Ultrahigh strength-high ductility 1 GPa low density austenitic steel with ordered precipitation strengthening phase and dynamic slip band refinement

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-03, Vol.838, p.142829, Article 142829
• Main Authors: Wei, L.L., Gao, G.H., Kim, J., Misra, R.D.K., Yang, C.G., Jin, X.J.
• Format: Article
• Language: English
• Subjects: Austenitic stainless steels; Cross slip; Deformation; Ductility; Dynamic slip band refinement; Edge dislocations; Electron microscopy; Elongation; k-carbides; Low density materials; Low density steel; Mechanical properties; Microscopy; Niobium; Planar glide; Plastic deformation; Precipitates; Precipitation hardening; Precipitation hardening steels; Shearing; Steel; Strain hardening; Strain localization; Twin boundaries; Ultimate tensile strength; Weight reduction; Work hardening
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.142829

Low density steels are of significant interest because of light weight combined with high strength-high ductility combination. We describe here a comprehensive understanding of the mechanical behavior of Fe–27Mn–9Al–1C austenitic steel microalloyed with Nb in terms of work hardening behavior and plasticity mechanisms. The evolution of deformed microstructure with strain was studied via post-mortem electron microscopy and electron back scattered diffraction (EBSD). The experimental steel was characterized by ultimate tensile strength and elongation to fracture of 1125 MPa and 30.8%, respectively. Plastic deformation was accommodated by pronounced planar dislocation slip and characterized by a single planar dislocation glide at low strain and multiple planar slip at high strain. Electron microscopy studies indicated that some of the ordered kappa carbide precipitates of size ∼5–7 nm, which were uniformly distributed in the austenite matrix were sheared by planar glide dislocations during deformation. The slip band spacing decreased gradually during straining and cross-slip of dislocations occurred at high strain. The planar dislocation glide phenomenon is attributed to the superposition of sheared ordered phase and short range ordering (SRO), which can lead to glide plane softening. Dynamic slip band refinement and shearing of precipitates led to constant strain hardening of austenitic steel. Annealing twin boundaries acted as dislocation source to generate dislocations during deformation, which were helpful in further sub-division of slip bands and suppressing strain localization.