Microstructural evaluation of molybdenum-containing stainless steel weld metals by a potentiostatic etching technique

Microstructure of austenitic stainless steel weld metals is complicated by the presence of delta-ferrite and microsegregated regions rich in chromium and molybdenum, as well as other minor alloying elements such as sulphur and phosphorus at the delta/gamma interphase boundaries. Detailed microstructural studies are required in order to establish correlation between various metallurgical as well as electrochemical corrosion properties with the weld metal microstructure. The conventional chemical etching technique was found to be inadequate in revealing different microconstituents. A powerful potentiostatic etching technique was used to reveal not only ferrite but also different microconstituents that had different specific electrochemical potentials at which they dissolved. This paper describes the weld metal microstructure developed by the addition of molybdenum (4.16-5.83 wt%) to type 316 stainless steel weld metals during Tungsten Inert Gas (TIG) welding with different heat inputs. (C) 1998 Chapman & Hall.