Investigation On The Orientation Dependency Of The Deformation Microstructure Of IF Steel

Dislocation slip is the basic mode for plastic deformation and also the intrinsic cause for formation of various deformation microstructures.The activation of dislocation slip is influenced by crystallographic orientation,and the deformation microstructure is thus dependent upon orientation.Consequently,investigation on the orientation dependency of deformation microstructure is of great importance,in order to have a good understanding on the formation and the evolution of deformation microstructure.Researchers have investigated and revealed the principles responsible for the orientation dependency of deformation microstructure for metals with face centered cubic crystal(FCC)structure.However,another category of metals with body centered cubic(BCC)structure have drawn surprisingly less attention.Such metals have more slip systems and unique deformation behaviors,of which the orientation dependency of deformation microstructure is keen to be addressed.Here we in the present study chose a body centered cubic IF steel as the experimental material to subject to plastic deformation via uniaxial tension and compression.The induced microstructure was quantitatively characterized by scanning electron microscope(SEM)+electron back scattering diffraction(EBSD)and transmission electron microscope(TEM)+convergent beam electron diffraction(CBED).The following results were obtained:1)A novel method to accurately determine the crystallographic orientation in TEM was developed.This determination was realized through analyzing and calculating via CBED induced Kikuchi diffraction pattern composed of as less as only one pole and one band.A computer program was built to realize analyzing on-line with a semi-automatic manner.2)BCC IF steel orientation-dependent deformation microstructure.Two types of extended boundaries were developed during the tension and compression at room temperature.One is non-crystallographic extended boundaries that are not aligned with any of the slip planes,and the other is crystallographic extended boundaries that are inclined a small angle(<10~o)with one of the slip planes.Non-crystallographic boundaries were formed in grains with their<011>close to the tension and/or compression axis,while grains with the rest orientations form crystallographic ones.Crystallographic extended boundaries can be classified into{110}-and{112}-type according to the aligned slip planes.3)BCC IF steel does not form dislocation cell structure during tension and compression under room temperature.Activation of screw dislocations is more difficult than edge and mixed dislocation.Such behavior is independent of grain size,strain amplitude and strain rate.4)The orientation-dependent deformation microstructure of BCC IF steel is related to the choice of slip systems.The slip systems that are aligned with the crystallographic extended boundaries usually have biggest Schmidt factor.Non-crystallographic extended boundaries are not aligned with any slip systems having biggest Schmidt factor.