DEVELOPMENT OF ANTI-DARK SPOT RAILWAY RAILS

随着铁路交通速度的提高，铁路系统产生了各种各样的缺陷。其中之一是钢轨黑斑缺陷或钢轨脱壳。黑斑缺陷的特征是主裂纹，它起源于接触面，并在交通方向上以锐角向轨道表面扩展；第二裂纹，从表面上几乎相同的点开始，在与交通相反的方向上以略浅的角度生长得更慢。主裂缝有许多子裂缝，在某一阶段，其中一个可能横向延伸到铁路头上，导致钢轨的灾难性拉伸破坏。因此，这种缺陷是一种非常危险的铁路故障。作者已经发现了黑斑破裂的机制。此外，他们还制造了一种贝氏体钢，这似乎对发生滚动接触疲劳失效是有效的。本研究的目的是在分析黑斑开裂机理的基础上，为抗黑斑缺陷铁路钢轨的研制提供设计指导。主要研究结果总结如下：1。裂纹是由局部直接接触产生的高牵引力产生的。在一段时间的湿运行过程中，由于水渗透到裂缝中，产生了水力效应，裂缝开始扩展。在平均牵引力较低的条件下，贝氏体钢的抗暗斑能力远高于普通珠光体钢。在平均牵引力较大的情况下，会产生塑性变形引起的表面损伤。提高钢的硬度对增强这种损伤是有效的。贝氏体钢的耐磨性比珠光体钢差得多。而提高贝氏体钢的硬度和含碳量可以提高其耐磨性。人们普遍认为较高的磨损率可以防止裂纹的产生，但事实却有些不同。贝氏体钢轨焊接部分的接头性能与传统珠光体钢轨的接头性能基本相同。目前，贝氏体钢铁路（HB=250 ~ 350）的滚动接触疲劳抗力试验正在实际铁路上进行。研究发现贝氏体钢轨抗黑斑缺陷的能力远远高于普通珠光体钢轨。考虑到以上结果，目前正在研究贝氏体钢的化学成分，以便贝氏体钢轨道的应用，以满足JIS关于珠光体轨道钢强度的标准和日本铁路公司制定的电阻标准。少

As traffic speed on railroads increases, various kinds of defects have been produced in rail systems. One of them is the rail dark spot defect or rail shelling. The dark spot defect is characterised by a principal crack, which initiates at the contact surface and propagates at an acute angle to the rail surface in the direction of traffic, and a second crack, which grows more slowly from almost the same point on the surface, in the opposite direction to traffic and at a slightly less shallow angle. The principal crack has many sub-cracks and at some stage one of these may extend transversely across the railhead leading to a catastrophic tensile failure of the rail. Thus, this defect is a very dangerous rail failure. The authors have found the mechanism for the dark spot cracking. Furthermore, they have made a bainitic steel, which seems to be effective for the occurrence of rolling contact fatigue failures. The purpose of this study is to establish the design instruction for the develo … More pment of anti-dark spot defect railway rails on the basis of the mechanism for dark spot cracking. The main results obtained are summarised as follows :1. Cracking is produced by a high traction force due to a local direct contact. The crack initiated propagates by a hydraulic pressure effect due to water penetrated into the crack in a period of wet running.2. Under conditions where the mean traction force is rather low, the dark spot resistance of bainitic steel is much higher than that of conventional pearlitic steel.3. Under conditions where the mean traction force is rather high, surface damages due to the plastic deformation are produced. The increase in hardness of steels is effective for the enhancement of such damages.4. The bainitic steel is much worse than the pearlitic steel in the wear resistance. However, the wear resistance of bainitic steel can be improved by increasing the hardness and the carbon content.5. Although a common opinion that the higher wear rate prevents the crack initiation is believed, the fact is somewhat different.6. The welded parts of bainitic steel rails are almost the same joint performance as those of conventional pearlitic steel rails.7. Presently, the rolling contact fatigue resistance test of bainitic steel railroads (HB=250-350) is in progress using actual railways. It has been found that the dark spot defect resistance of bainitic steel rails is much higher than that of conventional pearlitic steel rails.Considering above results, the chemical composition of bainitic steel is under investigation now for application of bainitic steel rails so as to satisfy JIS standard on pearlitic rail steel strength and the electrical resistance standard established by the Japan Rail companies. Less