Abstract
Corrosion tests were carried out on Ni-Cr-Mo overlays deposited by welding on to C-Mn steel substrates. Manual metal arc, pulsed metal inert gas, and hot wire tungsten inert gas processes were used, with conditions varied to obtain a range of dilutions of the overlay by the parent steel. Critical pitting temperatures were determined in FeCl3 solution and in an oxidising H2SO4-HCl environment. Overlay pitting resistance was reduced by increased dilution from the substrate steel. The results support a general recommendation that iron content should be below 5% for optimum performance, although corrosion behaviour was determined not by the iron level per se but by the bulk composition and the minimum alloy content developed in the solidification structure. Manual metal arc deposits tended to be inferior to gas shielded overlays. Only general correlation was found between pitting resistance in the two test environments so caution is necessary when using FeCl3 testing for weld procedure qualification purposes.
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