Microstructural evolution and strain hardening behavior during plastic deformation of Fe-12Mn-8Al-0.8C steel

Microstructural evolution and deformation mechanism of a Fe-12Mn-8Al-0.8C steel were investigated. The steel exhibited a good combination of strength over 900 MPa and ductility about 46%. The microstructure of the Fe-12Mn-8Al-0.8C steel in solid solution state was a mixture of the (α+γ+κ) phases. The κ phase carbides ((Fe,Mn)3AlCx) were formed by a spinodal decomposition during quenching. The deformation behavior of the austenite in the early deformation stage was fully determined by the size of the dislocation substructure, namely, dislocations alignment and Taylor lattices. With strain increasing, a gradual transition from Taylor lattices to highly dense dislocation walls and microbands was observed in austenite. Ferrite exhibited randomly distributed dislocations at a low strain and high dense dislocation tangles at a strain of 20%. TEM observations revealed ordered κ-carbide precipitates were sheared by slip bands at a strain of 30%. The present steel presented a multiple-stage strain hardening behavior which was associated with the changes of such dislocation substructures. The steel also exhibited a high initial strain hardening rate and a high specific strength about 130.5 MPa cm3/g.