Effect of process parameters on microhardness and microstructure of heat affected zone in submerged arc welding

Abstract

The aim of the present work was to study the effect of flux, welding current, arc voltage, and travel speed on changes in microhardness and microstructure of the heat-affected zone (HAZ) and to optimize the process so that minimal changes occur in the material properties after completion of a submerged arc welding (SAW) process following suitable Taguchi experimental design. Micrographs of the welded samples were studied to analyse the changes in the microstructure of the material and the resultant changes in ferrite percentage, pearlite, bainite, and martensite formations. Welding current and type of flux were found to be the most significant factors leading to changes in microhardness and metallurgical properties. The microhardness tended to increase significantly with the increase of welding current from 350 to 450 Amp whereas higher hardness was observed when flux type I (basicity index 0.8) was used. Travel speed and arc voltage were found to be insignificant in relative comparison. Flux with basicity index of 0.8 showed a significantly higher microhardness compared to flux with basicity index of 1.6 (flux II). A higher amount of CaO and MgO present in flux II has a tendency to pick up carbon from steel workpiece, thus lowering the microhardness.