The effect of the substitution of silicon by aluminium on the mechanical properties and the microstructure of cold rolled C-Mn-Si TRIP steels was investigated for different continuous annealing cycles.
The mechanical properties were evaluated using tensile testing. It was seen that the Al alloyed steel had very good mechanical properties with an improved formability compared to the conventional C-Mn-Si TRIP steel. The strain hardening behaviour was studied in detail. All the investigated specimens showed a very high n value but their strain dependence was different. For the conventional C-Mn-Si TRIP steel the maximum n value was reached at low strain, while the Al substituted TRIP steel showed a gradual increase of the n value. The latter effect resulted in a larger uniform elongation for the C-Mn-Al-Si TRIP steel.
Investigation of the microstructure using color etching and scanning electron microscopy revealed that the Al alloyed steel composition contained a larger amount of bainite with a finer structure than the C-Mn-Si TRIP steel. Furthermore, XRD measurements showed that the Al substitution resulted in a larger volume fraction of retained austenite.