Microstructure Evolution of a Pearlitic Steel during Hot Deformation of Undercooled Austenite and Subsequent Annealing

Microstructure evolution of a pearlitic steel (0.81 mass pct C) during hot compression of undercooled austenite and subsequent annealing was studied by means of field-emission scanning electron microscopy, electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). The experiments were performed at 923 K, between A ₁ and Ar ₁, at strain rates of 0.01 to 1 s⁻¹. Compared with the isothermal transformation and the spheroidizing annealing, the transformation of undercooled austenite and the spheroidization of pearlite were accelerated by hot deformation, leading to the formation of the microduplex structures that consisted of ultrafine ferrite grains with average size smaller than 1 μm and spheroidized cementite particles with average size smaller than 0.3 μm during hot deformation and subsequent annealing.