The Effect of the Austenitisation Temperature on the Transformation Kinetics of an Nb-Containing Steel

An experimental study on the effect of the austenitisation temperature on the austenite decomposition for an Nb-microalloyed steel is performed by means of Differential Thermal Analysis. The start temperature for the formation of allotriomorphic ferrite in a cooling experiment depends strongly on the austenitisation temperature through the austenite grain size. The austenite grain size in its turn depends on the austenitisation temperature and is strongly restricted by the presence of NbC-precipitates. Also the transformation rates depend on the presence and/or formation of NbC-precipitates. Precipitation of NbC during the phase transformation, likely to take place at the austenite/ferrite interface, reduces the effective transformation rate, in some cases leading to the formation of Widmannstatten ferrite and bainite.