Transformation Kinetics of Bainite during Isothermal Holding and Continuous Cooling

Abstract

To obtain a general cooling transformation kinetics of steels from its isothermal transformation kinetic data, a bainite transformation has been investigated in present study. The main results obtained are as follows:
(1) The isothermal transformation behaviour of bainite for the steel used in present investigation (JIS, SUJ2) can be expressed by the Johnson-Mehl type equation.
(2) The bainite trasformation is retarded with an increase in the austenite grain size. The nucleation site of bainite is mainly on austenite grain surface but some homogeneous nucleations in the matrix are also found.
(3) The equation expressing the transformation bahaviour of bainite during continuous cooling has been derived from the experimentally obtained isothermal transformation kinetics. It is examined that this equation well expresses the actual continuous cooling transformation behaviour.
(4) The above result showing that additivity rule for transformed fraction is hold for bainite transformation during continuous cooling and cooling transformation behaviour can weell be predicted using the isothermal transformation kinetics.