ZAHRADNÍK Radek Brno University of Technology

Spoluautoři RAUDENSKÝ Miroslav

The work roll surface in hot rolling mills suffers combined heat and mechanical load. The work roll surface degradation leads to formation of crack networks. The existing research describes a thermal fatigue like the governing degradation mechanism which causes the cracks formation perpendicular to surface. This paper describes additional effect of cyclic thermal loads – the cause of parallel-to-surface cracks formation within long and thin carbides which forms especially inside HiCr iron. The cracks formation is investigated by coupled a thermal and a structure FEA. These analysis are conducted with a special finite element model which represents microstructure of steel. The model is exposed to thermal load at the end of rolling gap. The result – the heterogeneous thermal field is applied like a BC for the structure analysis. The results are presented by histogram of relative frequency of first principal stress value for each microstructure portion separately. The distribution of the first principal stress within the matrix shows a compressive stress state which was anticipated. The distribution of the first principal stress within the carbide portion shows a tensile stress state which was unexpected. This unexpected behavior is explained by different thermal expansion coefficient of each portion of microstructure. The matrix with higher thermal expansion coefficient expands rapidly than carbides which are pressed from surrounding matrix and forcing them to lengthening which cause the tensile stress within carbides. Based on the comparison with microstructure typical to HSS materials, the recommendation for more durable and resistant microstructure structure are stated and explained.

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