Studying inhomogeneous deformation of bainite-retained austenite steel during cold drawing

Influence of inhomogeneous deformation on bainite-retained austenite (RA) steel wire during cold drawing is the subject of investigation in this paper. The differences of the microstructure and fracture morphology at the surface and center of drawn steel wire were studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Surface microstructure suffered large deformation while the microstructures in the center had almost no change during cold drawing. While cold drawing, banded microstructure tends to bend and tilt at first due to longitudinal sliding of bands with each other and then was separated by dislocation bands in further deformation. The results of micro-hardness test and numerical simulation disclosed that the peak value of inhomogeneous deformation was located on the sub-surface of the sample, due to severe plastic shear in the sub-surface portions. The clear boundaries between the small shallow dimple at the deformation region of the surface and the oval dimple with developed tearing ridges at the undeformed region indicated the differences in the mode of increase in the micro-voids caused by inhomogeneous deformation.