Vol 59, No 1-2 (2017)

The structure and magnetic properties of a powder alloy based on the Fe – Cr – Co system with elevated content of cobalt and boron are studied. The dependences of the magnetic induction and of the coercivity on the aging temperature are determined experimentally. It is shown that the introduction of boron into the alloy hinders precipitation of σ-phase and makes it possible to raise the cobalt content by 4% as compared to standard alloy 30Kh23K.

The contact fatigue resistance of carburized gears produced from chromium-nickel steels is studied. The curves of deep contact fatigue of the material of the gears are plotted in terms of the criterion of equality of the characteristics of diffusion layers. An expression for ultimate deep contact fatigue resistance of carburized gears is derived.

The phase composition of aluminum alloys of the Al – Ca – Ni – Sc system containing 0.3 wt.% Sc is studied. It is shown that the aluminum solid solution may be in equilibrium not only with binary phases (Al₄Ca, Al₃Sc and Al₃Ni) but also with a ternary Al₉NiCa compound. The temperature of attainment of maximum hardening due to precipitation of nanoparticles of phase Al₃Sc is determined for all the alloys studied. Principal possibility of creation of castable alloys based on an (Al) + Al₄Ca + Al₉NiCa eutectic, the hardening heat treatment of which does not require quenching, is substantiated.

Results of a study of the influence of the structural state of steel 9KhS on mechanical characteristics and parameters of elastic waves are presented. It is shown that the speed of elastic waves correlates with the values of impact toughness and hardness. A method for rapid determination of impact toughness and hardness from the speed of elastic waves is suggested.

Results of a study of the effect of heat treatment on the microhardness, structure and phase composition of diffusion zone in explosion-welded ‘refractory nickel alloy Kh20N80 + aluminum alloy AD1’ bimetal are presented.

The growth of austenite grains and the dissolution of carbonitrides under heating of a structural steel microalloyed with niobium and titanium are studied. The microstructure of the steel is investigated with the help of light and transmission electron microscopes. The content of elements in precipitated particles is determined using an energy dispersive spectrometer. The kinetic equation of grain growth is derived and the critical temperature above which the carbonitrides stop to hinder grain growth is determined. Recommendations are given on the temperature modes of hot rolling.

Ingots from stainless steel 21-4N are studied in the initial condition and after 7-h homogenizing at 1200°C. Compressive tests of specimens cut from surface layers and from the cores of the ingots are performed at 900 – 1250°C. The effect of the initial condition of the steel and of the test conditions on the critical stress of the start of dynamic recrystallization is determined. The conditions of formation of dangerous cracks in the ingots are considered.

The effect of the conditions of directed crystallization (the temperature gradient and the crystallization rate) on the dendrite spacing, on the size of the particles of the hardening γ′-phase in the arms and arm spaces of the dendrites, on the volume fraction and size of the pores, on the size of the particles of the eutectic γ/γ′-phase, and on the features of dendritic segregation in a single-crystal castable refractory alloy is studied.

Microarc thermochemical treatment (MTCT) is suggested for intensification of diffusion saturation of the surface layer of steel articles. The hardened article is immersed into powdered mineral coal and heated by passed electric current. The main stages of the MTCT process are determined. The diffusion layer is shown to be accelerated by carburizing. High-hardness coatings are obtained due to simultaneous diffusion of carbon, chromium, molybdenum and boron.

An attempt is made to advance Elagin’s principles of alloying of aluminum alloys with transition metals (TM) such as Mn, Cr, Zr, Ti, V with allowance for the ternary equilibrium and metastable Al – TM – TM phase diagrams. The key moments in the analysis of the phase diagrams are the curves (surfaces) of joint solubility of TM in aluminum, which bound the range of the aluminum solid solution. It is recommended to use combinations of such TM (two and more), the introduction of which into aluminum alloys widens the phase range of the aluminum solid solution.

The characteristics of low-cycle fatigue of high-chromium martensitic steel 10Kh10K3V2MFBR are determined at room temperature and specified deformation amplitude varied within 0.25 – 1.0%. It is shown that the steel is susceptible to softening under low-cycle loads. The endurance of the steel is determined by the Baskvin – Manson – Coffin relation. Permanent softening of the steel until failure is caused by lowering of the dislocation density and coarsening of subgrains.

The structure of a bimetal from structural steel 08kp and low-alloy iron ChNMSh obtained by explosion welding is studied. The effect of different heat treatments on the structure and properties of the bimetal is determined, and expedient modes of heat treatment for reliving the internal stresses in the zone of joining, which do not worsen the operating properties of the welded materials, are suggested.

Multilayer heat-resistant ion-plasma coatings for protecting the parts of the hot duct of gas-turbine engines produced from refractory nickel alloys based on VKNA intermetallics from high-temperature oxidation are considered. Coatings of the Ni – Cr – Al (Ta, Re, Hf, Y) + Al – Ni – Y systems are tested for high-temperature strength at 1200 and 1250°C. Metallographic and microscopic x-ray spectrum analyses of the structure and composition of the coatings in the initial condition and after the testing are performed. The effect of protective coatings of the Ni – Cr – Al – Hf + Al – Ni – Y systems on the long-term strength of alloys VKNA-1V and VKNA-25 at 1200°C is studied.

A mathematical model of structural transformations in an alloy steel under the thermal cycle of multipass welding is suggested for computer implementation. The minimum necessary set of parameters for describing the transformations under heating and cooling is determined. Ferritic-pearlitic, bainitic and martensitic transformations under cooling of a steel are considered. A method for deriving the necessary temperature and time parameters of the model from the chemical composition of the steel is described. Published data are used to derive regression models of the temperature ranges and parameters of transformation kinetics in alloy steels. It is shown that the disadvantages of the active visual methods of analysis of the final phase composition of steels are responsible for inaccuracy and mismatch of published data. The hardness of a specimen, which correlates with some other mechanical properties of the material, is chosen as the most objective and reproducible criterion of the final phase composition. The models developed are checked by a comparative analysis of computational results and experimental data on the hardness of 140 alloy steels after cooling at various rates.

The physical nature of formation and the special features of structure of “white zones” are studied. The experimental results are analyzed with allowance for the shear pattern of formation of austenite at a high heating rate and for the effect of Laplace pressure. A “white zone” is shown to be a nanosize martensitic structure.

Formation of structure and properties is analyzed in a number of stainless high-strength steels used in oil production for shafts of submerged centrifugal electric pumps. The factors elevating the cuttability and corrosion resistance of sparingly alloyed steel 14Cr17Ni2NV are determined.

The structure and properties of carbon-containing single-crystal alloy ZhS32 and carbonless single-crystal alloys ZhS36, VZhM4 and VZhM5U are studied after 500 – 3000-h aging at 850 – 1100°C. The resistance to elastoplastic strain, creep and fatigue and the characteristics of long-term strength of the alloys are determined. It is shown that the expected values of long-term strength and creep resistance of the single-crystal alloys should be corrected with allowance for the changes in their initial structure after long-term operation.