Alternative work roll material grade for the late-finishing stands of hot strip mills

¹ South African Roll Company, South Africa.
² Department of Material Science and Metallurgy Engineering, University of Pretoria South Africa.

Abstract

The ever-increasing demand for high productivity and strip surface quality in hot strip mills (HSMs) has been the driving force in the search for work rolls with excellent wear and mill incidence resistance. Indefinite chill double pour rolls (ICDPs), which are currently applied to the late finishing stands (LFS) due to their superior mill incidence resistance, exhibit relatively poor wear resistance. The inferior wear resistance negatively impacts mill productivity due to frequent mill stoppages. The superb wear resistance of high-speed steel (HSS) rolls is attributed to the presence of discrete high hardness carbides. A potential work roll for the LFSs presenting improved wear and mill incidence resistance was designed using Thermo-Calc software. The alloy was melted in an induction furnace and centrifugally cast into sleeves. Specimens from the sleeves were tempered at various temperatures. Characterisation of both as-cast and heat-treated samples involved chemical, microstructural (OM), SEM-EBSD, XRD), hardness and Ferritscope measurements. The amount and distribution of graphite particles was comparable to ICDPs. The microstructure consisted of graphite nodules, carbides and retained austenite (RA) in a tempered martensitic matrix. Hardness values up to 63HRC with <3% residual austenite (RA) were obtained, which makes this grade more superior to ICDPs.