Study On The Microstructures And Properties Of Fe-based Surface Layers Reforced By Fe₂B Prepared By TIG Cladding

Cladding, as a surface hardening technology, refers to the deposition of a filler metal ona base metal （substrate） to impart some desired property to the surface that is not intrinsic tothe underlying base metal. Fe₂B is a reinforcing phase with characteristics of low-cost andhigh-performance. The Fe₂B reinforced surface layer is mostly prepared by boronizing andlaser cladding at home and abroad, and there are few reports that it is produced by argoncladding technology. In the present study, argon arc cladding was taken to prepare the ironboride coatings on the surface of Q235steel using ferroboron and CaB₆powders as claddingmaterials. The effects of the different process parameters, such as cladding currents andspeeds, on the macrostructures, microstructures and mechanical properties of the claddinglayers were investigated systematically. The results show that:①With different arc currents or traveling speeds, hypoeutectic, eutectic and eutecticstructures can be obtained in TIG cladding layers. When ωB>3.8%, the cladding zone ishypereutectic, composed of primary crystal Fe₂B phase and lamellar eutectic borides（eutectic of Fe₂B+ferrite+martensite）; When ωB=3.8%, the cladding zone is eutectic, andconsists of eutectic borides （eutectic of Fe₂B+ferrite+martensite） with the shape offishbone, lamellar or honeycomb; When ωB<3.8%, the cladding zone is hypoeutectic andcomprised of ferrite, martensite and eutectic borides （eutectic of Fe₂B+ferrite）;②When the cladding zone is eutectic or hypereutectic, a transition zone appearsbetween cladding zone and fusion line, with a width of only0.1mm to0.3mm.The transitionzone is composed of microstructures of hypoeutectic+eutectic or just hypoeutectic, becauseof element B increasing from the fusion line to the cladding zone.③Fe₂B reinforcing phase significantly improves the micro-hardness and abrasive wearresistance of the cladding zone. The microhardness and relative abrasiveness of the claddinglayers are increased with the arc currents reducing or arc speed decreasing. When cladding ferroboron powders, the average microhardness is up to1274.1HV and the maximummicrohardness is up to1813.7HV, while the average microhardness and the maximummicrohardness is up to1512.8HV and1764.0HV respectively, when using CaB₆powder ascladding materials. Compared with Q235steel, the maximum relative abrasiveness reachesto4.95in the hypereutectic cladding zone. Micro-cutting and spalling caused by plasticdeformation are dominant abrasion mechanism, The primary crystal Fe₂B reinforcing phaseas a wear-resistant skeleton resists to abrasive wear.④Fe₂B reinforcing phase is successfully prepared by using ferroboron and CaB₆powders. It is much easier to obtain hypereutectic microstructure using low melting point offerroboron. While the microhardness and relative wear resistance of cladding layers preparedby using CaB₆powders are better than those of the cladding layers by using ferroboron.