In-Situ Electron Backscatter Diffraction Study of Deformation Behavior of Fine-grained Dual Phase Steel Subjected to Uniaxial Tension

In this work, the deformation behavior of fine grained dual phase steel with intragranular martensite distribution as thin boundaries is studied via in-situ EBSD investigation and full field fast Fourier transform based crystal plasticity simulation. The effect of grain size and intragranular martensite fraction on the crystal plasticity of grains is examined by analyzing the geometrically necessary dislocation (GND) density evolution and reorientation magnitude. The size of the grains/subgrains is found to profoundly govern the rotation magnitude and development of GNDs by controlling the effect of intragranular and grain boundary martensite on the stress/strain state of grains during deformation. It is observed that for comparable grain sizes and similar initial orientation, higher intragranular martensite fraction leads to higher initial GND density, lesser lattice rotation, and higher development of GND density under deformation. Alternatively, among grains of similar initial orientation and martensite content, coarse grain evolves with higher GND density and rotation magnitude under deformation than the finer ones. However, the initial GND density is higher in fine grains. The stress-strain development obtained from crystal plasticity simulation corroborates the above observations and demonstrates a strong dependence on the intragranular martensite. On the whole, the combined investigation of experimental and simulation results suggests that intragranular martensite fraction and ferrite grain size are the two major, interdependent parameters that govern the crystal plasticity behavior of dual phase steel studied with martensite morphology as thin boundaries.