Volume 59, Nº 11-12 (2018)

The possibility of sparing reconditioning of parts and mechanisms produced from high-strength cast iron by surfacing a metal identical to the base one but containing no scarce and expensive elements is studied. The chemical composition of the coating is determined experimentally. The mechanical properties of the deposited metal are determined. The results of the experiment are analyzed, and the composition of the powder wire blend providing formation of a ferrite-pearlite structure and globular graphite in the surfaced metal is determined. The structural components of the deposited metal are described. The optimum content of calcium in the cast iron with structurally free globular graphite is specified.

Dynamic and static recrystallization occurring under hot deformation at a rate of 1 and 100 sec ^{– 1} in high-strength medium-carbon wear-resistant steels developed at CRISM “Prometey” for die forming of parts of driven elements of tillage machines is studied. The critical strain of dynamic recrystallization and the threshold temperatures and times of finish of static recrystallization are determined for the studied deformation rates at various temperatures.

Results of a study of coiled stock from low-carbon steels alloyed with manganese and silicon and different additives of niobium and titanium are presented. The coiled stock is produced at foundry-rolling works by the method of direct rolling of thin slabs right after their continuous casting. The microdeformation of the crystal lattice and the crystallographic texture are determined. The conditions of formation of the most favorable structure and texture in the steels are specified.

The kinetics of cooling of sheet preforms from aluminum alloys in a quenching medium with polymer additions is analyzed. Reduction of warpage and residual stresses under quenching is a usual problem in the production of parts and semiproducts. It is shown that in the world practice this problem is solved for sheet and complex-configuration parts from aluminum alloys by quenching cooling in aqueous solutions with polymer additions (low-deformation quenching), which change the kinetics and the mechanism of the cooling.

Powder steels Vanadis 4 Extra, Vanadis 6 and Vanadis 10 with different contents of V, Cr and Mo are studied after 180-min nitriding at 570°C at nitrogen potential K_N = 2 and 10. The resistance of the steels to abrasive wear and the Vickers hardness of the surface layers are determined. An x-ray diffraction analysis is performed. Nitriding modes raising the endurance of tools from the powder steels are suggested.

Experiments on megaplastic deformation of magnesium at room temperature by transverse extrusion and subsequent cold rolling are described. The microstructure and mechanical properties of a 120-μm thick magnesium foil with total true compressive strain e ~ 6.0 are studied. It is shown that low-temperature annealing increases the strength and ductility properties of the specimens. The detected abnormal growth in the yield strength is explained from the standpoint of thermally activated processes of rearrangement of the dislocation structure and locking of dislocations.

The microstructure and the distribution of chemical elements in laser-welded joints of Al – Mg – Si alloy 6005-T6 are studied. Segregations of chemical elements are detected over grain boundaries in the heat-affected zones of the welded joints. The joints fracture by the intergrain mechanism. A Gleeble 3800 device is used to determine the temperature dependences of the mechanical properties of the alloy with allowance for the special features of the welding cycle. Amethod for evaluating the sensitivity of welded joints of aluminum alloys to formation of liquation cracks with allowance for the local properties of the metal, the welding conditions, and the rigidity of the construction is suggested.

A metallographic study of the carbide phase in rolled sections from bearing steels ShKh15 and ShKh15SG etched in different reagents is performed. The steels are treated by different variants. The experimental results are processed with the aim to correct the mode of spheroidizing annealing of steel ShKh15. The characteristic of the “carbide net remainder” is reduced from 4 – 5 divisions of scale 4 of the GOST 801–78 Standard to 2 scale divisions.

The orientation characteristics of structural components of titanium alloys with different types of structure determined by the method of EBSD analysis are shown to be interrelated with the deformation mechanism determining the properties of polycrystalline materials.

The effect of warm rolling (at 750 – 550°C) on the structure and mechanical properties of low-carbon steel 12GBA is studied in tensile tests in a wide temperature range. Metallographic analysis with the use of optical, scanning electron and transmission electron microscopy is performed. The strength and ductility properties are determined in tensile tests at from 20°C to –196°C. The suggested mode of warm rolling is shown to affect favorably the structure and the combination of mechanical properties of steel 12GBA.

The nature of separations arising in hot-rolled plates from high-toughness steels of the new generation like 05G2B and of cleavages arising in traditional building steels of type 09G2S is studied. Like and unlike features of separations and cleavages are determined. The concept of “critical stress \( {\upsigma}_{\mathrm{b}}^{\mathrm{cr}} \)” describing the strength of the interlayer boundaries responsible for formation of layered cracks is used to analyze various factors responsible for the susceptibility of rolled plates to layered fracture.

The effects of microdamage on the remaining life of high-temperature components of steam conduits from high-chromium steel 10Kh9MF-Sh and low-alloy steel 12Kh1M1F are compared. To simulate the microdamage, specimens with a circular notch and different relative diameters are fabricated. Specimens with a notch simulating the highest degree of microdamage and smooth specimens are tested for long-term strength. The coefficient of the remaining life of a conduit is computed for the range of relative damage presenting practical interest.

The crack resistance of welded joints of pipe steels of strength class K60 and different alloying systems is studied. The parameter of the crack tip opening displacement (CTOD) is shown to be dependent on the size of the austenite grains and on the morphology of bainite in the superheated region of the heat-affected zone of the weld. The crack resistance is shown to be controllable due to optimization of the alloying system.

A numerical three-dimensional model for computing residual stresses generated in cross section of steel 42CrMo4 after nitriding is presented. The diffusion process is analyzed by the finite-element method. The internal stresses are computed using the obtained profile of the distribution of the nitrogen concentration. The special features of the intricate geometry of the treated articles including edges and angles are considered. Comparative analysis of the results of the simulation and of the experimental measurement of residual stresses is performed by the Waisman–Philips method.