Abstract
Microstructure evolution, transformation behavior and mechanical property are examined for a Fe-0.35C-1.1Mn-4.1Al-0.38Si (in wt%) ferrite-based lightweight transformation induced plasticity (TRIP) steel under tensile deformation at room temperature (25 °C) to 450 °C. The influence of deformation temperature and strain on mechanical stability of retained austenite leads to the occurrence of various transformations in the TRIP steel. From room temperature towards 150 °C, strain induced martensitic transformation (SIMT) takes place resulting in the formation of twin-type martensite, and it is progressively suppressed with increasing deformation temperature. A phenomenon of strain induced bainitic transformation (SIBT) of retained austenite is observed at higher deformation temperatures, and it is enhanced with increasing deformation strain and temperature ranging from 150 °C to 300 °C. During the SIBT, the formation of carbide-free bainite with high dislocation density is primarily attributed to the increased carbon diffusivity. The occurrence of the SIBT reveals the significant importance of the diffusion-associated mechanism for the bainitic transformation. Above 300 °C, the activation of dislocation movement in retained austenite gradually replaces the SIBT with increasing deformation temperature. The highest tensile strength obtained at 300 °C indicates the strength enhancement due to the SIBT.
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