Application of response surface methodology (RSM) for optimization of welding process parameters for 9Cr-0.5 Mo-1.8 W-VNb (P92) steel

P92 (9Cr-0.5Mo-1.8W-VNb) steel is a candidate material for high temperature service in power plants. This has been chosen to achieve the higher steam temperature and pressure necessary for improved thermal efficiency of the power plants. Activated flux Tungsten Inert Gas (A-TIG) welding process has been found to enhance the penetration depth up to 300% in single pass autogenious TIG welding. Selection of welding parameters for autogenous A-TIG welding is very important to achieve desired weld bead geometry. In this study, the effect of welding process parameters on the weld bead geometry of P92 steel A-TIG weld joints have been analysed and optimized using response surface methodology (RSM). The design matrix that indicate the number of experimental runs for generating data on the influence of A-TIG welding process parameters mainly on depth of penetration and HAl width is generated by using central composite design of response surface methodology. Based on the design matrix, 30 bead-on-plate welds were made on 10 mm thick P92 steel plate. Weld bead shape parameters which are the responses in the present analysis were measured on each sample. Second-order response surface models have been developed based on the responses measured. Response optimization was carried out for obtaining the maximum depth of penetration and target HAl using desirability approach. ANOVA analysis was carried out. It was observed that the torch speed and the welding current have larger effect on the DOP. Increase in current increases HAl width and increase in torch speed decreases HAl width. Increase in arc gap widens the arc on the sample resulting in increased HAl width. The validation of the optimized process parameters were carried out for achieving the desired depth of penetration. There was good agreement between the predicted and actual values obtained on the samples. (author)