Research On Deformation Induced Ferrite Transformation Of V-N Microalloyed Steels

In this paper, deformation induced ferrite transformation (DIFT) behavior of twodifferent V-N microalloyed steels were systemically investigated. The hot deformationtests were carried on Gleeble3500thermal simulator and the effect of strain and strain rateon DIFT for microalloyed steel were studied at different deformation temperature (Ar3～Ae3or above Ae3). The characteristic of deformation induced microstructers wereobserved through optical microscope (OM), scanning electron microscope (SEM) andtransmission electron microscope (TEM). Meanwhile，some related date was obtained viaelectron backscattered diffraction (EBSD) technique.The results showed that the volume fraction of deformation induced ferrite (DIF)increased with the increase of strain at different deformation temperature. The tendency ofthe varriation represents S-type. The volume fraction of DIF increased slowly at lower andhigher strain, but increased rapidly at the medium stage. Deformation temperaturerestricted the DIFT process and the amount of DIF was hardly changed at870℃when80%deformation was employed. With the increase of strain rate, the amount of DIFincreased and the size reduced.The elongated austenite grain boundary, dislocation and deformation band could actas nucleation site for ferrite during deformation. Strain-induced precipitation promotesDIFT, for it could reduce the amount of vanadium dissolved in austenite, intragranularferrite nucleated at (Ti,V)(C,N) formed at the same time. Besides, continues dynamicrecrystalization of ferrite could be induced during the dynamic transformation process,which inhanced the grain refinement.