Abstract: In order to improve the overall performance of 43 kg/m climbing switch rail made of U71Mn steel after off-line heat treatment and avoid the spark defect at the small section step of switch rail during heat treatment, by changing the machining sequence and processing quantity, as well as using underspeed quenching heat treatment methods with different vehicle speeds and wind pressures for different section length ranges, the surface hardness, section hardness, morphology of hardened layer and microstructure of the heat-treated switch rail were tested and analyzed. The results show that after adopting the improved process of processing from the tip to the 35 mm section according to the 35 mm section size, processing from the 35 mm section to the heel end according to the finished product size, and then machining to the finished product size after heat treatment, the hardness of the small section significantly improves, reaching 32.0-34.5 HRC. Microstructure consisted of pearlite and a small amount of ferrite, without any abnormal structures such as martensite or bainite, and eliminated spark defects, fully meeting the relevant requirements.

Key words: U71Mn steel, climbing switch rail, off-line heat treatment, machining