Abstract
The aim of this work was to develop a method to evaluate the kinetics of bainite transformation by theoretical deduction and thermal dilatation curve analysis. A Gleeble-3500 thermomechanical simulator and dilatometer (DIL805A) were employed to study the isothermal transformation in deformed (360 ∘ C , 600 ∘ C , and 860 ∘ C ) and undeformed conditions. The thermal dilatation information during isothermal transformation was recorded, and the dilatation curves were well smoothed. By taking a derivative of the dilation curve with respect to the transformation time, the peak time of transformation rate (PTTR) was obtained, which can serve as the essence of isothermal transformation time. The relative change of length ( Δ L / L ) due to phase transformation was theoretically deduced, and the effect of temperature was taken into consideration. Combing experimental data, the volume fraction of bainite in isothermal transformation was calculated. Making a graph of volume fraction versus PTTR was a good method to evaluate the kinetics of bainitic transformation clearly and concisely which facilitated optimization of the preparation technique for low-temperature nanobainitic steel.
Highlights
Dilatometry is a powerful technique to study the phase transformation kinetics of steels [1,2,3,4,5,6,7,8].Compared with metallographic analysis, dilatometry is real-time, direct, and simple [9]
The volume of steels expands with temperature on the condition that no phase transformation occurs
The relative change of volume or length is proportional to increasing temperature
Summary
Dilatometry is a powerful technique to study the phase transformation kinetics of steels [1,2,3,4,5,6,7,8].Compared with metallographic analysis, dilatometry is real-time, direct, and simple [9]. Dilatometry is a powerful technique to study the phase transformation kinetics of steels [1,2,3,4,5,6,7,8]. The lattice structure of steels is temperature-dependent, and within a considerable temperature range, the volume of the sample is proportional to the temperature if no phase transformation takes place. When the driving force is large enough, a new phase appears which is accompanied by the changes of crystal structure and lattice parameters. These changes give rise to volume change in micron scale which can be monitored by a dilatometer. By observing the point at which the dilatation curve diverges from the trend caused by temperature, the onset and finish of phase transformation can be determined
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