The effect of the composition and microstructure of gray cast iron on preferential wear during parasitic drag and on intrinsic damping capacity

Propensity of cold judder was studied by investigating the correlation between the microstructure of gray iron brake disks and friction properties of commercial brake linings. Based on a brake disk for a mid-size passenger car, gray iron disks with 6 different microstructures were manufactured by changing the carbon equivalent (C.E.) and cooling speed in a commercial manufacturing facility. Graphite morphology of the gray iron changed proportionally according to the C.E. and cooling speeds, exhibiting longer graphite flakes with high C.E. at slow cooling speeds. After screening tests of 23 commercial brake linings, 4 different brake linings (two non-steel and two low-steel linings with high μ and low μ) were selected for parasitic drag tests. Results showed that the preferential disk wear was pronounced in the case of using low steel linings and the trend was marked with the disks containing short graphite flakes. Examination of the disks after the drag tests revealed that the initial DTV (disk thickness variation) pattern was preserved during the wear tests while the intensity of the DTV pattern was increased. Sonic resonance tests were also performed to investigate the effect of gray iron microstructures on vibration damping capacity. Results showed that the graphite morphology strongly affected the vibration damping capacity.