An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling

Abstract

The surface failure characteristics of different work roll materials, i.e. high speed steel, high chromium iron and indefinite chill iron, used in the finishing stands of a hot strip mill have been investigated using stereomicroscopy, three-dimensional optical profilometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical- and thermal-induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on second phase constituents such as the size, morphology and distribution of different carbide phases and graphite (in the case of indefinite chill iron), which was found to promote cracking. Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide-forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.