Localised corrosion had appeared on reels of wire after long term storage but investigations by the manufacturer had shown no correlation between the problem and the materials used. These included steel, drawing lubricants and post-drawing, lanolin protective coating.

XPS compositional analysis (below) of corroded and uncorroded areas, at CSMA, shows a significantly higher concentration of iron in the corroded areas coupled with lower levels of calcium and sodium from the drawing lubricants (a mixture of calcium and sodium stearates).

XPS Surface Compositions (figures in atomic%)

XPS images of a corroded area show an exposed iron area (rust) covering the lower part of the wire. The corrosion areas are associated with striations along the wire in the drawing direction. Surrounding areas are rich in carbon, calcium and sodium residues from the drawing lubricants. The chlorine distribution correlates with iron suggesting an association between the two.

XPS images of corroded wire (Analysis area 1.6 x 1.2 mm, resolution 10 - 15 mm).

SIMS imaging analysis (see images) showed that all corrosion areas contain tungsten (as tungsten oxide), as a result of the break-up of the wire-drawing dies during processing.
The combination of XPS and SIMS analysis proved that corrosion arises as a direct result of a reduced level of lubricant during wire drawing which also causes the break up of the drawing dies. The reduced level of organic material and the roughening of the surface leaves the steel exposed to attack by classical aqueous corrosion, accelerated by the presence of chlorine.

SIMS images of drawn wires showing uncorroded wire [left] (CH- cyan, FeO2- red) and corroded wire [right] (WO3- red, FeO2- blue, CH- green). Field of view ~300mm.