Effect of Extrusion Temperatures on Friction-wear Behavior of Chain-wheel Fabricated by 40Cr Steel under Oil-lubrication Condition

Abstract

A 40Cr steel was formed into a chain-wheel using a warm extrusion technology. The surface roughness and micro-structure, micro-hardness and phases of the extruded samples at different temperatures were analyzed using a three-dimensional optical microscope (OM), micro-hardness tester, and X-ray diffraction (XRD), respectively. The morphologies, chemical element distributions and phases of worn tracks at the extrusion temperatures of 550, 650 and 750 °C were analyzed using a scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and XRD, respectively. The friction-wear behaviors of extruded samples under oil-lubrication condition were observed using a wear test. And the effects of extrusion temperatures on the wear mechanism were discussed. The results show that residual austenite and pearlite exist on the sample at the extrusion temperature of 550 °C with the corresponding grain size and surface micro-hardness of 32.7 nm and 370.33 HV, respectively. The average coefficient of friction (COF) of extruded sample at the temperature of 550 °C is 0.196 5, and the wear mechanism is fatigue and abrasive wear. While the acicular martensite exists on the extruded samples at the extrusion temperatures of 650 and 750 °C, the corresponding grain sizes are 30.0 and 29.1 nm, respectively. The average COF (coefficient of friction) of extruded sample at the temperatures of 650 and 750 °C are 0.187 4 and 0.163 6, respectively, and the wear mechanism is abrasive wear. As a result, the friction performance of extruded sample at the temperatures of 650 and 750 °C is better than that at the temperature of 550 °C.