Bulletin PNRPU. Mechanical engineering, materials science

The article is devoted to the investigation of multilayer plasma surfacing on the straight line and reverse polarity of the current. The article describes the main provisions in the field of additive produc- tion using various technologies. The possibility and potential advantages of hybrid production of products of complex shape are described. It is shown that the use of a plasma heating source using direct and reverse polarity current has several advantages from both the technological and economic point of view. For the numerical implementation, the Comsol Multiphysics package is used, which allows solving adjacent problems of mathematical physics that occur during the course of welding processes. A software environment that provides all the stages of modeling (definition of geometric parameters, description of physics, visualization), allowing to model any physical processes that can be represented as a system of partial differential equations. A technique is developed and a mathematical description of the thermal source describing the plasma surfacing process taking into account the heat transfer from the plasma flow and near-electrode processes is presented. A three-dimensional numerical model of heat transfer into a product for plasma surfacing at a current of direct and reverse polarity is developed. Thermal cycles of plasma surfacing are obtained. On the basis of thermal cycles, the analysis of structural phase transformations and the description of the thermal situation on the surface of the article are made. It is shown that the use of reverse polarity favorably influences the formation of the deposited material. Numerical realization of the plasma surfacing process on the currents of direct and reverse polarity for steel 10Cr18Ni10Тi is made. The error in the test examples for numerical implementation did not exceed 10%.

The transformations, structure and mechanical properties of system-alloyed low-carbon steel 12Kh3G2МFS in comparison with the previously studied steels 10Kh3G3МF, 10Kh3G3МFS and 10Kh3G3МFТ were investigated. Considered technological limitations of commercially used structural steels 40KhN2MA, 40KhGМА, 42CrMo4V used in the production of highly loaded petroleum machinery products such as heavy-weight drill pipe and subs. The basic shortcomings of the classical steels were revealed. Shows the benefits of system-alloyed steels, for example, investigated brand 12Kh3G2МFS. The production technology industrial smelting of the investigated steel is given. The major technological transitions are shows. The critical points and built thermokinetic diagrams of decomposition of austenite were identified. The adaptability of the steel grade 12Kh3G2МFS, the ability to harden with cooling in calm air hardness HB 379-383, while ensuring end-to-end hardenability in sections up to 279мм are shows. Shows the quality of castings and forgings of the investigated steel after forging at different radial sections and with degrees from 3.98 to 5.17. The influence of temperature of heating for hardening on the structure and properties of steel is studied. The estimation of the grain size of austenite of investigated steel depending on the temperature of austenitization, in comparison with the previously studied steels 10Kh3G3МF, 10Kh3G3МFS and 10Kh3G3МFТ. The influence of cooling rate and the tempering temperature of the structure, hardness and mechanical properties of steel 12Kh3G2МFS in comparison with the previously studied steels were defined. Identifies the main alloying elements that affect the stability of the austenite during cooling. Conducted evaluation of the minimum content of such compositions. Considered the boundary conditions of the system of alloying of steels for obtaining the specified structure, provide the required hardenability and mechanical properties. The practical applicability and adaptability of the brand in mass production, РJSC “Motovilikhinskiye Zavody”.

Purpose of the article is corrosive resistances analysis of steels and alloys such as chrome iron, austenitic Ni-Cr stainless steel, iron-nickel alloy, monel metal, copper, aluminium, bronze, brass, lead, alloy Zr, titanium, argentum, aurum and platinum, in ammonium fluoride, ammonium befluoride, salt mixture ammonium fluoride and ammonium befluoride, alloy LiF-NaF-KF, ammonium hexafluosilicate, ammonium hexafluorotitanate and ammonium hexafluorozirconate. Corrosive resistances of steels and alloys in fluoride solution were pointed. Materials data tabulated with characteristics: alloy grade, fluid temperature, weight percentage of fluoride salt in solution, rate of corrosion (mm/year). Area of production were pointed, where corrosive resistances of steels and alloys data needs for performance assurance of equipments in corrosion environment. Alloy additives were noted and also their influence on corrosion resistance increase or corrosion resistance decrease in some circumstances was mentioned. It is found which corrosive resistances of steels and alloys in differential medium are missed.

The method of minimization of the volume of measurements of cylindrical surfaces of parts based on statistical modeling has been scientifically substantiated and implemented. According to this method, it is proposed to determine the minimum number of measurements of points on the surface based on the results of monitoring a limited sample from parts lots and subsequent statistical modeling of the control process. Such an approach allows us to give a preliminary interval estimation of mea-surement error, a-errors and b-errors. For a batch of 100 parts, a measurement simulation for four variants with a different number and arrangement of control points on a cylindrical surface is performed. As initial data, the results of measuring the coordinates of 110 cylinder points with a diameter of 50 mm and a length of 100 mm on a mobile coordinate measuring machine of the Faro Arm Edge model were taken. Four variants of the arrangement of control points on a cylindrical surface with a change in their number from 110 to 50 are investigated. It is revealed that the measurement error is well described by the normal distribution law, therefore the arithmetic mean and standard deviation can be used as an estimate. With a decrease in the number of control points relative to the basic variant, a measurement b-error is characteristic. It is established that when the number of control points decreases, the arithmetic mean decreases, the standard deviation of the measurement error increases and the probability of a measurement b-error increases. Practical implementation of the proposed approach makes it possible to reduce the number of control points while ensuring the required accuracy of measurement and to increase the measurementing performance.

The aim of this work is to study the influence of the parameters of sputtering of melts based on iron on the physical and technological characteristics of powders intended for selective laser fusion. For the production of metal powder 12X18H10T, the technology of gas atomization of liquid melt with argon on a laboratory atomizer VIGA-2B was used at a temperature of 1640 °C. In the production of powders, the gas flow rate was varied by changing the diameter of the metal pipe and the nozzle nozzle type differing in design. It was found that as the diameter of the metal pipe increased, the values of fluidity, the fraction of particles with satellites, the fraction of spherical particles decreased, but the amount of the target fraction increased and the fraction of particles with pores decreased. Values of Fere diameter, average particle size d50, pycnometric density and bulk density have changed insignificantly. It was found that when using the “Standart” nozzle, the characteristics of the powders were worse than when using the “SuperSonic” nozzle - the values of the fraction of particles with pores, the fraction of particles with satellites increased, the value of spherical particles decreased, and the fluidity was completely absent, but it was the highest target fraction value The experimental dependence of the increase in the yield of the target fraction (20-63 μm) of the powder is established with a decrease in the volume of supply of the atomizing gas. Dependences of the amount of the target fraction powder and the ratio of the particle size and the diameter of the metal orifice to the spraying gas supply volume are presented. The data obtained make it possible to predict the values of the output parameters of powders during the atomization of 12Х18Н10Т steel. The characteristics of the powders make it possible to use them for the manufacture of articles by additive technologies.

This article is devoted to the problem of transformation of nonmetallic inclusions in welded joints under the action of a plasma arc. The possibility of using a plasma arc to improve the quality characteristics of a welded seam is considered. The quantity, shape, size and distribution of nonmetallic inclusions in the weld metal before and after plasma treatment by the methods of quantitative metallography, as well as redistribution of nonmetallic inclusions over the thermal exposure zone are investigated. A significant difference was noted between the volume fraction of nonmetallic inclusions in the weld zone and in the zone of thermal action during plasma treatment of 16G2AF steel. In 100% of the samples examined in the thermal exposure zone, the total amount of nonmetallic inclusions is 20-30% higher than the number of inclusions in the weld zone, and this difference increases with increasing running energy. It is established that when the polarity of the plasma treatment changes from direct to reverse, an increase in the volume fraction of inclusions is observed, both in the weld zone and in the zone of thermal action. It is noted that irrespective of the polarity and protective gas with increasing current to 200 A, the volume fraction of nonmetallic inclusions decreases. And with a current strength of more than 200 A, the number of inclusions again increases. When carbon dioxide is used as the protective gas, a predominantly globular (rounded) form of inclusions characteristic of oxides and oxysulfides is observed. When using nitrogen as a protective gas in the weld metal, the appearance of faceted particles of complex shape - nitrides and carbonitrides - is observed. Non-metallic inclusions larger than 10 μm can be serious stress concentrators - the stress level near the inclusion may exceed the yield strength of steel and even reach the ultimate strength. The rate of floating of non-metallic inclusions depends on their size, the viscosity of the liquid metal, the difference in the specific gravity of the particle and the metal. The velocity of the particles ascending is the greater, the bigger the particle, the less its density. The rate of emergence of slag particles is significantly affected by the presence of convective flows in the metal, the release of bubbles from the metal that mix the metal and entrain the slag particles to the surface of the metal bath.