The effect of cast iron graphites on friction and wear performance: II: Variables influencing graphite film formation

Cast iron may be classed as a self-lubricating metal-base composite material. The cast iron graphites have an excellent lubricity which is similar to that of a solid lubricant and contributes to the decreases in the wear loss and the friction coefficient. Factors affecting graphite film formation are discussed. The coefficient of friction increases with substrate hardness because graphite film formation is influenced by the relative difficulty of substrate deformation. Although adhesive wear and the friction coefficient increase with decreasing air pressure, the cast iron graphites contribute to the decrease in wear rate in the region of 10^?2 Torr. Water vapour pressure has a direct effect on film formation and film hardening, particularly above 16 Torr. The lubricity of cast iron graphites was confirmed at temperatures below 100°C. The friction coefficient increases with the temperature rise owing to hardening of the graphite film. The effect of cast iron graphites on rolling wear resistance is discussed.