Development of novel welding techniques for dissimilar joining of 12 mm thick plates of AISI347H and IN625 for CSP power plants

Abstract

• The study compares welding processes for joining AISI347H and IN625 for CSP plates. • The welding processes adopted are SP-MIG and DP-MIG. • DP-MIG has lower heat-input and residual stress than SP-MIG. • On comparing all the results, DP-MIG has better properties than SP-MIG. AISI347H and IN625 alloys are commonly used in for applications requiring higher strength at higher operating temperatures. However, the dissimilar joining of these materials is mostly used in fabrication of CSP energy storage tanks. While joining dissimilar metals, there are several practical challenges. The major concern regarding joining dissimilar materials is the selection of suitable welding techniques. Additionally, welding of thick sections requires more passes, which results in a higher heat-input, it will adversely affect the metallurgical and mechanical properties of the weldments. As a result, pulsed welding is a viable option for reducing overall heat input. In the present study two different pulsed current welding techniques namely, DP-MIG and SP-MIG welding were tried out successfully. It was observed that DP-MIG showed 27% reduction in the heat-input when compared to SP-MIG. Similarly, when DP-MIG was compared to SP-MIG, the residual stress was decreased by 75 MPa. In the fusion zone (FZ) micro segregation of alloying elements are lower to avoid secondary phase formation in DP-MIG technique. DP-MIG has better tensile strength and hardness than SP-MIG due to finer grain formation. The overall studies shows that DP-MIG shows better mechanical properties compared to conventional arc welding techniques.