In Situ Observation of the Lengthening Rate of Bainite Sheaves During Continuous Cooling Process in a Fe–C–Mn–Si Superbainitic Steel

Abstract

The evolution of lengthening rate of bainite sheaves during continuous cooling process in a Fe–C–Mn–Si superbainitic steel was investigated by in situ observation on high-temperature laser scanning confocal microscope. The lengthening rates of bainite sheaves in three temperature ranges were calculated. The results indicate that the lengthening rate of bainite sheaves continuously decreases with the decrease of temperature during continuous cooling process. The lengthening rate of bainite sheaf depends on undercooling, transformation temperature, the diffusion of carbon atoms and the carbon content in parent austenite etc. The lengthening rate at high temperature is large due to the favorable carbon diffusion, smaller carbon content and less plastic deformation in untransformed austenite. Additionally, the microstructures after different isothermal holding temperatures were analyzed, indicating that the larger lengthening rate of bainite sheaves due to the high isothermal transformation temperature does not mean more amount of bainite transformation. Lower bainitic transformation temperature results in more and finer bainite plates.