Effect of Water Quality on the Corrosion of Carbon Steel in Wire Cut Discharge Machining

摘要

The corrosion behavior of carbon steel in working water of wire cut discharge machines, whose conductivity is typically controlled to around 10 mu S centre dot cm~(-1), has been investigated in terms of the water quality. Among several samples of the working water, those which contained higher level of sulfate ion (0.6 g centre dot m~(-3)) caused corrosion of carbon steel even when the water was flowing. The effect of concentration of several kinds of anions (sulfate, nitrate, hydrogenphosphate, carbonate and chloride) on the corrosion of carbon steel was also studied to know which anion was most aggressive. The result showed that 0.7 g centre dot m~(-3) of sulfate and 3 g centre dot m~(-3) of chloride caused severe corrosion when the solutions were flowing at 2.36 g centre dot s~(-1). The steel did not passivate in any solutions when they were static. On the assumption that nitrite ion is introduced into the working water by an anion exchange method, the critical concentration of nitrite ion for inhibition was determined as a function of concentrations of sulfate and chloride.