Effect of B₂O₃ enrichment on microstructural inhomogeneity of high strength steel weldments

The present work attributes the role of boron on the high strength steel submerged arc weld using an undermatching filler wire. Mild steel filler wire was used for welding in constant machine parameters setting to evaluate the joint strength due to the enrichment of boron. To change the chemical composition of the weld metal, boron trioxide powder was blended with virgin flux in various proportions (2.5% − 12.5%), which led to an increase in boron weight percentage in the range of 0 − 0.0065. The results show that weld metals (WM) optical micrographs depict the various types of ferrites, pearlites and secondary phases like martensite-austenite (M-A). Acicular ferrite content was influenced by the boron trioxide addition. Heat affected zone (HAZ) micrographs were not showing appreciable changes with oxide enrichment. Hardness and toughness of weld metals showed the mixed trend with B₂O₃ enrichment whereas, small reduction in ultimate tensile strength (UTS) and yield strength (YS) was observed.