Welding Characteristics and Process Requirements for Standard Rails
- What are the main difficulties in welding foreign-standard steel rails?
Foreign-standard steel rails have large differences in alloy element content. For example, European standard EN rails often contain chromium, nickel and other elements, which are prone to form hardened structures during welding, leading to joint embrittlement. American standard ASTM rails have a high carbon equivalent, and hot cracks are easy to occur during welding, especially near the weld fusion line. In addition, the thickness and cross-sectional size of foreign-standard steel rails are diverse, which brings difficulties to heat control during welding. If heating is uneven, it will lead to stress concentration at the joint, affecting the overall strength. At the same time, different standards have different performance requirements for welded joints, so it is necessary to strictly control the welding quality to meet their specific standards.
- Which foreign-standard steel rails is flash welding suitable for? Why?
Flash welding is suitable for Japanese standard JIS and European standard EN series rails. The carbon content and alloy element ratio of these rails are moderate. During flash welding, the end of the rail is melted by the high temperature generated by the current, and then the upsetting force is applied to form the joint, which can effectively avoid cracks. The heat-affected zone of flash welding is small, which can reduce the performance change of the rail joint, meeting the requirements of Japanese and European standards for the toughness and strength of welded joints, especially suitable for foreign-standard rails for high-speed railways, ensuring the smoothness and reliability of the joint.
- What are the characteristics of thermite welding in welding foreign-standard steel rails?
Thermite welding is easy to operate, does not require complex equipment, and is suitable for field operations, which is more applicable to the welding of American standard ASTM and UIC standard rails. It melts the rail end and flux through the high temperature generated by the thermite reaction to form a weld, with high welding efficiency. However, the joint strength of thermite welding is relatively low, and the heat-affected zone is large, so it is usually used in non-trunk railways or temporary repair scenarios. When welding foreign-standard steel rails, it is necessary to adjust the flux composition according to their materials to match the chemical properties of the rails and avoid brittle fracture of the joint.
- What are the joint inspection items after welding foreign-standard steel rails?
After welding foreign-standard steel rails, it is necessary to inspect the appearance size of the joint to ensure that the weld height and width meet the standards, and there are no defects such as pores and slag inclusions. Mechanical property tests are carried out, including tensile strength and impact toughness tests. For example, European standard EN requires that the tensile strength of welded joints is not less than 90% of the base metal. It is also necessary to inspect the hardness distribution of the joint to avoid too hard or too soft areas, preventing cracks during use. In addition, ultrasonic flaw detection and magnetic particle testing are also necessary items, which can timely find internal hidden cracks or incomplete fusion defects, ensuring welding quality.
- How to adjust the welding parameters of different foreign-standard steel rails?
The welding current is adjusted according to the cross-sectional area and material of foreign-standard steel rails. For example, when welding UIC60 rails, the current needs to be 10%-15% higher than that for welding Japanese standard 50N rails to ensure sufficient melting amount. In terms of heating time, American standard ASTM rails with high carbon content need to extend the heating time to make the temperature evenly distributed and reduce the hardened structure; while low-alloy Japanese standard rails can appropriately shorten the heating time to avoid coarse grains. The size of upsetting force is related to the rail specification. The welding upsetting force of heavy-duty foreign-standard rails needs to be increased. For example, the upsetting force of UIC71 rails is about 20% higher than that of UIC60 to ensure close joint combination.