DYNAMIC TRANSFORMATION OF AUSTENITE TO FERRITE IN LOW-CARBON STEEL

The design of thermomechanical processing schedules to control microst ructures requires the knowledge of the austenite-to-ferrite transforma tion start temperature (Ar3). In this industrial process, during defor mation, the temperature usually decreases continuously. Thus, two new methods to determine the Ar3, based on continuous cooling compression (CCC) and continuous cooling torsion (CCT), have been developed. While the former is applicable for low strains only, the latter can be used for low and high strain processes. The aim of this investigation was to determine the effect of deformation in the single phase austenite a nd two phase austenite plus ferrite region on the transformation and d ynamic transformation behaviour of austenite-to-ferrite. CCC tests wer e carried out on a low carbon steel and the influence of strain was ex amined. As expected, deformation in the single phase austenite region increased the kinetics of the austenite-to-ferrite transformation, rai sing the Ar3. The faster kinetics leads to a finer polygonal ferrite g rain size after transformation. Straining in the two phase region caus es strain concentration on the softer ferrite and, consequently, recry stallization of this phase. Deforming close to the Ar3 maximizes the s train effect on dynamically transformed ferrite.