Metal Science and Heat Treatment最新文献

The effect of laser cladding process technological parameters, as well as of the addition of nickel (5 – 15 wt.%) on the structure and mechanical properties of WC – 10Co – 4Cr laser cladding on mild steel, has been studied. The most effective laser cladding process parameters were determined when applying single-pass clad tracks and tracks with 50% overlap. The microstructure and the phase composition of the coatings were determined using EDS and XRD. The microhardness of the coatings and their erosion wear resistance were measured. The maximum microhardness (3.6 times higher than that of the substrate material) was exhibited by the WC – 10Co – 4Cr coating (without Ni). The WC – 10Co – 4Cr – 5Ni coating (with 5% Ni) exhibited the highest erosion wear resistance as compared to the coatings with 10 and 15% Ni.

Cross sections prepared using a focused ion beam are used for a transmission electron microscopy study of the microstructure and elemental composition of the intermetallic phases formed after long-term holding a 900 and 1150°C at the boundaries of dispersed particles of niobium carbide in a heat-resistant alloy of type HP40NbTi. Formation of a well-known G-phase is detected at 900°C. When the temperature is raised to 1150°C, an fcc intermetallic phase with parameter a = 1.084 nm (space group Fd3m) is detected. The elemental composition of the high-temperature intermetallic compound and participation of atmospheric nitrogen in its formation are established.

The effect of tempering temperature on the mechanical and corrosion properties of modified martensitic steel CA6NM is studied. Mechanical characteristics are determined in tensile and hardness tests, and corrosion properties are investigated using potentiodynamic and cyclic polarization in an artificial brine solution. The relationship between the microstructure and the mechanical and corrosion properties of the steel in the heat-treated state is revealed. It is shown that the best combination of mechanical and corrosion properties is achieved by tempering at a temperature of 600°C.

The efficiency of replacing traditional quenching in a bath by spray quenching to manufacture grinding balls ∅120 mm made of 70SiMnCr steel to reduce stresses and control the phase composition is investigated. A process of forging grinding balls with the use of water spray cooling is suggested, which ensures bainite transformation under isothermal conditions and formation of the specified structure. The W70A45W20 process, implemented at 200°C for 4.5 h, yields balls with a final volume hardness of 56 HRC and a toughness of 73 J. After this mode of heat treatment, the steel balls have a high wear resistance, and the main mechanism of their surface wear is plastic deformation and micro-cutting.

The effect of complex alloying with iron, nickel, aluminum, zinc, zirconium and titanium in an amount of 0.5 – 1.2% each on the damping capacity of binary alloys Mn – 50% Cu and Mn – 40% Cu in the range of amplitude-independent damping is studied after aging at 643 K for 0.5 – 40 h and natural aging for 7 months. It is shown that alloying of the Mn – Cu alloys in cast condition may either raise their damping capacity or leave it invariable. With increase of the aging time, the values of the frequency of resonance vibrations of specimens of the Mn – Cu alloys fall to a minimum and then grow to a maximum level. The high damping capacity of the multicomponent Mn – 45.6% Cu – 1% Fe – 1% Ni – 1% Zn – 0.9% Zr – 0.5% Ti alloy (ψ = 2.9%) and of the Mn – 35.8% Cu – 1%Fe – 1%Ni – 1%Al – 1.2% Zr alloy (ψ = 3.5%) cast and aged for 40 h at 643 K does not decrease after 7 months of natural aging at 293 K.

Special features of structural and phase transformations, position of critical points, quantitative parameters of the structure, and hardness under continuous transformation of supercooled austenite in steels 30KhNMFRA, 30KhGNMFRA and 30KhN3MFRA are determined. Thermokinetic diagrams of decomposition of supercooled austenite in the steels are plotted using a Gleeble 3500 research complex. Recommendations are developed for selection of chemical composition and cooling rate for billets in order to provide a high strength and enough impact toughness of the steels after quenching and low tempering. The results may be used for development of high-strength cold-resistant steels and modes of their heat hardening.

The microstructure of nanostructured bainite formed by austempering in high-carbon silicon steel is characterized by high resolution electron microscopy. The results show that the bainitic sheaves consist of nanoscale subunits. The found kinds of crystal lattice distortions of each subunit in one bainite lath show clear difference. The latest generated subunit has most distortions. As the subunit grows up, the lattice distortion gradually gets relaxed. This indicates that the subunits form with high phase transformation strain energy, which causes severe lattice distortion. The results provide new experimental evidence on subjects relevant to the understanding of the mechanism of formation of bainitic ferrite.

The deformation behavior of duplex stainless steel 2205 is investigated by the method of high-temperature tensile and compressive tests using Gleeble 1500. The results of the tensile tests show that the tensile strength gradually decreases with increase in the deformation temperature; in the temperature range from 1020 to 1260°C the reduction of area is more than 60%. The incoordinate deformation of the two-phase tested steel in the range of 1020 – 1080°C leaves 1100 – 1200°C a suitable range for hot deformation. The results of compressive tests at the temperatures from 1100 to 1200°C show that the flow curve has typical features of dynamic recrystallization; with increase of the deformation temperature or decrease of the deformation rate, the peak stress and strain decrease separately; from this the Zener–Hollomon parameter is determined, which reflects the flow property of the tested steel, and an equation is proposed to describe the hot deformation.

Electron microscopy and x-ray diffraction analysis are used to study the structure of coatings deposited on steel 12Kh18N9T by non-vacuum electron beam cladding of TiC and Ti + C particles. Wear tests of the coated samples are performed under the conditions of friction against fixed abrasive particles and hydroabrasive impact. It is shown that cladding of the Ti + C powder mixture produces composite titanium carbides with dominantly dendritic structure. The reinforcement of the surface layers of steel 12Kh18N9T (AISI 321) with TiC particles doubles its wear resistance.

The structures of metal matrix composites based on the Fe – Cr – Mn – Mo system and fabricated by an aluminobarothermal process with the use of argon or nitrogen as the gas atmosphere in the reactor are compared. Chemical analysis for the content of the metals, nitrogen and oxygen in the samples is performed. The structure is studied in different conditions. The total hardness of the samples and the microhardness of their matrixes are determined. It is shown that the morphology of the reinforcing nonmetallic particles depends on the type of the gas atmosphere in the reactor during the synthesis and remains unchanged after a 2-h hold at 1250°C and water cooling. The determined coefficients of recovery of nitrogen from the nitrided chromium and the data of the diffraction analysis are used to show that the aluminobarothermal synthesis under nitrogen pressure is an optimum variant.