Plasticity instability behavior of hot rolled medium-Mn steel after inter-critical quenching during uniaxial tension

Combined with digital image correlation （DIC）， infrared thermal imaging （IRT）， electron backscatter diffraction （EBSD）， and microhardness distribution， the plastic instability behavior of medium-Mn steel processed by inter-critical quenching during uniaxial tension was analyzed. The results show that the strain-induced martensite transformation of experimental steel mainly occurs in the early stage of uniaxial tension. The Portevin-Le Chatelier（PLC）bands are obviously formed and propagated during this process， accompanied by thermal fluctuations. Moreover， the type of the PLC bands has transitioned from type A to type B and then to type A. The PLC bands are formed by the interaction between dislocation multiplication and interstitial solute atoms， i.e.， dynamic strain aging （DSA）. In the early stage of deformation， the dislocation will preferentially move to the low-density dislocation area， i.e.， propagate unidirectionally along the axis （the type A band）. Then， in the middle stage， the dislocation multiplication and initial interaction leads to the jumping （type B） PLC band formation. Finally， dislocation density and interactions increase in the later stage of deformation， leading to the formation of the type A PLC band again.