Corrosion Resistance Behavior of GTAW Welded AISI type 304L Stainless Steel

Stainless steel (SS) has broad application in nuclear and several industries as structural material attributed to the desirable mechanical and suitable corrosion resistance properties. Corrosion resistance behaviors and microstructural evolutions of type 304L SS gas tungsten arc welded (GTAW) joint of different thickness were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction, micro-Vickers hardness test and electrochemical techniques. Microscopic analsis reveals the weld microstrcture, interdendritic δ-ferrite of lathy and skeletal features along with austenite structure. Hardness is more in 6-mm-thick welded sample attributed to δ-ferrite contents. The measured corrosion rate in boiling HNO3 increases with the increase in the thickness of the welded specimen, and base metal shows a marginally higher corrosion rate compared to weld metals. The corrosion rate of the base and weld metals of the AISI type 304L SS in 65% nitric acid is in the acceptable range. However, as the delta ferrite with a higher amount of chromium is present, the austenite matrix in the microstructure results in a lower corrosion rate of the weldment compared to its base material. The electrochemical corrosion behaviors of type 304L SS base metal and weldments in 6 M HNO3 solution at 25 ± 1 °C are evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy methods. The corrosion resistance, hardness and microstructure behavior of GTAW welded AISI type 304L SS are elaborated and discussed.