Kinetics of the massive martensitic transformation in commercial carbon steels

Abstract

1. Raising the quenching temperature of commercial carbon steels to 1180–1200°C produces a mixture of massive and twin martensite. 2. The temperature range in which massive martensite is formed is higher than the range in which twin martensite is formed and coincides with the range in which bainite is formed. 3. The limit concentration of carbon corresponding to a shift from the massive to twin martensite transformation depends on the cooling rate-with increasing cooling rates the carbon concentration at which twin martensite is formed decreases. 4. The critical cooling rate for formation of massive martensite is lower than for twin martensite. 5. The nature and kinetics of the formation of bainite and massive martensite are similar. Differences in the structures are due to the carbon content, since diffusional redistribution of carbon occurs in the process of the transformation. Thus, it is expedient to use the term bainite for carbon-containing alloys and massive martensite (isothermal) for carbon-free alloys (<0.1% C).