Abstract
Considerable residual stress is produced during heat treatment. Compressive residual stress at the shell is conductive to improving the thermal fatigue life of a work roll, while tensile stress in the core could cause thermal breakage. In hot rolling, thermal stress occurs under the heating-cooling cycles over the roll surface due to the contact with the hot strip and water spray cooling. The combination of thermal stress and residual stress remarkably influences the life of a work roll. In this paper, finite element method (FEM) simulation of hot rolling is performed by treating the residual stress as the initial stress. Afterwards, the effects of the initial roll temperature and cooling conditions on thermal stress considering the initial residual stress are discussed. Lastly, the thermal fatigue life of a work roll is estimated based on the strain life model. The higher initial roll temperature causes a higher temperature but a lower compressive thermal stress at the roll surface. The surface temperature and compressive stress increase significantly in the insufficient cooling conditions, as well as the center tensile stress. The calculation of the fatigue life of a work roll based on the universal slopes model according to the 10% rule and 20% rule is reasonable compared with experimental results.
Highlights
The surface deterioration of work rolls used for hot strip rolling mills constitutes a significant constraint on the operation of hot mills, as the mill efficiency and rolled product quality are greatly influenced by the performance of the surface condition of the work rolls in service
It is generally accepted that the thermal fatigue of a work roll is the typical low cycle thermal fatigue, since the accumulation of plastic strain under high thermal stress exceeds the elastic range of the shell material [14,15,16]
Simulations of the temperature and stress of high speed steel work roll during heat treatment and hot rolling were performed by means of thermo-elastic-plastic finite element method (FEM)
Summary
The surface deterioration of work rolls used for hot strip rolling mills constitutes a significant constraint on the operation of hot mills, as the mill efficiency and rolled product quality are greatly influenced by the performance of the surface condition of the work rolls in service. The work roll surface in hot rolling is subjected to the combined effects of thermal and mechanical loadings. Considerable residual stress is introduced into work rolls due to the high temperature gradient and phase transformation during heat treatment. This stress is expressed as compression at the shell and tension at the core [1]. An investigation on thermal stress considering the initial residual stress in the work roll during hot rolling is important for the clarification of the roll failure mechanism and to conduct a roll fatigue life evaluation. Various methods have been used to investigate the thermal behavior of high speed steel (HSS) work rolls during hot rolling. The thermal fatigue life of the work roll is estimated using the strain-life model
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