Study On Deformation Induced Pearlite Transformation Of Eutectoid Steel

Deformation induced phase transformation is an effective method to refine grains and improve the properties of steel materials.At present,a large number of studies have been conducted in the field of deformation induced ferrite transformation and deformation induced martensite transformation in low carbon steel,many research achievements have been applied in industrial production.However,the study on the deformation induced pearlite transformation is mainly focused on the ordinary carbon steel at present,it still needs to carry on the experiment to complete.In this paper,the study of deformation induced pearlite transformation(DIPT)of the eutectoid steel without V and with V is carried out.By the means of microstructural observation(by OM,SEM,TEM)and critical strain calculation,the paper mainly discusses the evolution and properties of deformation induced pearlite transformation under different deformation conditions and the influence of V element on the deformation induced pearlite transformation.The results show that:(1)the application of stress can advance the phase transformation kinetics,and the deformation induced pearlite transformation can occur rapidly during the deformation process.The microstructure shows dynamic change under different deformation conditions.Increasing the deformation degree,the density of dislocations increases,at the same time,the driving force of phase transformation accelerates the occurrence of phase transformation and the process of cementite spheroidization.Beacause of the diffusion-controlled phase transformation,the deformation rates decrease to prolong the deformation time,so the carbon atoms can diffuse sufficiently to obtain spheroidized cementite;At lower deformation temperature,significant refinement of the fragmentation of cementite occurs due to the increase of supercooling and spheroidized time.The ultrafine microstructure of cementite particles can be obtained through the high deformation degree,low deformation rates and low deformation temperature.(2)V can refine the cementite particles and obtain the ultrafine microstructure of cementite particles.The addition of V makes the induced pearlite phase transformation not only take precedence in the original austenite grain boundary,but also exist in the austenite crystal.In addition,the hardness of the material is improved by adding V under the same deformation condition because of the strengthening mechanism.(3)the pro-eutectoid ferrite transformation at the grain boundary is affected by the diffusion of C atoms in the eutectoid steel with higher carbon content than the eutectoid point.The volume fraction of pro-eutectoid ferrite increases with the increasement of the deformation degree,but decreases with the increasement of the deformation rate.The addition of V significantly promoted the phase transformation of pro-eutectoid ferrite at grain boundaries.In addition,due to the pinning effect of V precipitates,the pro-eutectoid ferrite was refined,and the diameter of pro-eutectoid ferrite slightly reduced.