Effect of deformation parameters on the austenite dynamic recrystallization behavior of a eutectoid pearlite rail steel

Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.

Corrosion Test of the Steel Plate in a WJ-8 Fastener for High Speed Rail

It was found that the steel plate in the composite plate in the WJ-8 fastener used in high speed rail is rusty. The objective of this study is to test the zinc coating of the steel plate. A literature review was conducted to identify the zinc coating techniques, and the companies that can provide different coating service was identified. A salt fog chamber was built that was in compliance with the ANSI B117 code, and the steel plates that were coated by the identified companies were tested using the salt fog chamber. The results indicated that the coating technique that had the best performance in preventing corrosion was the Greenkote plates with passivation. The galvanized option had the roughest coating layer, and it was the most reactive in the salt water solution. This makes it non-ideal for the dynamic rail environment because the increased friction of the plate could damage the supports, especially during extreme temperatures that would cause the rail to expand or contract. Greenkote with Phosphate and ArmorGalv also provided increased corrosion prevention with a smooth, strong finish, but it had more rust on the surface area than the Greenkote with ELU passivation. The ArmorGalv sample had more rust on the surface area than the Greenkote samples. This may not be a weakness in the ArmorGalv process;rather, it likely was the result of this particular sample not having the added protection of a colored coating.

Effect of Rare Earths on Properties of BNbRE Rail Steel

The development and properties of BNbRE rail steel and the effect of RE on rail steel were studied. The results show that the properties of rail steel ( σ b≥980 MPa, δ 5≥8%) can be improved by adding RE and niobium and adjusting the content of C, Si and Mn in steel. At the same time, the abrasion resistance, contact fatigue and fatigue property of BNbRE rail steel are excellent. It also shows that RE in rail steel has the functions of purifying steel, modifying inclusion and micro alloy action effect. The improved steel making process enhances the quality of molten steel. Although the content of RE is low, excellent properties of BNbRE rail steel are achieved.

THE STRAIN CYCLIC CHARACTERISTICS AND RATCHETING OF U71Mn RAIL STEEL UNDER UNIAXIAL LOADING

An experimental study was carried out of the cyclic behavior of U71Mn rail steel subjected to uniaxial strain and stress. The effects of cyclic struin amplitude, mean struin,strain loading rate and their histories on the strain cyclic characteristics were studied.Under the asymmetrical stress cycling, the effects of stress amplitude, mean stress,stress loading rate and their histories on the ratcheting were analyzed. The interaction between strain cycling and stress cycling was also discussed. It is shown that either the cyclic characteristics under strain cycling or the ratcheting under asymmetrical stress cycling depends not only on the cumnt loading state, but also on the previous loading history. Some significant results are obtained.

Internal Friction in Rail Waist of BNb and BNbRE Steels

The internal frictions of the specimens in the waist centre of the commercial BNb and BNbRE rails, which were left in air for two years, were measured. It is found that there is an obvious Snoek-Kê-Koester （SKK） peak in both steels, and still exists a measurable deformation-enhanced Shock peak（DESP） in the specimens of the BNbRE steel. The internal frictions in the deformed specimens of the both steel rails were also measured. Unlike the case of the tread specimens showing a decrease of SKK damping due to deformation, the SKK damping of the rail waist specimens increases after deformation; and the specimens containing rare earth（RE） show more noticeable damping increase than those without RE. The results of the internal friction measured during ascending and descending temperature under 700℃ show that there is a high temperature damping which can be completely disappeared during descending temperature for both steels.

Effect of Rare Earth (Niobium) on Costed and Hot-Rolled Microstructure and Properties of Heavy Rail Steels

A compared investigation was made on the microstructure and mechanical properties of continuous casting square blanks of BNbRE and U71Mn heavy rail steels having eutectoid composition. The variation of solidified structure of the square blanks was demonstrated by measuring hardness. The observation to the structure and inclusions in the head, waist and base of the hot-rolled rails of the test steels were carried out with optical microscope and SEM. It is found that the casting blanks of both tested steels compose of three areas with constant hardness and three hardness varying areas, and there is considerable P-eutectic structure in the blank of the U71Mn steel. The distribution of the inclusions in the UT1Mn steel rail is mainly oxides in both rail head and rail base, and is mainly MnS in the waist of the rail. There has strong effect of the addition of rare earth elements on them. The discussion on these results was made.

Application of Al-free deoxidizer in rail steel manufacture

Because there are a lot of influences of alumina inclusions on the performance of rail steel,it is reasonable to adopt the deoxidization method with Al-free deoxidizer. According to the characteristics of Al-free deoxidization process,the control of aluminum content,the deoxidization with ladle furnace（LF） slag,the deoxidization process under vacuum by carbon,and the inclusions modification technology by calcium treatment were studied. All of them were applied to practical production. The results indicate that the adoption of Al-free deoxidization process leads to the total oxygen content in the steel below 20 ppm,which meets the requirement of clean rail steel.

New pearlitic steels for 21st century rail applications

To improve competitiveness,the nation's railroads have increased the axle loads and speed of the trains.This has led to a rapid decrease in the life expectancy of premium rails through accelerated wear,rolling contact fatigue and fracture.To counter this effect,the railroads need rails that exhibit better performance in these areas.A research program has been initiated to study the microstructural aspects of near-eutectoid steels that would improve these properties.The first phase of the work was to carefully characterize the existing commercial rail steels in terms of pearlite interlamellar spacing,steel cleanliness and the presence of pro-eutectoid cementite on prior-austenite boundaries.These characterizations were then correlated with both mechanical properties and overall rail performance.The second phase of the program was to develop a better microstructure through control of composition,thermomechanical processing and cooling path.This was achieved through the use of laboratory-melted heats of experimental near-eutectoid compositions and a computer controlled MTS compression machine modified for axisymmetric compression testing and subsequent controlled cooling.The optimum processing route for these new steels has been determined,and pilot-scale heats have been melted,hot rolled and cooled using the information gained from the MTS investigations.The mechanical properties of these new steels have been determined and the rail performance tests are being conducted using laboratory-scale evaluation.Ultimately,these new rail steels will be tested under commercial conditions on the TTCI test track in Pueblo,Colorado.This paper will report on the alloy and processing design and resulting properties of the steels developed in this research program.Guidelines for future rail compositions and processing to obtain improved properties and performance will be presented.

Life Cycle Assessment of CCA-Treated Wood Highway Guard Rail Posts in the US with Comparisons to Galvanized Steel Guard Rail Posts

A cradle-to-grave life cycle assessment is done to identify the environmental impacts of chromated copper arsenate (CCA)-treated timber used for highway guard rail posts, to understand the processes that contribute to the total impacts, and to determine how the impacts compare to the primary alternative product, galvanized steel posts. Guard rail posts are the supporting structures for highway guard rails. Transportation engineers, as well as public and regulatory interests, have increasing need to understand the environmental implications of guard rail post selection, in addition to factors such as costs and service performance. This study uses a life cycle inventory (LCI) to catalogue the input and output data from guard rail post manufacture, service life, and disposition, and a life cycle impact assessment (LCIA) to assess anthropogenic and net greenhouse gas (GHG), acidification, smog, ecotoxicity, and eutrophication potentially resulting from life cycle air emissions. Other indicators of interest also are tracked, such as fossil fuel and water use. Comparisons of guard rail post products are made at a functional unit of one post per year of service. This life cycle assessment (LCA) finds that the manufacture, use, and disposition of CCA-treated wood guard rails offers lower fossil fuel use and lower anthropogenic and net GHG emissions, acidification, smog potential, and ecotoxicity environmental impacts than impact indicator values for galvanized steel posts. Water use and eutrophication impact indicator values for CCA-treated guard rail posts are greater than impact indicator values for galvanized steel guard rail posts.

Effect of Preheating Temperature on the Mechanical and Fracture Properties of Welded Pearlitic Rail Steels

The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200℃, 300℃, 350℃ and 400℃?before gas metal arc filling to simulate defects repair. Another sample, welded at room temperature (RT) with no preheat, was studied in comparison. The parent rail steel has ultimate strength, yield strength and strain to failure of 1146 MPa, 717 MPa and 9.3%, respectively. Optimum values of these properties for the welded rail steels were found to be 1023 MPa, 655 MPa and 4.7%, respectively, for the 200℃ preheat temperature. On this basis, the optimum weld efficiency was found to be 89.2%. The average apparent fracture toughness KI for the parent rail was 127 MPa.m0.5, while that for the optimum welded joint (200℃ preheat) was 116.5 MPa.m0.5. In addition, the average hardness values of the weld, fusion zone, and heat affected zone (HAZ) were 313.5, 332 and 313.6 HB, respectively, while that for parent rail steel was about 360 HB. Dominance of bainite and acicular ferrite phase in the weld microstructure was observed at 200℃ preheat.

VARIATION OF HYDROGEN CONTENT IN MOLTEN HEAVY RAIL STEEL AT PANZHIHUA IRON AND STEEL COMPANY

At panzhihua Iron and Steel Company,hydrogen content in molten heavy rail steel is rather low during smelting in the oxygen top-blown converter,and sloightly increases in tapping and pouring.Average H content varies from 2.0(dry season)to 2.4 ppm(rainy season)at smelt- ing end;2.8 ppm in ladle;and 2.1 ppm(dry season)to 2.3 ppm(rainy season)in mould, which is on a level with RH vacuum circle.The low hydrogen content in molten steel,which is due to both the very dry climate in Panzhiihua region and the LD smelting process,is the main reason why there is little flake in the heavy rail produced by Panzhihua Iron and Steel Com- pany.

EFFECT OF REMOVING HYDROGEN FROM HEAVY RAIL STEEL BLOOMS BY STACK COOLING IN PANZHIHUA IRON AND STEEL COMPANY

The determination of dffusible hydrogen in U71Mn heavy rail steel,and hydrogen diffusivity as well as the hydrogen distribution in the cross section of blooms with stack cooling were stu- died.The results showed that,most of the hydrogen in blooms of heavv rail steel is diffusible, the hydrogen diffusivity in U71Mn rail steel blooms at room temperature is(0.85—1.02)× 10^(-6)cm^2/s,after stack cooling,the hydrogen content in bloom will decrease greatly which is helpful to form the flake-free phenomenon in the heavy rail produced by Panzhihua Iron and Steel Company.

MICROSTRUCTURE AND FATIGUE PROPERTIES OF RAIL STEEL

The subcritical propagation of fatigue cracks and the microstructure of rail steel with relation to stress ratio have been studied.The effect of mierostrueture of the rail steel on their fatigue lives has been discussed.

Influence of Rare Earths on Contact Fatigue of Rail Steels

Rail/wheel contact fatigue of NbRE rail, Nb rail and U74 rail was investigated using contact fatigue tester. Microstructure and morphology as well as microhardness in the fatigue profiles were analyzed by scanning electron microscope and Vickers hardness respectively. The experimental results show that rare earths are able to delay the initiation and the propagation of fatigue cracks and postpone the surface shelling or spalling, even more, to reduce the crack propagation angle and the crack propagation depth in steady stab as well as the plastic deformation area, and to improve work-hardening of the rail steel.

EFFECTS OF La ON STRUCTURE AND PROPERTIES OF HEAVY RAIL STEEL

The mechanisms of La in heavy rail steel were studied by means of experimental measurements, microstructure observation and theoretical analysis in the present work. For heavy rail steel, the state and the content of La were measured, and the mechanisms and the effects of La on sulfide inclusions, microstracture and properties of steel were determined. Strip-like sulfides disappear in heavy rail steel with La/（O＋S）〉3.50, which is shown that the metallurgical function of modifying sulfide inclusions has been achieved by La. La can fine the grain size of the austenite in heavy rail steel. Under the experimental condition, the plasticity and the impacting toughness of heavy rail steel with 0.005wt% La can evidently be improved.

Damage Accumulation in Rail Steel under Rolling with Slippage and Its Analysis

Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influence of loading regime upon wear of rail is considered. The estimation of characteristics of surface fracture resis tance for rail steel is made. The method to predict the life of rail steel under given conditions of regular loading is proposed.

Peculiarities of Structural Transformations in HAZ Metal of Rail Steel M76 Joint Produced by Flash-Butt Welding

The railway transport is one of the main types of communications in the world. Analysis of service conditions of the most critical elements of the railway transport rolling stock （mils, wheels and tyres） shows that one of the main factors determining their reliability and service life is the structural-phase state of steel, which is formed in the process of its producing. Complication of service conditions leads to the more severe requirements, specified by the consumers, where the high level of strength and hardness should be combined with high values of ductility and toughness. Realization of these requirements is possible only at the integrated approach to the improvement of technology of their production on the basis of profound knowledge in kinetics of austenite decay processes of structure formation and its contribution to the mechanical properties. With the formation of mainly bainite-martensite structures in the HAZ （heat-affected zone） metal of welded joints of these steels and saturation of this region with diffusive hydrogen their susceptibility to the cold cracking is increased. In this connection this work presents the results of investigations of effect of the WTC （welding thermal cycles） on the nature of structural transformations, hardness, static strength and resistance to the formation of cold cracks in HAZ metal of high-strength carbon rail steel M76. For this purpose, the structure and kinetics of transformation of an overcooled austenite was studied using the advanced methods of physical materials science by the modeling of phase transformations in the Gleeble 3800 unit. It was found that the cause of reduction in mechanical properties of welded joints of steel M76 is the formation of regions with a completely martensite structure in the amount of up to 5%. Results of investigations will be applied for the optimizing the technology and conditions of FBW of the advanced rail steels. 10 Ref., 4 Tables, 11 Figures.

Microstructure-Fatigue Crack Propagation Kinetics Relationships of Rail Steels

Microstructural analysis and fatigue crack propagation behavior of three types of rail steels, was performed. These are premium pearlitic, austenitic manganese （AM） and bainitic rail steels. Rectangular un-notched and notched test specimens were machined from railheads of each material using electrical discharge machining （EDM） and used for the mechanical properties and fatigue evaluation respectively. Bainitic steel has the highest yield strength, ultimate strength, and strain to failure as compared to both pearlitic and austenitic manganese steels. Fatigue studies showed that the crack speed for the bainitic steel is lower than that for the pearlitie and the AM steels over the entire range of the energy release rate. The bainitic steel exhibits a higher rate of crack deceleration in the second stage, as indicated by the lower slope of the fatigue crack propagation kinetics curve in comparison with the pearlitic and manganese rail steels. This attests to the superior fatigue damage tolerance of the bainitic rail steel in comparison to pearlitic and austenitic manganese rail steels. Microstructural analysis of the three rail steels revealed that bainitic steel has a more intricate structure than AM and pearlitic steels. AM steel shows very few signs of being work hardened or toughened, which usually increases the mechanical properties of the material. As the number of alloying elements increase, the microstructure of the steel becomes more complex, resulting in the increase of mechanical properties and fatigue fracture resistance of bainitic rail steel.

Study on wear characteristics and authorized limits of switch rails of high-speed turnout

Purpose-It is quite universal for high-speed turnouts to be exposed to the wear of the stock rail of the switch rail during the service process.The wear will cause the change of railhead profile and the relative positions of the switch rail and the stock rail,which will directly affect the wheel-rail contact state and wheel load transition when a train passes the turnout and will further impose serious impacts on the safety and stability of train operation.The purpose of this paper is to provide suggestions for wear management of high-speed turnout.Design/methodology/approach-The actual wear characteristics of switch rails of high-speed turnouts in different guiding directions were studied based on the monitoring results on site;the authorized wear limits for the switch rails of high-speed turnout were studied through derailment risk analysis and switch rail strength analysis.Findings-The results show that:the major factor for the service life of a curved switch rail is the lateral wear.The wear characteristics of the curved switch rail of a facing turnout are significantly different from those of a trailing turnout.To be specific,the lateral wear of the curved switch rail mainly occurs in the narrower section at its front end for a trailing turnout,but in the wider section at its rear end when for a facing turnout.The maximum lateral wear of a dismounted switch rail from a trailing turnout is found on the 15-mm wide section and is 3.9 mm,which does not reach the specified limit of 6 mm.For comparison,the lateral wear of a dismounted switch rail from a facing turnout is found from the 35-mm wide section to the full-width section and is greater than 7.5 mm,which exceeds the specified limit.Based on this,in addition to meeting the requirements of maintenance rules,the allowed wear of switch rails of high-speed turnout shall be so that the dangerous area with a tangent angle of wheel profile smaller than 43.68 will not contact the switch rail when the wheel is lifted by 2 mm.Accordingly,the lateral wear limit at the 5-mm wide section of the curved switch rail shall be reduced from 6 mm(as specified)to 3.5 mm.Originality/value-The work in this paper is of reference significance to the research on the development law of rail wear in high-speed turnout area and the formulation of relevant standards.

城市轨道交通正交异性钢桥面板疲劳损伤系数研究

基于城市轨道交通正交异性钢桥面板疲劳性能的重要性,对国内多个城市的轨道交通的交通荷载进行了调研,发现各线路各时段的客流量差异较大,各线路的载客平均轴重与空车平均轴重的比值不同,比值为1.02~1.51。轨道交通因乘客流量带来的轴重比例变化相对较小,因此每一列车都对钢桥结构的疲劳有一定影响。研究了疲劳损伤系数的组成,基于不同的应力循环次数,提出了基于列车荷载作用频次的城市轨道交通桥梁的3个疲劳损伤系数。研究结果可为城市轨道交通钢桥的疲劳设计提供参考,并为规范的修订提供技术依据,对完善城市轨道交通钢桥疲劳设计具有理论意义。