Effect of dual phase stabilization via varying Ti/Nb ratios on the pitting behavior of AISI 347 welds

Abstract

The aim of the present work was to study the role of Ti additions made to Nb contained stabilized austenitic stainless steel grade AISI 347 welds for improving their metallurgical stability and pitting corrosion resistance. For achieving this, gas tungsten arc welding process (GTAW) was used to fabricate multi-pass and multi-layer weld pads comprising of 28 weld passes; and using AISI 347 (Nb based) and AISI 321 (Ti based) solid fillers in a systematic combination, so as to obtain different weld metals’ surfaces with varying Ti/Nb ratios of 0.45, 0.66, and 1.57. These surfaces were examined for their pitting behavior using electrochemical method, an electron probe microanalyzer (EPMA) equipped with a wavelength dispersive X-ray spectrometer (WDS) for chemical composition analysis, and X-ray photoelectron spectroscopy (XPS) depth profiling of passive films. Austenitic stainless steel welds with Ti/Nb ratio of 0.45 exhibited maximum pitting potential of 380.5 mVSCE as compared to sole Nb weld with 270.7 mVSCE. The atomic concentration profiles of oxygen across different weld surfaces indicate that estimated passive film thickness values for sole Nb (347 weld metal) and Nb weld stabilized with Ti/Nb ratio of 0.45 were calculate to be 8.43 nm and 7.11 nm, respectively. Ti addition suppressed the carbide formation tendencies resulting in higher levels of Ni in the matrix as well as different dendritic regions of 347 weld metal. Thus, this study establishes that Ti additions of 0.21 wt% in Nb weld can significantly enhance its pitting resistance.