Deformation mechanism of ferrite in a low carbon Al-killed steel: Slip behavior, grain boundary evolution and GND development

The forming quality and performance of double walled brazed tube formed by steel sheet are seriously affected by the deformation behavior of the initial sheet. In this work, the deformation mechanism of ferrite in a low carbon Al-killed steel sheet was investigated by in situ tensile and electron backscatter diffraction (EBSD) tests. It is found that ferrite presents single slip, double slip and cross slip as well as slip transfer behavior in the deformation process. The activation of the {110}< 111 > slip system is the main deformation mode, the less activation number of {112}< 111 > and {123}< 111 > is due to the orientation dependence and high critical resolved shear stresses (CRSS), respectively. A high Schmid factor (SF) or geometric compatibility factor m' will contribute to slip transfer. Meanwhile, the evolution of low angle grain boundaries (LAGBs) is the main deformation feature for ferrite polycrystals, and the fraction of 2-5 degrees LAGBs in the whole LAGBs shows a strong linear relationship with strain. The subdivision of grains and rotation of different parts lead to the gradual evolution of LAGBs into high angle grain boundaries (HAGBs). Furthermore, small grains are more likely to accumulate the geometrically necessary dislocation (GND) because the microstructural unit size restricts the movement of dislocation, while the less effect of grain orientation is related to the high SF for all grains.