E. V. Kapralov

Structural-phase states and properties of coatings welded onto steel surfaces using powder wires

Structural-phase states and mechanical properties of coatings welded onto Hardox 400 steel using En-DOtecDO*30, EnDOtecDOtec*33, and SK A 70-G weld wires are investigated via X-ray structural analysis, optical and scanning electron microscopy, and measuring microhardness, wear resistance, and friction coefficients. It is shown that the coatings had microhardnesses and wear resistances were higher than those of their substrate by factors of 2–3 and 2, respectively, while the friction coefficients of coatings were lower than those of the substrates by a factor of 1.2. Hardening was due to the formation of disperse structures containing up to 40 vol % of Fe3C, Fe23(C, B)6, NbC, Fe3B, and Fe3Si0.97 particles.

Structure gradient in wear-resistant coatings on steel

As shown by scanning electron microscopy, electric-arc surfacing of steel produces a multilayer structure, including the surface coating itself, a transition layer, and a thermal-influence zone. Solidification of the coating is accompanied by the formation of a columnar structure, with alternating layers (thickness 8–10 μm) of two types. The first type is characterized by plate structure, oriented perpendicular to the substrate surface; the thickness of the plates and the interlayers between them is 50–100 nm. The second type has plate and globular structure. On moving away from the surface, the plate structure of the first type breaks down; none remains at the boundary with the transition layer. The globules measure 1.5–3.0 μm; they are fragmented. The structure gradient is also apparent in the transition layer and in the thermal-influence zone. The boundary between the coating and the steel is in an elastic stress state on account of the superhigh heating and cooling rates, as indicated by the presence of microcracks, micropores (in rows), and extended secondaryphase layers.

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.

Structure of the surface layer of a wear-resistant coating after treatment with a high-intensity electron beam

Transmission electron microscopy is used to investigate the carbon extraction replicas of a wearresistant surface layer formed on Hardox 400 steel and its phase composition. The formation of a multiphase state is revealed, which includes a-iron grains and inclusions of carbide phases based on iron, chromium, and niobium. The surface layer is additionally treated by a high-intensity pulsed electron beam. The relative position of α-iron grains and particles of carbide phases is examined by the electron-diffraction microscopy of thin foils. The main carbide phase is iron carbide located as extended interlayers which separate a-iron grains. Nanoscale particles of chromium and niobium carbides are located at the interfaces of the a-iron–iron-carbide system and in the body of the a-iron grains. It is established that the surface layer is in the elastic-stress state during pulsed electron-beam treatment due to ultrahigh heating and cooling rates. It is shown that stress concentrators are the interphase boundaries between the carbide and the a-phase of iron.

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.

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.

Phase composition and defect substructure of double surfacing, formed with V–Cr–Nb–W powder wire on steel

The analysis of phase composition, defect substructure, and mechanical and tribological properties of Hardox 450 steel after single and double surfacing of C–V–Cr–Nb–W containing wire was carried out by methods of modern physical materials science. The increase in the wear resistance of the material compared to the original steel by 140–150 times and reduction of the friction coefficient by 2–2.5 times was established. The change in the fine structure and phase composition of the surfaced metal was analyzed. It was shown that the established effects could be associated with the formation of a multiphase nanoscale and submicron structure, hardening of which was associated with the formation of martensitic structure of α-matrix and the presence of a high volume fraction of carbide phase inclusions based on Fe, Cr, W and Nb. Formation of resurfacing led to repeated increase in the volume fraction of the carbide phase and the absence of the oxide phase.

Formation of the Increased Wear-Resistant Properties of Hardox 450 Steel by Deposited Coatings

The structure-phase conditions formed during the deposition of surface coatings on Hardox 450 steel by the wire comprising C, V, Cr, Nb, W were examined by the methods of X- ray phase analysis and transmission electron diffraction microscopy. It was established that after the hardened layer was deposited, the wear-resistance increased 153 times and the coefficient of friction in the material decreased 2.5 times. It was concluded that the increased properties of the surface coating were due to the formation of martensitic structure and the occurrence of high volume fraction of carbide phase inclusions.

Wear resistance and structure–phase states in the surface of the welding-deposited coating on steel

The elemental and phase composition, the state of a defect substructure, and the tribological characteristics of the layer deposited on the surface of a low-carbon low-alloy steel by a welding method are studied. The deposited layer on the steel surface causes the formation of a multilayer structure, and the wear resistance of the deposited layer is found to increase.