Failure of Tungsten Carbide-Cobalt Lamination Dies: A Corrosion Evaluation

Sudden failures of cemented tungsten carbide (WC)-cobalt punching dies are rare but expensive. Corrosion of the cobalt matrix, or cobalt leaching, by water-based lubricants usually is considered the cause of such failures. The validity of this mechanism was evaluated by measuring the corrosion behavior of cobalt, WC, and WC-15% Co die material in water and seven made-up lubricants. In the worst lubricant, the cobalt matrix corroded at an estimated rate of < 3 mpy. In chlorinated, chloride (Cl–)-bearing (> 0.01% sodium chloride [NaCl]), aerated water of pH 7, the rate could be 80 mpy. Such a rate still was not high enough to explain die failures because of the short contact time between lubricant and sliding surfaces during punching operations. Excessive adhesive wear caused by low lubricity and resulting in removal of large wear particles may have been responsible. Such particles wedged between sliding surfaces may have exerted forces sufficient to cause breakage of the dies.