The effect of prior compressive deformation of austenite on toughness property in an ultra-low carbon bainitic steel

For the purpose of investigating the trend of toughness versus variation of microstructural constituents for an experimental ultra-low carbon bainitic steel, the experiments (with and without prior compressive deformation) have been carried out on a Gleeble 1500 machine. The Charpy impact specimens were prepared from the samples treated by the Gleeble machine. The Charpy impact absorbed energy for toughness was measured, and the corresponding fractographs, optical metallographs and transmission electron micrographs have been examined. The result shows that the prior compressive deformation of austenite promotes the formation of intragranular non-parallel plates of acicular ferrite but stifles the formation of sheaf-like parallel plates of bainitic ferrite. Furthermore, the study emphasizes that the microstructure containing a high volume fraction of acicular ferrite possesses better toughness and strength than the microstructure containing mainly bainite.