Microstructural and Mechanical Properties Examination of High-Power Diode Laser-Treated R260 Grade Rail Steels Under Dif
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SURFACE hardening by laser applications is a remarkable technology. Even though this technology has been applied successfully already in different industrial fields, it is not common in the railway sector.[1,2] Laser hardening provides distinct advantages for localized processing of complex areas with precision. High productivity, elimination of postprocessing, a vast reduction in distortion, no requirement of auxiliary quenching, high process flexibility, and maneuverability in an industrial environment are additional benefits.[3] Furthermore, laser beam hardening is a precise and easily controllable method for local heat treatment.[4] Engineering the surface of materials to produce improved performance is a well-established technological field. Increased performance could be gained with a OZAN YAZICI is with the 1st Regional Directorate, Railway Maintenance Department, Turkish State Railways (TCDD), 34716 Kadikoy, Istanbul, Turkey. Contact e-mail: [email protected] SUAT YILMAZ and SELIM YILDIRIM are with the Faculty of Engineering, Department of Metallurgical and Materials Engineering, Istanbul University–Cerrahpasa, 34320 Avcilar, Istanbul, Turkey. Manuscript submitted February 25, 2018. Article published online December 6, 2018 METALLURGICAL AND MATERIALS TRANSACTIONS A
coating, chemical modification, or structural change. Heat treatment of the surface of carbon steels to produce a hardened layer while retaining a tough core is the most practical and common process, and many energy sources, such as flame and induction heating, have been used for this aim. Additionally, the use of high-power diode lasers on ferrous materials is a well-known process to produce a hardened surface.[1,5] In a previously reported work,[3] a notable improvement in the mechanical properties of pearlitic rail steel was obtained after laser surface hardening/melting using a CO2 laser source. Glassy/nanocrystalline phases were formed due to high cooling rates. Such laser processing was reported to potentially serve as solid-state lubricants and mitigate subsurface cracking in rails while also being compliant with contacting wheel profiles.[6,7] Considering the superiorities of high-power diode laser against complex Nd: YAG or CO2 lasers and Yb fiber lasers, this laser system is compact, robust, relatively cheaper, and has higher efficiency.[8,9] The advantages of this system were discussed in detail by Li,[10] Chen et al.,[11] and Bachmann.[12] In recent studies,[8–11] 2 kW diode laser was used to harden medium carbon steel and a processing depth of 1 mm was achieved.
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The use of a diode laser for surface treatment was widely reported.[13] Pashby et al.[14] demonstrated the technical feasibility of using diode lasers for hardening both plain carbon and alloy steels. In another study, laser surface treatment was applied to different railroad steels using high-power diode laser, and mechanical features were investigated.[15] It was noticed that this application had a positive effect on the mechanical properti
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