Corrosion Behaviour of High Alloyed Stainless Steel Weld Metals, Joints and Overlays in Standardized Corrosion Tests with some Examples

Abstract

As already described earlier, stainless steels can form on their surface a protective, passive film on exposure to a service environment. This passive film, especially its stability and homogeneity, is responsible for the corrosion resistance of these materials. Welding can have a strong impact due to the typical segregated, multiphase weld metal structures and the additional influence of the weld heat cycle. This may result in a lower corrosion resistance of the weld metal compared to the base metal in case of a similar chemical composition. To describe the corrosion behaviour, many different tests have been developed, using different environments, different test temperatures and different test specimen preparation. But due to the variety of parameter settings and test conditions, the corrosion test results are often not comparable. To overcome this problem, standardized corrosion tests were established. Specimen preparation, test solution composition, test duration and temperature setting are defined to allow a “world wide” comparison. This paper gives an overview of which standardized tests are applied in practical use for typical types of material. Additionally some results of weld metal and joint testing are shown from which the influence of different thermal cycles, alloying concepts, surface conditions and shielding gases on the corrosion behaviour can be derived.