Investigations on high temperature wear and metallurgical characteristics of Stellite 6 GTA (Gas Tungsten Arc) weld claddings

Abstract

Stellite 6, a cobalt based superalloy was deposited on mild steel AISI 1020 using Gas tungsten arc welding (GTAW) process. The claddings were overlaid in four conditions viz. single layer cladding, double layer cladding, single layer cladding with remelting and double layer cladding with remelting, where remelting of the topmost layer was carried out using autogeneous GTA arc itself. The chemical composition, microstructure, wear mechanism and phase composition of the substrate and coatings were characterized by spectroscopy, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and x-ray diffraction. The hardness and wear characteristics of different cladded samples were measured using microhardness tester and pin on disc high temperature tribometer respectively. The results show that remelting of Stellite 6 clad layers resulted into microstructural modification that increased their hardness significantly which consequentially improved their wear performance. Oxidative layer formation that occurred at 300 °C reduced frictional resistance which resulted into better wear performance of Stellite 6 clad pins. Further, a critical clad thickness was established based upon the wear performance of these claddings and it was observed that 5 mm Stellite clad thickness was sufficent enough to impart uniform wear behavior to these claddings when subjected to high temperature two body abrasive wear applications.