| Rail steels for switch-point component are basic parts in railway system. As the railway industry worldwide is introducing heavier axle loads and higher vehicle speeds, it has become essential to explore the possibility of developing new grades of high strength frog steel. Since 1980's, railroad researchers and manufacturers have begun to study bainitic steel for track, and have developed some new bainitic steels for frog steel.In this paper, after investigating and analyzing the development steels all over the world, the influence of tempering on the microstructures and mechanical behavior were extensively investigated and with optical microscope, mechanical tests, SEM, TEM and X-ray analyzer,and the transition mechanics of bainite in tempering was discussed. The results of tensile test and Charpy U notch (CUN) impact test showed that, when the bainitic steel was tempered at 350℃, its yield strength, ultimate tensile strength, elongation, reduction of area and Charpy U notch (CUN) impact toughness were 1,193MPa, 1, 437MPa, 13%, 50 and 71J/cm~2, respectively. The steels appear obviously temper brittleness when tempered at 500℃to 600℃.TEM and optical observations showed that the microstructure of bainitic steels was mainly consisted of carbide-free bainite after low tempering process.The result showed that, the mechanical stability of retained austenite was excellent when tempered at 350℃. The strength and toughness of bainitic steels with different tempering procedure has a close relation to mechanical stability of retained austenite.
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