Wear of Roll Surface in Twin-roll Casting of 4.5% Si Steel Strip.

Abstract

The rolls are one of the most important components of the twin-roll casting process, determining not only strip quality, but due to their expense, add to the price of the as-cast strip. The potential for reducing operational cost and ensuring required strip quality may be achieved through a reduction in wear of the roll surface and hence reduced frequency of roll surface reconditioning and replacement. To achieve this, it is imperative to understand the mechanisms of roll surface wear which occur during casting operations.The present study was aimed at determining the influence of liquid metal, roll separation force and strip incline from the vertical casting direction on the wear of the roll surface in a twin-roll casting process.It was found that roll wear in the twin-roll casting process is accompanied by removal of material from the roll surface and redistribution of topography of the roll surface. Applying high roll separation forces lead to increase erosion of the roll surface and coarsening of the roll surface topography. Roll surface wear caused by deformation occurs by imprinting of the strip surface on the roll surface as well as grinding of the roll surface by the strip. Even with the application of high roll separation forces the highest contribution to wear of the roll surface is by the interaction of the melt with the roll surface in the very early stages of solidification.KEY WORDS: rapid solidification process; twin-roll process; strip casting; wear; surface roughness.surface. To achieve this, it is imperative to understand the mechanism of roll surface wear which occurs during casting operations. It is of particular interest to relate the influence of liquid metal attack, roll separation force and effect of strip incline to the roll surface wear.The term wear remains a subject of some debate, 22) so to avoid confusion in this discussion the term wear in this work is accepted as "damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting substance or substances". 23) Experimental Equipment and Procedure Twin-roll Casting ProcessAn experimental investigation was carried out on a twin roll caster 24,25) schematically showed in Fig. 1. Steel melt was prepared from 50 kg ingots which were melted under an argon atmosphere in an induction furnace, yielding the following composition: 4.5% Si, 0.0013% Cu, CϽ0.007%, PϽ0.010%, NiϽ0.07%, TiϽ0.02%, CoϽ0.02% and AlϽ0.01%.The superheat was maintained at ϳ30°C and the melt entered the gap between the rolls through a slot in a ceramic nozzle. The cylindrical, water-cooled rolls constructed from Cu-Cr sleeves were ϳ440 mm in diameter and 150 mm in length. The casting speed was 7 m s Ϫ1 and the thickness of the as-cast strip 0.1-0.2 mm.The roll surface before casting was treated with an emery wheel. The roll surface obtained in this manner was further treated with fine emery paper to obtain a roughness of the roll surface, R a ϭ0.4 mm.The roll separation force per unit length of the ro...

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