gas (A-TIG) welding has been reported to overcome the limitations of GTA welding and enhance creep rupture life in F–M steels. In the present work, 10 mm thick RAFM steel is welded by conventional TIG and A-TIG welding processes and the effect of welding techniques on the microstructure and mechanical properties are compared. Post Weld Heat Treatment (PWHT) conditions are optimized in A-TIG weld joint to get improvement in impact toughness values. TEM investigation on weld metals revealed that the martensite lath and prior austenitic grain boundaries are decorated with M₂₃C₆ precipitates and the lath size was in the range of 0.3 -0.4 μm. Very fine MX precipitates are seen in intra martensite laths and very fine sub grain formation was observed after tempering treatment. Hardness and strength properties are higher for A-TIG weld joint while ductility is similar for both the weld joints. An impact toughness of 155 J was obtained in the A-TIG weld joint on full size sample.