Investigation of the oxide film on 308L weld surface produced during welding process

The oxide film formed during welding on the inner surface of 308L weld was investigated. The morphology, composition and structure of the oxide film were characterized by optical microscopy, scanning electron microscopy, laser Raman spectroscopy, X-ray diffraction, Auger electron spectroscopy and transmission electron microscopy. The results indicated that the oxidation degree of the weld metal was generally uniform from the weld center to the fusion line. Micro-scale cracks were found on the outer surface of the oxide film and nano-scale gaps scattered on the inner oxide film-weld interface. The oxide film exhibited a duplex structure including outer and inner layers. The outer layer, made of tightly bound particles, was mainly composed of Fe2O3 oxide particles with a diameter of 50-150 nm. And the inner layer, made of relative loosely bound particles, was mainly composed of Fe3O4 and FeCr2O4 oxide particles with a diameter of 10-50 nm. The corresponding oxidation behavior and mechanism of the oxide film were also discussed.