No abstract

Cyclic temperature changes in the working layer of a roll during hot rolling cause thermal stress which leads to damage on the surface layer of the roll due to thermal fatigue. The pre-conditions of crack initiation are described. The intensity of crack propagation could be influenced by optimizing the chemical composition and physical-mechanical properties of the material on the working layer. This reduces the tendency of the material with respect to damage due to thermal fatigue and extends the lifetime of the rolls. The microstructure as well as the operational characteristics of the developed HSS working rolls resistant to thermal fatigue are presented.

A stress analysis for cast compound rolls is presented. Stress is divided into components as residual stress, stress implied by load, stress implied by torque, Hertz’ian contact stress and thermal stress. Furthermore, heat transfer is considered. Residual stress is measured and a 3D representation is given. All further stress components are calculated by FEM calculations. The data allow a complete description of the roll behavior in operation.

The causes of a composite roll fracture were investigated. The result of an FEM analysis showed that the occurrent stress could not have led to this fracture. Metallographic investigations in the area of the crack start site clearly showed non-metallic inclusions. These affect structural weak points and activate malfunctions. They significantly accelerated the cracking process due to the local notch effect which significantly reduced the performance of the material and thus the service life of the roll shaft.