Key Engineering Materials Vol. 854

Abstract: An analytical review of the effect of high-temperature thermomechanical treatment on the structure and properties of steels as a possible effective method of strengthening the teeth of excavator buckets. It is shown that the application of this method can have a positive effect not only on the hardness, but also on the entire complex of their mechanical characteristics, such as plasticity, impact toughness and fatigue resistance. In relation to Hadfield steel as the most frequently used material of the bucket teeth, it is noted that with increasing deformation grade of billets from 1 to 5, tensile strength of steel increases from 570 to 1030 MPa, yield strength – from 480 to 790 MPa, relative elongation – from 14.3 to 17.9 %, relative contraction – from 17.2 to 20.1 %, impact strength KCU – from 1.51 to 2.14 MJ/m². This article presents the results of metallographic analysis and comparative tests for abrasive wear of Hadfield steel samples after typical heat treatment practiced at bucket teeth manufacturers and thermomechanical treatment. It is established that high-temperature plastic deformation of steel samples before quenching increases their wear resistance by 1.7 times. The authors attribute the detected increase in wear resistance to the formation of fine martensite in the surface layers of steel with a needle size of 3-10 nm, which increases its hardness by 47%. It is concluded that the presence of fine martensite in the structure of Hadfield steel can increase the service life of excavator bucket teeth made of this material. The results of this study are planned to be used in the development of an improved technological process for manufacturing bucket teeth of excavators.

Abstract: A series of experiments on measuring of difference between the main mechanical stresses (DPMS) was carried out using a mechanical stress scanner based on the magnetoanisotropic method. The magnitude of the DPMS is fixed when a magnetic field is induced on a carbon steel plate under uniaxial tension. A direct proportional relationship is shown between the magnitude of the DPMS signal recorded by the scanner and the magnitude of tensile stresses in the plate in the region of elastic deformation of steel. Measurement of the DPMS signal in the central part of similar plates previously subjected to elastic-plastic bending showed that positive values of the signal are fixed in the surface layers of the metal on the inside of the plate, which corresponds to tensile residual stresses, while the negative ones concentrate at the external surface, which corresponds to compressive stresses. A transverse incision on a curved plate from the inside leads to a decrease in the value of the signal of the DPMS, which indicates a decrease in the level of residual stresses in the metal. The values of the DPMS signal in the central part of the curved plate, recalculated using the established calibration dependence on the value of the residual stresses, were compared with the values of the stresses established by calculation, based on the Henki’s theorem on the unloading of an elastic-plastic body. A satisfactory convergence was obtained between the experimental and calculated data.

Abstract: Austenitic stainless steels are widely used in industry. Increased requirements for the quality of products from these steel grades, the difficulties associated with the implementation of technological processes, as well as the high cost of steel, determine the necessity to assess probable causes of defects. This article presents an analysis of the influence of main process parameters on the quality of products from the grade 08X18H10T steel. Based on the results of statistical analysis and thermodynamic modeling, it was concluded that the increased content of titanium and nitrogen affects the quality of products, which is caused by the formation of titanium carbonitrides in the process of steel solidification.

Abstract: In addition to property anomalies, a distinguishing feature of the intermediate phase is the qualitative change of the crystallization or recrystallization interval (Q∆LS) that occurs at congruent and incongruent melting phases, at eutectic or eutectoid points, at the ends of eutectic or eutectoid horizontals, and also at any nonmonotonicity of the liquidus, since the solidus or solidoid is a horizontal in eutectic or eutectoid systems. A technique has been developed that allows us to associate anomalies in the properties of industrial alloys with state diagrams based on the first established criterion - a qualitative change (length in temperature) of the crystallization (recrystallization) interval (Q∆LS), as well as with a difference in the structural heredity (genealogy) of the component atoms that make up dual system. A joint analysis of the anomalies in the properties of binary alloys with state diagrams (based on the established criterion (Q∆LS)) allows us to relate the latter to the presence of intermediate phases in Al − Si, Fe − C, Al − Cu systems. The intermediate phases AnBm-Q∆LS explaining the anomalies of properties are declared: ~Al₇Si, Al₄₁Cu₉ − correspond to the eutectic point; Fe₂₄C − eutectoid point; Al₁₁Si, AlSi₆ − the bend of the liquidus; Fe₄₂C − bending liquidoid; Al₄₉Cu, Al_98.5Si_1.5 − the end of the eutectic horizontal; Cu₄Al, Cu₇Al₃ − to the ends of the eutectoid horizontal.

Abstract: The prospects of production of special properties steels in the Russian and global metal market are estimated. The necessity of using new types of steels is substantiated. The prospects of introducing steels with special properties developed by PJSC “Magnitogorsk Iron and Steel Company” to the market are determined. Evaluation of measures for the production of large volumes of products showed that there is a problem of a significant increase in the time of manufacturing and delivery of output products to the consumer. As measures to ensure the modernization of the technological complex of the steel enterprise and reduce the time for steel production, the system of jet heat treatment of metal is proposed. According to the results of comparative analysis of the MAGSTRONG H500 and HARDOX 500 alloys used in mining equipment under conditions of increased wear, it was revealed that the proposed method of heat treatment allows one to achieve high wear resistance properties, with high coefficients of tensile strength and toughness.

Abstract: The main areas of work are related to the synthesis of a two-phase composite (1-x)PbSe·xPbSeO₃ in the form of a powder, faceted single crystal, film and compacted material with the possibility of changing the fraction (x) of the PbSeO₃ phase from 0 to 1 by oxidation of PbSe in a dry atmosphere in the temperature range 20-550 °С and the study of its physicochemical properties. All initial samples are obtained by the original method from Pb_1-ySe_y powder, in which the composition corresponds to the maximum melting temperature of the compound and is defined as y_smax=0.500025±0.000025 at. Se. The powder is crushed, after which homogenizing annealing is performed at a constant temperature (~750 °C) in a dynamic vacuum in order to achieve the minimum general pressure condition. The noted precursor-related technological procedures are necessary to achieve congruent evaporation conditions in all types of samples and help minimize the concentration of inherent defects and inclusions in phase two. Depending on application, it is possible to form crystalline powders with a given ratio of volumetric phases PbSe and PbSeO3 in a separate grain. For all cases, the "shell" for semiconductor particles PbSe is the dielectric phase PbSeO₃. The principal possibility of forming the smallest (up to nanometer) grains of lead selenide in the dielectric matrix of lead selenite is shown. According to the proposed method, the synthesis of lead selenite by oxidation of lead selenide is possible.

Abstract: The paper presents the process of sol-gel synthesis of titanium dioxide nanoparticles, the peculiarities of the influence of component composition (titanium precursor content, solvent and stabilizer − surfactant) on the properties of sol and powder obtained on its basis. As a result of the study, the nature of the influence of the type and content of the surfactant in the solution of tetrabutoxytitanium in ethanol on the size of the synthesized particles of titanium dioxide was revealed. The optimal composition of the reaction mixture of TiO–R sol was obtained and the optimal ratio of tetrabutoxytitanium and ethyl alcohol was revealed using which a material with a high content of nanosized titanium dioxide was obtained.

Abstract: The method for synthesis of zirconium oxide nanopowder in low-pressure arc plasma was developed. The physicochemical properties of the nanopowder were studied. The estimation was carried out by means of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The sequence and kinetics of structural transformations occurring in the specified time-temperature heating regimes have been examined using differential thermal analysis. It was shown that the particles have a nanometer size, a narrow particle size distribution and an amorphous-crystalline structure. The maximum specific surface area detected by the method of sorption of surfactants was 470 m²/g. The issues of crystallization were discussed. From comparison between the results of experimental studies from earlier works with the results obtained for zirconium oxide, it is concluded that the proposed method for producing NPs in a low-pressure arc discharge plasma is universal.

Abstract: Gd₂O₂S:Tb phosphors with different terbium content are prepared in a reducing atmosphere at various synthesis conditions. The effect of an activator and Na₄P₂O₇ flux concentrations upon photo-and X-ray induced luminescence of the synthesized samples as well as on their acid-base properties and morphology is studied. The addition of Na₄P₂O₇ flux into the charge mixture leads to a significant increase of the phosphor particle size. A positive correlation is found between the particle size and pH value of the phosphor aqueous slurry. The photoluminescence intensity is found to mostly depend on the activator concentration, while X-ray luminescence intensity primarily depends on the particle size and crystal structure perfectness of the phosphor matrix. Charge mixture compositions and synthesis conditions providing Gd₂O₂S:Tb phosphors with the highest photo-and X-ray luminescence intensity are determined. A Gd₂O₂S:Tb phosphor with X-ray luminescence intensity exceeding the values for the commercial phosphor KEP-45 of a similar composition is developed. The obtained phosphors can be used for the manufacture of intensifying screens applied in industrial X-ray flaw detection.