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Metals 2019, 9(3), 367; https://doi.org/10.3390/met9030367

Strain Hardening, Damage and Fracture Behavior of Al-Added High Mn TWIP Steels

1
Steel Institute (IEHK), RWTH Aachen University, Intzestraße 1, 52072 Aachen, Germany
2
Central Facility for Electron Microscopy (GFE), RWTH Aachen University, Ahornstraße 55, 52074 Aachen, Germany
3
Institute of Metal Forming (imf), TU Bergakademie Freiberg, Bernhard-von-Cotta-Straße 4, 09599 Freiberg, Germany
*
Author to whom correspondence should be addressed.
Received: 15 February 2019 / Revised: 18 March 2019 / Accepted: 19 March 2019 / Published: 21 March 2019
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
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Abstract

The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m 2 and 29 mJ/m 2 . The evolution of microstructure, deformation mechanisms and micro-cracks development with increasing deformation was analyzed. Al-addition has led to the decrease of C diffusivity and reduction in tendency for Mn-C short-range ordering resulting in the suppression of serrated flow caused due to dynamic strain aging (DSA) in an alloy with 0.3 wt.% C at room temperature and quasi-static testing, while DSA was delayed in an alloy with 0.6 wt.% C. However, an alloy with 0.6 wt.% C showing DSA effect exhibited enhanced strain hardening and ductility compared to an alloy with 0.3 wt.% C without DSA effect. Twinning was identified as the most predominant deformation mode in both the alloys, which occurred along with dislocation glide. Al-addition has increased SFE thereby delaying the nucleation of deformation twins and prolonged saturation of twinning, which resulted in micro-cracks initiation only just prior to necking or failure. The increased stress concentration caused by the interception of deformation twins or slip bands at grain boundaries (GB) has led to the development of micro-cracks mainly at GB and triple junctions. Deformation twins and slip bands played a vital role in assisting inter-granular crack initiation and propagation. Micro-cracks that developed at manganese sulfide and aluminum nitride inclusions showed no tendency for growth even after large deformation indicating the minimal detrimental effect on the tensile properties. View Full-Text
Keywords: TWIP steel; deformation twinning; serrated flow; dynamic strain aging; damage; fracture TWIP steel; deformation twinning; serrated flow; dynamic strain aging; damage; fracture
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Madivala, M.; Schwedt, A.; Prahl, U.; Bleck, W. Strain Hardening, Damage and Fracture Behavior of Al-Added High Mn TWIP Steels. Metals 2019, 9, 367.

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