Railhead Quenching Process and Wear Resistance of National Standard Rails
- What are the common rail head quenching processes for national standard rails?
Common ones include induction heating quenching, where the rail head is heated to 850-900℃ by a high-frequency induction coil and then cooled by water spray, with a hardened layer depth of 8-12mm and uniform hardness; flame quenching uses acetylene-oxygen flame for heating, with a shallow hardened layer (5-8mm), suitable for lines with small traffic volume; contact heating quenching heats the rail head directly through electrodes, with controllable hardened layer depth but complex equipment, which is rarely used.
- What are the requirements for hardness indicators after rail head quenching?
The surface hardness of the quenched rail head must reach HB380-420, the hardness of the tread center area is not less than HB390, and the edge area is not less than HB380. The hardness gradient in the hardened layer should be gentle, with a hardness drop of no more than 20HB per millimeter from the surface to the core, avoiding stress concentration due to sudden hardness changes. The transition section between the unquenched and quenched areas must be ≥50mm to reduce performance differences.
- How effective is the quenching process in improving rail wear resistance?
Induction heating quenching can improve rail wear resistance by 2-3 times. The service life of quenched rails in ordinary lines can reach 10-15 years, while unquenched rails only 5-8 years. Flame-quenched rails have their wear resistance improved by about 1.5 times, suitable for medium traffic lines. Quenched rails can effectively resist wheel-rail contact fatigue and reduce rail head spalling and wavy wear.
- How to test the quality of the rail head quenched layer?
Use a Rockwell hardness tester to measure the surface hardness, measuring 3 points per meter of rail and taking the average. Observe the hardened layer structure with a metallographic microscope, requiring martensite content ≥90% to avoid pearlite or bainite. Use ultrasonic flaw detection to detect the depth of the hardened layer, with the deviation controlled within ±1mm to meet design requirements.
- How to select rail head quenching processes for lines with different traffic volumes?
Heavy-haul lines with an annual traffic volume exceeding 50 million tons must use induction heating quenching to ensure a hardened layer depth ≥10mm; trunk railways with an annual traffic volume of 20-50 million tons can use induction heating quenching (8-10mm) or high-quality flame quenching; branch railways with an annual traffic volume below 20 million tons can use flame quenching (5-8mm) to meet needs, balancing cost and performance.