Machining Hardening Mechanism And Grain Coarsening Toughening Mechanism Of Nitrogen-strengthened High Manganese Austenitic Steel

The effect of solution temperature and holding time on grain size and impact value of 22Mn-13Cr-3Ni-1Mo-1Cu-0.2N steel was studied by solution treatment.The deformation of experimental steel at room temperature was analyzed by means of metallography,XRD,TEM and TEM in situ tension,and the processing hardening mechanism and toughening mechanism of grain coarsening of experimental steel were discussed.The results show that the austenite structure of the experimental steel at room temperature is FCC structure.Dislocation hardening,gamma-epsilon transformation,TWIP effect,TRIP effect and dynamic H-P strengthening effect occur during deformation at room temperature.The experimental steel has strong work hardening and dynamic toughening behavior.The mechanism of work hardening of experimental steels is dislocation slip and multiplication,gamma-epsilon transformation and dislocation interaction to form slip bands.When the slip of dislocations is hindered,the shear deformation of crystals becomes stacking faults and twins.The interaction of dislocations,stacking faults and twins leads to work hardening.The impact toughness of the experimental steel increases with the increase of grain size.The twin formed during deformation has dynamic H-P enhancement effect.On the one hand,the formation of twins adjusts the orientation of crystals and makes the hindered dislocations slip again to increase plasticity;on the other hand,the sliding dislocations can not cross the twin boundary and are confined to a small area,thus forming the effect of grain refinement.The larger the grain size,the larger the twin crystal integral,the more the dislocation slip induced plasticity and the dynamic grain refinement effect of twin grain boundary,the higher the impact toughness.It is also found that the total dislocations of the extended dislocations in the experimental steel are easily entangled with the matrix dislocations to form slip bands,which hinder the slip and cross-slip of the stacking dislocations and strengthen the material.The stacking dislocations formed during deformation can slip together with the total dislocations and incomplete dislocations to increase the plasticity of the material;It is difficult for stacking faults to cross-slip,and the increase of the area of stacking faults leads to lattice distortion.