Ironmaking & Steelmaking: Processes,Products and Applications

This paper presents the experimental and model results of the response of an alternating current field measurement (ACFM) sensor to clusters of rolling contact fatigue (RCF) cracks typical of those found in rails and rail wheels. Both artificial and real cracks occurring in rails taken from service are considered. Currently, commercially available ACFM software is capable of producing an estimate of crack pocket length for isolated cracks, assuming they are regularly shaped. The results presented are part of continuing work to link the ACFM signal to the whole range of complex shaped RCF cracks that appear in rail and rail wheels, including those appearing in clusters. The challenges in accurately sizing clustered RCF cracks using the ACFM technique are discussed.

The high contact stresses between a railway wheel and rail result in local plastic deformation in both the rail and wheel steel. Optical metallography and hardness testing have traditionally been used to quantify the extent of deformation present; however, these methods only give limited information about the deformation mechanism and the role of microstructure. In this study, electron backscattered diffraction has been used to assess the depth and degree of deformation using the kernel average misorientation function; where the crystallographic misorientation between and within pearlite colonies has been quantified using a local average misorientation function. This technique gives invaluable crystallographic information about the deformed microstructure to aid understanding of the deformation mechanism. The application of the kernel average misorientation function has been modelled for idealised rail microstructures, including after the simulation of deformation via shear, in order to understand how the average kernel average misorientation values are developed under the high levels of deformation seen in rail steels.

Increased traffic speeds and axle loads on modern railways enhance rail track degradation. To eliminate track failure due to rail defects, a condition monitoring system requires methods for the early detection of defects which grow in service. Acoustic emission (AE) monitoring is the only non-destructive technique which might be applied online to study the defect growth under traffic loading. However, a high level of traffic noise and a limited signal from crack growth, especially at low crack growth rates, significantly complicate the AE signal analysis. In the present work, the AE monitoring of rail steel fatigue was carried out in a ‘noisy’ laboratory environment using different methods of signal analysis. Signal parameters of AE for machine noise, sample deformation and crack growth were identified. The crack growth related AE signature was found to be dependent on fracture mode.

Network Rail is involved in a number of initiatives to reduce rolling contact fatigue (RCF) crack initiation on wheels and rails on the GB network. One of these is the trial of premium grade rail materials to determine whether they provide enhanced resistance to RCF crack initiation. The sites where trials have been undertaken have been selected to comprise a range of track and traffic conditions, and were regularly monitored. This paper describes the results from one of these trial sites, on a tight radius curve, where it was found that the risk of RCF actually increased with the use of premium grade rail. It is shown that, although this was initially considered surprising, it is consistent with the current understanding of the mechanisms of RCF initiation. This demonstrates that premium grade rail steels may not always be the best solution to prevent track damage and that careful consideration of the track geometry, operating conditions and traffic should be taken when considering the most appropriate rail grade to select for use at a given location.

To investigate the mechanisms behind rolling contact fatigue (RCF) and wear, a collaborative test program was conducted by voestalpine Schienen GmbH (Leoben, Austria) and Kelsan Technologies Corp. (a part of LB Foster Friction Management) on the full scale test rig of voestalpine. A reference grade was compared to a series of pearlitic rail grades under dry and friction modifier (FM) contact conditions. Rail and wheel profiles were collected at predefined intervals, allowing the calculation of wear rates. The initiation and development of RCF cracks were monitored using optical means and magnetic particle inspection. Metallographic sectioning of the samples was conducted to characterise crack growth and crack orientation as well as the evolution of surface and subsurface material flow. Additionally, the test rig results were compared to the results obtained from the extensive track test network of voestalpine and Kelsan to outline similarities and differences between test rig conditions and the conditions in track. The combination of rail grade, FM application and an appropriate maintenance strategy is seen to have a significant effect on the development and propagation of wear and RCF. This offers a huge potential for reducing the track LCC costs for the infrastructure owners.

Managing the contact conditions between train wheels and the running rail is key to controlling the dynamic behaviour of railway rolling stock and preventing rail defect initiation and growth. This paper describes the rail profile management strategies deployed by Network Rail. The development of policies and standards is discussed, highlighting the reasons behind the selection of target rail profiles and friction management techniques. Practical implementation of the strategies is described, with consideration given to the challenges faced delivering rail profile management on the operational railway. Recent developments in rail friction management and reprofiling technology are presented, e.g. top of rail friction modifiers, rail milling and high productivity grinding. The costs and benefits of the new technologies are examined. The impact of these developments on the Network Rail’s approach to managing rail profile is discussed. Drawing conclusions from this analysis, a future vision of rail profile management on Network Rail infrastructure is presented.

Flue gas recirculation (FGR) has been incorporated into the sintering process with the aim of improving productivity while fulfilling tightened environmental regulations. The incorporation of FGR inevitably requires changes in the process equipment as well as incoming and outgoing gas conditions such as temperature, composition and flowrate. These changes may affect not only the reactions in the bed but also the factors related to the design and operation of the plant, which requires the checking of possible effects on gas conditions over the entire bed. The modelling approach proposed in this study for a sintering bed uses a flowsheet process simulator as the starting point for studying the effects of FGR on the sintering process. This paper is the first of two which will present comprehensive information on the modelling approach, and details of the modelling cases and the corresponding results will be described in the companion paper.

As issues of productivity, quality control, energy efficiency and environmental regulation become ever more important in the iron ore sintering process, controlling combustion inside the sinter bed is attracting renewed interest in terms of flue gas recirculation (FGR) and oxygen or gaseous fuel enriched combustion. The application of combustion control schemes inevitably brings changes to incoming and outgoing gas conditions as well as to plant configuration. The objective of this study is to build a process model of a sintering bed using a flowsheet process simulator and to obtain information on material flows for various process configurations and operating conditions. The process modelling was designed to quantify the heat and mass flow in each of the bed segments, which could then be integrated to represent the overall material and energy flow of the entire bed. Variations in incoming and outgoing gas conditions were compared among different configurations of recirculation using the model.

The pre-reduction of higher manganese oxides with post-consumer plastics as reductants has been investigated through experiments conducted in a laboratory scale horizontal tube furnace coupled with an off gas analysis through an online infrared (IR) gas analyser. Composite pellets of calcined manganese oxide (Mn₃O₄) with high density polyethylene (HDPE) (at C/O molar ratios of 1·5, 2·0 and 3·0) were heated rapidly to 1150°C under pure argon and the off gas was measured continuously by an IR analyser for CO, CO₂ and CH₄. The extent of reduction of Mn₃O₄ to MnO was calculated from a mass balance for removable oxygen. Solid reaction products were characterised by scanning electron microscopy and X-ray diffraction analysis was used to confirm the presence of MnO. The results indicate that Mn₃O₄ can be successfully pre-reduced to MnO using HDPE as a reductant. Gas analysis studies indicated that the polymer is first converted to CH₄ which cracked partially or reformed to H₂, C and/or CO. Reduction of Mn₃O₄ to MnO was subsequently effected by C, CO, H₂ and the residual CH₄.

The organic Rankine cycle low temperature waste heat power generation technology can be applied in water quenching blast furnace slag. To select a suitable fluid and improve the effectiveness of the process, 10 different working fluids were selected based on their characteristics (refrigerant, alkyl hydrogen, siloxane, etc.) and their application range in the co-generation project. Each co-generation system using the selected fluids was calculated by Matlab simulation programming. The results show that, in the case of constant evaporation and condensation temperatures, the thermal efficiency of the system increases, but the pressure decreases, with the rise in fluid critical temperature. Based on the comprehensive analysis of thermal efficiency, irreversible loss, unit mass flow power generation capacity, pressure level and environmental effect of the system, fluid R245fa, which is a hydrocarbon fluorine group type, is the best choice from the fluids tested.

Electroslag casting with liquid metal (ESC LM) is a new technology in electroslag metallurgy. Solid ingot, hollow ingot and bimetal composite can be produced by the ESC LM process. Using both internal and external current carrying moulds for ESC LM is a new method for manufacturing hollow ingots. Liquid metal is employed directly during the ESC LM process rather than the conventional consumable electrode. The process was simulated using infinite element software ANSYS. The results indicate that the conductive path of the ESC LM process is entirely different from the conventional electroslag remelting process. There are two conductive current paths: one conductive path is transformer→external current conductive mould→liquid slag→internal current conductive mould→transformer, and another conductive path is transformer→external current conductive mould→liquid slag→molten steel pool→liquid slag→internal current conductive mould→transformer. Current density, magnetic inductive intensity, electromagnetic force, Joule heat distributions and fluid flow are concentrated on the upper area of the slag pool. In addition, the higher temperature region of the slag pool is at the upper area of the slag pool. The superheat of the molten steel pool is lower than the conventional electroslag remelting process, which favours improving the quality of the hollow ingot. Simulation of the ESC LM process will help understanding the process and choose better operating parameters.