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Microbreaks near nonmetallic inclusions after plastic deformation; x600 Рис. 1. Микроразрушения вблизи неметаллических включений после пластической деформации; x600
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It is well known that formation of defects of many types during railway wheels service somehow or other is connected to nonmetallic inclusions in wheel steel. Microbreakes connected with nonmetallic inclusions have different origin. The first one is “deformational”, the second is “thermal” and the third is “hydrogenous”. The objective of this work...
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Thermal load of the block-braked solid wheel railway vehicles is dominant on the other types of loads. This load, which is mainly consequence of long-term braking on downgrades for maintaining the defined constant speed purpose, is the main cause of occurrence of cracks on treads of wheel and finally fractures of wheel. The paper gives the analysis...
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... The experience shows that nonmetallic inclusions often play a key role in the initiation of the processes that cause the fracture of parts and structures [1][2][3][4][5]. Nonmetallic inclusions are known to be stress and strain concentrators [6][7][8][9][10]. A lot of works showed that the difference in the physical, mechanical, and chemical properties of inclusions and the steel matrix gives rise to stresses at their interface. ...
... Apparently, the stress concentrations in inclusions in constrained strain zones do not have time to relax because there are no conditions for efficient energy dissipation in both the steel matrix and the inclusion. Therefore, cracking grows into the inclusion, into the steel matrix, and along the inclusion/matrix interfaces [7,9,10]. Microplastic shear in inclusions during deformation can partially redistribute the stress concentrator field. ...
... Achievement maximum permissible concentration defects of crystalline structure in metal of wheels determine the conditions for the formation and growth of fracture centres [18]. In addition, dispersion and morphology of phase components that determine the level of strength properties, reliability operation of the wheels largely depends on the sensitivity of metal to stress concentrators from micro-and macro-mechanical damage rolling surface, cracks various origin [6], etc. Of the many characteristics, certain propagation was obtained by the stress intensity factor at beginning of interval unstable crack growth (K1c) [15]. ...
... The practically absent effect of carbon content in steel can be considered as evidence of a certain sensitivity, this characteristic to concentration of harmful impurities at austenite grain boundaries. In general, the stress intensity factor is estimated by the dependence [6,15]: ...
From an analysis of the dependence complex of carbon steel properties on structural parameters, it was found that for an isostructural state, the influence of austenite grain size on impact strength exceeds the dependence on carbon content. As a result of explaining correlation relationships between individual mechanical characteristics, to evaluate critical stress intensity factor, a relationship is proposed based on the use of impact strength. The proportionality coefficient in proposed dependence is determined by ratio of elongation to narrowing at tensile test.
... Compared to the mechanism influence of a non-deformable non-metallic inclusion considered in detail on the formation system of internal stresses in carbon steel [14], the compact arrangement dispersed particles can have a qualitatively different effect. This was confirmed by the results of a study in which a site with a local arrangement of dispersed carbide particles in ferrite during plastic deformation was able to behave as a whole [15]. ...
The systematization results of microstructure studies of carbon steel has made it possible to explain the mechanism of formation of certain damages to the rolling surface of railway wheels during operation. The evaluation ability of metal to strain hardening was used to explain the nature of the influence compactly located non-deformable dispersed particles on the strength properties steel during cold plastic deformation. In the process of the interaction of a railway wheel with a rail, successively occurring heterogeneities in the distribution of the plastic flow metal are one of the main reasons for the formation of defects on the rolling surface of the wheel.
... thermal hardening [3,4], is impossible without explaining the mechanism behind the formation of damage to the metal on the rolling surface [5]. From the interaction with the rail, the resulting nonuniform distribution of plastic deformation of the metal over the rolling surface of the wheel [5,6] receives an additional gain from the presence of non-metallic inclusions [7,8]. ...
... The assessment of the level of internal stresses that are formed in the metal close to the particles [9] indicates the total effect not only of size, shape and distribution but also the nature of the origin of non-metallic inclusions. Indeed, as shown in [7,10], differences in the type of crystal lattice, the ability to thermally expand, etc. metal matrix and particles of non-metallic inclusions, leads not only to a change in the magnitude of residual stresses but their sign as well [11,12,13]. ...
... One evidence of this is the result of the study of causes of reduction in cyclic crack resistance of high-strength wheels during operation [19]. The observed effect of non-metallic inclusion particles is in fact much more complicated if one considers the effects of a thermal nature [2,5,7,20]. ...
On a fragment of the rim of a railway wheel removed from service, the volume of the metal with non-metallic inclusions located near the tread surface was investigated. The use of the microhardness measurement technique made it possible to establish the nature of strain hardening of carbon steel near non-metallic inclusions. It showed that with a normal orientation of the plastic flow relative to the inclusion surface, the metal volumes undergo hardening. In proportion to the appearance of a fraction of the tangential component of the deformation near the nonmetallic inclusion, a decrease in the degree of hardening of the metal was observed.
... On the basis of analysis reasons of premature withdrawal of railway wheels it is discovered from exploitation, that except for the unrationed amount of nonmetallic inclutions of different morphology and nature of origin at arrangement near-by with railway wheels tread [3], substantial value, arising up acquire additional moving of wheelpair in relation to the frame of light cart [4]. The indicated displacements of wheelpair during exploitation are reason of origin shear component of deformation to the constituent of metal on a contact surface wheelrail. ...
... As a result of quenching from the normal temperatures of heating the structure of martensite was formed with hardness 65 HRC, and after subsequent tempering at temperatures 450 − 470°C is a structure of the tempered martensite with hardness 39 HRC. Heat higher than temperature 3 Ac , the required self-control for homogenization of аustenite and cooling with a furnace allowed to get lamellar pearlitic structure in steel with hardness 13 HRC. ...
... The analysis of known experimental of facts [1,3,7] bear witness that to the formation of extrusions and intrusions (Fig. 1) on the railway wheels tread which become the turn into of superficial damages in future, local changes are preceded in the area of contact wheel-rail. Taking into account high-rate of heating at the local slipping, the temperature of beginning of phase transformations in steel of wheel can be arrived in thin of layer near railway wheels tread. ...
Causes of reasons and explanation of mechanism forming damages
of railway wheels tread were investigated. At slipping on contact surfaces wheelrail a between by simultaneous development of processes of work-hardening and softening metal determines the terms of origin damages of railway wheels tread were fixed.
... 2. So for the wheel that has the form shown inFig. 2 consideration the given facts it is possible to suppose that the increase of curvature in transition areas between the elements of the wheel reduces the equivalent stresses that occur in it during the operation. The magnitude of railway wheel skidding from interaction in the places of contact with the rail connected with durable properties significantly, as metal on the rolling surface and on the working surface of the rail [20] . On the basis of a sufficiently large number of studies on modeling the process of wear, as well as field testing it is determined that the minimal values of the railway wheels' wear and rails are achieved by the conditions of approximately the same values of their hardness [11, 20]. ...
... The magnitude of railway wheel skidding from interaction in the places of contact with the rail connected with durable properties significantly, as metal on the rolling surface and on the working surface of the rail [20] . On the basis of a sufficiently large number of studies on modeling the process of wear, as well as field testing it is determined that the minimal values of the railway wheels' wear and rails are achieved by the conditions of approximately the same values of their hardness [11, 20]. On the other hand it is known the same level of durable properties in steels can be achieved by various structural condition – after thermal hardening treatment –improvement, when the carbide phase has globular form or after accelerated cooling (at speeds below the critical value) laminar form [19]. ...
Purpose. The dependence analysis of structural changes in the metal of railway wheels and tires from indicated influences in operation, for the further development of strategy of service reliability growth. Methodology. Test materials are the details selected from railway wheels which were taken out of operation beforehand because of various damages. Micro-structural researches were made with the use of light microscope Epiquant and electron microscope. The sizing of structural elements was done by using the methods of quantitative metallography. Findings. Over the past few decades the rapid development of industry was supported by the steady growth of intensity of using railway transport. In this case simultaneous increase of load at wheel set axle, with the increase of speed was accompanied by natural increase of the amount of cases of premature wheels and tires’ withdrawing out of operation. Railway wheel, except the formation of metal layer at rolling surface with the high defects concentration of crystal structure and first of all dislocations, falls under thermal influence from interaction with break blocks. The nature of joint influence (cold deformation and heating) on the metal rim of a wheel is conditioned by the appearance of sufficiently high gradients of structural changes that can be considered as the influence on the level of internal residual stresses. In case of the rise of volume part of carbide phase at a constant ferrite grain size, it is achieved only by the increasing of dislocation nucleation sources without changing the number of annihilation positions. In this case the accumulation of dislocations at the initial stages of plastic deformation (in metal volume in front of delta arm crack) will lead to the formation of cementite globes around certain interlocked dislocation density. In contrast the sharp increase of deformation hardening carbon steel parameters is observed. Originality. During the braking of locomotive the speed rise of metal heating at rolling surface is provided with the increase of temperatures that is enough for the beginning of phase transformations. Under the further cooling there is the formation of a number of structures formed from sliding to diffusive mechanisms. As a result the chosen areas become the centers of future metal deformations on wheels’ rolling surface and tires. Practical value. Based on the study of patterns of damages’ formation in railway wheels and tires from the peculiarities of internal metal structure and the working conditions «Classifier of defects» was developed аnd «Technical tips for determination of causes of cracks in solid-rolled railway wheels and destruction in general», which have been implemented on Ukrzaliznytsia.
... Fatigue degradation is a type of damage that occurs over time and causes significant losses. Examples of such damage are standard failures in the railway [1, 2], aviation [3] and power generation industries [4]. Fatigue occurs and develops gradually due to cyclic service load that causes stress. ...
The experimental material comprised semi-finished, high grade, medium-carbon structural steel for the production of mining chains. Steel was melted in a 140 ton electric furnace and desulfurized (E). In the second analyzed variant, steel was additionally refined with argon (EA). In the third variant, steel was melted in a 100 ton converter. Secondary treatment involved vacuum circulation degassing. Specimens with a diameter of 10 mm were prepared by hardening and tempering at 200, 300, 400, 500 and 600°C. Fatigue tests were performed with the use of a rotary bending machine at a frequency of 6000 cpm. The results were processed and presented in graphic form.
The operational ability of a rolling bearing selected for a specific application is assessed based on service life. The basic formula
for bearing rating life was established more than 70 years ago by A. Palmgren. The first standard presenting a basic mathematical model for
rating life calculation was published in 1962 (ISO/R281). The content of this standard has been revised and the next version was published
in 1977 (ISO 281-1). The novelty was the introduction of adjustment factors for reliability other than 90%. This standard was replaced by
the ISO 281 standard in 1990, which introduced additional adjustment factors for special bearing properties and operating conditions. The
latest version of the ISO 281 standard was published in 2007. This standard provides a procedure for calculating the modified service life by
taking into account the additional impacts of lubrication condition, lubricant contamination and limit fatigue load. Furthermore, the
document ISO/TS 16281 was published in 2008 introducing the influence of bearing internal clearance and misalignment in the rating life
calculation. An overview of the development of a standardized formula for bearing rating life is given in this paper, on the example of deep
groove ball bearing under radial operational loading.