Weld Fusion Line Corrosion of Stabilized Austenitic Stainless Steels

Abstract

Carbidic precipitation and structural changes at elevated temperatures that markedly affect the susceptibility of austenitic CrNi welded stainless steels to intercrystalline corrosion, knife line attack, fissure attack and others in the fusion line zones, are considered. The areas of occurrence of intercrystalline attacks are connected to the potentiodynamic polarization curves for studied stainless steels. Special attention is given to the temperature conditions near the welded metal with regard to the corrosion failures of various areas of the welded joints. The generally encountered phenomena are the formation of chromium carbides after the dissolution of stabilizer carbides in a solid solution or the formation of nitric acid soluble dendritic titanium carbides. There is also the possibility of fusion line corrosion not associated with carbides but with either delta ferrite, segregation effects in austenite or existence of significant internal stresses.