Studies on corrosion behavior of AISI 316L cold metal transfer weldments in physiological solutions

Abstract

Evaluating the mechanical integrity and corrosion performance of welded joints is vital to replace the malfunctioning parts in human body. This research aims to study the effect of Cold Metal Transfer (CMT) process on the corrosion behavior of austenitic stainless steel (AISI 316L) weldments in physiological solution. ER316L filler wire is used to weld thin sheets of 2mm to butt joint configuration. Optical microscopy and Scanning electron microscopy (SEM) are used to study the microstructural evolution in base metal (BM), heat affected zone (HAZ) and weld metal (WM). For determining the phases in BM and WM, X-ray diffraction (XRD) spectrums are captured. WM microstructure illustrated the presence of equiaxed grains while columnar dendrites were observed at HAZ. Energy Dispersive X-Ray Spectroscopy (EDS) analysis highlighted the increase in wt. % of Fe and Cr in WM due to the thermal variations. EDS elemental mapping revealed uniform distribution of Cr, Mo and Fe elements in the WM. AISI 316L WM exhibited higher tensile strength and reduced ductility compared to BM. Micro-hardness measurements showed higher hardness at the WM as result of the increased ferrite content and ductile mode of fracture was characterized with dimples and micro voids. During Corrosion test, the WM and the BM revealed lower corrosion potential and the pitting tendency is relatively less than HAZ. The delta ferrite (δ) formation in the HAZ and WM did not affect the corrosion behavior significantly as confirmed from Tafel scans and Nyquist plots. The corrosion rate is within the acceptable range, ie. First level for WM (<1 mpy) and second level for BM and HAZ (1-5 mpy), respectively.