Papers by Keyword: Rail Steels

Abstract: Hydrogen diffusivity was estimated in three different eutectoid rail steels (C-Mn, Cu-Mo and Ni-Cu-Cr) at ambient temperatures using the technique of sub-surface microhardness profiling after cathodic hydrogen charging in 0.5mol/l sulphuric acid at a current density of 0.1A/cm2 for 24 hours. The increase in the concentration of hydrogen at a certain depth below the surface was related to the microhardness increase at this location as compared to the bulk value. The procedure used to obtain the diffusion coefficient of hydrogen from the microhardness profiles is discussed. The hydrogen diffusivity values in all of the rail steels were found to be similar (of the order of 10-13m2/sec). The estimated hydrogen diffusivity in the rail steel was lower than in pure iron (10-8m2/sec). Possible reasons for the difference are discussed.

Abstract: Severe Plastic Deformation (SPD) is known to be an effective method of producing nanocrystalline materials, for instance by HPT and ECAP. These techniques are also capable of reproducing microstructures which arise naturally when high pressure and friction is involved, for example in wheel-rail contact problems. The resulting deformation layers build the origin point for fatigue cracks. For that reason the knowledge of the mechanical properties of these deformation layers are of vital importance. In the framework of this study a baintic rail steel quality was deformed by High Pressure Torsion up to distinctive equivalent strains at a nominal pressure of 6 GPa up to a final equivalent strain of 16. Afterwards the evolution of the resulting microstructure was investigated by Scanning Electron Microscopy, by microhardness measurements and X-ray diffraction. The bainitic structure showed a strong alignment and fragmentation into the shear direction with increasing strain, which was accompanied by an increase in hardness as well. X-ray diffraction measurements showed that the amount of retained austenite decreases dramatically after small amounts of strain, which indicates that retained austenite cannot be stabilized by high pressures. Torque measurements during deformation showed after strong hardening at the beginning, a saturation behaviour for higher strains, whereas for instance pearlitic rail steel qualities show further hardening.

Abstract: The transverse crack, which is the most dangerous damage among the various types of rail defects, is developed from shelling near the rail running face, and grows perpendicular to the rail surface. Therefore, to assure the safety of rolling stocks, it is necessary to investigate the fatigue crack growth behavior of a gas pressure welded part of rail steel under mode I and mixed mode loadings. In this study, the fatigue crack growth behavior under the mixed mode was discussed by using comparative stress intensity factor ranges proposed by Richard. In addition, to evaluate the effect of the crack closure quantitatively, the crack opening load was determined a using clip-on gauge and computerized image processing system. As a result of this, a mixed mode crack growth rate regardless of the stress ratio could be correlated with the effective comparative stress intensity factor ranges derived from the crack opening loading.

Abstract: In this paper, the continuous in-situ observations of the fatigue crack growth in U71Mn and U75V rail steel are made by using the scanning electronic microscope (SEM). The microstructure patterns of cracks under the mode I fatigue loads and quasi-static loads are presented. The results indicate that the short fatigue crack growth in rail steel is a quasi-cleavage fracture. The ductility and the performance of fatigue resistance of U71Mn rail steel are better than those of U75V rail steel.

Abstract: The choreography of atoms during the course of the bainite transformation has major consequences on the development of structure. In particular, the scale and extent of the structure is dependent directly on the fact that the atoms move in a disciplined fashion. This information can be exploited to develop unconventional alloys - for example, rail steels which do not rely on carbides for their properties, and the hardest ever bainite which can be manufactured in bulk form, without the need for rapid heat treatment or mechanical processing.

Abstract: In the present study, fatigue tests have been performed to study the effect of pre-strain on fatigue properties of NHH (New Head-Hardened) rail. The objectives of this study were: (1) to observe the microscopic behavior of specimens during pre-strain process, (2) to research the influence of pre-strain on fatigue strength of NHH rail and (3) to investigate initiation and propagation behavior of the fatigue crack. The results showed that plastic pre-strain decreased the fatigue strength of NHH rail; fatigue limits had no obvious variation among the different pre-strain ratios. Fatigue cracks initiated in the microscopic cracking or slip lines that were originated in the pre-strain process and propagated from these sites in the later fatigue test.