Characterization of microstructure and corrosion properties of cold worked Alloy 800

Abstract

X-ray diffraction studies indicated that cold worked (~50%) Alloy 800 was austenitic and transmission electron microscopy revealed the presence of a small volume fraction of hexagonal ε-martensite along with deformation bands, high dislocation density and primary TiN particle with a few dislocations within it. The passivity of cold worked alloy was very stable in H₂SO₄ solution but unstable in HCl solution at room temperature. The exposure of cold worked alloy in 673 K steam (initial pH of water was 10.1) for a period of 264 h showed almost nil corrosion rate. Scanning electron microscopy revealed a number of small oxide particles on the surface exposed in steam indicating initiation of oxide formation. Energy dispersive X-ray analyses of the surface containing small oxide particles indicated that the surface composition was similar to bulk composition of the alloy. X-ray photoelectron spectroscopy revealed that the alloy surface exposed in steam contained mixed oxides of iron and chromium as well as elemental form of iron, nickel and chromium.