Mechanisms of Sticking Phenomenon Occurring during Hot Rolling of Two Ferritic Stainless Steels
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INTRODUCTION
STICKING refers to a phenomenon occurring during hot rolling, in which fragments of a rolled material are stuck to a work roll surface and deteriorate surfaces of both roll and rolled materials.[1] Especially during hot rolling of stainless steels, the sticking usually appears at rear parts of roughening rolls or at front parts of finishing rolls, and leaves various defects such as dents or scratches on surfaces.[2–6] This also induces problems of reduction in roll life and hot-rolling productivity, and seriously deteriorates the surface quality of rolled products. At hot-rolling plants, instead of coming up with fundamental solutions to this sticking problem, it is generally addressed by making adjustments in hotrolling conditions according to rolling plans, for instance, by controlling the kind of lubricants or the spraying amount used to reduce the friction coefficient between rolls and rolled plates. However, because working conditions should vary with rolling conditions such as the variety of rolled plates and rolls, rolling temperature, rolling load, and lubrication, it is hard to CHANG-YOUNG SON, Research Assistant, CHANG KYU KIM, Postdoctoral Research Associate, and DAE JIN HA, Research Assistant, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, Korea. SUNGHAK LEE, Professor, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, is jointly appointed to the Materials Science and Engineering Department, Pohang University of Science and Technology, Pohang, 790-784 Korea. Contact e-mail: [email protected] JONG SEOG LEE, KWANG TAE KIM, and YONG DEUK LEE, Principal Researchers, are with the Stainless Steel Research Group, Technical Research Lab., POSCO, Pohang, 790-785 Korea. Manuscript submitted November 7, 2006. Article published online September 26, 2007 2776—VOLUME 38A, NOVEMBER 2007
come up with fundamental and systematic methods to prevent the sticking. It has been reported that the sticking occurs more seriously in ferritic stainless steels than in austenitic stainless steels.[7] This indicates that it is affected by microstructures and high-temperature properties of the rolled materials, even when they are rolled by the same roll. The amount of sticking in the same stainless steels also varies with mechanical properties of the rolls. For example, the sticking in ferritic stainless steels is less serious when a high speed steel roll (HSS roll) is used than when a high-chromium cast iron roll is used.[8–10] These results imply that it is determined by mutual interaction of the rolls and rolled materials, in which the rolling load and temperature also play a role as important factors. In the present study, mechanisms of the sticking occurring during hot rolling of ferritic stainless steels were investigated by analyzing microstructures and mechanical properties of the roll and rolled materials. STS 430J1L and STS 436L, representative ferritic stainless steels, were used for the rolled materials. An HSS
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