Simulation of thermal fatigue in hot strip mill work rolls

The surface deterioration of work rolls constitutes a significant constraint on the operation of hot mills, as the duration of rolling campaigns are greatly restricted by the surface condition of the rolls. Work roll changes account for a large proportion of downtime in the operation of hot strip mills, resulting in financial penalties for the mill operators in terms of lost production and roll maintenance. It is generally accepted that thermal fatigue represents one of the main factors influencing work roll wear in the finishing stands of a hot strip mill. In order to assess the thermal fatigue behaviour of typical work roll alloy grades, a series of tests were performed on high-speed steel (HSS) and high-carbon high-chromium steel samples using a stand alone twin-disc simulation machine under conditions that are comparable to those of hot rolling of steel. The progressive changes in surface condition of the roll samples were monitored and anal ysed by means of stylus profilometry, optical and scanning electron microscopy. The experimental results were compared with fragments of scrapped work rolls taken from the mill. Tests performed on the HSS samples did not result in appreciable surface degradation of the test sample. On the other hand, examination of the high-carbon high-chromium samples after testing revealed thermal crack morphologies and surface defects comparable to those observed in mill roll samples