Engineering the Surface of Grey Cast Irons for a Sugar Milling Application

Abstract

An investigation has been carried out on a series of 22 grey cast irons to determine the influence of carbon equivalent and sulphur content on tensile strength, and on the ability of cast iron to develop a roughened surface under the action of a high speed open arc weld deposition process. The tensile strength decreased linearly with increasing carbon equivalent, in the expected manner, but showed no significant dependence on sulphur content. The surface roughness, quantified as the mean aspect ratio of the deposited weld metal droplets, showed a significant dependence on carbon equivalent and a very strong dependence on sulphur content. The effect exerted by sulphur on the roughening phenomenon was shown to be consistent with a model developed earlier to account for the surface perturbations formed under the action of a gas tungsten arc. In the model, sulphur exerts a strong depressive influence on the surface tensions which exist in the system, but since its effect on the solid-vapour surface tension is greater than on the liquid-vapour surface tension, non-wetting tends to develop as the sulphur content increases. The results have been used to formulate a modified grey cast composition for the manufacture of sugar cane crushing roll shells, which possesses both adequate strength, by virtue of its lowered carbon equivalent, and an adequate roughening ability, by virtue of its enhanced sulphur content.