Intercrystalline corrosion of surface-welds of nickel alloys on carbon steel

Surface-welds of Hastelloy C4 and some mixed welds of Inconel 600 and Hastelloy C4 were prepared by the plasma-hot-wire-surface-welding method. Intercrystalline corrosion tests were performed in a diluted Streicher-solution. On-line recording of the corrosion potential uses the stability of the redox-pair, Fe(III)/Fe(II) (called the chemical potentiostat). Microscopic observations of specimens after corrosion accompanied the potential recording and gave valuable information about the morphology changes that occur due to intercrystalline corrosion. Potential measurements in a 1/3-diluted Streicher-Test solution showed that 2-layer surface-welds of Hastelloy C4, prepared by the hot-wire-surface-welding method with arc-deflection, were the most resistant to intercrystalline corrosion. A mixed 2-layer surface-weld of Inconel 600 inner-layer and Hastelloy C4 outer-layer was not effective due to the heterogeneous interface formed between both layers.