V. E. Kormyshev

Formation features of structure-phase states of Cr–Nb–C–V containing coatings on martensitic steel

By methods of modern physical materials science the investigations analysis of phase composition, defect substructure, mechanical and tribological properties of Cr–Nb–C–V containing coatings formed in surfacing on martensitic wear resistant steel Hardox 450 were carried out. It was shown that surfacing resulted in the formation of high strength surface layer 6 mm in thinness. This layer had wear resistance 138 times greater than that of the base and friction coefficient 2.5 times less. On the basis of the investigations by methods of X-ray structural analysis and transmission diffraction electron microscopy it was shown that increase strength and tribological properties of surfacing metal were caused by its phase composition and state of defect substructure, namely, availability of interstitial phases (more than 36%) and martensitic type of α-phase structure.

Metallographic Examination of Forming Improved Mechanical Properties via Surfacing of Steel HARDOX 450 with Flux Cored Wire

Phase composition, defect substructure, and mechanical and tribological properties of the steel Hardox 450 surfaced with С-V-Cr-Nb-W wire are analyzed relying on procedures of transmission diffraction microscopy, mechanical and tribological methods. As a result of surfacing, wear resistance of the material is 138 – 153 times higher than that of the steel Hardox 450, and the friction factor diminishes 2 – 2.5 times. The changing dislocation substructure and phase composition of the deposited metal are analyzed in the paper. The authors have come to the conclusion that the change in analyzed properties is caused by initiation of a multiphase nanostructure. It has been revealed that its strengthening is possible due to the developing of the α-matrix martensitic pattern and a high inclusion of the volume fraction of iron-, chromium-, tungsten,- and niobium-based carbide phase. It has been ascertained in the paper that the iterative surfacing results in attenuation of the oxide phase and in the significant growth of the volume fraction inclusion of the carbide phase.

Electric arc surfacing on low carbon steel: Structure and properties

By the methods of modern materials science, the structure-phase state and microhardness distribution along the cross-section of single and double coatings surfaced on martensite low carbon steel by alloy powder-cored wire were studied. It was established that the increased mechanical properties of surfaced layer are determined by the sub-micro and nanodispersed martensite structure formation, containing iron borides forming the eutectic of lamellar form. The plates of Fe2B are formed mainly in the eutectic of a single-surfaced layer, while FeB is formed in a double-surfaced layer. The existence of bend extinction contours indicating the internal stress fields formation at the boundaries of Fe borides-α-Fe phases were revealed.

Gradient Structure Generated in Hardox 450 Steel with Built-Up Layer

This article investigates the phase composition and the defect substructure of a modified layer built up on Hardox 450 steel by wire containing C, Mn, Si, Cr, Nb, W, and Fe. It is established that, upon surfacing, a high strength surface layer with increased microhardness is formed. Using transmission electron microscopy, it is demonstrated that strengthening of the surface layer can be attributed to generation of multiphase submicron- and nanosized structure with inclusions of niobium carbide particles of submicron size.

Nanohardness of wear-resistant surfaces after electron-beam treatment

The nanohardness, Young’s modulus, and defect substructure of the metal layer applied to Hardox 450 low-carbon martensitic steel by high-carbon powder wire (diameter 1.6 mm) of different chemical composition (containing elements such as vanadium, chromium, niobium, tungsten, manganese, silicon, nickel, and boron) and then twice irradiated by a pulsed electron beam are studied, so as to determine the correct choice of wear-resistant coatings for specific operating conditions and subsequent electron-beam treatment. The metal layer is applied to the steel surface in protective gas containing 98% Ar and 2% CO2, with a welding current of 250–300 A and an arc voltage of 30–35 V. The applied metal is modified by the application of an intense electron beam, which induces melting and rapid solidification. The load on the indenter is 50 mN. The nanohardness and Young’s modulus are determined at 30 arbitrarily selected points of the modified surface. The defect structure of the applied metal surface after electron-beam treatment is studied by means of a scanning electron microscope. The nanohardness and Young’s modulus of the applied metal after electron-beam treatment markedly exceed those of the base. The increase is greatest when using powder wire that contains 4.5% B. A system of microcracks is formed at the surface of the layer applied by means of powder wire that contains 4.5% B and then subjected to an intense pulsed electron beam. No microcracks are observed at the surface of layers applied by means of boron-free powder wire after intense pulsed electron-beam treatment. The boron present increases the brittleness. The increase in strength of the applied layer after electron-beam treatment is due to the formation of a structure in which the crystallites (in the size range from tenths of a micron to a few microns) contain inclusions of secondary phases (borides, carbides, carboborides). The considerable spread observed in the nanohardness and Young’s modulus is evidently due to the nonuniform distribution of strengthening phases.

Structure and properties of the layer deposited onto a low-carbon steel and then irradiated by an electron beam

The phase composition and the mechanical and tribological properties of the layer that is deposited onto a martensitic low-carbon steel using a C–Cr–Nb–W flux cored wire and is additionally twice irradiated by a pulsed electron beam are studied by optical microscopy, scanning electron microscopy, transmission electron diffraction microscopy, X-ray diffraction analysis, wear resistance tests, and durometry. The wear resistance and the microhardness of the deposited layer increase manyfold with respect to the base material, and the friction coefficient of the layer decreases after electron-beam treatment. The increase in the mechanical and tribological properties of the deposited layer subjected to electron-beam treatment is shown to be due to the formation of a submicrocrystalline structure hardened by this treatment and due to the precipitation of the NbC niobium carbide.

Structure and properties of strengthening layer on Hardox 450 steel

ABSTRACT The microstructure and microhardness distribution in the surface of low-carbon Hardox 450 steel coated with alloyed powder wires of different chemical compositions are studied. It is shown that the microhardness of 6–8 mm-thick surfaced layer exceeds that of base metal by more than two times. The increased mechanical properties of surfaced layer are caused by the submicro and nanoscale dispersed martensite, containing the niobium carbides Nb2C, NbC and iron borides Fe2B. In the bulk plates, a dislocation substructure of the net-like type with scalar dislocation density of 1011 cm−2 is observed. The layer surfaced with the wire containing B possesses highest hardness. The possible mechanisms and temperature regimes of niobium and boron carbides in surfacing are discussed.

Structure and Properties of the Surface Layer of a Wear-Resistant Coating on Martensitic Steel after Electron-Beam Processing

The paper reports electro-contact welding on Hardox 450 steel with С-V-Cr-Nb-W flux-cored wire. Supplementary irradiation by intense pulsed electron beam was carried out to improve mechanical properties. Micro-and nanohardness, Young modulus and tribological parameters of the modified surface were tested mechanically. It is pointed at the significant increase in the friction coefficient because the surface layer fractures and particles of the surfaced layer are involved in the process of friction. Using the methods of optical and scanning microscopy a great number of micro-pores were detected both on the irradiated surface and through the surfaced layer modified by intense pulsed electron beam. It is demonstrated that electron-beam processing of the deposited layer surface is the reason for occurrence of multi-layer structure. According to measurements it was determined that the modified (surface and transition) layers are 0.3 to 0.5 μm on overage. It was also found out that irradiation of the surfaced metal leads to significant refining of structural elements because of ultrahigh speeds of crystallization and further cooling down of the modified layer. The phase composition of the surfaced metal modified by pulsed electron beam is explored. Niobium carbide (NbC) is reported to form in the surface layer.

Intense Pulsed Electron Beam Modification of Surface Layer Facing Formed on Hardox 450 Steel by Electrocontact Method

Using methods of modern material science the structure-phase states and tribology properties of coating surfaced on martensite low carbon Hardox 450 steel by powder Fe-C-Ni-B wire and modified by following electron-beam treatment are studied. It is shown that electron-beam treatment of layer leads to the formation of multiphase state with the main phases: α-phase, iron boride FeB, boron carbide B4C. The surfaced structure formed by intensive electron beam irradiation is characterized by high value of wear resistance. It is in 20 times more that wear resistance of steel and in 11 times more than wear resistance of surfaced layer without of electron beam treatment, friction coefficient decreased in 3.5 and 2.2 times, correspondently.

Structure and properties of a low-carbon steel surface modified by electric arc surfacing

The structural-phase state and the distribution of microhardness over the cross section of single and double coatings deposited onto martensitic Hardox 450 low-carbon steel by alloyed flux-cored wire, are studied using modern physical materials science. It is demonstrated that the microhardness of a double deposited layer 10 mm in thickness exceeds the microhardness of the base metal by more than three times. It is found that the improved mechanical properties of the deposited layer are due to the formation of a submicro- and nanodisperse martensitic structure containing iron borides forming a plate-type eutectic. Plates of iron boride Fe2B are formed in the eutectic in a single deposited layer, and in a double-deposited layer, plates of FeB are formed. The existence of bend extinction contours, indicating the formation of internal stress fields at the interface between the phases of iron borides and α-iron borides, is revealed.