Structure and Properties of the Wear-Resistant Facing Modified by Electron-Beam Processing

Abstract

By the methods of modern physical materials science, the structure, phase composition, defect substructure, and tribological properties of the coating formed on low-carbon Hardox 450 steel by electric arc surfacing of powder Fe–C–Nb–Cr–W wire and modified by subsequent irradiation with high-intensity pulsed electron beams are studied. In the initial state, Hardox 450 steel has the structure of packet morphology martensite formed during low-temperature tempering. The surfacing results in the formation of high-strength layer with thickness of above 6 mm and with microhardness of ≈ 10.5 GPa that is 1.7 times higher than microhardness of the substrate. Along the surfacing–steel interface, the structure is formed, in which sizes of the grains vary within the range of 30–50 µm. With distance from the in-terface to the steel bulk, the grain size decreases and amounts 5–7 µm for the distance of 1.0–1.2 mm. In the bulk of martensite crystals, the dislocation substructure is observed in a form of multilayer nets with scalar dislocation density of ≈ 1⋅1011 cm−2. Niobium carbide particles, whose sizes vary as 0.2–1.5 µm, constitute the main strengthening phase of the surfaced layer. In the transition-layer structure, the formation of special carbide particles is revealed, namely, chromium carbides (Cr3C2 and Cr7C3), carbide of complex composition М23С6 ((Fe,Cr)23C6) and, rather rarely, WC tungsten carbide. The particles of special carbides are located in the bulk and at the boundaries of martensite crystals, and they have a round shape; the particle sizes vary within the range of 30–50 nm. The cellular type structure is formed on the surface of the surfaced layer as a result of irradiation by intensive pulsed electron beam. The sizes of cells vary within the range of 20–100 μm. The extended interlayers separate the cells. The cells have submicro- or nanocrystalline structure, the characteristic sizes of which vary within the range from 100 nm to 1 µm. Electron-beam treatment of the surfaced layer results in decrease in grain sizes to 1.5–2.0 μm. The strengthening phases of the surfacing layer are α-phase (martensite), niobium carbides, iron of the Fe3C and M6C(Fe3W3C). It is established that wear resistance of the surfaced layer is increased by more than 70 times after the electron-beam treatment as compared with that for the initial steel, while the friction coefficient is decreased by ≈ 3 times.

Keywords