Metallurgical and mechanical investigations of Inconel 625 overlay welds produced by GMAW-hardfacing process on AISI 347 pipes

Abstract

Inconel 625 is a widely employed material for hardfacing to protect components of aircrafts, oil refinery and power generation, possessing better corrosion resistance behaviour at high temperature applications. These characteristics are related with the hardfacing material composition and microstructure of overlaid welds which is influenced by the process parameters and the substrate composition of the component to be protected. Hardfacing has been extensively used for modifying surface and repairing. In this research, single bead overlays of Inconel 625 were deposited on the surface of AISI 347 pipe by GMAW process. Overlaid welds were deposited at three different heat inputs (0.48 kJ/mm, 0.53 kJ/mm and 0.59 kJ/mm) to synergic mode, while the voltage and wire feed rate are pre-programmed. The overlaid weld thickness varied from 1.5 mm to 2.62 mm on substrate with suitable overlaying parameters. This study was explored with Optical microscopy, Energy-dispersive x-ray spectroscopy (EDS), scanning electron microscopy (SEM), and mechanical tests were used for microstructural and mechanical characterization. The results showed that the overlay welds of Inconel 625 exemplified a noticeable microstructure upon solidification, while the bond interface can be observed and divided into distinct zones. Near the bonding interface, a non-mixed zone with precipitated ferrite of different formations were observed. The surface of overlaid weld microstructure to interface of substrate/weld overlay comprised of cellular, columnar and fine dendrites. An increase in Fe wt% in the partially mixed zone is corroborated to the melting and dispersion of the substrate. Uni-axial tension test and Vickers-micro hardness test were carried out on the specimen sectioned from overlay welds. The mechanical test responses revealed that the tensile strength and micro-hardness of the overlaid welds improved significantly compared to substrate. The mechanical properties of hardfaced area were better than bonding area and superior to substrate, revealing an excellent overlay weld deposition using Inconel 625.