Influences of Alloying Elements on Continuous Cooling Phase Transformation and Microstructures of Extremely Fine Pearlite

In the present research, the cooling phase transformation characteristics and microstructures of a Co- and Al-containing high-carbon steel were investigated under slow cooling rates (0.02–2.0 °C/s). In addition, by means of a Thermecmastor thermal simulator, the phase transformation temperatures were measured, and the corresponding continuous cooling transformation (CCT) curves were plotted. It was found that an extremely fine, fully pearlitic structure with an interlamellar spacing of 45 nm, and a hardness of 425 HV1 (Vickers hardness under 1 kg load) were obtained at a cooling rate of 0.1 °C/s. The addition of Co and Al accelerated the pearlitic reaction and reduced the interlamellar spacing by increasing the free energy of phase transformation, thus a fully pearlitic structure was obtained at slow cooling rates.