Study of weld bead chemical, microhardness & microstructural analysis using submerged arc welding fluxes for linepipe steel applications

Abstract Linepipes above 16″ diameter are often submerged arc welded. Weld mechanical as well as metallurgical properties are widely affected by the flux composition. Flux composition and welding parameters play an important role in determining the good bead quality and mechanical properties of the welded joint. In present study submerged arc welding fluxes were formulated using constrained mixture design approach. Twenty one submerged arc welding flux compositions based on CaF2–CaO–SiO2 and Al2O3–CaO–SiO2 flux system were designed using extreme vertices design approach. Regression models were developed in terms of individual, binary and ternary mixture flux constituents for submerged arc series of bead on plate weld deposits (API 5 L X70 pipeline steel). By using F-test regression mathematical models have been checked for 95% significance level. Effect of formulated fluxes on silicon, copper, molybdenum, titanium and chromium content was studied using a multi-layer weld deposits. All binary mixtures C·Al, S·CF, S·Al and C·Al have significant increasing effect on silicon content in a bead on plate weld deposits while S·Al is the most effective synergistic binary mixture. Individual and binary flux mixtures tend to decrease the copper content in a bead on plate weld deposits.