Experimental investigation on mechanism and weld morphology of activated TIG welded bead-on-plate weldments of reduced activation ferritic/martensitic steel using oxide fluxes

Abstract

This work attempts to investigate the influence of different single component oxide fluxes in the activated TIG welding of reduced activation ferritic/martensitic (RAFM) steel. Six different fluxes Al2O3, Co3O4, CuO, HgO, MoO3, and NiO were used for bead-on-plate welding, carried out under same conditions and process parameters. The weld dimensions such as depth of penetration (DOP), depth/width (D/w) ratio, bead width (BW) and Heat affected zone (HAZ) width were studied and compared in addition to the peak welding temperatures. Experimental results indicated that enhanced penetration was achieved with use of fluxes Co3O4, CuO, HgO and MoO3. Further investigation of weld dimensions and the peak temperature values indicated that the reversed Marangoni effect was present with the use of these fluxes. However, fluxes Co3O4 and CuO gave through penetration (greater than plate thickness) under the additional effect of arc constriction. Thus a dual mechanism effect is proposed in this study with the use of these two fluxes. Furthermore, the metallurgical characterisation of the weldment produced with Co3O4 and CuO fluxes were evaluated using optical microscopy and Vickers micro-hardness and compared with TIG welded sample. The resultant microstructures and hardness profile indicated presence of coarser and harder martensitic structure in the weld and HAZ regions.