Wheel Steel Research Articles

Microstructure and Failure Analysis of Flash Butt Welded HSLA 590CL Steel Joints in Wheel Rims

The aim of the present investigation was to evaluate the microstructures, mechanical properties and failure behavior of flash butt welded high strength low alloy 590CL steel joints. Acicular ferrite, Widmanstatten ferrite and granular bainite were observed in the weld. The micro-hardness values of the welded joints varied between 250 HV and 310 HV. The tensile strength of the welded joints met the strength standard of the wheel steel. The Charpy V-notch impact absorbing energy of the welded joints was higher than the base metal, and the impact fracture of the welded joints was composed of shearing and equiaxed dimples. The fracture mode of the wheel rim in the flaring and expanding process was brittle fracture and ductile fracture, respectively. A limited deviation was found in the terminal of the crack for the wheel in the flaring process. A transition from the weld to the Heat Affected Zone was observed for the wheel in the expanding process.

Influence of rare-earth modification on the formation of nonmetallic inclusions in high-carbon steel

The content of nonmetallic inclusions when rail and wheel steel is produced by intensive modern technology and modified by rare-earth metals is analyzed. The composition, morphology, dimensions, and distribution of the inclusions in the steel are determined in the case without oxidation by aluminum or treatment by silicocalcium and also with treatment of aluminum-bearing steel by both rare-earth metals and silicocalcium. Modification with rare-earth metals reduces the content of oxide inclusions in the rail and wheel steel. That improves the plasticity and impact strength of the products.

TERMS OF ENSURING QUALITY OF THE RAILWAY WHEELS BUILT UP BY WELDING

Purpose. The paper assumes to set the basic laws in determining the structure and physical-mechanical properties of wheel steels during arc welding technology and to develop the recommendations for reconstruction of railway wheel wear surfaces that will improve the reliability and safety of traffic in terms of increasing operating loads. Methodology. To achieve this purpose the paper studied 1) the influence of operating loads on structural changes and properties of metal wheels; 2) the impact of arc welding on structural and phase composition and properties of the metal heat-affected zone, its resistance to brittle and slow fracture; 3) the impact of welded metal on the formation of the stress state of the welds and their resistance to formation cracks; 4) wear resistance of built up metal during friction-slip of the «wheel-rail» pair. Findings. The most intense zone of the rolling profile of freight railway wheels during operation is a place of transition from rolling surface to the ridge. Therefore, the wheel building up by welding requires first of all the increased resistance to brittle fracture of metal in this area. It is established that welding in the metal of the wheel heat-affected zone cause formation of the hardened bainite-martensite structures. The minimum metal cooling rate, at which the martensite start forming is 8°C / s (in the range of 600…500°C) when the content of carbon in steel is 0.58% and 2°C/s at 0.65% of carbon. It is shown that to increase resistance to cracking it is necessary to limit the cooling rate to 16.0°C/s when the carbon content is C < 0.60% and to 8.0°C / s when C = 0.60…0.65%. Under these conditions, the metal has rather high ability to mikroplastic deformation without cracking. It was founded that to improve the critical stress intensity factor К1С at brittle fracture it is necessary to provide conditions when welding would result in the built up structure that does not contain upper bainite and the martensite share does not exceed the number of lower bainite (ratio of M/Bn < 1). It is proved that exposure of wheels within 3.5-4.5 hours at 100°C after welding, during their slow cooling improves resistance to brittle fracture of metal heat-affected zone by 1.8-2.3 times. This is due to the removal of diffusion hydrogen from the metal and reduction of the ІІ type stress in the lath volume of bainite and martensite by 1.5. Originality. The author has developed the idea of the structural-phase changes that occur in the metal of railway wheels during arc welding. The relation between the carbon content in steel, cooling rate during welding and resistance to cracking and brittle fracture was found. The authors determined the influence of after-welding wheel cooling conditions on the metal properties. Practical value. Technological recommendations for railway freight wheel building up by welding were developed. Their application will improve quality of the railway wheels built up by welding, reliability and safety of traffic in conditions of growing operating loads.

The Dynamic Tensile Behavior of Railway Wheel Steel at High Strain Rates

The dynamic tensile tests on D1 railway wheel steel at high strain rates were conducted using a split Hopkinson tensile bar (SHTB) apparatus, compared to quasi-static tests. Three different types of specimens, which were machined from three different positions (i.e., the rim, web and hub) of a railway wheel, were prepared and examined. The rim specimens were checked to have a higher yield stress and ultimate tensile strength than those web and hub specimens under both quasi-static and dynamic loadings, and the railway wheel steel was demonstrated to be strain rate dependent in dynamic tension. The dynamic tensile fracture surfaces of all the wheel steel specimens are cup-cone-shaped morphology on a macroscopic scale and with the quasi-ductile fracture features on the microscopic scale.

Improved measurement on probabilistic fatigue limits/strengths by test data from staircase test method

Appropriate approach, local true and/or virtual S–N relations deduced maximum likelihood approach (GMLA), is proposed for improving measurement on probabilistic fatigue limits by test data from staircase test method. The test data are distinguished as three cases, i.e. fully paired failure–survival specimens, partial paired plus individual survival specimen(s), and partial paired plus individual failure. Innovative way for deducing fatigue strength data is found by constructing physically paired local S-N relations for all test failure or survival specimens. Non-liner exponent law is introduced physically for describing the local relations under addressing the concaved character of fatigue S–N curves. The deduced data are determined by addressing physically the fatigue life for defining the test method to assure the strength data distributed orthogonally projection to the life section. Statistical parameters for fatigue limits and key element, the exponent to decide shape of the local relations/curves, are finally solved mathematically from a statistics by a maximum likelihood function for the deduced data from entire test data. Therefore, fatigue limits/strengths relative physics and math have been addressed by the present approach. Two existent approaches, Dixon–Mood approach (DMA) and Zhang–Kececioglu approach (ZKA), are reviewed together with the present approach by checking their effects of treating the test data of railway EA4T axle steel and wheel rim material of CL65 wheel steel. Applications verify that the present approach can give minimum evaluation on standard deviation and appropriate evaluation on average value for fatigue limits. While DMA and ZKA show a bigger evaluation on standard deviation and bias evaluation on average value. Basic case is that their deduced strengths do not address the concaved character and the defined fatigue life. They are not gotten from reasonable locations of local relations so to give the bias evaluation of average value. And they not distributed orthogonally to the life section so to give the bigger evaluation of standard deviations.

Numerical Analysis of Wheel Cornering Test Incorporating the Stamping Effects

A reliable but cost-effective method is proposed to improve the FE strength analysis of stamping parts. In the proposed method, a mapping theory of mesh field variables is introduced to eliminate the difference of mesh density in heterogeneous codes using the mesh area of weighting factor method, and a database modification approach is developed to solve the difference of data organization between DYNAFORM and ANSYS. Last, the method is applied in the simulation of car wheel cornering test, the stress states of wheel with and without regard to sheet metal forming effects are comparatively analyzed, and the reliability and validity of the proposed method is verified by the experiment. The further analysis reveals that the thickness change and the residual stress occur during the drawing process of wheel disc, and the stress state of wheel is in asymmetric multi-axial stress during wheel cornering test. It is also revealed that the effect of thickness change on the stress history of steel wheel is different with the effect of residual stress, and their superposition effects are nonlinear with the applied stresses.

Research on the stamping residual stress of steel wheel disc and its effect on the fatigue life of wheel

The steel wheel is an important safety component of a passenger car, which mainly consists of wheel disc and rim. The steel wheel disc is generally formed by the stamping process, and in this process the great residual stress is generated in the surface which may significantly affects the fatigue life of the wheel. In this paper, a method is proposed to introduce the stamping residual stress of steel wheel disc so as to predict the fatigue life of the wheel accurately. Firstly, the residual stress is obtained from the simulation of stamping process, and the experimental verification is conducted. Then the operating stress is simulated based on the cornering fatigue test. Finally, these two stresses are superposed to predict the fatigue life of the steel wheel. The results show that the predicted fatigue life using this method is closer to the experimental one than the fatigue life without considering the residual stress. The proposed method may provide an accurate and effective tool for predicting the fatigue life of the steel wheel in the cornering fatigue test.

Experimental Characterization of the Dynamic Compressive Properties of Railway Wheel Steel

The dynamic compressive mechanical behavior of railway wheel steel at room temperature was investigated experimentally for strain rates up to ~2300/s, by using a split Hopkinson pressure bar (SHPB) apparatus. Experimental results indicate that the wheel steel exhibits an obvious strain rate-dependence; both yield strength and flow stress enhance with the increase of strain rate. Based on experimental data, an empirical dynamic constitutive model was used to describe the strain rate effect of wheel steel. These research results could provide reliable and accurate material constitutive parameters for wheel-rail impact simulations, to guide the design and assessment of the safety of the wheel-rail system.

The use of fatigue tests in the manufacture of automotive steel wheels.

Production for the automotive industry must be particularly sensitive to the aspect of safety and reliability of manufactured components. One of such element is the rim, where durability is a feature which significantly affects the safety of transport. Customer complaints regarding this element are particularly painful for the manufacturer because it is almost always associated with the event of accident or near-accident. Authors propose original comprehensive method of quality control at selected stages of rims production: supply of materials, production and pre-shipment inspections. Tests by the proposed method are carried out on the originally designed inertial fatigue machine The machine allows bending fatigue tests in the frequency range of 0 to 50 Hz at controlled increments of vibration amplitude. The method has been positively verified in one of rims factory in Poland. Implementation resulted in an almost complete elimination of complaints resulting from manufacturing and material errors.

Quantitative comparison of measured crystallographic texture

A new approach for the determination of a quantitative measure to compare pole figures for different specimens is presented. The suggested approach is based on the Kolmogorov–Smirnov test. A new quantitative similarity measure between the textures of different specimens is suggested. This measure is verified by means of numerical models for both cubic and hexagonal crystalline symmetry, and it is applied to real experimental data for railway wheel steel. A comparison between the existing RP value and the introduced KSP value is presented to illustrate the specific character of the latter.

Effects of rail materials and axle loads on the wear behavior of wheel/rail steels

Four kinds of rail steels were tested to investigate the wear behaviors of wheel–rail materials under three kinds of axle loads. Results indicate that the increase in axle load not only significantly enlarges the wear loss but also enlarges the depth and the length of the fatigue cracks. However, with the decreases in the hardness ratios, some ripples are exhibited on the surface, and the wear surfaces become much rougher; the subsurface analyses deliver the presence of extremely rough surface, and the deformation depths are irregular. The relationship between the total wear loss of the wheel/rail system and the hardness ratio indicates that the hardness ratio of wheel/rail steels has slight impact on the total wear loss at a low axle load; however, the decrease in the hardness ratio enlarges the total wear loss significantly at a high axle load. In summary, a quenched rail should be chosen for the heavy-haul railway, and the hardness of the wheel steel should be raised to a degree close to the rail. However, a hot rolled rail is much suitable for the high-speed railway, and the wheel hardness should be smaller than the rail.

Residual stresses generated by repeated local heating events – Modelling of possible mechanisms for crack initiation

The hypothesis of thermal damage mechanisms by short-term local friction heating of rail or wheel steels leading to initiation of cracks, specifically squats (in some works called studs) in rails and crack clusters in wheels has given the inspiration for this study. A Finite Element (FE) model incorporating phase transformation from near pearlitic steel to austenite, and then to martensite was developed to examine developing strength and stress fields. Thermal strains on heating, cooling and phase transformations are naturally included, and the FE model also incorporates shrinkage due to tempering of the martensite during subsequent heat pulses. The material behaviour implemented in the model has been rationalised from experiments done on near pearlitic wheel steels, however the qualitative results are deemed applicable also for local thermal damage on pearlitic rail steels. The material is currently modelled as isotropic, with properties varying with phase, temperature and tempering state. The main contributions of this work is the modelling framework developed, specifically the careful modelling of martensite tempering combined with phase transformation. Different thermal sequences are examined to demonstrate the model´s capability. The computed strength and stress fields are used to discuss possible mechanisms of crack initiation.

Improving rail wear and RCF performance using laser cladding

Laser cladding has been considered as a method for improving the wear and RCF performance of standard grade rail. This paper presents results of small scale tests carried out to assess the wear and RCF performance of rail which had been laser clad. Using the laser cladding process premium metals can be deposited on to the working surface of standard rail with the aim of enhancing the wear and RCF life of the rail. Various laser clad samples were tested using a twin-disc method. The candidate metals were clad on to standard R260 grade rail discs and were tested against a disc of standard wheel material. During the tests, wear rates and RCF initiation were monitored and compared to those of a standard rail disc. Six candidate cladding materials were chosen for this test: A multi-phase Manganese Steel Variant (MMV), Martensitic Stainless Steel (MSS), TWIP Steel, NiCrBSi, Stellite 12 and Stellite 6. The MSS, Stellite 6, and Stellite 12 samples showed reduced wear rates relative to the standard R260 Grade rail discs, and also produced a reduction in wheel steel wear. The RCF initiation resistance of all of the candidate materials was superior compared to the R260 Grade material.

Effect of elevated temperature on shelling property of railway wheel steel

A type of tread damage called thermal mechanical shelling (TMS) is one of the main causes for heavy haul wheel removals in North America. Wheels are considered to have a shorter service life for TMS than other causes of removals as rolling contact fatigue (RCF) strength decreases because of elevated temperature from tread brakes. In this study, to evaluate the relationship between RCF life and elevated temperature, RCF tests and FE analyses were conducted. Twin disc type RCF tests with induction heating were applied to evaluate RCF life under thermal cycling simulating tread brakes. Test results show that RCF life was shorter with the higher maximum temperature and the longer holding time at elevated temperature. Softening of the material because of microstructure change was observed for the test specimens tested at the maximum 500°C. Then, crack tip opening behaviour was evaluated by elasto-plastic FE analysis. FE analysis results showed that crack tip opening displacement (CTOD) was larger with the higher temperature and the longer holding time at elevated temperature. Moreover, CTOD increased with a decrease of the material strength. These results indicate that wheel life of TMS decreases by acceleration of fatigue crack propagation with elevated temperature.

Sensitivity analysis of the wheel–rail normal contact on the basis of continuous factors

The exact characterization of the wheel–rail normal contact situations is essential for its wear, fatigue, and guidance analysis. To simulate this contact, numerous input parameters are required. Many of them have to be estimated. The aim of this sensitivity analysis was to investigate the direct effects and interactions of the input parameters on the contact pressure distribution of a freight wagon wheel on a straight track. For this purpose, a finite element model was parametrized in such a way that all the parameters were continuous. This research demonstrates that the output parameters of the wheel–rail contact simulations have a broad deviation and the input variable with the most influence on the contact form and position is the lateral displacement of the wheelset. Nevertheless, the profile shape of the wheel and rail, the wheel radius, and the relative wheel–rail inclination are important input parameters as well, and also need to be considered for exact simulations of the wheel–rail contact. On the other hand, the deviation of material parameters of wheel and rail steel can be neglected.

Temperature-dependent evolution of the cyclic yield stress of railway wheel steels

The evolution of the cyclic yield stress for a railway wheel steel (UIC ER7T) during cyclic plastic straining has been characterized at different temperatures from −60 to 600°C. Different constant strain amplitude levels were examined and for temperatures above 200°C, hold periods were included to study stress relaxation during constant compressive strain. The results are of use in predicting material deformation and damage. This is demonstrated by the application to improve a criterion for surface initiated rolling contact fatigue damage.

Effect of different strengthening methods on rolling/sliding wear of ferrite–pearlite steel

The object of this paper is to study the influence of different strengthening methods on wear resistance of ferrite–pearlite steel. Rolling/sliding wear tests were conducted for five railway wheel steels which were hardened by carbon addition, solid solution strengthening and precipitation strengthening, respectively. Wear rate, subsurface plastic deformation and strain-hardening of tested steels were examined. The test results show that wear resistance of ferrite–pearlite steel is improved by both carbon addition and solid solution strengthening, whereas it is deteriorated by precipitation strengthening. Wear resistance of ferrite–pearlite steel depends on the worn surface hardness that is influenced by bulk hardness and strain-hardening. Strengthening methods increase the bulk hardness to different extents, where the highest and lowest bulk hardness increments are obtained by the solid solution strengthening and precipitation strengthening, respectively. The strain-hardening is promoted by carbon addition, while it is reduced by solid solution strengthening and precipitation strengthening where precipitation strengthening makes a greater reduction in strain-hardening. Strain hardening of ferrite–pearlite steel is reduced by a high content of proeutectoid ferrite with a low ductility, which is caused by solid solution strengthening and precipitation strengthening.

Design and validation of a slender guideway for Maglev vehicle by simulation and experiment

ABSTRACTNormally, Maglev (magnetic levitation) vehicles run on elevated guideways. The elevated guideway must satisfy various load conditions of the vehicle, and has to be designed to ensure ride quality, while ensuring that the levitation stability of the vehicle is not affected by the deflection of the guideway. However, because the elevated guideways of Maglev vehicles in South Korea and other countries fabricated so far have been based on over-conservative design criteria, the size of the structures has increased. Further, from the cost perspective, they are unfavourable when compared with other light rail transits such as monorail, rubber wheel, and steel wheel automatic guided transit. Therefore, a slender guideway that does have an adverse effect on the levitation stability of the vehicle is required through optimisation of design criteria. In this study, to predict the effect of various design parameters of the guideway on the dynamic behaviour of the vehicle, simulations were carried out using a dynamics model similar to the actual vehicle and guideway, and a limiting value of deflection ratio of the slender guideway to ensure levitation control is proposed. A guideway that meets the requirement as per the proposed limit for deflection ratio was designed and fabricated, and through a driving test of the vehicle, the validity of the slender guideway was verified. From the results, it was confirmed that although some increase in airgap and cabin acceleration was observed with the proposed slender guideway when compared with the conventional guideway, there was no notable adverse effect on the levitation stability and ride quality of the vehicle. Therefore, it can be inferred that the results of this study will become the basis for establishing design criteria for slender guideways of Maglev vehicles in future.

FUNDAMENTAL INVESTIGATIONS AS THE BASIS OF CREATION OF NEW MATERIALS AND TECHNOLOGIES IN METALLURGY. PART 1

The article provides an overview developed by the scientists of the Russian Academy of Sciences, on the basis of fundamental research of new metallic and ceramic materials and technologies, including new nitrogen-containing high-strength corrosion-resistant steels, heat-resistant lightweight alloys and composites based on intermetallides; modifi ers for wheel steels, complex V-, Cr-, Ni-containing ferroalloys; anti-corrosion protective coatings based on ultrathin Zn powders; catalytic converters of exhaust gases of vehicles; magnetically hard materials with high thermal and temporal stability and mechanical characteristics; nanostructural stents for endovascular operations in a sparing mode; corrosion – and wear-resistant coatings and method of their plasma spraying. The methods were developed for: longitudinal rolling with macroshift deformation (to improve the properties of sheet rolling); recycling of oiled scale; control of the lining deterioration at any point in the blast-furnace hearth. The monitoring methods for the integrity of rail steels by inclusions were carried out. The paper includes the developed processes and technologies of: special electrometallurgy to produce the steel for the power industry; synthesis of the massive single-crystalline samples of nitrides of transition metals, nanopowders of W, Pt, Ti and Ti carbides and nitrides; processing of Yarega fi eld leucoxene concentrates; production of titanium implants with porous coatings; metallic fraction and powders of ferrous and non-ferrous metals; ultrafi ne Zn powders; recycling of metallurgical wastes with the extraction of Zn, Sb, Sn, Fe; obtaining agglomerated nanocrystalline powders of Ta for capacitors; processing of sulphide Mo-containing raw materials and obtaining of rare earth metals, MoO3 , CaMoO4 and utilization of sulfur dioxide. The authors described the created injection installations and their application technologies; high-performance system for plasma spraying of metals, including paint coatings, plastics, cardboard. There were obtained the data on thermodynamic functions of the reaction of dissolution of oxygen in Fe-based molts and of the interaction reactions of dissolved in these molts elements (Cr, Mn, Nb, V, Si, B, C, Ti, Zr, Al) with oxygen.

Wear behaviour of bainitic rail and wheel steels

The paper presents a short review on the past research and recent trends in the development of rail and wheel steels using bainitic morphology from the angle of mechanical and wear performances. The enhancement in mechanical properties as well wear resistance of the bainitic rail and wheel steels is very promising. In addition, the mechanical behaviour of a bainitic rail steel and a wheel steel along with their linearly reciprocating dry sliding wear characteristics in comparison to the existing pearlitic rail and ferritic–pearlitic wheel steels used in Indian Railways is discussed. The steels were subjected to austempering heat treatment at different temperatures and durations in the bainitic region as determined from the TTT diagrams of the respective steels. Bainitic steels show better mechanical properties and wear resistance due to the typical morphology of bainitic microstructural.