Effect of C and Cr on Corrosion Resistance in WC-Ni-Cr System Cemented Carbide
Shuichi IMASATO, Shigeya SAKAGUCHI and Yasunori HAYASHI
WC-Ni-Cr Cemented Carbide , corrosion resistance, polarization curve, sea water
Cemented carbides with nickel binder have been widely used in place of those with cobalt binder because of its improved corrosion resistance. The effects of carbon and Cr3C2 on the corrosion resistance in WC-Ni and WC-Ni-Cr cemented carbides were investigated by immersion test and electrochemical measurements in 3%NaCl and 3%NaCl+0.1NH2SO4 solutions. In immersion test, Ni was the main dissolved element, and the amount of dissolved Ni in 3%NaCl+0.1NH2SO4 was 20 times lager than in 3%NaCl solution. And the amount of dissolved metals depended on the carbon and Cr3C2 content of the alloy.
In electrochemical measurement, the anodic reaction was dissolution of the binder metals in both solutions, and the cathodic reactions were reduction of dissolved oxygen in 3%NaCl solution, and reductions of protons and dissolved oxygen in 3%NaCl+0.1NH2SO4 solution. The anodic current densities showed that corrosion resistance of WC-Ni-Cr alloy was superior to that of WC-Ni alloy. WC-Ni alloys with low carbon content showed a higher corrosion resistance than that of high carbon alloy, which was revealed by both conspicuous appearance of passivated region and low anodic current densities in polarization curve. Anodic current density was decreased with increasing of Cr3C2 content, and the corrosion resistance was improved in both 3%NaCl, and 3%NaCl+0.1NH2SO4 solutions.