Development and characterization of multilayer laser cladded high speed steels

Two high speed steel (HSS) alloys were laser cladded on 42CrMo₄ steel cylindrical substrate by using a 4 kW Nd:YAG laser source. After optimization of the laser material processing parameters for single layers, multilayered clads were produced. Microstructural characterization of the laser deposits constitutes studies of the carbides and matrix, which was done by using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Backscattered Diffraction (EBSD) and High Resolution Transmission Electron Microscopy (HRTEM). The strengthening mechanism of LC1 (Fe-Cr-Mo-W-V) was comprised of a martensitic matrix and retained austenite along with networks of VC and Mo₂C eutectic carbides. Cr enriched fine carbides (Cr₇C₃ and Cr₂₃C₆) were embedded within the matrix. During laser cladding of the multilayer deposits, cladding of subsequent layers had a detrimental effect on the hardness of previously cladded layers, which was due to tempering of existing lath martensite. To overcome the hardness drop, a new alloy LC2 (Fe_bal−x-Cr-Mo-W-V-Co_x) was blended by addition of 3–5% of Co in LC1. The addition of Co resulted in an overall increase in hardness and a reduction in the hardness drop during sequential layer cladding; the latter was due to the presence of Co in the solid solution with Fe. HRTEM was performed to characterize the nanometer-sized precipitates evolved during the re-heating. These carbides were either enriched with V and W or formed from a complex combination of V, Mo, W and Cr with lattice spacings of 0.15 nm to 0.26 nm.