Solid State Phenomena Vol. 303

Abstract: The paper discusses the results of the numerical simulation of high-speed impact effect of compact projectiles made of steel and tungsten alloy with steel obstacles of equal mass. The obstacles have different initial porosity of the material. Conducted the final evaluation of the penetration speed of the projectile depending on the porosity of the obstacle and the initial speed of the shock interaction. The initial impact velocity range from 1 to 16 [km/s]. The destruction, melting and evaporation of the interacting bodies are taken into account. The analysis of porosity influence evaluation of obstacles material revealed that the protective advantage of porous obstacles disclose at the higher impact velocities, greater than 1.5 [km/s] for steel strikers and 2 [km/s] for projectiles of tungsten alloy. The more impact velocity the more protective effect of porous obstacles.

Abstract: In the paper the authors study how the kinetic plasticity effects the temporary and residual stresses formed in instrumental steels when cooling. They also present the results of temporary stresses relaxation. This phenomenon was applied within the temperature range of the martensite transformation to reduce the cold cracking of the surfaced metal. The paper shows that the superplasticity effect emerging at the moment of martensite transformation plays the crucial role in temporary stresses relaxation.

Abstract: The study considers the theoretical and technological aspects of the friction units’ resource increasing made of ferritic-pearlitic gray cast iron. It is found that chemical and thermal treatment has the best combination of criteria by the integrated technical and economic analysis for the cast iron parts’ hardening methods. The methods of the cast iron hardening used in practice are not applicable in the real production conditions. It happens because of the technological processes’ complexity and the equipment. Alternatively, the hardened layer thickness does not exceed 0.3 mm. The study considers the main aspects of the new technology application for the surface hardening, The recommendations for its application are formulated. They depend on the intended service of the part. The technical level of the offered solutions is estimated in comparison with traditional technologies of cast iron hardening.

Abstract: The studies on cementation focus exclusively on the carbon’s movement. It is described by diffusion equations, often with constant coefficients and without regard to the liaising with temperature. It does not allow to have regard to the further carbon diffusion into the workpiece with the lower temperature range. The most accurate prediction of carbon concentration profiles depending on the parameters of the carburization regime and the chemical composition of steel is possible with the mathematical models using. However, most models show good results for Fe-C austenite without affecting the effect of alloying substitution elements. Taking into account the influence of alloying elements leads to complex empirical dependencies with difficult selected coefficients. It makes their use difficult. The study describes the simulation using the finite element method for the process of austenite’s diffusion saturation Fe-C-Cr system with carbon during cementation. Here is an example of a steel gear 15Cr2 with the temperature influence. The COMSOL Multiphysics program is used to solve the problem numerically. It is found that the model of carbon diffusion in unalloyed austenite for the single-stage cementation regime is in good contact with the experimental data for the Fe-C-Cr austenite of 15Cr2 steel. For a two-stage process, the calculation of the carbon concentration in the surface layer has a slightly greater deviation from the experimental data than it is at a greater depth.

Abstract: The paper presents data of experimental research into the importance of protective surface coatings in welded products for MMA stability; heat field distribution patterns on their surfaces, and structure and phase composition of the welded metal. The study has revealed that a protective surface coating in a welded item in MMA has a positive effect on shortcut duration, increasing it by 5-11 %, raising its formation and transformation time by 10-12 %; 15% dimensional increase of a welded metal grain is registered as well, and a heat impact zone expands by 25%.

Abstract: A two-strip electrodes surfacing with controlled transfer of electrode metal is proposed for applying an anti-corrosion layer to the surface of the base metal with a variable angle to the horizon. To prevent the formation of defects in the formation of the deposited layer, it is proposed to adjust the parameters of the surfacing mode in places where the angle of inclination of the surface changes.

Abstract: The process of formation of pores, cavities and similar defects in welded joints of stainless steels and aluminum alloys, affecting their quality, directly depends on spatial weld position in laser welding. Reducing the angle of inclination from 90° to 0° during downhill and uphill welding of AISI 321 stainless steel in the pulse mode of laser generation leads to an increase in both the number of pores and their size. At the same time, defects in the form of pores are not observed in the continuous mode of laser generation. In laser welding of butt joints of AISI 321 steel, the flat and vertical weld positions are the most promising, as they provide the highest level of quality. In order to provide a stable formation of a high-quality butt joint of aluminum AMg6M alloy and to prevent the failure of laser equipment, the welding process should be carried out in a vertical uphill weld position.

Abstract: Using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) we studied the distribution of structural parameters, phase composition and alloying elements concentration across the coatings obtained by cladding of chromium and titanium carbides mixture on low-carbon steel. The beam of relativistic energy electrons extracted into the atmosphere was used to form the coatings. The homogeneity in the allying elements distribution is shown to be defined by the lifetime of the melt bath while the phase composition distribution depends on the thickness of the melt layer. Both above parameters are determined by the density of the entered energy.

Abstract: Developed was a computer model of temperature field in the tool and parts in the process of their friction stir welding (FSW). Modeling of the temperature field was carried out for both successive stages of welding process, i.e. plunging of pin of tool working element into the part (1^st stage) and progressive motion of plunged pin in the part (2^nd stage). The mathematical model represents a nonlinear equation of transient heat conduction, which takes into account progressive pin movement during the 2^nd stage of welding. Two constituents describe the heat sources, appearing in welding. The first one considers power of heat sources, caused by friction of the tool with the parts on contact surfaces, the second one takes into account heat generation, promoted by mechanical deformation of the part material. Mathematical modeling and experimental examination of temperature field were carried out for tool from cubic boron nitride (cubonit) and hard alloy in copper parts during FSW. Adequacy of the developed model was determined based on correlation of numerical and experimental results.