Atmospheric Corrosion Estimation of Welded Low Alloy Steel in Wet and Dry Condition Containing Chloride Ions

The atmospheric corrosion resistance of Al and Si bearing steels welded by MIG (Metal Inert Gas welding) or MAG (Metal Active Gas welding) was evaluated by the wet and dry corrosion test. It was found that welded Al-Si steels experienced much less corrosion than carbon steel (SM). In SEM-EDS analysis, the rust of welded Al-Si steel had the enrichment of Al and Si in inner rust, which made the protective rust. The distribution of corrosion pits was measured with a laser microscope and estimated by Gumbel analysis. A higher corrosion depth was observed near the weld metal of Al-Si steel in the case of large amount of heat input during welding. From Transmission Electron Microscopy (TEM), the layer structure of a and. phase was observed near the weld metal of Al-Si steel. Increased corrosion sensitivity was present only at the beginning of the test time. At later times in the test, the welded Al-Si steel displayed high corrosion resistance as a result of the forming of the protective rust containing Al and Si in inner rust.