Volume 59, Nº 7-8 (2017)

Decomposition of supercooled austenite in steel 70Kh3G2VTB under continuous cooling is investigated. The thermokinetic diagram of decomposition of austenite in the pilot steel is plotted. The temperature-time ranges of the structural transformations are obtained. The effect of the parameters of austenitizing on the processes of dissolution of the carbide phase under heating is described. The fine structure of the pilot steel is studied in different stages of heat hardening.

The methods of scanning electron microscopy, differential scanning calorimetry and x-ray diffraction are used to study the morphological and thermal characteristics of cooling-induced martensite in alloy Fe – 30% Ni – 3% Pd. It is shown that the kinetics of the martensitic transformation is athermal and the morphology is lamellar. The mean values of the parameters of the austenite and martensite lattices are 0.35704 and 0.28614 nm respectively. The thermocycling leaves the points A_s and A_f invariable.

Alloys of the Mg – Zn – Zr – Nd system with composition matching that of ML10 (NZ30K) and different contents of the main alloying components within the standardized range are studied. Four-component Mg – Zn –Zr – Nd phase diagrams are simulated, and the stages of crystallization of the alloys are considered. The structure of the alloys is determined in cast condition and after a T6 heat treatment. Fracture surfaces are analyzed. The distribution of the alloying elements in the structure is studied. The changes in the content of zirconium within the standardized range are shown to affect the grain size in the cast and heat treated states.

The mechanical and relaxation properties of corrosion-resistant aluminum-containing austenitic-ferritic steel 03Kh13N10K5M2Yu2T are considered as a function of the mode of preliminary thermoplastic treatment and its temperature-time conditions.

The possibility of fabrication of rapidly quenched fibers from alloy Ti – 22Al – 27Nb by extracting a hanging melt drop is studied. The special features of the production of electrodes for spraying the fibers by sintering mechanically alloyed powdered components of the alloy, i.e., titanium hydride, niobium, and aluminum dust, are studied. The rapidly quenched fibers with homogeneous phase composition and fine-grained structure produced from alloy Ti – 22Al – 27Nb are suitable for manufacturing compact semiproducts by hot pressing.

Special features of the transformations of supercooled austenite occurring under continuous cooling of a promising high-strength steel grade not standardized in the Russian Federation are determined. A method for evaluating the volume fractions of structure constituents formed in the steel as a result of cooling from 925°C at various constant rates within 0.025 – 75 K/sec is proposed and tested. The results are generalized in the form of a thermokinetic diagram of transformations of supercooled austenite.

The proportion of hardening and softening under plastic deformation at room temperature in metals and alloys of the Al – Zn system has been studied as dependent on the regime of preliminary heat treatment. The influence of the strain rate on the dependence of alloy hardness on the degree of plastic deformation is estimated.

The structure of laser-welded joints of parts having different thicknesses fabricated from alloys based on aluminum and titanium has been studied. Results of transmission and scanning electron microscopy measurements and x-ray diffraction analysis show that the diffusion interaction of microvolumes of two alloys in the weld leads to the formation of two interlayers: (i) a continuous intermetallic TiAl layer with thickness below 1 μm adjacent to the titanium alloy and (ii) a layer consisting of TiAl₃ intermetallic dendrites with thickness of 2 – 6 μm adjacent to the TiAl layer. The average microhardness of the intermetallic layer is about 490 HV.

A novel high-strength refractory alloy VMD16 of the Mg – Zn – Zr – REE system is described. The advantages of the alloy with respect to the counterparts are considered. The processes of formation of phase composition and of structural evolution are studied. A fine dispersed subgrain structure is shown to exist in the deformable magnesium alloy. The combination of the specific morphology and topology of the intermetallic phases with their thermal stability provides a high level of strength properties at room and elevated (300 – 350°C) temperatures at a low anisotropy.

The influence of temperature fields on the structure and properties of corrosion-resistant chromium steels under different modes of laser treatment is investigated. A model of heat transfer under laser impact on target is used to plot thermal fields and cycles and cooling rates. It is shown that the model used for computing thermal fields gives tentative geometric sizes of the fusion zones under laser treatment and selective laser fusion. The cooling rate is shown to have decisive influence on the structure of corrosion-resistant steels after laser treatment with surface fusion in devices for pulsed, continuous, and selective laser melting.

The characteristics of strength, static crack resistance, rate of growth of fatigue cracks and cyclic endurance of annealed sheets from weldable alloys of the Al – Mg – Sc system are studied as compared to annealed sheets from alloy AMg6. The compositions of aluminum alloys with scandium (01545 and 1570S) with characteristics substantially superior to those of AMg6 and level of properties comparable to that of the base aircraft not weldable alloy 1163 in state T6 are determined.

An experimental study of the morphology of particles of a filler powder and of the characteristics of beads produced by laser gas-powder surfacing is performed. The main laws of formation of bead in the course of laser surfacing are determined. The optimum modes of deposition onto a substrate from steel 09G2S are suggested.

Centrifugal casting into a massive slot chill mold was used to prepare two series of specimens of alloys of the Al – Cu system, containing from 10 to 32.2 at.% Cu. The first series was fabricated without a homogenizing heat treatment of the melt, while the second series was fabricated with heating of the melt to 1400°C. Both kinds of specimens were cast at the same temperature in order to provide for the same cooling rate of about 10⁴ K/sec. The structures, phase compositions and microhardnesses of the structural components are compared. It is established that the homogenizing heat treatment changes the kinetics of crystallization and, hence, the proportion of phases in the alloy structure and the copper content in them.

Peculiarities of the structure of a refractory eutectic alloy of the Nb – Si system, formed by the method of directed crystallization with liquid-metal coolant, have been studied. Characteristic zones of microstructure of the ingot obtained upon directed crystallization are considered, the alloy composition is analyzed, and volume fractions of phases in the Nb – Si composite are determined.

The influence of high-pressure gas nitriding on the structure and properties of martensitic steels VKS-5, VKS-7, 20Kh3N3MFB, and 25Kh5M is investigated. It is shown that the high-pressure nitriding increases the thickness of the diffusion zone at substantial reduction of the process time as compared to the traditional gas-phase nitriding. Increase of the post-treatment cooling rate above 30 K/min favors the formation of diffusion layers with greater hardness.

The structure and phase composition of welded joints of austenitic steel 08Kh17N10T and titanium alloy PT-3V formed by diffusion welding with an intermediate layer of ultrafine nickel powder have been studied. The microstructure of joints welded in various regimes was studied using metallographic and energy-dispersive x-ray microanalysis techniques. Good prospects of the application of ultrafine dispersed media for diffusion welding of steels and titanium alloys are shown.