Steel R18 Research Articles

Representation of the microstructure of pearlitic steels for DEM simulations of fatigue

The fatigue behavior of pearlitic steels in wheel-rails is correlated to the microstructure. However, existing models do barely take this correlation into account. In this work, we propose a hierarchical meshing to describe the microstructure of pearlitic steels. The mesh includes grain and block/colony boundaries, lamellae orientations, and orientation perpendicular to lamellae. We use the Voronoi Tessellation method to generate elements with the specific area fraction distribution for pearlite colony areas. The colony and block information is obtained from SEM and EBSD measurements of R260 steel to construct the mesh that represents the microstructure. Finally, we obtained the deformed microstructure via simple geometrical shearing. This meshing method is the first step for modeling fatigue crack growth anisotropy due to plastic deformation.

Structure and Properties of the Product Sintered from the Powder Produced by Electroerosion of R18 Steel Waste

Structure and Properties of the Product Sintered from the Powder Produced by Electroerosion of R18 Steel Waste

A new scaled testing methodology for the analysis of rolling contact fatigue in railway steels.

Twin disc testing is a relatively cost effective and practical method of investigating the damage resistive properties of rail steels in a scaled environment. The loading conditions and dimensions used in testing are scaled in such a way that the Rolling Contact Fatigue (RCF) generated on a twin disc rig are representative of the conditions experienced at the full-scale. Typical methodologies to generate RCF on a twin disc rig involve the application of water to the contact patch throughout the test, with perhaps a few thousand dry cycles being run beforehand. This research explores the use of weather data to reflect the real-world contact conditions more accurately between a wheel and rail. Met Office weather data collected from 1981 to 2010 shows the average annual precipitation in the UK is around 133 days of rain or snow, which is nearly 36 % of the year. In this study, weather data was used to determine the ratio of wet to dry cycles in the testing methodology.  50k dry cycles are run in intervals of 5k and then transitioned to 25k of wet cycles, which is 30% of the total cycles. Intervals were kept at 5k so attaining 36%. If RCF is not initiated after the first 75k cycles, which ends with 25k wet cycles, then the same dry and wet cycles are repeated. RCF data generated using this methodology demonstrated expected differences in the RCF resistive properties of two rail steel grades, R260 and R350HT. In test 1 the point of initiation for each grade was not captured, though cracks were visible around the expected cycles to initiation, which was verified using optical microscopy. The cracks viewed on the softer R260 steel samples, ‘’260’’ referring to the Brinell hardness value of the steel, were more developed at 85k cycles and showed signs of spalling, whilst the cracks on the harder R350HT sample were much smaller. In test 2 the point of initiation was found for each grade. Optical microscopy was also used to show the depth and direction of head check cracks to ensure the damage viewed from the head was RCF and not plastic flow or cyclic wear. This paper shows the necessity for considering the number of wet cycles applied during twin disc testing and demonstrates it is possible to run a high number of wet cycles which are more representative of real-world conditions when generating RCF on twin disc rigs.  

An innovative small-scale testing procedure to study damage in shoe-braked wheels

The diffusion of brake-shoe system has made it necessary to study brake–wheel–rail interactions. This study aims to elucidate this topic with an innovative small-scale test rig, the ‘4-contact machine’. A test procedure is designed in which an ER7 steel wheel is coupled with a R260 steel rail and two different brake-shoe materials (cast iron and sintered material). The results show that the 4-contact machine reproduces the effects of wheel–rail–brake shoe contact and damage similar to those observed on a railway wheel at the end of its life, highlighting marked differences in behaviour between the two brake materials.

Effect of thermal deformation treatment modes of steel vessels on curvature and hardness of piercing mill mandrel

An experimental hot screw rolling is carried out on a three-roller TPA 30-80 mill with incomplete piercing of round steel vessels under the conditions of a machine-building enterprise BВ AO "NPO "Pribor". It is shown that the existing temperature-deformation modes of vessels processing on a screw mill lead to an uneven distribution of temperature from 175 to 605 °C and hardness along the length of the mandrel made of R18 steel. Temperature fluctuations negatively affect on the hardness, which decreases from 57 to 38 HRC, and the durability of the piercing mandrel, due to the high heating of its nose up to 605 °C. It is established that after 100 vessels rolling the maximum deviations from the mandrel axis are about 0.72 mm and are observed closer to the toe of the mandrel at a distance of 10...20 mm. Loss of stability relative to the rolling axis leads to increased wear of the piercing mandrel, to nades and risks and, as a result, to defects in the geometric dimensions of produced steel vessels made of 50 steel. Experimentally established quantitative patterns of uneven distribution of temperature and hardness along the length of the mandrel can be used to develop technological solutions to improve the quality indicators of the deforming tool and steel vessels on the piercing TPA 30-80 mill.

Railway Rail Material Quality Tests

The article presents the obligatory qualitative tests of the material of railway rails, performed for the railway industry and having the status of qualifying tests, to which railway rails are subjected. They include tests of fracture mechanics (determination of the critical stress intensity factor KIC, determination of the fatigue crack development velocity da / dN), determination of stresses in rail feet and fatigue tests. The article presents the results of tests of standard-gauge rails type 60E1, rolled from R260 steel by selected European producers, and an analysis of the results was carried out based on the guidelines of the PN-EN 13674-1 + A1: 2017-07 standard. Keywords: quality tests of rails, KIC coefficient, propagation da/dN, stress

Electrochemical behavior of coatings AlN, MAlN on different substrates in 3 % NaCl solution

AlN, AlTiN, AlZrN, and AlCrN coatings obtained by pulsed magnetron sputtering on substrates made of R18, 40X and St3 steels are considered. The experimental technique and the obtained nanostructured and amorphous layers of coatings with different properties are described. The results of studies of the microstructure, defects, elemental composition and electrochemical parameters of the obtained coatings are shown. The analysis of the corrosion behavior by the characteristics of corrosion currents density, polarization resistances, coatings electrochemical activity in 3 % NaCl solution is presented. The effect of the coating microstructure and the substrate material on the corrosion resistance is shown.

Investigation of Tribological Properties of Rail and Wheel Steels

The wear resistance characteristics of AISI 51B60H and 30MnB5 steels with different carbon and boron contents were investigated. The analysis of the microstructure and hardness of steels was carried out. The specific wear rates in the conditions of dry and wet friction were calculated, and the friction coefficients were determined. The worn surfaces of rail samples were studied by electron microscopy. The possibility of using boron steels instead of R260 steel, which is used for manufacturing high-speed railways, was considered.

Metalografik İncelemelerle Ray Yüzeyindeki Soyulmaların Nedeninin Araştırılması

Railways are increasingly used for passenger and freight transportation worldwide. This increased traffic causes more quick and frequent formation of defects on train tracks. In this study, rail sets used in Bursa province, that had been reported to experience rapid wear and scaling, were examined. The rail sets were manufactured from R260 steel and the problem occurs more frequently on curves. For comparison, rail sets from straight lines were also examined. After visual examination, specimens from gauge and field corner regions were taken and prepared for metallographic examination. The microstructure of the specimens was examined under optical and scanning electron (SEM) microscopes. Moreover, Vickers micro-hardness tests were also performed. Micro-chemical analyses were performed using an energy dispersive X-ray spectroscopy (EDS) system attached to the SEM. For macro-chemical analysis, an optical emission spectrometer (OES) was used. The cross section of the rails was macro-etched for macro-examination. The results show that the microstructure of the rails is composed of 100% pearlite. On the other hand, the pearlitic structure degenerates at parts of the rail which are under loading. Due to severe plastic deformation, the pearlitic structure changes into a fiber-like structure composed of sub-micron ferrite and cementite. Those degenerated pearlitic regions have higher hardness due to strain hardening and cause crack initiation. Those cracks can then grow into inner sections of the rail easily due to the presence of non-metallic inclusions in the microstructure. Iron oxide particles were found in the vicinity of cracks; which indicate that cracks do not grow rapidly, they rather grow in time according to usage and atmospheric conditions. The examinations revealed that the wear, cracks and scaling problems were formed due to rolling contact fatigue (RCF). The presence of inclusions enhanced the growth of RCF-cracks and later cause “shelling”. In order to delay or prevent this problem, using higher strength rails at critical locations such as curves, controlling and rating the non-metallic inclusions in accordance with the international standards, checking the lubrication and maintenance strategies of rails and wheels, working on optimization of rail-wheel contact characteristics are recommended. The last recommendation involves developing a sustainable model by identifying technical limitations of the line and cruise depending on vehicle characteristics.

Structure and phase composition of high-speed steels

This work is devoted to the study of the structure and phase composition of high-speed steels R6M5, R9 and R18. High service properties of high-speed steel tools are achieved by heat treatment. Therefore, the sample blanks for the study were cut from cutting tools from R6M5, R9 and R18steels, which were subjected tothe usual standard heat treatment for these steels. Installed that the structure of high-speed steels R6M5, R9 and R18 in the initial state, i.e. after standard heat treatment, consists of martensite and special carbides. The carbide particles are evenly distributed in the matrix and are close to the correct spherical shape. Thus in the structure of steels R6M5 and R9 are carbides of type М6С, MC, and in the structure of steel R18 only carbides of the type М6С. EBSD analysis showed that M6C carbides are most optimally combined with the Fe3W3C cubic phase, and the MS type carbide corresponds to the VC phase. Electron microscopic analysis showed that in addition to M6C and MС carbides, high-speed steel contains small amounts of «cementite» type М3С carbides.

Comparison of microstructure changes induced in two pearlitic rail steels subjected to a full-scale wheel/rail contact rig test

This study focused on the comparison of the microstructure changes induced in two pearlitic rail steels subjected to full-scale wheel-rail contact rig tests (DB Systemtechnik, Germany): a conventional R260 steel grade and a heat-treated premium R370CrHT rail grade (also known as MHH400). The total loading of the wheel/rail contact rig test was computed to be 2.4 million gross tons but aimed at reproducing large deformations caused by loadings around 100 million gross tons into the materials. The description of the microstructure showed the ability of the rig to reproduce large loadings. Through the coupling of optical and SEM observations, EBSD measurements and hardness tests along the depths of the tested rails, it was shown that the plastic deformation was much more confined in R370CrHT than in R260. This thorough comparison of the microstructure changes will help the building of wear scenarios.

A rotary compression test for determining the critical value of the Cockcroft–Latham criterion for R260 steel

A method for determining the critical value of the Cockcroft–Latham damage criterion is presented using the example of R260 railway steel. The determinations were performed using a rotary compression test specially developed for that purpose. The main object of the proposed test was to provide the best possible representation of the state of stress generated by cross-wedge rolling. The rotary compression test was performed in two stages: in the first stage, experimental tests were conducted to establish the moment of cracking of the specimen, and in the second stage, numerical modeling was used to determine the critical value of the Cockcroft–Latham criterion for the experimentally established cracking moment. The critical value of the Cockcroft–Latham criterion was determined under hot forming conditions.

Использование тлеющего разряда для изменения дислокационной структуры быстрорежущей стали

The paper reports the investigation results of changes in a dislocation structure of high-speed steel R18 after processing in a glow discharge. As a result of processing a dislocation structure changes to a depth of 2-3mm from the surface obtained and it is rebuilt under its impact. At that the dislocation substructures are close to the observed ones at different kinds of plastic deformation.

On the Influence of Curvature of the Trajectories of Deformation of a Volume of the Material by Pressing on Its Plasticity Under the Conditions of Complex Loading

In the experimental investigations of the plasticity of cylindrical specimens of R9, R12, and R18 steels, subjected to simultaneous torsion with tension, it is discovered that, under the conditions of complex loading, the rate of accumulation of defects and their healing in the form of derivatives of the parameters of stressed state exerts a significant influence on the characteristics of plasticity. It is shown that, under these conditions, when the first and second derivatives of the dimensionless parameter of stressed state grow, the influence of curvature of the deformation paths of particles in the material on plasticity becomes more pronounced. The accumulated results enable us to select the phenomenological criteria of fracture, which give more reliable results of estimation of the applied plasticity resource in the technological processes of pressure treatment.

Plausible extension of Anand's model to metals exhibiting dynamic recrystallization and its experimental validation

Modeling and optimization of industrial hot-working operations by means of commercial finite element computer codes require robust constitutive descriptions, which could be easily implemented. Also, it is expected that such formulations are able to describe as accurate as possible the flow stress, work-hardening and work-softening rate of the material, as a function of microstructure and deformation conditions. The present communication describes the development of a novel constitutive description of metals which exhibit dynamic recrystallization during deformation under hot-working conditions. The formulation is founded on the extension of the model earlier developed by Anand and co-workers for the constitutive description of metals which exhibit dynamic recovery as the only dynamic restoration mechanism during hot deformation. The advanced constitutive formulation has been validated by conducting axisymmetric compression tests with samples of a R260 steel employed for the manufacture of rail tracks. The specimens were deformed in a wide range of temperatures and strain rates, both under constant and variable strain rate conditions. The latter involve either an increase or a decrease in the Zener-Hollomon parameter as plastic deformation is applied. The results obtained indicate that the proposed constitutive description is able to reproduce quite accurately the experimental flow stress data. It has also been shown that the correct computation of the recrystallization time and volume fraction recrystallized dynamically, by means of an appropriate differential or incremental formulation of the Avrami equation, constitutes an essential aspect of the model. Such an approach is particularly important for predicting correctly the changes in flow stress under variable strain rate conditions.

Determining the physical-chemical characteristics of the carbon-thermal reduction of scale of tungsten high-speed steels

We determined that scale of the high-speed steel R18 is composed of the phases of Fe 3 O 4 , Fe 2 O 3 , FeO, with the presence of alloying elements as the replacement atoms. The microstructure is disordered and non-uniform. In the examined area, in addition to Fe, we revealed the presence of, % by weight: W – 16.34, Cr – 2.68, V – 1.82, and others. The content of O was 15.32 %. It was established that the reduction of scale at 1,523 K proceeds with the formation of α-Fe and carbides Fe 3 W 3 C, (Fe, Cr) 7 C 3 , W 2 C, V 2 C, Fe 3 C, Fe 2 C. Manifestation of carbides of alloying elements decreased with an increase in the degree of reduction. The microstructure of reduction products is heterogeneous, containing particles with a different content of alloying elements and has a spongy structure. The conditions are provided for the absence of phases subject to sublimation. We conducted experimental-industrial tests of using the metallized scale while smelting high-speed steel with a degree of disposal of alloying elements at the level of 92‒94 %. Improvement of environmental safety was implemented by the replacement of reduction melting with the newest methods of powder metallurgy employing the solid-phase reduction.

Modeling of kinematic hardening at large biaxial deformations in pearlitic rail steel

Using an Axial-Torsion testing machine, pearlitic R260 steel specimens are twisted until fracture under different axial loads. A well established framework for finite elastoplasticity with kinematic hardening is used to model the deformation of the specimens. In particular, we evaluate the ability of different kinematic hardening laws to predict the observed biaxial load versus displacement response. It is found that the combination of Armstrong–Frederick dynamic recovery and Burlet–Cailletaud radial evanescence saturation is efficient even for the large strains achieved in this study. The results are less conclusive on the appropriateness of replacing the Armstrong–Frederick with an Ohno–Wang type of kinematic hardening law.

The Properties of the New Composite Antifriction Parts for Printing Equipment’s Friction Units

The paper summarizes the formation of new materials’ structure and properties after using a new hot isostatic-pressing technology. It shows the efficiency of the developed technology of production and the following heat treatment for the new high speed bearings, which is confirmed by the results of complex experimental and industrial tests. Such technology is able to ensure the high and stable level of the functional properties.The experimental results of the new composite bearing material’s properties in a comparison with the already known nickel composite have been presented. The article shows that the dense friction films were formed on the contact surfaces during tribological tests. All the friction surfaces are covered by the dense antiscoring films, the so-called as secondary structures. They consist of the chemical elements of bearing and counterface, and solid lubricant СаF2. During the friction process, the different chemical reactions took place between O2 of the air and elements of researched specimen and steel R18 counterface at high rotation speeds and loads. Such chemical processes result in formation of friction films, which protect contact pairs against intensive wear and stabilize a work of friction unit in printing machine.So, we have developed a new effective bearing materials, based on Ni alloy ЕP975–CaF2 system with high physical mechanical and tribotechnical properties performing well in more severe conditions than the already known sintered alloy. The new materials have an advantageous level of tribotechnical characteristics due to the tribofilms formed on the contact surfaces by dragging of calcium fluoride to cover the entire friction area.The full-scale industrial tests of ЕP975–CaF2 bearings showed increase in wear resistance by a factor up to 10 compared with the already known bearings in high speed printing machines’ friction units (in particular, Heidelberg Speedmaster SM-102-FPL and KBA Rapida-105) at a load up to 5 MPa and a rotation speed up to 6000 rpm.

Application Features of the Cutting Tool, Hardened by Laser Pulsed Radiation

The performed studies of the application features of the cutting tool, hardened by laser pulsed radiation are based on the comprehensive cutting process analysis. In this approach, the modeling results of the cutting process with hardened tool allowing to define the area of the effective use of laser treatment (LT). In particular, the increase in the tool life only for the certain values of the cut depth at the fixed irradiation energy was observed. The causes of the observed phenomena were determined based on durometric researches and studies of the microstructure in the contact zone. The measurements were performed for the cutters (steel R18) after turning structural steel 12Kh2N4A under various cutting modes. It was found that the processes of tool material softening, observed at turning with high feed values, limits the scope of cutting conditions by hardened tool. It is shown that LT leads to increased tool life, operating at the cutting conditions when the growth of tension thermodynamic in the cutting zone does not result in the development of softening processes. It is established that the area cutting modes are restricted to the values of cut depth not exceeding 1.5 mm (V=42.5 m/min, s=0.2 mm/rev) for the investigated pair of tool-workpiece (R18-12Kh2N4A). Tool life increases by more than 4 times compared to the durability of the non-irradiated tool provided the optimal combination of laser processing and hardened tool cutting modes is achieved.

Synthesis of transition metal borides layers under pulsed electron-beams treatment in a vacuum for surface hardening of instrumental steels

The saturation of the surface layers of metals and alloys with boron is conducted for increasing their surface hardness, wear resistance, etc. Multicomponent layers containing in its composition borides of refractory metals, as a rule, are formed by the methods of chemical- thermal processing in the interaction of boriding component with refractory one or by the method of saturation of refractory metal impurities or alloy with boron. In this work, we studied the features of vanadium and iron borides formation on the surface of instrumental steels U8A and R18 under the influence of intense electron beams in continuous and pulse modes.