Hot work roller surface layer degradation progress during thermal fatigue in the temperature range 500-700 °C

A new test rig for thermal fatigue testing was used to investigate and characterise surface layer degradation of indefinite chill double pour (ICDP) cast iron hot work roller. Thermal fatigue tests were performed at three temperatures (500 °C, 600 °C and 700 °C) using a Gleeble 1500 D thermomechanical simulator. Appearance of cracking was evaluated quantitatively for each test temperature by following the average length of the seven longest cracks, the average length of all cracks and crack density after the preselected number of thermal cycles. We found that crack nucleation, crack propagation (growth), their linking and subsequent material spalling are related to the cementite and graphite particles characteristics. Revealed, were the appearance of internal cracks in cementite and graphite, propagation towards and from the test surface, cracks linking and material chipping. Based on observations, a better understanding of degradation mechanisms and their temperature related intensity was gained. Finally, suggestions for improved thermal fatigue resistance of cast iron rollers are given.