Influence of surface roughness and phosphate coating on galling resistance of medium-grade carbon steel

The aim of this research work was to investigate the influence of surface roughness and presence of phosphate coating on the galling resistance of medium-grade carbon steel. Galling resistance was evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation, surface quality, and volume of adhered material, analysed by load-scanner test rig as a function of load. Results of the investigation show that best galling resistance is not provided by very smooth surfaces but with semi rough ones (Ra = 0.21-0.28 mu m), obtained by fine turning. Furthermore, by phosphating and formation of low-friction Mn-P coating superior galling resistance for medium-grade carbon steel is provided, at the same time diminishing effect of surface roughness.