Hardening Modes Research Articles

Investigation of new steel with increased strength for low temperature applications

Abstract The work established the patterns of a structural and phase transformations which occurs in the new steel of the 0,21C-1,0Mn-1,8Ni-0,3Cu-0,3Mo-0,03Ti-0,004B (%, mass) alloying system at different cooling rate. A thermokinetic diagram has been constructed. Laboratory samples of rolled products were manufactured and the mode of hardening of rolled sheets from a temperature of 860 ° C in water was tested to develop the industrial production of new steel using specialized equipment of the laboratory complex of LLC “EC Termodeform-MSTU”. The results of mechanical tests of rolled sheet samples after heat treatment showed that the steel under study in a hardened state has high strength characteristics in complex with increased impact strength at a test temperature of minus 70 °C: tensile strength σUTS = 1500 MPa, yield strength σ0.2 = 1150 MPa, relative elongation A5 = 12.5 %, hardness 429 HBW, impact strength KCV−70 = 50.3 J/cm2. This confirms its high quality and the possibility of using it for the production of heavily loaded mechanical engineering structures operated at low temperatures in the conditions of the Far North and the Arctic zone of the Russian Federation.

Влияние параметров плазменного упрочнения на качество поверхностного слоя тяжелонагруженных изделий

There has been studied the effect of the hardening current, the distance between the nozzle and the hardened surface of the product, the flow rate of the plasma-forming gas, the dependence of the cooling rate during plasma hardening on the speed of the plasma torch movement (treatment speed), and the diameter of the nozzle. Based on the theory of thermal processes, the cooling rates have been calculated for various values of the current strength. It has been shown that the ratings characterizing the significance of the main technological parameters of the plasma hardening mode for the depth and width of the hardened zone are practically the same. While the effect of the current strength on the dimensions (depth and width) of the plasma hardening zone significantly exceeds the effect of the other parameters of the hardening mode. This indicates that the arc current is the main controlled parameter of the plasma hardening process. There has been shown the possibility of regulating the mechanical properties of the hardened surface of the solid-rolled railway wheel rim depending on the required level of mechanical characteristics by means of controlling the speed of the wheelset.

Research on welding simulation for vacuum chamber test specimens

The vacuum chamber is an important component of nuclear fusion devices, and the deformation control of the welding process is relatively strict. In this paper, the isothermal multi-level cyclic loading tests have been conducted to explore a nonlinear mixed hardening mode, which can be used as the material input for the welding simulation. Then, welding simulation has been performed for test specimens of the vacuum chamber, and the deformation of test specimens has been obtained under different welding paths. After the first welding simulation is completed, the clamp and limiting plates have been designed based on the deformation of the test specimens. The welding simulation has been performed again with the clamp and limiting plates, in order to evaluate the rationality of the welding process and the design for the clamp and limiting plates. Finally, according to the determined welding process and design for the clamp and limiting plates, welding tests have been conducted, and the welding deformation has been measured. It is found that the difference between the measurement values of the tests and the simulation results is small, which implies that the welding simulation is reasonable.

Simulation of thermal processes in a half-space under heating by a moving source with a uniformly distributed heat flow

Using the method of applying instantaneous point sources, a solution was obtained to the problem of heat conduction during surface heating of a body in the form of a half-space by a uniformly distributed highly concentrated heat flux moving at a constant speed along a rectilinear trajectory with a different shape of the heating spot at constant thermophysical characteristics of the material. The effect of temperature loading modes and the shape of the heating spot on thermal processes in the heat-affected zone is studied. The surfaces and lines of the temperature level are constructed for different moments of time and speed loading modes in different planes of the heating zone. Time dependences of temperatures, heating and cooling rates for body points are given. The shortcomings of the methods used for linear thermal conductivity, the lack of direct consideration in the design scheme of the surface melt zone of the material do not allow one to reliably assess the effect of heat treatment modes on changes in material properties, focusing only on the level of the maximum design temperature. In this regard, the structure formation of metal in the zone of thermal action is proposed to be associated with a thermal impulse, i.e. the total thermal energy perceived by the material at a given point of the body, as well as with the effective structurization impulse introduced into consideration, which characterizes the energy spent on the process of structural transformations of the material, and the structurization time at a point and some volume of the body. The dependencies of these values on the speed of movement and the shape of the heating spot are presented. The considered approaches can be applied to various metals and alloys. The research results can be used to develop more effective methods for determining the optimal modes of surface hardening of metal products with a high-energy source.

Determination of optimal laser hardening mode of hard alloy pins for mining tools

Determination of optimal laser hardening mode of hard alloy pins for mining tools

Оценка влияния параметров режима лазерной закалки на качество поверхности и поверхностного слоя деталей станков (обзор)

This review provides an assessment of the influence of the parameters of the laser hardening mode on the quality of the surface and the surface layer. It is presented how the processing speed, radiation power, surface heating temperature, initial structure during, the number of passes laser hardening affect the geometric parameters of the laser exposure zone, roughness, hardness and wear resistance of the surface, deformation, magnitude and sign of residual stresses in the surface layer. The conclusion is made in the form of recommendations on the selection of parameters of the laser hardening mode to obtain a given surface quality and surface layer of machine parts.

Application of combined wave hardening and heat treatment for wear resistance increase

The article describes the results of studies on abrasive wear after combined hardening by wave strain and heat treatment of steels 65G and 30HGSA. Recommendations are given for combined hardening modes that contribute to an increase in abrasion resistance by 15—16 % compared to thermal hardening alone. It has been established that the highest wear resistance is achieved as a result of combined hardening, which provides a more homogeneously hardened structure.

ОБРАБОТКА РЕЗУЛЬТАТОВ ЭКСПЕРИМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ ИСПОЛЬЗОВАНИЯ ТЕХНОЛОГИЙ КОМПЛЕКСНОГО МИКРОПЛАЗМЕННОГО УПРОЧНЕНИЯ РАБОЧИХ ОРГАНОВ И ДЕТАЛЕЙ СЕЛЬСКОХОЗЯЙСТВЕННЫХ МАШИН

Today, the problem of maintaining the efficiency of complex modern domestic and foreign agricultural machines is quite acute. The working units of agricultural tillage machines operate in an aggressive abrasive environment, which leads to their intensive wear and, as a result, to the loss of geometric shape. This, in turn, leads to a violation of agrotechnical requirements, which significantly affects the yield of cultivated crops. Serial working units of soil-cultivating machines are made of alloy steels of the ST65G type with a working hardness of HRC 55 ... 60. The purpose of the research is to increase the wear resistance of the working bodies of tillage agricultural machines by using the technology of complex microplasma hardening, with the development of a methodology for determining rational modes of processing working surfaces. To evaluate the effectiveness of complex hardening of laboratory samples, studies of the elemental composition of the hardened layer were carried out. Plates made of ST65G steel were used as laboratory samples. Hardening was carried out using various combinations of cermet powders and microplasma hardening modes. Determination of wear resistance was carried out on a friction machine 77 MT-1. The best results were noted after vibro-arc hardening followed by electrospark alloying and the use of a cermet powder consisting of 80% PG-10N-01 matrix powder and 20% B4C boron carbide. Based on the indicators of hardening regimes, Lagrange interpolation polynomials were constructed, which describe the dependence of the amount of sample wear on the current and voltage, an algorithm was developed for determining rational hardening regimes to achieve maximum wear resistance of the studied samples. The microhardness of the surface of products during electrospark hardening increased up to 2 times, and with vibroarc in combination with electrospark alloying and the use of special pastes with cermet powders - more than 3 times. The depth of the hardened surface layer with complex hardening is about 0.3 mm.

Influence of laser hardening modes on the properties of 40X13 steel

We have studied the dependence of the characteristics, strength and plasticity, as well as the microhardness of specimens made of corrosion-resistant steel 40X13 on the modes of laser surface hardening by a fiber laser. Depending on the size of the scanning spot and the scanning speed, 3–5 tracks were applied on opposite planes of the sample with overall dimensions of 20 × 200 mm. Samples were tested for static fracture and the microhardness of the material of the samples was studied in terms of the depth of the changed structure. It was found that the fracture of the treated samples in all cases was of a brittle nature with a low level of destructive deformations at stresses below the tensile strength of the original material. The plotted tension diagrams indicate an insignificant effect of laser processing on the value of the elastic modulus of the material. Studies of the hardness of the material of the laser-hardened track and the microhardness of the material along the depth of the zone of the changed structure showed their increase up to 3–4 times compared with the initial characteristics. The results obtained can serve as a basis for studying the relationship between the modes of heating by a laser beam and the properties of the material of the hardened zone.

Degree and depth of hardening under pendulum surface plastic deformation of carbon steel

The article discusses influence of the main technological parameters of pendulum surface plastic deformation (SPD) on the mechanical properties of surface layer of cylindrical parts made of carbon steel. Using the hardness tester HBRV-187.5 and the microhardness tester HMV-G21, we determined hardness of the surface layer, microhardness and depth of the work-hardened layer of hardened parts. In addition, the results of calculating the hardening degree are presented, which is important information for evaluating the effectiveness of SPD method in terms of improving the metal mechanical properties. Experimental studies showed that after pendulum SPD (at different processing modes), hardness of the surface layer increases by 9 – 12 % compared to hardness of the original surface, and the microhardness increases by 1.5 – 1.7 times, which leads to a significant hardening of the cylindrical billet surface layer. Depth of the hardened layer varies in the range of 0.9 – 1.1 mm, while the hardening degree is 45 – 65 %. Using the software package Statistica 10.1, which allows solving optimization problems based on statistical analysis and building an optimization model, we determined the optimal modes of hardening by pendulum SPD. These modes simultaneously provide both the maximum depth of the hardened layer and the highest hardening degree of the surface layer. They are formed under the following processing modes: radial interference t = 0.15 – 0.2 mm; longitudinal feed s = 0.07 – 0.11 mm/rev; billet rotation frequency nb = 160 – 200 min−1; frequency of the working tool pendulum movement nt = 110 – 130 strokes/min; angular amplitude of the working tool α = 35 – 40°. According to the results of experimental data and numerical calculations, it was established that the average grain size in pendulum SPD decreases by 30 – 40 % compared to the initial size, and the dislocation density increases by 2.5 times.

ОПЫТ ПРОИЗВОДСТВА ЯЧЕИСТЫХ БЕТОНОВ НА ОСНОВЕ ГЕОПОЛИМЕРНЫХ ВЯЖУЩИХОСНОВЕ ГЕОПОЛИМЕРНЫХ ВЯЖУЩИХ

Geopolymer systems are currently quite promising among scientists in the field of building materials science in terms of free of cement binders and athermal synthesis materials due to a wide list of their positive properties that compete well with traditional analogs such as cement and cement concrete. The article provides a literary review of the current research and practical experience among Russian and foreign scientists on the issue of the synthesis of cellular concrete based on geopolymer. Based on a review analysis of modern publications in this field over the past 20-25 years, it has been shown that the key parameters that dominate the formation of a high-quality pore structure, as well as the thermophysical and mechanical properties of cellular geopolymer concrete are the following: choice and preparation of the main raw material, taking into account its chemical the nature and microstructure of the system, the type of modifying and pore-forming component, the sequence of introduction of components, the conditions and mode of hardening, the technology of pore formation, etc. As a result of analytical research, it was also revealed that, despite the rather large number of works devoted to obtaining cellular geopolymer systems, in general, today there is no deep understanding of the principles of formation and behavior of the pore structure during the operational period in geopolymer systems.

Features of the combined technology based on laser metal deposition with layered laser heat treatment

The results of combined using of laser metal deposition technology with layer-by-layer laser heat treatment technology are presented and the experimental setup is described to unite the laser metal deposition technology with layer-by-layer laser remelting and/or laser surface hardening implementation. The layers formed at the stages of laser metal deposition and additional layer-by-layer laser heat treatment alternate in the material. The ratio between the thicknesses of the layers obtained during crystallization at the laser metal deposition stage and at the laser remelting stage is shown to vary widely depending on the technological parameters. The surface temperature of the irradiated layer is maintained in laser surface hardening mode in the range of 1100 °C – 1400 °C with present laser power function. It is proposed to use this mode for local structural-phase transformation of the material.

Трибологические характеристики конструкционных легированных сталей после лазерной модификации поверхности

The microstructure and tribological characteristics of the modified surface of AISI E3310 and AISI A290C1M structural alloy steels after laser treatment using an ytterbium continuous fiber laser have been studied. Laser surface treatment was carried out on air with laser power outputs of 75 W and 100 W and scanning speeds from 2 to 14 mm/s. Metallographic analysis and durometer testing were applied to determine the structure of laser action zones and the steel structural components there. It has been shown that the scanning speed at a laser power of 100 W has the most significant effect on the dimensions of the laser action zones. The maximum depth of the laser action zone during laser treatment without surface melting is 310 and 170 µm for E3310 and A290C1M steel, respectively. Depending on the mode of hardening, the microhardness in the laser action zones varies from 1.36 to 1.97 times for E3310 steel; as for A290C1M steel, it increases by 2.0 – 2.6 times. At 100 µm hardening depth, the reduction in linear wear and wear intensity reaches 26.6 % and 43.9 % for E3310 and A290C1M steel, respectively.

Mechanical properties of hardened layer under reversible surface plastic deformation

The article presents the results of experimental studies to determine the influence of the parameters of reverse surface plastic deformation (RPD) on the mechanical properties of the surface layer of cylindrical parts made of carbon steel 45. To implement the proposed method of finishing and hardening processing, a device has been developed that provides reverse circular motion of the working tool. Using the HBRV-187.5 hardness tester, HMV-G21 microhardness tester and MET-2 microscope, the hardness of the surface layer, microhardness, grain structure and depth of the hardened layer of hardened parts were determined. Experimental studies have shown that after reverse SPD, the hardness of the surface layer increases by 9...15 % compared to the hardness of the original surface, and the microhardness increases by 1,6...1,8 times, which leads to a significant hardening of the surface layer. The depth of the hardened layer is 0.8...1.6 mm, and the degree of hardening is 55...80 %. According to the results of experimental studies and using the PyCharm computer program with the Python programming language, the optimal modes of hardening by reverse SPD were determined, providing both the maximum depth and the highest degree of hardening of the surface layer, which are formed under the following processing modes: longitudinal feed 0.08...0,10 mm/rev; workpiece rotation frequency 280...300 rpm; the value of the radial interference 0.28...0.30 mm; reverse speed RI 290...300 strokes/min; the initial installation angle of RI is 90° and the value of the angle of reverse rotation of RI is ±15°.

Effect of parameters of reversible surface plastic deformation on temperature in contact zone of tool with workpiece

The article presents the results of experimental studies to determine the influence of the main technological parameters of reverse surface plastic deformation (SPD) on the temperature in the contact zone of the working tool with the workpiece. To implement the proposed method of finishing and hardening processing, a device has been developed that provides a reverse circular movement of the working tool. Using a FLIR SC7000 series thermal imager, the temperature in the contact zone of the working tool with the workpiece was determined. Experimental studies have shown that the value of the temperature on the surface of the workpiece with reverse SPD varies from 42 to 123 °C and depends on the main technological parameters of the process. It has been established that the temperature exceeding 123 °C at the contact leads to a decrease in the maximum intensity of residual stresses in the surface layer of the part. Based on the results of experimental studies and using the PyCharm computer program with the Python programming language, optimal hardening modes were determined that provide the minimum surface temperature of the part, which makes it possible to maintain the quality of the surface layer after hardening.

Technology of hardening surfaces of working bodies by electromechanical processing

The article presents the results of research on technology development and substantiation of the modes of strengthening the working surfaces of earth-moving machines by the electromechanical method. The types of wear and the appearance of defects on the working surfaces of the part are analyzed, taking into account the operating conditions. Based on the conducted studies on the study of surface wear, the arithmetic mean values were determined using the example of a plowshare of a bulldozer blade. A technology for restoring a part with subsequent electromechanical hardening has been developed. The influence of processing modes on the surface hardness was studied, and using a multifactorial experiment, a regression equation was identified, and optimal hardening modes were substantiated.

Investigation of Changes in the Structural-Phase State and the Efficiency of Hardening of 30CrMnSiA Steel by the Method of Electrolytic Plasma Thermocyclic Surface Treatment

Electrolytic plasma thermocyclic surface hardening is an attractive solution for both chemical and heat treatment used to improve the properties of the steel surface by structural and phase transformation. Structural and phase transformations occurring during the process of electrolytic plasma thermocyclic hardening are performed repeatedly at varying heating–cooling temperatures, which radically improve the quality of the part and give them properties unattainable by means of one-time processing. The impact of electrolytic plasma thermocyclic hardening modes on the structure and mechanical and tribological properties of 30CrMnSiA steel is investigated. The structural and phase components were examined using optical and scanning electron microscopy, as well as X-ray phase analysis. It is established that the structure of the cross-section is characterized by the following zonality: zone 1—a near-surface hardened zone, which is composed of hardened martensite; zone 2—thermal influence; and zone 3—a matrix consisting of pearlite and ferrite. The microhardness and wear resistance of the hardened surface were evaluated by nanoindentation and “ball on disk” methods, respectively. Nanoindentation analysis demonstrated that the indentation hardening process provides a maximum increase in hardness by three times and an increase in stiffness with a decrease in the elastic modulus by 38% compared to the original steel. The results of tribological studies show that electrolytic plasma thermocyclic hardening increases the resistance of steel to friction by increasing the surface hardness and reduces the area of actual contact during friction. It is established that the microhardness of the cross-section decreases proportionally from the surface to the depth of the layer, which is associated with a decrease in the volume content of martensite.

Research of the stress-strain state of parts hardened by plastic deformation under cyclic loading

The dependences of the indices of the stress-strain state (temporary and residual stresses, hardening depth) of cylindrical parts on the parameters of the mode of hardening by plastic deformation under cyclic loading are investigated. Keywords: hardening, plastic deformation, cyclic loading, stress-strain state, temporary and residual stresses, modeling, hardening depth. zsa@istu.edu, minhquanho2605@gmail.com

Investigation of the influence of technological factors and compositions of binders on the strength characteristics of blast–furnace cement with magnetized ferromagnetic additives

Cement production is a significant source of carbon dioxide emissions. One of the ways to reduce emissions is to reduce the proportion of clinker in cement by introducing active mineral additives into its composition, particularly granulated blast-furnace slag. One of the ways to increase the activity of such cement is the effect of magnetic fields on the spin multiplicity of the substances involved in the hardening reaction. In this case, the maximum effect is ensured by introducing a magnetized finely dispersed ferromagnetic substance into the cement composition. The activation effect depends on the additive’s adding method to the cement’s composition, the components ratio in the cement, and the cement hardening mode. This work aims to identify the influence of the adding method of the additive, the slag and additive proportion in cement, and the steam curing temperature on the activity effect of the binder. Three groups of studies were carried out to determine the strength characteristics of laboratory samples hardened both in natural conditions and during steaming. In the first group, cement samples have tested containing 40% slag obtained by joint grinding and joint mixing of the additive with cement for 0.5, 1, 2, 4 and 8 minutes. In the second group, samples have tested with the additive amount varied from 0 to 2.5%, and slag amount from 0 to 80%. Finally, cement samples were tested in the third group containing 50% slag and from 0 to 2.5% additive. The samples were steam cured at temperatures ranging from 50 to 90° C and tested one day, 28 and 90 days after steam curing. As a result of the research, it has revealed that to obtain the maximum effect, the additive must be introduced into the cement composition by joint grinding. The factors influencing the activity have been determined. At the same time, the time of joint grinding should ensure uniform mixing of the components and the formation of new surfaces of cement grains in the presence of magnetic fields. Too long joint grinding leads to the loss of the magnetic properties of the addition. It was found that the activation effect from the additive addition increases with an increase in the proportion of slag. In cement without slag, an increase in the additive content leads to a drop in strength. It was revealed that the introduction of magnetized ferromagnetic dust additives into the composition of the SPC makes it possible to reduce the steam curing temperature of products by 20-25° C. Studies have shown that using a finely dispersed ferromagnetic substance as an activating additive can save energy resources and reduce emissions.

Behavioral Characteristics of Cement Concrete Pavements in South Kazakhstan: Climatic Changes and Optimal Construction Method

The present paper describes experiments and research outcomes concerning the construction of cement concrete pavements in South Kazakhstan, taking into account significant climate changes. The study has identified potential problems in the construction of cement concrete pavements in the region, where there was no experience of their construction until the mid-2000s. In order to develop an optimal solution, the technical factors that characterize the process of arranging these coatings using sliding molds are analyzed and quantitatively normalized. These factors include the optimal amount of mortar for curing concrete, the optimal joint cutting time, the interval and effective width of expansion joints to prevent the formation of cracks in concrete at an early age. The effectiveness of the use of polyethylene film to prevent the formation of contraction cracks and maintain the required mode of hardening of the cement concrete pavement is shown. The main cause of damage to the expansion joints along the length of the day coverage of coatings in the conditions of South Kazakhstan has been established. Recommendations have been developed for the installation of cement-concrete pavement and expansion joints during the construction of roads in this region. The accumulated data on climatic factors and methods of work with the use of polyethylene film have made it possible to create an optimal method for the construction of cement concrete pavements, which will improve the quality of roads in South Kazakhstan.