Abstract :
[en] Fe-Cr-C-based alloys known as High Speed Steels (HSS) have been found useful in a wide variety of applications as machining and cutting, hot stamping and hot strip mills, thanks to their complex microstructure containing very hard carbides (V-rich MC, Mo- or W-rich M2C, Cr-rich M7C3 or M3C). Direct laser deposition, also known as laser cladding, has recently emerged as a very promising technique for the production and repair of thick coatings made from these alloys. Indeed, the very high cooling and solidification rates imposed by laser cladding result in strongly refined out-of-equilibrium microstructures and potentially enhanced wear resistance. However, the progressive accumulation of heat in the deposit during fabrication leads to variations of the thermal history as a function of position inside the build, resulting in turn into local variations of microstructure and wear properties.
Consequently, this work aims to investigate the influence of the local thermal history and microstructures on the wear behaviour of three HSS grades with varying contents of V, Mo and W in order to vary the type, size, morphology and amounts of the hard carbides. In a first step, 2D finite element simulations compute the thermal field during the direct laser deposition of 20 mm thick HSS deposits (a similar FE approach has already been published by the present group on Ti alloy Ti6Al4V [1]). The validated thermal history yields a deeper understanding of the microstructure generated as a function of the position inside the deposits. In a second step, the wear behaviour of the deposits is characterised at two different depths (i.e. at 2 mm from the free surface or at 2/3 of the total height) and for two constant test temperatures (i.e. room temperature [2] and 300°C) using a pin-on-disc tribometer. In analysing the results of these tests, a particular attention was given to the role of the various carbides – including their type, morphology, hardness and failure mode – in determining the wear mechanisms of laser clad HSS deposits at the two tested temperatures.
[1] Tran H.S., Tchuindjang J.T., Paydas H., Mertens A., Jardin R.T., Duchene L., Carrus R., Lecomte-Beckers J. and Habraken A., 2017, “3D thermal finite element analysis of laser cladding processed Ti-6Al-4V part with microstructural correlations” Mater. Des. 128, 130.
[2] Hashemi N., Mertens A., Montrieux H.-M., Tchuindjang J.T., Dedry O., Carrus R. and Lecomte-Beckers J., 2017, “Oxidative wear behaviour of laser clad high speed steel thick deposits: Influence of sliding speed, carbide type and morphology” Surf. Coat. Technol. 315, 519
