The corrosion of carbon steel and high-chromium white iron grinding balls was investigated. Electrochemical measurements in an ultrasonic apparatus used to abrade the ball demonstrated that pyrite in a test slurry of ph 8 increased the corrosion rate of a steel ball from 27 mils per year (mpy) without pyrite to 80 mpy with pyrite. The rate depended upon ph and the metal-to-metal surface area ratio. When magnetite was substituted for pyrite, the rates were lower. Using an impactor apparatus to simulate grinding action, passivation rates on high-chromium iron balls in mill water were measured. At ph2, passivation rates for 22%, 29%, and 31% cr balls were statistically equal. At ph 5, 7, and 9, the passivation rates of the 31% cr ball fell between those of the 22% and 29% cr balls. Microstructural analyses indicated that the longer time for the 31% cr ball, compared with the 29% cr ball, was attributed to carbides that reduced the chromium content in the matrix. In a mill, the passivation layer may be removed faster than it is formed; consequently, passivation may have a minor effect in reducing corrosion.
Paper 364 in Corrosion 85. Natl. Assoc. Corros. Eng., Houston, Texas, 1985, 15 Pp