Coordination Deformation Mechanism And The Orientation Relationship Between Ferrite And Cementite In Steel

Pearlitic steel is one of the most important structural steels.The orientation relationship(OR)of ferrite-cementite in pearlitic steel would influence the mechanical properties and physical properties of steels.Investigating plastic deformation mechanism and then analyzing the influence of deformation on the two-phase OR,which are of great academical significance.In this thesis,it was obtained ferrite-spherical cementite organization through normalizing and isothermal spheroidizing annealing treatment in T10 A steel.Then the specimens were compressed with strains of 11%,30%,49% and 77% under electronic universal testing machine at room temperature.The micro-Vickers hardness of specimens before and after deformation was tested.Meanwhile,deformation behaviors of ferrite-cementite were observed systematically and their plastic deformation mechanism,the evolution of the OR was analyzed comprehensively by applying the methods of OM?SEM?XRD?EBSD and TEM.The results show that the ferrite grain size decreases,the dislocation density increases after cold compression deformation.The subgrain generates under large deformation.The micro-Vickers hardness values increases linearly with the increase of the deformation.The micro-Vickers hardness values after being compressed to 77% is about 2 times of the original hardness value before deformation,which show obvious work hardening phenomenon.TEM observations show that there are a few dislocation within the ferrite substrate under the low deformation,which caused the bent stripes within the cementite.Dislocation piled-up near grain boundaries under the large deformation and the dislocation piled-up force squeezed the cementite which pushing the dislocation source of cementite.It would cause the crystal defects such as dislocations,stacking fault in cementite and the grain plastic deformation.EBSD analysis show that the number of dislocations and Low Angle grain boundary after being compressed from 0% to 30% increased sharply,which caused {111}-type texture within ferrite.The greater the deformation strain,the higher the values of KAM.The high KAM values are mainly distributed in ferrite grain boundary,subgrain boundary and the ferrite-cementite interface.Through the electron diffraction pattern calibration and the OR matrix calculation,the OR between ferrite and cementite can be obtained.The results show that the primary OR is Pitsch-Peth OR,the secondary OR is Bagaryatsky OR and Isaichev's OR before deformation.The OR deviated from Pitsch-Peth OR after being compressed to 30%.The Pitsch-Peth OR disappeared after being compressed to 49 %.The OR matrix B tends to be uniform which indicate the original OR change to a new OR.