Submerged Arc Welding With a Mixture of Fresh Flux and Fused Slag-Modeling with Quadratic Response Surface Methodology

Abstract

In the present research work the reconsumption of the slag, generated during conventional submerged arc welding, has been proposed during subsequent runs by incorporating appropriate treatment and mixing it with fresh flux, with certain proportions. Experiments have been carried out by using four different levels of process parameters like welding current, flux basisity index and slag-mix percentage (percentage of slag in the mixture of fresh flux and fused slag) to obtain bead-on-plate weldment on mild steel plates. Parameters associated with bead geometry like bead height, bead width, depth of penetration have been measured for each experimental run. Heat affected zone (HAZ) geometry in terms of HAZ width has also been obtained. Assuming simple geometry of the weld bead and unit length of the job, approximate bead volume has also been calculated. All these data have been efficiently utilized to develop mathematical models for prediction of geometry and quality of weld bead as well as heat affected zone. Quadratic response surface methodology (RSM) has been applied to develop the mathematical models between predictors and responses. Based on multiple linear regressions, the coefficients of the predictors, used in the models, have been determined. Analysis of Variance Method (ANOVA), F- test and Student's t test have checked the significance of the coefficients. Reduced models with significant coefficients have also been developed. Experimental data as well as generated data have been used to represent graphically the direct and interactive effects of process parameters (slag mix% has given special emphasis in this exercise) on selected response variables associated with weld bead and HAZ. Hardness Test has also been carried out to reflect graphically, the influence of using slag-mix in SAW process on mechanical property of the weldment i.e. hardness of weld metal as well as HAZ. Finally it has been concluded that effect of using slag-mix (up to 20%) do not impose any alarming adverse effect on features of bead geometry and HAZ. Therefore, the use of slag-mix, in submerged arc welding can be recommended to apply it in practical cases, which may make the process more economical.