Finite element simulation for prediction of bead geometry and residual stresses in stellite hardfaced gate valve by PTAW process

Abstract

Hardfacing plays a major role in improving the material performance for longer life of component. While hardfacing, an important factor, dilution should be minimised by controlling the process parameters. Dilution is expressed as the percentage of parent metal included in the weld overlay and decides the quality of hardfaced layer. The developed residual stresses within the hardfaced component due to hardfacing reduce service life of the component. Therefore, controlling the dilution, studying the effects of process parameters, and estimating the magnitude and nature of residual stresses are deemed necessary. Among the various surfacing techniques, Plasma Transferred arc welding (PTAW) is selected for the fabrication of high quality intricate parts due to improved flexibility, productivity, and product quality in a manufacturing environment. The deposition of Stellite 6 on both sides of the low alloy steel gate valve was carried out by plasma transferred arc welding process and the effects of PTAW process parameters on dilution was analysed using ANN model. To study the effects of PTAW hardfacing process parameters such as arc current, travel speed, powder feed rate, centre gas flow rate, and oscillation speed on bead geometry parameters namely penetration, reinforcement and bead width, a five level five factor factorial technique of response surface design was selected. The results obtained from thermal analysis were given as input for the structural analysis to estimate the residual stresses and distortion both at as hardfaced condition and the post weld heat treated condition. Longitudinal and transverse residual stress profiles at different planes and locations were predicted. Predicted residual stresses were compared with experimental results obtained from X ray diffraction technique. It was found that the predicted residual stresses and experimental results have similar trend. newline newline newline