Nucleation Behavior Analysis of Intragranular Acicular Ferrite in a Ti-killed C-Mn Steel

By using a Gleeble 3500D thermo-mechanical simulator, the nucleation behavior of intragranular acicular ferrites (IAF) was studied in a Ti-killed C-Mn steel. During continuous cooling transformation, the allotriomorphic ferrite (AF) and ferrite side plate (FSP) microstructures grew more rapidly with the temperature decreasing from 800 to 650 degrees C, and the IAF microstructure was dominant within austenite grain with further cooling to 600 degrees C. The diffusion bonding experiment and the effect of C, Mn and Si concentrations on the A(e3) temperature by thermodynamic calculation confirm that Ti2O3 itself absorbs neighboring Mn atoms to form Mn-depleted zone (MDZ), which promotes the nucleation of IAF microstructure effectively. High temperature holding tests indicate that the nucleation potential of IAF microstructure was lowered in the Ti-killed C-Mn steel when it was treated at high temperature (1250 degrees C) for a longer time, which is attributed to the saturated absorption degree of Mn atoms by titanium oxide.