Abstract
A novel medium manganese steel with composition Fe–8.3Mn–3.8Al–1.8Si–0.5C–0.06V–0.05Sn was developed and thermomechanically processed through hot rolling and intercritical annealing. The steel possessed a yield strength of 1 GPa, tensile strength of 1.13 GPa and ductility of 41 pct. In order to study the effect of cold rolling after intercritical annealing on subsequent tensile properties, the steel was further cold rolled up to 20 pct reduction. After cold rolling, it was observed that the strain hardening rate increased continuously with increasing cold rolling reduction but without a significant drop in ductility during subsequent tensile tests. The microstructural evolution with cold rolling reduction was analysed to understand the mechanisms behind this phenomena. It was found that cold rolling activated additional twinning systems which provided a large number of potent nucleation sites for strain induced martensite to form during subsequent tensile tests in what can be described as an enhanced TRIP effect.
Highlights
MEDIUM Mn steels (4À12 wt pct Mn) are an emerging class of duplex (c þ a) steels that have received considerable research attention
Si content was chosen to be below 3 wt pct as Si might stabilise and embrittle d-ferrite at room temperature when added in excess.[24]
Al can significantly reduce the density of steel,[25] Al content was chosen to be kept below 4À5 wt pct as Al is known to clog continuous casting nozzles[26] and form brittle j-carbides in medium Mn steels when added in excessive amounts.[25,27]
Summary
MEDIUM Mn steels (4À12 wt pct Mn) are an emerging class of duplex (c þ a) steels that have received considerable research attention. Medium Mn steels have shown to exhibit a successive twinning and transformation induced plasticity (TWIP + TRIP) effect if the Stacking Fault Energy (SFE) and stability of the austenite phase are adjusted into the correct regime during an Intercritical Annealing (IA) heat treatment.[1,2]. The TWIP + TRIP effect allowed some medium Mn steels to possess large ductilities of 60À70 pct[2–5] and show great potential for use in energy absorbing applications. Many medium Mn steels which exhibit the TWIP + TRIP effect are manufactured by a thermomechanical process composed of hot rolling followed by cold rolling and IA. IA is greatly enhanced with prior cold rolling such that IA can be completed
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