This article presents the results of examining pilot bainite steel railroad rails and their tests. It is shown that the set of properties typical of these rails is unreachable in standard perlite steel rails and includes a combination of high strength, hardness, ductility, and impact toughness. Bainite steel rails exhibit a better resistance to fatigue defect formation and a greater fracture toughness and, at the same time, increased contact-fatigue strength and reliability at low temperatures. Considering the demand for rails designed for use at high loads, complex track plan, and low temperatures on the railroads of the Eastern Testing Area and Northern Latitudinal Railway, bainite steel seems an expedient alloy for application.

Microstructural parameters of clad metal from Fe – C – Si – Mn – Cr – Ni – Mo – Vpowder wire with an addition containing carbon and fluorine cleaning dust of aluminum production instead of amorphous carbon are determined. The chemical composition and the microstructural parameters including the grain diameter, the interlamellar distance, the type of the structure of the deposited layer and its chemical composition are determined.

Surfaced layers formed by arc cladding of powder wires produced by the Siberian State Industrial University and used for surfacing articles operating under abrasive wear are studied. The chemical composition, the microstructure and the hardness of the deposited layers and of the nonmetallic inclusions formed in them are analyzed. Titanium addition in the wires is shown to affect positively the wear resistance of the layers.

Исследованы наплавленные слои, изготовленные дуговой наплавкой порошковых проволок, разработанных в условия СибГИУ и используемых для наплавки изделий, работающих в условиях абразивного изнашивания. Проведен анализ химического состава, микроструктуры и твердости наплавленных слоев, а также образующихся в них неметаллических включений. Показано положительное влияние на износостойкость добавки титана в состав проволоки.

A thermokinetic diagram of decomposition of supercooled austenite of R350LHT steel was constructed based on the results of its dilatometric, metallographic and hardness analysis during continuous cooling and in isothermal conditions. It was found that cooling at a rate of 0.1 and 1 °C/s causes the austenite decomposition in R350LHT steel by the pearlite mechanism. After cooling at a lower rate, the pearlite structure is coarser and has lower hardness (289 HV). This is due to the higher temperature range of transformation, in which diffusion processes associated with the transformation of austenite into pearlite occur more actively. In the range of rates from 5 to 10 °C/s, the austenite decomposition occurs according to the pearlite and martensitic mechanism, which leads to the formation of a pearlite-martensite structure. When the austenite of the steel under study is cooled at a rate of 30 and 100 °C/s, the austenite transforms according to the martensitic mechanism, and a martensitic structure with high hardness is formed. With an increase in the cooling rate of R350LHT steel, an increase in hardness is observed from 289 (at 0.1 °C/s) to 864 – 0 896 HV (at 100 and 30 °C/s, respectively). The conducted studies allow the boundaries of the search for optimal parameters of welding and heat treatment modes of the investigated rail steel to be narrowed. To obtain the required structures and physical and mechanical properties (austenite of R350LHT steel undergoes decomposition by the pearlite mechanism), cooling should be carried out at a rate of no more than 1 °С/s.

The structure and composition of the arc sprayed coatings formed using a flux cored Fe–C–Si–Mn–Cr–Ni–Mo wire are studied. A carbon-fluorine-containing additive, namely, the gas purification dust of aluminum production ((wt %) 21–46 Al2O3, 18–27 F, 8–15 Na2O, 0.4–6 K2O, 0.7–2.3 CaO, 0.5–2.5 SiO2, 2.1–3.3 Fe2O3, 12.5–30.2 Ctot, 0.07–0.9 MnO, 0.06–0.9 MgO, 0.09–0.19 S, 0.10–0.18 P) is introduced into the charge of the flux cored wire instead of amorphous carbon. The problems of the influence of the carbon–fluorine additive on the weldability and the contamination of the deposited metal with oxide nonmetallic inclusions are considered; the microstructure and the contamination of the deposited metal are studied. The microstructure of the deposited layer formed using a flux cored electrode of the Fe–C–Si–Mn–Cr–Ni–Mo system consists of acicular and lath martensite arranged in the former austenite grains, along the boundaries of which ferrite layers precipitate. Silicates (undeformable) and oxides (point) are found to exist in the deposited metal. According to the results of quantitative analysis of the chemical composition of the nonmetallic inclusions obtained using a Teskan Mira 3 scanning electron microscope, the nonmetallic inclusions in the deposited metal are at most 10 μm in size; their globular shape positively influence the wear resistance of the deposited layer. The chemic composition of the nonmetallic inclusions shows that they mainly consist of silicon, aluminum, and manganese oxides; there are also traces of sulfur, calcium, and magnesium. The metallic matrix contains iron (dominant amount), chromium, manganese, and silicon; the molybdenum content is substantially lower.

The composition of the non-metallic inclusions and microstricture of the electric arc coating using the flux-cored wire of Fe–C–Di–Mn–Cr–Ni–Mo system has been studied. The electric arc coating has been formed with the help of the ASAW-1250 automatic arc welding machine using the investigated flux-cored wire. To reduce the level of contamination of the deposited metal with non-metallic oxide inclusions, aluminum gas purification dust was introduced into the flux-cored wire (instead of amorphous carbon). The composition of the electric arc coating was determined by using the XRF-1800 spectrometer. The microstructure of the electric arc coating has been studied by optical microscopy. The phase and elemental composition have been studied using scanning electron microscopy at the MIRA 3 LMH instrument. The non-metallic inclusions in the electric arc coating consist of oxides of silicon, fluorine, calcium, aluminum, and magnesiums. The darker component in the inclusion, which looks like rectilinear crystals directed from the surface deep into the inclusion, has a similar phase composition. However, the content of chemical elements in it is somewhat different. A small dark component with a rounded shape (aluminum and magnesium oxides) is observed in the inclusion. Traces of sulfur are distinct along the contour of the globules. Metallographic analysis of the deposited surface has shown that the microstructure of the deposited layer is a coarse-needle martensite. Its structure is uniform and has a dendritic (columnar) structure characteristic for cast metal. The results of the performed investigations allow elaborating the measures to reduce the content of non-metallic inclusions containing elements of fluorine, sodium and aluminum, which, in turn, may adversely affect the physical and mechanical properties of the deposited layer, for example, by using refining additives to reduce the contamination of the deposited layer with non-metallic inclusions.

The creation of modern technologies for the formation of wear-resistant coatings by the electric arc method requires research on the structure and composition of the electric arc surface layer. The composition of nonmetallic inclusions and microstructure of electric arc coating using flux-cored wire of Fe‒C‒Si‒Mn‒Сr‒Ni‒Mo system were studied. The formation of electric arc coating was carried out with a welding tractor ASAW-1250 using fabricated flux-cored wire on plates of 09Г2С steel. In order to influence the level of contamination of the deposited metal with oxide nonmetallic inclusions, aluminum production gas cleaning dust (instead of amorphous carbon) was introduced into the composition of the cored wire. The chemical composition of the deposited metal was determined by X-ray fluorescence spectrometer XRF-1800 and atomic-emission method using spectrometer DFS-71. The microstructure of electric arc coatings was studied using an optical microscope Olympus GX51. The study of the phase and elemental composition was carried out on a scanning electron microscope MIRA 3 LMH. The non-metallic inclusions in the arc coating consist of oxides of aluminum, silicon, fluorine, with a low content of sodium and magnesium. The dark component in the inclusion consists of aluminum and magnesium oxides with a low content of manganese. Traces of sulfur are observed along its contour. The metallographic analysis of the clad surface showed that the microstructure of the clad layer is coarse-needle martensite. The structure is uniform and has a dendritic (columnar) structure characteristic of cast metal. The results of the studies allow us to develop measures to reduce the content of non-metallic inclusions containing elements of fluorine, sodium and aluminum, which in turn can adversely affect the physical and mechanical properties of the clad layer. For example, by using refining additives to reduce the contamination of the cladding layer with nonmetallic inclusions.

Isothermal diagram of decomposition of overcooled austenite of R350LHT steel has been plotted on the basis of dilatometric, metallographic, and durometric studies. While comparing thermal kinetic and isothermal diagrams of decomposition of overcooled austenite of R350LHT steel, it has been established that the thermal kinetic diagram plotted during continuous cooling is displaced downwards and rightwards in comparison with the isothermal diagram. This result completely agrees with the known regularities. During the studies, the critical points of R350LHT steel have been determined: Ac1 = 711°C; Ms = 196°C. Using the isothermal diagram of decomposition of overcooled austenite of R350LHT steel, the temperature of minimum resistance of overcooled austenite has been determined equaling to 500°C. Under the isothermal conditions, the pearlitic structures are formed in the temperature range from 700 to 600°C. A mixture of pearlitic and bainitic structures is formed at 550°C. In the range from 500 to 250°C, the bainitic structures are formed: at 500–400°C, the upper bainite is formed; at 350°C, the mixture of upper and lower bainite is formed; at 300–250°C, the lower bainite is formed. The increase in the hardness of transformation products upon decrease in the holding temperature from 246 HV (at 700°C) to 689 HV (at 250°C) is observed nearly in the overall studied temperature range of isothermal decomposition of overcooled austenite. However, at 500°C, the hardness slightly drops, which could be attributed to the occurrence of residual austenite in the course of bainitic transformation.

To increase the wear resistance of products to abrasive wear, various electric arc coatings are used, applied by cladding method. For this purpose, the flux-cored wires of the Fe‒C‒Si‒Mn‒Cr‒Mo‒Ni system are used. The effect of introducing titanium microadditives into flux-cored wires has been studied. To apply them to plates made of steel 09G2S, a welding tractor ASAW-1250 was used. The properties of the fused layers containing carbon (0.19‒0.24%), titanium (0.014‒0.025%), chromium (3.23‒6.54%), manganese (1.16‒1.55%), silicon (0.63‒0.98%), molybdenum (0.62‒0.72%), aluminum (0.013‒0.023%) with an increased sulfur content (0.058‒0.076%) were investigated. The chemical composition of the deposited metal was determined by the X-ray fluorescence method using the XRF-1800 spectrometer and the atomic emission method on the DFS-71 spectrometer. The microstructure of the electric arc coatings was studied using the OLYMPUS GX51 optical microscope. The study of phase and elemental composition was carried out by scanning electron microscopy methods using the MIRA 3 LMH device. It has been established that the microstructure of welded coatings is lower bainite of varying degrees of dispersion, which is due to the significant content of chromium and the low carbon content in the deposited metal. In the composition of the non-metallic phase of the deposited metal there are fluorine compounds, oxide and sulfide inclusions. According to the data obtained, the dependencies of the influence of the chemical composition of the cladding on the hardness and rate of wear are con-structed. All the studied experimental coatings have a characteristic structure and consist of zones: deposited metal, thermal influence, recrystrallized grain. In the metal of all samples of experimental coatings there are large inclusions containing fluorine atoms trapped from flux, in combination with oxygen and iron atoms. The size of such inclusions reaches 30 μm. A large number of globular inclusions of manganese sulfides were detected, due to the significant sulfur content in the composition of the cladding materials, as well as silicon and aluminum oxides. Based on the results of the research, the measures have been developed that allow cladding with the studied flux-cored wire under welding fluxes with a high sulfur content without deterioration in the quality of the deposited layer.

It is known that the value of impact toughness is sensitive to the geometric accuracy of manufacturing, the quality of the surface and concentrator of samples for impact bending. These parameters have a particularly strong influence on samples made of high-carbon materials. At present, the main regulatory document for the manufacture of samples for impact bending is GOST 9454‒78, which does not regulate the method of applying concentrators. Currently, methods of drawing, milling and electroerosion processing are used to apply the concentrator. The issue of the influence of processing methods on the magnitude of impact strength, in particular rail steel, has not been fully studied. To study the effect of electroerosion processing on impact toughness value we made specimens of P65 rail of DT350 category from 76ХФ steel of current EVRAZ ZSMK production using CNC milling machine and electroerosion processing. It has been established that the decrease in the values of impact strength of samples made using electroerosive machining was due to martensite released during local melting of the metal and non-ferrous metals (Cu and Zn) released during processing. During the operation of the electroerosion processing machine, an uneven surface was formed when the arc locally knocked out “holes”, which serve as additional stress concentrators during impact bending tests. The application of the concentrator by a milling machine leads to the formation of a deformed layer up to 80 µm deep, which is not a stress concentrator and does not reduce the impact strength of the rail steel. As part of a further study, it is planned to investigate the effect of the application of the concentrator by the pulling method on the value of the impact toughness.

During contact flash welding of rails, the metal in the area of thermal impact is heated and continuously cooled. Accelerated heating and subsequent intensive cooling during pulse flash welding lead to the formation of quenching structures, which subsequently leads to cracking and to brittle destruction upon operation of rail weld joint. This work studies capabilities of contact heating after welding in order to eliminate formation of quenching structures in metal weld joint of R350LHT rail steel. Thermal cycles during welding and subsequent contact heating have been recorded. The regularity of structure formation of metal weld joint (including the area of thermal impact) was determined during pulse contact heating for R350LHT rail steel. It is demonstrated that the contact pulse heating allows to prevent the formation of quenching structures and decelerates cooling of weld joint. In the case of non-optimum modes, the contact pulse heating can result in reverse effect. It has been determined that upon significant contribution of heat by contact heating, the metal cooling rate exceeds critical value and the transformation runs according to diffusion free mechanism with formation of coarse grain martensite structure. The use of thermal kinetic and isothermal diagrams of austenite decomposition with known thermal welding cycles allows to restrict significantly the search ranges of optimum modes of electric welding of railroad rails and subsequent contact heating. The use of optimum modes of contact heating allows to obtain minimum length of areas of thermal impact without the formation of quenching structures in weld joint of railroad rails.

Исследованы параметры микроструктуры наплавленного металла порошковой проволокой системы Fe - C - Si - Mn - Cr - Ni - Mo - V, в состав шихты которой взамен аморфного углерода введена добавка, содержащая углерод и фтор - пыль газоочистки алюминиевого производства. Проведен анализ химического состава и изучены параметры микроструктуры, такие, как диаметр зерна, межпластинчатое расстояние, тип получаемой структуры наплавленного слоя.

Mathematical modeling of differentiated thermal processing of railway rails with air has been carried out. At the first stage, the one-dimensional heat conduction problem with boundary conditions of the third kind was solved analytically and numerically. The obtained temperature distributions at the rail head surface and at a depth of 20 mm from the rolling surface were compared with experimental data. As a result, the coefficient values of heat transfer and thermal conductivity of rail steel were determined. At the second stage, the mathematical model of temperature distribution in a rail template was created in conditions of forced cooling and subsequent cooling under natural convection. The proposed mathematical model is based on the Navier–Stokes and convective thermal conductivity equations for the quenching medium and thermal conductivity equation for rail steel. On the rail–air boundary, the condition of heat flow continuity was set. In conditions of spontaneous cooling, change in the temperature field was simulated by a heat conduction equation with conditions of the third kind. Analytical solution of a one-dimensional heat conduction equation has shown that calculated temperature values differ from the experimental data by 10%. When cooling duration is more than 30 s, the change of pace of temperature versus time curves occurs, which is associated with change in cooling mechanisms. Results of numerical analysis confirm this assumption. Analysis of the two-dimensional model of rail cooling by the finite element method has shown that surface temperature of the rail head decreases sharply both along the central axis and along the fillet at the initial cooling stage. When cooling duration is over 100 s, temperature stabilizes to 307 K. In the central zones of the rail head, the cooling process is slower than in the surface ones. After forced cooling is stopped, heating of the surface layers is observed, due to change in heat flow direction from the central zones to the surface of the rail head, and then cooling occurs at speeds significantly lower than at the first stage. The obtained results can be used to correct differential hardening modes.

During contact flash welding of rails, the metal is heated and continuously cooled in the zone of thermal influence. Accelerated heating and subsequent intensive cooling, implemented by the pulsed flashing-off method, lead to the formation of quenching structures. Subsequently, during the operation of the rails welded joint, this leads to the formation of cracks and to brittle destruction. We have investigated the possibilities of using contact heating after welding to avoid the formation of quenching structures in the metal of the welded joint made of R350LHT rail steel. The thermal cycles during welding and subsequent contact heating were recorded. The regularity of formation of the weld metal structure was established including the zone of thermal influence during pulsed contact heating for R350LHT rail steel. It is shown that contact pulse heating slows down the welded joint cooling and prevents the formation of quenching structures. However, contact pulse heating when using suboptimal modes can also lead to the opposite effect. It is determined that with a significant investment of heat by contact heating, cooling rate of the metal exceeds the critical one, transformation process passes through a diffusion-free mechanism with the formation of martensite coarse-grained structure. The use of thermokinetic and isothermal diagrams of austenite decomposition at known thermal welding cycles allows us to significantly narrow the search limits for optimal modes of contact butt welding of railway rails and subsequent contact heating. The use of optimal contact heating modes makes it possible to obtain a minimum length of heat-affected zones with reduced hardness without the formation of quenching structures in the welded joint of railway rails.

An isothermal diagram of decomposition of supercooled austenite of R350LHT steel was constructed based on the results of dilatometric, metallographic and hardness analysis of this decomposition during continuous cooling and under isothermal conditions. When comparing the thermokinetic and isothermal diagrams, it was found that the thermokinetic diagram plotted during continuous cooling shifts downward and to the right in comparison with the isothermal diagram. This result is fully consistent with the known regularities. During the research, the critical points of R350LHT steel were determined: Ас1 = 711 °С; Мn = 196 °С. This isothermal diagram was used to determine the temperature of the minimum stability of overcooled austenite, which was 500 °C. Under isothermal conditions, pearlite-type structures appear in the temperature range from 700 to 600 °C. At 550 °C, a mixture of pearlitic and bainitic structures is formed. In the temperature range from 500 to 250 °C, bainitic structures are formed: at 500 – 400 °C – upper bainite; at 350 ° C – a mixture of upper and lower bainite; at 300 – 250 °С – lower bainite. Almost in the entire studied temperature range of overcooled austenite isothermal decomposition, an increase in the hardness of the transformation products is observed with a decrease in the holding temperature from 246 HV (at 700 °C) to 689 HV (at 250 °C). However, at a temperature of 500 °C, a slight drop in hardness occurs, which is apparently caused by the appearance of retained austenite during the development of bainitic transformation.

To determine weldability and quality of a rail welded joint, information on kinetics of the rail steel overcooled austenite transformation is high importance. Thermo-kinetic diagrams of overcooled austenite dissociation of steels Э76ХФ, Э76ХАФ and Э76Ф, built based on results of dilatometric, metal science and durometric tests of rail steel samples. It was shown, that increase of chrome content in steels Э76Ф and Э76ХФ composition from 0.09 to 0.39% results in expanding of dissociation area of overcooled austenite at temperature scale for ferrite-cementite mixture and increasing of resistivity of the overcooled austenite against dissociation in the area of ferrite-cementite mixture formation. This can be characterized as decrease of critical quenching velocity from 100 to 30 °С/sec. It enables to obtain structural states of higher hardness at cooling with velocities in the area of 0.1−30 °С/sec. It was established, that increase of vanadium content from 0.04 to 0.07% does not cause quality changes at the thermo-kinetic diagram of overcooled austenite dissociation. However, it known, that vanadium is a strong carbide-formation element, which combines with carbon at low cooling velocities and removes it out of the solid solution. Due to this effect, sample of steel Э76ХФ with lower vanadium content at cooling with velocities from 0.1 to 10 °С/sec, had somewhat higher hardness level comparing with steel Э76ХАФ sample. Increase of chrome content in alloy content results in an increase of temperature of austenite formation completion at heating from 760 to 774 °С, while the temperature of martensitic transformation commencement at that remains practically unchanged at the level of 230 °С. In steels Э76ХФ and Э76ХАФ in the chemistry of which chrome was added in the amount of 0.37−0.39%, after cooling with velocities of 1 °С/sec and lower, apart from ferrite-carbide mixture of perlite type, formation of redundant ferrite with a volume share of 4−5% was observed as a result of overcooled austenite dissociation. However, in a steel Э76Ф sample, the content of which has chrome at the level of 0.09% at close content of carbon, after cooling in an analogue range of velocities, a ferritecarbide mixture of perlite type is formed with a slight trace of redundant ferrite in the structure as a result of overcooled austenite dissociation.

To determine weldability and quality of a rail welded joint, information on kinetics of the rail steel overcooled austenite transformation is high importance. Thermo-kinetic diagrams of overcooled austenite dissociation of steels Э76ХФ, Э76ХАФ and Э76Ф, built based on results of dilatometric, metal science and durometric tests of rail steel samples. It was shown, that increase of chrome content in steels Э76Ф and Э76ХФ composition from 0.09 to 0.39% results in expanding of dissociation area of overcooled austenite at temperature scale for ferrite-cementite mixture and increasing of resistivity of the overcooled austenite against dissociation in the area of ferrite-cementite mixture formation. This can be characterized as decrease of critical quenching velocity from 100 to 30 °С/sec. It enables to obtain structural states of higher hardness at cooling with velocities in the area of 0.1−30 °С/sec. It was established, that increase of vanadium content from 0.04 to 0.07% does not cause quality changes at the thermo-kinetic diagram of overcooled austenite dissociation. However, it known, that vanadium is a strong carbide-formation element, which combines with carbon at low cooling velocities and removes it out of the solid solution. Due to this effect, sample of steel Э76ХФ with lower vanadium content at cooling with velocities from 0.1 to 10 °С/sec, had somewhat higher hardness level comparing with steel Э76ХАФ sample. Increase of chrome content in alloy content results in an increase of temperature of austenite formation completion at heating from 760 to 774 °С, while the temperature of martensitic transformation commencement at that remains practically unchanged at the level of 230 °С. In steels Э76ХФ and Э76ХАФ in the chemistry of which chrome was added in the amount of 0.37−0.39%, after cooling with velocities of 1 °С/sec and lower, apart from ferrite-carbide mixture of perlite type, formation of redundant ferrite with a volume share of 4−5% was observed as a result of overcooled austenite dissociation. However, in a steel Э76Ф sample, the content of which has chrome at the level of 0.09% at close content of carbon, after cooling in an analogue range of velocities, a ferritecarbide mixture of perlite type is formed with a slight trace of redundant ferrite in the structure as a result of overcooled austenite dissociation.

An isothermal diagram of decomposition of supercooled austenite of R350LHT steel was constructed based on the results of dilatometric, metallographic and hardness analysis of this decomposition during continuous cooling and under isothermal conditions. When comparing the thermokinetic and isothermal diagrams, it was found that the thermokinetic diagram plotted during continuous cooling shifts downward and to the right in comparison with the isothermal diagram. This result is fully consistent with the known regularities. During the research, the critical points of R350LHT steel were determined: Ас 1 = 711 °С; М n = 196 °С. This isothermal diagram was used to determine the temperature of the minimum stability of overcooled austenite, which was 500 °C. Under isothermal conditions, pearlite-type structures appear in the temperature range from 700 to 600 °C. At 550 °C, a mixture of pearlitic and bainitic structures is formed. In the temperature range from 500 to 250 °C, bainitic structures are formed: at 500 – 400 °C – upper bainite; at 350 ° C – a mixture of upper and lower bainite; at 300 – 250 °С – lower bainite. Almost in the entire studied temperature range of overcooled austenite isothermal decomposition, an increase in the hardness of the transformation products is observed with a decrease in the holding temperature from 246 HV (at 700 °C) to 689 HV (at 250 °C). However, at a temperature of 500 °C, a slight drop in hardness occurs, which is apparently caused by the appearance of retained austenite during the development of bainitic transformation.

The quality of welded rail joints depends on various factors, in particular, on the type and quantity of non-metallic inclusions, formed at their contact arc welding. To check a hypothesis of the cause-effect of welded joint mechanical properties decrease and composition of non-metallic inclusions in the welded seams, their chemical and metallographic analysis accomplished. To study the non-metallic inclusions, samples of 90×30×10 mm dimensions used, cut of Э76ХФ steel rail head. After contact butt welding at MC-2008 machine, the samples were cut by electro-erosion method perpendicularly to the welding seam into two parts. One part of the sample was used for tensile test, the other – for metallographic analysis for non-metallic inclusions and structure of the welded joint. The microstructure of the welded butts studied after milling and intensive etching in the 50% water solution of hydrochloric acid. The microstructure was studied at the optical microscope OLYMPUS GX71 in the light field at magnification 100–1000 folds after etching in an alcohol solution of nitric acid. The chemical composition of all the revealed inclusions were determined at the scanning electron microscope MIRA 3. It was established, that silicon and manganese oxides were the basic components of inclusions, revealed in the welded seam, as well as oxides of aluminum, iron, titanium, chrome – to a less amount. In the samples seam microstructure the ferrite net, typical for rail butts, was not discovered, which is probably stipulated by their accelerated heating due to the small section of the samples.