Tungsten Carbide • Properties of Cemented Tungsten Carbide • Corrosion Resistant Tungsten Carbide Grades • Design Considerations • Fluid Handling and Flow Control Applications
Brazing Tungsten Carbide Components • Grade Chart • Grade Application Guide

Corrosion Resistant Tungsten Carbide Grades

Cobalt is by far the most widely used binder metal or “cement” in cemented tungsten carbides because it most effectively wets tungsten carbide grains during liquid phase sintering. For this reason cobalt is believed to be superior to other binder metals in terms of eliminating residual porosity and achieving high strength and toughness values in sintered products. The failure of cemented carbides in corrosive environments, however, is generally due to the chemical reaction of cobalt with corrosive agents. The corrosion process involves the dissolution of the cobalt binder at exposed surfaces leaving a loosely knit skeleton of tungsten carbide grains having little structural integrity. This mechanism is often referred to as cobalt “leaching” and is typically accompanied by a flaking off of unsupported carbide grains in the affected surface areas.

Although WC + Co grades have fairly good resistance to attack by acetone, ammonia, ethanol, most bases, weak acids, and tap water, exposure to acetic, formic, hydrochloric, hydrofluoric, phosphoric, sulfuric, and other strong acids can result in a relatively rapid deterioration of the binder phase. Corrosion rates are affected also by temperature, the concentration and electrical conductivity of the corrosive agent, and by other environmental factors. Alloying cobalt with chromium, molybdenum, and/or nickel can significantly improve the resistance of the binder to corrosion, but the complete substitution of nickel for cobalt has proven to be the most effective means of extending the life of cemented carbides in highly corrosive environments. WC + Ni grades and other special formulations designed to resist corrosion without compromising strength or other attributes are therefore ideal for applications such as seal rings, fluid control components, choke valves, nozzles, and bearings. The chart below depicts the relative corrosion resistance of Co and Ni binders as a function of pH value.

Corrosion Resistance of Co and Ni Binders as a Function of pH Value

Federal Carbide offers a complete family of standard Ni-bonded tungsten carbide grades for applications requiring resistance to corrosion. In addition, Federal has developed numerous custom grades for use in extremely corrosive environments, in situations demanding both high toughness and corrosion resistance, and where strict food processing equipment requirements must be met. Take advantage of our experience and expertise to solve your corrosion-related carbide wear problems.