Thermal fatigue of high chromium steel rolls

Abstract

Within the master work the phenomenon of appearance of firecracks on the surface of the work rolls that occur during hot rolling of flat products in the case of regular rolling conditions and in the case of the rolling mill stalls was investigated. During hot rolling work rolls are subjected to successive heating and cooling conditions. Their surface is exposed to rapid temperature changes due to the contact with hot rolled material and due to cold water used for rolls cooling. These cyclic heating/cooling conditions cause thermal fatigue which is one of the most important factors affecting the rate of surface deterioration as well as mechanical fatigue and abrasion. Two different tests for the laboratory assessments of the thermal fatigue resistance of the high-chromium steel rolls were used. The first test enables a simulation of the work roll thermal fatigue in the case of regular rolling conditions. Furthermore, with the second test thermal fatigue of work rolls in the case of the rolling mill stalls was investigated. Both tests were implemented in a thermo-mechanical simulator of metallurgical states, the Gleeble 1500D. Finite elements method simulations were performed to determinate the temperature distribution in the work rolls by using NSC.SuperForm software. Evident dependence of the crack nucleation and their growth with the temperature and the cooling medium was found but no dependence due to the length of contact time was found. The influence of slab thickness and slab initial temperature to the temperature evolution in the surface layer of the work roll was estimated. The master work contributes to better understanding of crack nucleation and their growth during the usual hot rolling conditions, as well as for the case of rolling mill stalls.