Materials Characterization | 2019
Oxidation behavior of the dilution zone of a dissimilar metal weld between low alloy steel and Alloy 82 in high temperature water
Abstract
Abstract The investigation on oxidation behavior of the dilution zone of a dissimilar metal weld (DMW) between low alloy steel (LAS) A508-III and Alloy 82 weld metal (WM) in high temperature water was carried out. The results indicated that there were two types of oxide films in the dilution zone of the weld metal depending on the types of the neighboring fusion boundaries (FBs). One of the oxide films has a single crystal grain with spinel structure as internal layer which formed in the dilution zone of weld metal close to the martensite FB (area B). The other oxide film has a compact internal layer composed of nano-sized Cr-rich oxides found in the dilution zone of WM close to the sharp FB or other areas in the dilution zone (area A). Both the two types of oxide films exhibited double layer structure,regardless of the thickness of the oxide film. The single crystal grain of the internal layer of the oxide film in area B was attributed to the low Cr content of the substrate matrix, which resulted in a small number of nucleation of oxides at early stage of oxidation and the low-oxidation-rate was because of the stability of Fe-rich oxide and the protection of martensite due to galvanic corrosion.