Failure mechanism of cemented tungsten carbide dies in wet drawing process of steel cord filament

Cemented tungsten carbide die has been used in wire drawing for almost a century. A combination of strength and wear resistance has made this material widely accepted in the steel wire industry, particularly in drawing steel cord filament. Used cemented tungsten carbide dies, collected from different sources where different lubricants were applied in the wet drawing process, were dissected with high speed diamond saw and examined by using scanning electron microscopy. Failure modes of cemented tungsten carbide dies were classified. Electrochemical properties of pure cobalt wire and cemented tungsten carbide were examined by anodic and cyclic polarization measurements to investigate the corrosion resistance of cobalt and cemented tungsten carbide in wire drawing lubricants. Results show that binding agent (cobalt) in cemented tungsten carbide might be selectively leached in certain lubricants, and the leaching rate increased as oxygen concentration decreased in the lubricants and pH was lowered inside the crevice. Contact of steel wire on the cemented carbide die due to the mismatch of slip during drawing could be the original source of stress. Synergic effect of stress and leaching could be the answer for the severe cracking of cemented carbide dies in the wet drawing process. (C) 2008 Elsevier Ltd. All rights reserved.