WC-Ni-Cr系超硬合金のNaOH溶液中での腐食挙動

抄録

WC-Ni-Cr cemented carbides have been used even under corrosive condition because of its excellent corrosion resistance. The corrosion characteristics of this alloy in acidic and neutral solution had been investigated by immersion test and polarization test, and reported that corrosion resistance was improved in the low carbon and high Cr₃C₂ content alloy.
In this report, these corrosion tests were carried out in 1N NaOH solution. In immersion test, most of the dissolved element in the solution was W. The corrosion rate of WC-Ni-Cr was the higher with the lower carbon and the lower Cr₃C₂ contents, and these results were quite opposite to the tendency in acidic and neutral solutions. In polarization test, a large difference in polarization curves by the change of carbon content was not observed. The passivation region, which was observed in acidic solution, was not observed. In the vicinity of the corrosion potential, the corrosion current density (irorr) decreased with the increase in the carbon and Cr₃C₂ contents. The difference of corrosion rate with carbon and Cr₃C₂ contents of WC-Ni-Cr in 1N NaOH solution was considered to be caused by the difference in the amount of W dissolved in the binder Ni phase.