Evolution of dislocations and twins in a strong and ductile nanotwinned steel. (1st June 2016)

• Record Type: Journal Article
• Authors: Zhou, P.; Liang, Z.Y.; Liu, R.D.; Huang, M.X.
• Is Part Of: Acta materialia. Volume 111(2016)
• Page Start: 96
• Page End: 107
• Publication Date: 2016-06-01
• Subjects: Nanotwin -- TWIP steel -- Twin volume fraction -- Dislocation density -- Synchrotron X-ray diffraction; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2016.03.057
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: A twinning-induced plasticity (TWIP) steel was subjected to a simple processing route (i.e. cold rolling followed by a recovery heat treatment) suitable for large-scale industrial production, resulting in the production of a strong and ductile nanotwinned steel. This nanotwinned steel combines high yield strength (1450 MPa), high ultimate tensile strength (1600 MPa) and good ductility (25% total elongation). Detailed transmission electron microscopy observation reveals that the twin volume fraction of the nanotwinned steel remains constant during tensile deformation. This is different to the deformation behaviour of recrystallized TWIP steels whose twin volume fraction increase continuously with strain during tensile deformation. The constant twin volume fraction indicates that a maximum twin volume fraction has been reached during the cold rolling process. In contrast, the dislocation density of the nanotwinned steel increases with strain as measured by the synchrotron X-ray diffraction experiments. In other words, the plastic deformation of the nanotwinned steel is mainly accommodated by glide and multiplication of dislocations. Based on the experimental results, an analytical model was developed to capture the respective effects of dislocations and twins on the strength and ductility of the present nanotwinned steel. The modelling results indicate that the strength is contributed by both twins and dislocations while the ductility is mainly attributed to dislocation multiplication. Graphical abstract: (a) TEM bright field image showing intensive nanotwins in the nanotwinned steel. Selected area diffraction pattern obtained within the red circle. (b) The engineering stress–stain curve of the nanotwinned steel.