| Rolls are the main consumptive parts which can deform the metals and determine the efficiency of the rolling mills and the quality of the mill bars. How to improve the wear resistance and elongate the service life of rolls matters a lot in reducing the consumption of rolls. High vanadium high speed steel (HVHSS) has better red-hardness, wear property and its carbide has better morphology than normal high speed steel. In recent years, as a new wear-resistance material, high speed steel with high vanadium content has been studied and used in some countries for making steel rolls.Laser cladding is a new rapid manufacturing technology, which can fabricate dense coating with a metallurgical bonding with substrates, thus improving the wear resistance of the substrates. It has been studied to manufacture rolls with laser cladding, but researches about manufacturing high speed steel rolls with high vanadium by laser cladding have not been reported until now. The aim of the present work is to use laser cladding technique to fabricate dense, wear resistant high vanadium high speed steel coatings which have a metallurgical bonding with the substrates. It can offer theoretical instructions on repair rolls and manufacture composite rolls by laser cladding, and technical support for their further application.In this paper, the substrates for laser cladding were nodular cast iron rolls, YAG solid pulsed laser and diode laser were used to explore the feasibility of preparation high vanadium high speed steel coatings. Coatings with good metallurgical bonding with substrates were fabricated with optimal processing parameters. Optical microscopy (OM), scanning electron microscopy (SEM) attached with energy dispersive x-ray spectrometry (EDS), X-ray diffractometer (XRD), microhardness tester, wear tester and electrochemical workstation were used to analyze the microstructure, composition, phase, hardness, wear-resistant property and corrosion property of the coatings.The Nd:YAG pulsed laser was applied to nodular cast iron rolls coated with high vanadium high speed steel. The optimized laser processing parameters for pre-pasted single-path laser cladding layers were as follow:the current is180A, scanning velocity is2.5mm/s, the defocus amount is+14mm, the thickness of coating is0.2mm, frequency is15Hz and impulse width is3.0ms. The multi-channel laser cladding results that the coated layers combined metallurgically with the substrate with a lot of cracks. After preheated the substrate, the cracks in the coating are much less than before. After laser remelting, a fully dense and crack free HVHHS coating with an excellent metallurgical bonding was deposited. The average microhardness650HV0.1is about2times as high as that of the substrate. The high-temperature (500℃) wear loss is56%of nodular cast iron’s in30min. The main wear mechanism of the laser cladding and the frictional pair is abrasive wear.The diode laser was also applied to nodular cast iron rolls coated with high vanadium high speed steel. The optimized laser processing parameters for single-path laser cladding layers were as follow:the power2300W, scanning velocity10mm/s, spot size11.5mmX2.5mm, the thickness of coating1mm. The coating with a lot of VC-rich particles was dense, pore and crack free. The average microhardness of the coating is about750HV0.1and it is more than2times than that of the substrate. The high-temperature (500℃) wear loss is43%of nodular cast iron’s in30min. The main wear mechanism of the laser cladding and the frictional pair is abrasive wear. The corrosion resistance of the HVHSS coating is higher than that of the substrate. |
PDF Full Text Request