Controlling factors of pearlite transformation rate of 0.4 mass% C steels

Kinetics of austenite to pearlite phase transformation in 0.4mass%C-X (X = Cr, Ni) steels were investigated. The isothermal transformation curves were analyzed with of the Avrami Equation: X(t)= 1-exp(-Gtⁿ) where X(t) is the fraction transformed and n and G are constants. The exponents n were found to be about 2 except for Cr steels. The value of n for steels containing 0.5 and 1.0 mass% Cr were about 3. This results indicated that the pearlite transformation in 0.4 mass% C steels in present study is controlled by the site saturation mechanism. The parameters G, transformation rate constant of pearlite, were independent of the supercooling from A₁ temperature and the driving force of pearlite transformation. These values were dependent on the energy differences of ferrite phase from supercooled austenite phase. This energy difference was equivalent to the driving force of eutectoid ferrite. The predicted transformation rate of pearlite is independent of transformation temperature and containing alloy. The pearlite transformation rate of 0.4 mass% C steels was found to be controlled by eutectoid ferrite growth.