Optimization of Process Parameters in Double Pulse MIG Welded In 617 SS 304h Plates

Abstract

The dissimilar joining of nickel-based superalloys with austenitic stainless steel plays a vital role in the fabrication of Advanced Ultra-Super Critical (A-USC) boilers. Hence, in this research work, an effort is made to join Inconel 617 (IN 617) with Stainless steel 304H (SS 304H) using Double-Pulse Metal Inert Gas (DP- MIG) welding process. Welding trials were carried out based on the Taguchi L9 array using two different filler wires, viz. IN 617, and ER 308H. Wire feed speed (WFS), frequency, and amplitude were considered as input parameters. Butt joints were carried out between 5 mm thick plates in a single pass. Weld quality was assessed based on the depth of penetration (DOP), bead width (BW) and mechanical properties such as tensile strength, hardness, and impact toughness. TOPSIS multi-objective function was used to identify the optimized parameters. Based on TOPSIS, WFS: 2.5 m/min, welding frequency: 1Hz, amplitude: 1.5 m/min was identified as the optimized parameter combination while using ER 308H filler wire. For the IN 617 filler wire, WFS: 3m/min, welding frequency: 1Hz, amplitude: 2m/min was identified as the optimized parameter combination. On comparing the two filler wires, ER 308H filler wire had weld with superior mechanical properties. Tensile strength and impact toughness of the weld obtained through ER 308H filler were 12.20 % and 32.25 % higher than the weld obtained through IN 617 filler wire. Hence, for further studies, all the welding trials were conducted using ER 308H filler wire. A detailed study was conducted to examine the impact of welding frequency on the metallurgical and mechanical properties, better mechanical properties were achieved at higher frequency. The segregation coefficient (k) value was used to evaluate the segregation of Mo. Increased frequency led to a reduction in the segregation of Mo. A trend of increase in weld quality was observed to increase in welding frequency. In the final study, an attempt was made to study the influence of pulse duration such as thermal p