SURFACE NANOHARDNESS OF WEAR RESISTANT SURFACING IRRADIATED BY ELECTRON BEAM

The nanohardness, Young elastic modulus and defect substructure of the layer surfaced on the low carbon martensite Hardox 450 steel by the high carbon power wires with diameter of 1.6 mm of different chemical composition (containing such elements as V, Cr, Nb, W, Mn, Si, Ni, B) and two times additionally irradiated by the pulse electron beam were studied for the purpose of substantiated selection of coating material corresponding to the product operation conditions and the modes of subsequent electron beam treatment. The formation of the fused layer on the steel surface was carried out in the shielding gas medium containing 98 % Ar, 2 % CO₂ , with a welding current of 250 – 300 A and a voltage on the arc of 30 – 35 V. Modification of the deposited layer was carried out by irradiating the surface of the deposited layer by a high-intensity electron beam in the mode of melting and high-speed crystallization. The load on the inductor was 50 mN. Determination of the nanohardness and Young elastic modulus was carried out at 30 arbitrarily chosen points of the modified surface. The defect structure of the surface modified by of an electron beam of the surfacing was studied by scanning electron microscopy. A multiple increase in nanohardness and Young elastic modulus of the welded layer was revealed during electron-beam treatment according to the base material. It was found that the maximum hardening effect is observed at surfacing by a flux-cored wire containing 4.5 % of boron. It is shown that on the weld deposit surface formed by the wire with 4.5% of boron and additionally irradiated with an intense pulsed electron beam, the formation of a microcrack system on the surface of irradiation was revealed. Investigations of weld deposits, formed by non-boron-containing powder wires, have shown the absence of microcracks on the modified surface after pulsed electron beam treatment. The increase in the strength properties of the deposited layer modified by the electron beam is due to the formation of structures which crystallite sizes vary from tenths of a micrometer to one micrometer and contain second phases (borides, carbides, carbborides). A significant spread of the values of the nanohardness and the Young elastic modulus was established, which was apparently due to the inhomogeneous distribution of the strengthening phases.

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