Nucleation, coarsening and deformation accommodation mechanisms of ε-martensite in a high manganese steel

Abstract

The nucleation, coarsening and deformation accommodation mechanisms of ε-martensite in an Fe-17Mn-3Al-2Si-1Ni-0.06C wt.% high manganese steel subjected to plane strain compression and coldrolling up to 88% thickness reduction was studied using a combination of electron microscopy techniques.

Effect of Uniaxial Tension on the Microstructure and Texture of High Mn Steel

“…On the other hand, the ϵ ‐martensite recorded the appearance of a small peak between 86° and 90° around the axis after tension; corresponding, to extension twinning. The extension twin formation in ϵ ‐martensite was also observed during the plane strain compression of the present steel to 20% thickness reduction . Parallel extension twins with similar orientations were observed inside a single ϵ ‐martensite lath during the uniaxial tension of an Fe–15Mn–0.005C steel .…”

“…Using in situ tensile testing accompanied by neutron diffraction, Saleh et al demonstrated the ϵ ‐martensite to undertake compressive strains, which also indicated that ϵ ‐martensite accommodates deformation. During the plane strain compression of the present steel to 20% thickness reduction, the transformation of γ to deformation‐induced ϵ and α ′‐martensite was also observed without the formation of deformation‐induced twins in γ . The microstructure of the 500 °C sample indicated that the reversion of ϵ and α ′‐martensite phases back to γ was underway (Figure b).…”

Effect of isochronal annealing on the microstructure, texture and mechanical properties of a cold-rolled high manganese steel

“…During cold-rolling, the γ grains undergo subdivision and phase transformation to ε-martensite and α′martensite. Furthermore, the thick ε-martensite plates carried over from hot-rolling also transform to α′-martensite [27]. The delayed transformation of unfavourably oriented γ grains to ε-martensite and the sub-division of thick ε-martensite plates by α′-martensite leads to the presence of γ and εmartensite pockets in the cold-rolled sample ( Fig.…”

“…In this regard, in-situ neutron diffraction and combined TEM/TKD results by Saleh and Gazder et al [5,6,33] showed the feasibity of deformation accommodation in ε-martensite. In an following detailed TEM study, ε-martensite was found to accommodate deformation via the formation and change in stacking fault character when the steel is progressively cold-rolled up to 42% thickness reduction [27]. A mechanism enabling the change in stacking fault character was proposed which involves the motion of Shockley partial dislocations on every plane below the stacking fault plane.…”

“…After hot-rolling, the microstructure consists of coarse γ grains containing plate like ε-martensite and lenticular α′-martensite with the area fractions 68%, 12% and 20%, respectively [27]. The EBSD maps of the 600, 625 and 650 °C annealed samples were segmented into reverted/recovered and recrystallised γ grain fractions by modifying the modifying the procedure developed by Gazder et al [28,29].…”