Wear-resistant alloy overlay welding technology for imported standard rails and its adaptation to heavy-load lines
What are the core material selection standards for the wear-resistant alloy layer surfacing on the rail head of foreign standard rails?
The core material selection standards for the wear-resistant alloy layer surfacing on the rail head of foreign standard rails are high hardness, high toughness and good surfacing compatibility, and the commonly used materials are iron-based wear-resistant alloys and nickel-based wear-resistant alloys. The hardness of iron-based wear-resistant alloys can reach HRC60-65, which contain alloy elements such as chromium, molybdenum and vanadium. The chromium carbide reinforcement phase formed by chromium can improve wear resistance, molybdenum improves the toughness of the alloy, and vanadium refines the grains. This material has low cost and is suitable for heavy-haul lines with medium axle load. The hardness of nickel-based wear-resistant alloys is HRC58-62, which has better toughness than iron-based alloys and strong impact resistance. It is suitable for heavy-haul lines with large axle load and high impact, such as North American AAR standard 30t axle load lines. The surfacing compatibility of the material requires good metallurgical compatibility with the base metal of foreign standard rails, no cracks, pores and other defects after surfacing, and the dilution rate should be controlled at 10%-15% to avoid performance degradation of the alloy layer.
What are the process methods and technical characteristics of surfacing on the rail head of foreign standard rails?
The core process of surfacing on the rail head of foreign standard rails is open arc automatic surfacing, supplemented by preheating and post-welding heat preservation treatment, with the technical characteristics of high efficiency and precision. Before surfacing, it is necessary to preheat the rail head to 200-250℃, and the preheating range is 50mm on both sides of the rail head to reduce the temperature gradient during surfacing and reduce welding cracks. Surfacing adopts a special surfacing robot, the welding current is controlled at 200-250A, the arc voltage is 25-30V, and the welding speed is 150-200mm/min to ensure uniform thickness of the alloy layer, and the thickness of the surfacing layer is controlled at 5-8mm. After welding, heat preservation treatment should be carried out: place the rail in a heat preservation cover and cool it slowly to room temperature with a cooling rate ≤50℃/h to eliminate welding residual stress. The technical characteristics of this process are high surfacing efficiency, the surfacing time of a single rail is ≤2 hours, the bonding strength between the alloy layer and the base metal is ≥450MPa, and the wear resistance is 3-4 times higher than that of the original rail.
What is the differentiated design of surfacing parameters for different foreign standard rail models?
The differentiated design of surfacing parameters for different foreign standard rail models is core to matching the rail base metal composition and cross-sectional dimensions. For EU EN54E1 rails with base metal of U71Mn, the surfacing current is 200-220A, the arc voltage is 25-27V, the surfacing layer thickness is 5-6mm, and the dilution rate is controlled at 10%-12% to avoid excessive melting of the base metal due to excessively high parameters. For North American AAR136RE rails with base metal of T1 steel and large axle load, the surfacing current is 230-250A, the arc voltage is 28-30V, the surfacing layer thickness is 7-8mm, and the dilution rate is controlled at 12%-15% to improve the bearing capacity of the alloy layer. For Australian AS1085.1 rails with narrow rail head cross-section, the surfacing speed should be increased to 180-200mm/min, and the welding current is 210-230A to ensure that the surfacing layer covers the entire rail head contact surface without missing welding areas. The differentiated design of surfacing parameters must be verified by welding tests to ensure that the straightness deviation of the rail after surfacing is ≤0.5mm/m.
What is the adaptation verification method of foreign standard rails with surfacing wear-resistant alloy layers for heavy-haul lines?
The adaptation verification method of foreign standard rails with surfacing wear-resistant alloy layers for heavy-haul lines includes two links: laboratory performance testing and on-site trial laying test. Laboratory performance testing includes hardness testing, wear testing and impact testing. Hardness testing requires the hardness of the surfacing layer ≥HRC60, the hardness of the base metal is HRC30-35, and the hardness transition zone is uniform; wear testing uses a pin-on-disk wear testing machine, the wear loss should be ≤0.1mg/m, which is more than 70% lower than that of the original rail; impact testing is carried out at a low temperature of -40℃, the impact energy is ≥30J to ensure that the alloy layer has no brittle fracture. The on-site trial laying test selects a typical section of the heavy-haul line with a laying length ≥1km and a monitoring period of 1 year. The monitoring indicators include rail head wear, wheel-rail contact stress and joint smoothness. The trial laying results require that the annual wear of the rail head is ≤1mm, the peak wheel-rail contact stress is ≤800MPa, and the smoothness indicators meet the line operation standards.
What are the on-site welding and maintenance points of foreign standard rails with surfacing wear-resistant alloy layers?
The on-site welding and maintenance of foreign standard rails with surfacing wear-resistant alloy layers need to focus on welding process adjustment and surfacing layer wear monitoring. On-site welding adopts flash butt welding process. Before welding, it is necessary to grind and remove 2-3mm of the surfacing layer to expose the base metal, avoiding the alloy layer affecting the welding quality. After welding, local tempering treatment should be carried out on the welded joint at a temperature of 400-450℃ for 1 hour. During maintenance, it is necessary to regularly detect the wear thickness of the surfacing layer with an ultrasonic thickness gauge. When the wear thickness exceeds 3mm, repair welding should be carried out with the same parameters as the original surfacing. In addition, it is necessary to regularly grind the rail head surface to remove fatigue cracks and wear steps. The grinding cycle is 6 months, and the grinding amount is controlled at 0.1-0.2mm to ensure good wheel-rail contact state. At the same time, the surfacing layer should be prevented from contacting acidic substances to avoid corrosion of the alloy layer.