EFFECTS OF C AND Cr CONTENTS ON CORROSION RESISTANCE OF WC-Ni-Cr CEMENTED CARBIDES

摘要

The effects of carbon and Cr_3C_2 on the corrosion resistance in WC-Ni and WC-Ni-Cr cemented carbides were investigated by immersion test and electrochemical measurements in neutral 3%NaCl, acidic 3%NaCl+0.1NH_2SO_4 and alkaline 1N NaOH solutions. Ni was the main dissolved element in neutral solution and the amount of dissolved metals depended on the carbon and Cr_3C_2 content of the alloy. In alkaline solution W was the main dissolved element. 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 curves in acidic solution. In alkaline solution, not much difference in polarization curves by the change of carbon content was observed. The difference of corrosion rate with carbon and Cr_3C_2 contents of WC-Ni-Cr was caused by the difference in the amount of W dissolved in the binder Ni phase.