Low alloy TRIP aided steels are of particular interest to the automotive industry as they offer an excellent combination of strength and ductility at affordable costs. These unique properties depend primarily on the deformation induced transformation behaviour of retained austenite to martensite, which was the focus of the present study. This work was carried out on two steel compositions. While one of them was a commercially produced hot rolled CMnSi TRIP aided steel with polygonal ferrite as the matrix phase, the other steel was a CMnAlSi composition, received in the form of cold rolled sheets with ferrite + pearlite as the initial microstructure. The second steel was subjected to three heat treatment schedules to produce TRIP-aided steels with polygonal ferrite (PF), annealed martensite (AM) and bainitic ferrite (BF) matrix microstructures. The transformation behaviour of the steels during continuous cooling was determined using dilatometry. Continuous cooling transformation (CCT) diagrams were constructed from the experimental data. The microstructure development during heat treatment was studied in some detail.