Abstract
ABSTRACTThe conventional alloy design of medium Mn steel is to optimize the transformation-induced plasticity (TRIP) effect. Here we show that a dual-phase heterogeneous structure is sufficient to develop a medium Mn steel with high yield strength (∼1.2 GPa) and large uniform elongation (∼14.5%). The ultra-high strength is contributed by high back-stress while the large ductility is induced by strain-gradient plasticity and back-stress hardening, both of which are inherent to dual-phase heterogeneous structure. TRIP effect is suppressed during plastic deformation. Therefore, medium Mn steel can be strong and ductile by engineering dual-phase heterogeneous structure without resorting to TRIP effect.IMPACT STATEMENTWe demonstrate that medium Mn steel can be strong and ductile by engineering dual-phase heterogeneous structure without resorting to the conventional transformation-induced plasticity (TRIP) effect.
Highlights
Advanced high-strength steels (AHSSs) are designed for structural applications in automotive industry to improve energy efficiency and reduce greenhouse gas emission [1]
We demonstrate that medium Mn steel can be strong and ductile by engineering dual-phase heterogeneous structure without resorting to the conventional transformation-induced plasticity (TRIP) effect
High-strength medium Mn steel developed by strategies that are not relying on TRIP effect will be desirable for avoiding the delayed fracture in automotive applications
Summary
Advanced high-strength steels (AHSSs) are designed for structural applications in automotive industry to improve energy efficiency and reduce greenhouse gas emission [1]. Medium Mn steel is a promising candidate in the 3rd generation AHSSs due to its excellent combination of strength and ductility [2–7]. Medium Mn steel has a dual-phase microstructure with retained austenite grains embeded in the ferrite matrix [4,5]. The retained austenite grains may transform into martensite during plastic deformation, providing a tranformation-induced plasticity (TRIP) effect to enhance the work-hardening behavior [4,5]. The mechcanical stability of retained austenite grains should be optimized to achieve medium Mn steel with high strength and high ductility. The formation of fresh martensite during plastic deformation will facilitate the delayed fracture induced by hydrogen embrittlement in high-strength medium Mn steels with TRIP effect [9,10]. High-strength medium Mn steel developed by strategies that are not relying on TRIP effect will be desirable for avoiding the delayed fracture in automotive applications
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