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INTRODUCTION

STEELS have been widely used as basic structural materials in all industries because of their excellent strength and ductility, but are increasingly exposed to severe industrial working environments. These exposures are primarily limited to their surface region, and thus efforts to improve surface properties or to strengthen the steel surface have been made. Recently, research has been conducted on ferrous surface composites in which the excellent resistance to heat, corrosion, and wear of carbides are fully utilized by direct irradiation of high-energy electron beam.[1–4] This high-energy electron-beam irradiation method can achieve required surface properties while maintaining substrate properties, because cooling rate is fast and input energy hardly affects the substrate during the irradiation.[5] Surface compositing is a fabrication method in which hardness, wear resistance, and thermal resistance can be enhanced by depositing desired elements on a substrate to form a composite layer. This method not only contributes to the development of new materials having excellent properties, but also reduces production costs by compositing the surface only when fabricating steels or alloys that require high-priced elements.

DUKHYUN NAM, Research Assistant, and KYUHONG LEE, Postdoctoral Research Associate, are with Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784 Korea. SUNGHAK LEE, Professor, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, is with the Materials Science and Engineering Department, Pohang University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted November 6, 2007. Article published online September 13, 2008 2626—VOLUME 39A, NOVEMBER 2008

When high-energy electron beam was irradiated on the steel substrate surface, electrons with high kinetic energy strike into material lattices and form phonons. These phonons are transformed to high thermal energy which can easily melt carbides with high melting points.[6–8] When high-energy electron beam is irradiated on a steel substrate, where carbide powders are evenly deposited, the substrate surface and carbide powders are completely melted and solidified to form a ferrous surface composite layer, thereby fabricating carbide-reinforced ferrous surface composites. This high-energy electron-beam irradiation has several advantages: (1) strong interfacial bonding between surface composite layer and substrate, (2) prevention of surface oxidation and interruption of inclusions because of the short irradiation time, (3) prevention of pores or cracks because of homogeneous heating and cooling, and (4) possible continuous processing of largescale structures or parts because the technique allows working in the air.[5] In this study, ferrous surface composites with improved surface properties were fabricated by depositing TiC or Cr3C2 powders on the surface of a plain carbon steel substrate and irradiating with a high-energy electron beam. T