稀土对钢轨钢相关性能的影响研究

通过实验研究、金相观察和工业试验分析,研究了稀土对钢轨微观组织和性能的影响.研究发现,稀土处理对高碳钢中硫化物夹杂物形态有较好的变性功能,少量的固溶稀土可以细化钢轨钢的珠光体片层结构,从而改善钢轨的性能.     

钒对高强钢轨钢可焊性的影响

通过焊接热模拟试验,研究了不同钒含量对高强钢轨钢可焊性的影响。结果表明,中０．０８％左右的钒对钢轨钢焊接热影响区的组织、性能没有不利的影响。     

再论高强、超高强钢轨的生产

本文论述了钢轨生产工艺、技术的发展,简述了发展高强钢轨生产的技术方针,及超高强钢轨的生产方法,及强度性能指标。     

裂扩门槛值试验数据与钢轨性能关系的探讨

文章在U71Mn、U75V和U20Mn淬火轨、以及加稀土镧和铈的U75V试验钢裂扩门槛值ΔK_th试验的基础上,通过试验获取的数据和图表,分析了钢轨组织、夹杂物、氢超标和残余应力等因素与Crack Length-Cycle曲线的关系,以及钢轨加入稀土镧合金、铈合金之后对钢轨裂纹扩展的影响,为分析钢轨性能、延长钢轨寿命提供新的手段。     

高强度耐大气腐蚀钢中稀土提高耐蚀机理研究

采用SEM、XRD、电化学阻抗和干湿周浸实验法,研究稀土对高强耐候钢耐大气腐蚀性的影响.稀土净化钢液,变质夹杂,改善了点蚀和晶间腐蚀.钢中固溶稀土提高钢基体的耐蚀性并促进稳定致密锈层的形成.稀土微合金化作用提高高强耐候钢的耐大气腐蚀性能.     

稀土Ce对热轧U75V钢轨低温韧性的影响

在实验室进行了不同稀土Ce含量的热轧态U75V钢轨冶炼及轧制,重点针对轧后钢轨低温冲击性能、低温断裂韧性进行对比分析。试验结果表明,热轧态U75V钢轨加入0.0056%稀土Ce后,钢轨常温冲击韧性可提高30%左右,-60℃低温冲击韧性可提高60%左右;钢轨-20℃KIC平均值提高14%左右,钢轨-60℃KIC平均值提高15%左右,稀土Ce的加入进一步提升了热轧态U75V钢轨低温韧性。     

高强热处理钢轨试验研究

利用钢轨热处理生产线的技术装备,研究了包钢第二代稀土轨的热处理工艺和钢轨性能。试验结果表明：第二代稀土轨热处理工艺合理,热处理后钢轨硬化层形状及深度均达到预期目标。     

稀土对高强IF钢退火过程中的第二相析出行为的影响

以不同稀土含量的440 MPa高强IF钢为研究对象,在盐浴炉中模拟现场的连续退火,退火温度810℃,分别保温30 s、60 s,通过TEM与XRD对退火后的试样进行第二相分布、形状及成分分析,以研究稀土对高强IF钢第二相析出行为的影响。实验结果表明,保温时间基本不影响第二相的析出;不加稀土的高强IF钢析出的第二相呈弥散分布,且尺寸大小均匀,均在30 nm以下;加了稀土的高强IF钢析出的第二相分布在晶界处,并且伴随着团聚的现象,第二相尺寸不均匀,大颗粒在30 nm^100 nm之间;不加稀土的试验钢在810℃保温60 s下的析出相种类有FeTiP、TiC、TiN、NbN。实验结果为440 MPa高强IF钢在退火条件下第二相析出奠定了理论基础。     

U76CrRE稀土钢轨性能研究

在钢轨钢中加入铬和稀土元素,通过金相显微镜、扫描电镜检验观察其夹杂物、组织,研究新一代稀土钢轨的冲击韧性,耐磨性和耐腐蚀性.实验结果表明,新一代稀土钢轨改善了夹杂物形态,提高了冲击韧性,改善耐磨和耐腐蚀性.     

稀土镁合金的研究现状及应用

镁合金具有质轻、高比强度、高比刚度等优异性能.但其强度不高,高温性能较差,为了改善其性能,在熔炼过程中加入稀土制成具有高强、耐热、耐蚀等性能的稀土镁合金,大大增加了材料的抗拉强度、延展性及抗蠕变性能,从而使镁合金在航空航天、汽车工业及电子通讯行业得到了广泛应用.总结了稀土对镁合金的净化和阻燃作用,分析了稀土元素对合金组织和性能的影响,综述了稀土耐热镁合金、稀土高强镁合金、稀土阻燃镁合金的研究现状,并简述了稀土镁合金的应用及发展前景.     

残余奥氏体对贝氏体钢轨性能的影响

 无碳化物贝氏体组织中的残余奥氏体对提高贝氏体钢轨的韧塑性作出了突出贡献,为了在铁路运营时使钢轨仍保持较高的韧塑性,需要控制好贝氏体钢轨残余奥氏体的稳定性。通过对热轧空冷、热轧空冷+低温回火贝氏体钢轨在不同环境温度下残余奥氏体稳定性的分析,回火贝氏体钢轨在不同试验温度（包括低温）条件下拉伸性能的分析,在模拟钢轨运营的试验条件下疲劳性能的分析及相应条件下残余奥氏体含量的测定,说明低温回火处理提高了贝氏体钢轨中残余奥氏体的稳定性,模拟钢轨运营的试验条件下,贝氏体钢轨中的残余奥氏体基本是稳定的。     

Structure and metallurgical quality of rail steels produced by various manufacturers

The effect of the microstructural parameters and the nonmetallic-inclusion content in a steel on its service properties is analyzed for the rail steels of experimental batches that are produced in Russia and abroad and exhibit different service durabilities upon full-scale tests. The dendritic structures of these steels are different. Measurements of the primary austenite grain size show that it is maximal in the rail steel produced in Austria. The pearlite-colony size in Russian steels is almost half that of Japanese steel. The interlamellar spacings in pearlite of the rail steels of various manufacturers are virtually the same. The Russian steels contain up to 3 vol % grain-boundary ferrite. As compared to the Russian steels, the fracture toughness of the foreign steels is substantially lower. The service durability of a rail is assumed to depend mainly on the nonmetallic-inclusion cleanness of the rail steel. It is shown that quantitative metallography and fractional gas analysis can be used to control the oxide-inclusion cleanness of rail steels. The oxidic cleanness of steel calculated from fractional-gasanalysis data can be used to predict the service durability of rails.     

Reciprocating Sliding Wear Behavior of Newly Developed Bainitic Steels

The present work discusses the mechanical properties and wear behavior of newly developed bainitic rail steels with nominal composition of 0.71 pct C, 0.35 pct Si, 1.15 pct Mn, 0.59 pct Cr, 0.40 pct Cu, and 0.20 pct Ni (all in wt pct)). Isothermal transformation has been carried out at different time and temperatures for obtaining different bainitic morphologies. Linearly reciprocating sliding wear behavior of the steels has been studied and compared with that of the conventional pearlitic rail steel. Considerable improvement in mechanical properties of the bainitic steels has been noticed. The hardness of the bainitic steels increases with decrease in isothermal transformation temperature. It leads to enhancement of wear resistance of the bainitic steels compared to the conventional rail steel. Finally, it clearly draws correlation between mechanical properties, wear resistance, and microstructural variation of a series of bainitic rail steels.     

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.     

U71Mn和74SiMnV重轨钢的焊接性研究

研究了Ｕ７１Ｍｎ和７４ＳｉＭｎＶ重轨钢接触闪光焊的焊接性，利用Ｇｌｅｅｂｌｅ模拟技术研究了Ｕ７１Ｍｎ和７４ＳｉＭｎＶ重轨钢的连续冷却转变行为，测定了模拟热影响区的各项力学性能，分析了焊后冷却速度，化学成分等对焊接性的影响，并与５种国外重轨钢的焊接性进行了对比。     

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

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

轧后热处理温度对热轧钢轨组织和性能的影响

 通过在Gleeble-1500热模拟试验机上对珠光体钢轨的轧后热处理模拟试验,研究了热轧后不同加热温度进行奥氏体化后,同一等温温度下得到的珠光体轨钢的显微组织和力学性能。试验结果表明：与热轧态相比,热处理后的钢轨钢在保持硬度稳定的基础上,冲击韧性随着奥氏体化温度降低得到明显改善。观察轧后热处理钢轨的组织,从原始奥氏体晶粒尺寸、相变后珠光体组织中珠光体域的尺寸和珠光体片层间距大小等方面,对轧后热处理温度对热轧钢轨性能的影响规律和原因进行了分析,阐明了轧后热处理温度对于控制珠光体钢轨的组织和性能的影响作用。     

Corrosion of novel rail steels in 3.5 % NaCl solution

Eutectoid steels, which are traditionally used as rails in railway systems, are prone to corrosion, especially in coastal environments. In order to minimize this problem, four new rail steel compositions, with different combinations of microalloying elements Cu, Cr, Ni and Si, were designed and processed as per the thermomechanical schedule for normal rail steel processing in industry. Corrosion behavior of the rail steels were studied by weight loss measurement after immersion test and Tafel polarization in freely aerated 3.5 % NaCl. The rust obtained after immersion test were characterized by Fourier transform infrared spectroscopy (FTIR). Corrosion rate obtained weight loss measurement was similar for all the rail steels. γ-FeOOH (lepidocrocite) and δ-FeOOH were identified as the major rust phases from the FTIR spectra of the rail steels. The relative absorption intensities of these rust phases were similar for all the rail steels. Corrosion rates calculated from Tafel polarization tests were similar for all the rail steels. The corresponding free corrosion potentials were also similar for all the rail steels. The zero corrosion potential obtained from Tafel polarization of Cu-Mo, Cr-Mn, Cu-Ni, Cr-Cu-Ni and Cr-Cu-Ni-Si rail steels was more noble compared to C-Mn and Cu-Si rail steels indicating better corrosion resistance of these alloys. The importance of conducting alternate wetting and drying test has been emphasized.     

Microstructure-Fracture Behavior Relationships of Slot-Welded Rail Steels

Microstructural analyses of the parent pearlitic and bainitic rail steels were performed, and the results were compared with the microstructure of the welded pearlitic and bainitic steels. An increase in the ASTM grain size number of the heat-affected zone (HAZ) for both pearlitic and bainitic slot welds was observed. The microstructural features that were identified in the weldment of both slot-welded steels were very similar. This was expected since the same welding wire was used to weld both rail steels. The weld consisted of mainly ferrite and had similar grain size. The fusion zones of the welded pearlitic and bainitic rail steels were examined after flexural tests to determine if there were any cracks present due to improper or weak fusion. Examination of the entire fusion zone under high optical magnification revealed no cracks, indicating that a perfect fusion was achieved. The three-point flexural behavior of the parent pearlitic and bainitic steels was evaluated and compared with that of the slot-welded steels. It was found that that the welded pearlitic steel has superior fracture resistance properties when compared to the parent pearlitic steel. The average fracture resistance of the parent pearlitic steel was 79 MPa√m compared to 119 MPa√m for the welded pearlitic steel. The slot-welded bainitic steel, however, showed similar fracture resistance properties to the parent bainitic steel with average values of 121 and 128 MPa√m, respectively. The failure mechanism of the welded and parent pearlitic and bainitic steels was also identified. Microvoid coalescence was observed in both welded rail steel samples. This was manifested by dimpled features, which are associated with ductile failure.     

Oxidation behavior of novel rail steels at 500°C

Thermo gravimetric analysis (TGA) was used to study isothermal oxidation behavior of four novel rail steels at 500∧C in static air condition. These steels contained different combinations of microalloying elements, Cu, Cr, Ni and Si. The results were compared with the oxidation behavior of three rail steels already in commercial application (C-Mn, Cr-Mn and Cu-Mo). The lowest parabolic rate constant was obtained in case of Cr-Cu-Ni-Si contained rail steel. Spallation of the oxide layer was not observed in any of the rail steels. C-Mn, Cu-Mo and Cu-Si rail steels showed higher values of parabolic rate constants k_p. In contrast to others Cu-Si exhibited linear rate law and larger weight gain compared to all other rail steels. X-ray diffraction (XRD) analysis confirmed that the major phase in the oxides was magnetite (Fe₃O₄). The surface morphology of the oxide scales were correlated with the oxidation rate.