Unique transition of yielding mechanism and unexpected activation of deformation twinning in ultrafine grained Fe-31Mn-3Al-3Si alloy

Abstract

Tensile mechanical properties of fully recrystallized TWIP steel specimens having various grain sizes (d) ranging from 0.79 μm to 85.6 μm were investigated. It was confirmed that the UFG specimens having the mean grain sizes of 1.5 μm or smaller abnormally showed discontinuous yielding characterized by a clear yield-drop while the specimens having grain sizes larger than 2.4 μm showed normal continuous yielding. In-situ synchrotron radiation XRD showed dislocation density around yield-drop in the UFG specimen quickly increased. ECCI observations revealed the nucleation of deformation twins and stacking faults from grain boundaries in the UFG specimen around yielding. Although it had been conventionally reported that the grain refinement suppresses deformation twinning in FCC metals and alloys, the number density of deformation twins in the 0.79 μm grain-sized specimen was much higher than that in the specimens with grain sizes of 4.5 μm and 15.4 μm. The unusual change of yielding behavior from continuous to discontinuous manner by grain refinement could be understood on the basis of limited number of free dislocations in each ultrafine grain. The results indicated that the scarcity of free dislocations in the recrystallized UFG specimens changed the deformation and twinning mechanisms in the TWIP steel.

Tailoring the microstructure to enhance the cryogenic mechanical properties of a Fe–34.5Mn–0.04C steel

“…Based on these results, Fe-Mn-C steels with >30% Mn and high C content (possibly up to 0.6% or even higher) as well as grain a size of a few micrometers are recommended for cryogenic applications. It should further be noted that in other high Mn steel systems, such as the Fe-Mn-Al(Si) system, an even better combination of strength and elongation can be obtained at both RT and cryogenic temperature [11,12,41,42]. The best combination of grain size and Mn-Al content for such systems, and the underlying deformation mechanisms at cryogenic temperatures, have yet to be explored.…”

Dependence of Charpy Impact Properties of Fe-30Mn-0.05C Steel on Microstructure

“…In Figure 4, the A600 and A700 specimens exhibit discontinuous yielding behavior, while other specimens demonstrate continuous yielding. Discontinuous yielding was normally observed in metals with grain sizes in the near-micrometer range, which was attributed to a lack of dislocation sources [29][30][31]. The tensile properties strongly depend on the microstructure.…”

<i>Plaston</i> Concept and Activation of <i>Plaston</i> in Bulk Nanostructured Metals

“…) のほか，純銅 (18) (23) ，Cu Al 合 金 (15) ，Cu Ag 合 金 (23) ，純 チ タ ン (12) ，チ タ ン 合 金 (21)(25)( 26) ，純マグネシウム ( 20) ，マグネシウム合金 (19) ，フ ェライト鋼 (11) ，高 Mn オーステナイト鋼 (17)(22) (24) ，オース テナイト系ステンレス鋼 (28) ，準安定オーステナイト鋼 (27) ， FCC ミディアムエントロピー合金 (16)…”