Novel 1.5 GPa-strength with 50%-ductility by transformation-induced plasticity of non-recrystallized austenite in duplex steels

Abstract

Needs for steel designs of ultra-high strength and excellent ductility have been an important issue in worldwide automotive industries to achieve energy conservation, improvement of safety, and crashworthiness qualities. Because of various drawbacks in existing 1.5-GPa-grade steels, new development of formable cold-rolled ultra-high-strength steels is essentially needed. Here we show a plausible method to achieve ultra-high strengths of 1.0~1.5 GPa together with excellent ductility above 50% by actively utilizing non-recrystallization region and TRansformation-Induced Plasticity (TRIP) mechanism in a cold-rolled and annealed Fe-Mn-Al-C-based steel. We adopt a duplex microstructure composed of austenite and ultra-fine ferrite in order to overcome low-yield-strength characteristics of austenite. Persistent elongation up to 50% as well as ultra-high yield strength over 1.4 GPa are attributed to well-balanced mechanical stability of non-crystallized austenite with critical strain for TRIP. Our results demonstrate how the non-recrystallized austenite can be a metamorphosis in 1.5-GPa-grade steel sheet design.

Development of a Cr-Ni-V-N Medium Manganese Steel with Balanced Mechanical and Corrosion Properties

“…In the same context for V-alloyed MMn steel, Hu et al [38] reported a small increment in yield strength due to grain refinement, however, they emphasized the role of VC precipitates and dislocation hardening in increasing the yield strength. The observed increase in yield strength due to V alloying is in agreement with several studies [39][40][41][42] that reported solely the pronounced effect of V precipitates; however, the current study emphasizes additional effects, such as grain-boundary, solid-solution, and dislocation strengthening. Furthermore, the formation of precipitates is considered to be responsible for the suppression of the complete dislocation annihilation during annealing and hence increasing the yield strength via the dislocation hardening effect.…”

Tailoring heterogeneities in high-entropy alloys to promote strength–ductility synergy

“…In Fig. 7 we summarize some recently designed HEAs that emphasize the TRIP effects 33,34,69,[74][75][76][77][78][79][80][81][82][83] ; some of these have already been included in Fig. 3, e.g., ref.…”

“…Moreover, for samples aged at an elevated temperature, e.g., homogenization at 1200 K, LCO can develop to various degrees, from short-to-medium range all the way to ordered domains on nanometer scale 89,93 . The dislocation lines become wavier due to such complex spatial : [74] : [75] : [76] : [77] : [78] : [79] : [80] : [81] : [82] : [83] Fig . 7 Yield strength versus uniform tensile strain observed in recently reported multi-principal-element steels.…”

Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength

“…Even though stacking faults (SF) are stored in large numbers due to the well-known low SF energy (SFE) of these FCC HEAs/MEAs ( 1 , 2 , 8 , 12 ), twinning became difficult in UFG grains, and, at room temperature, strain hardening remained inadequate to sustain uniform elongation after the MEA yields at >1 GPa ( 3 ). In general, plasticity-enhancing mechanisms in low-SFE alloys such as phase transformation [transformation-induced plasticity (TRIP)] ( 10 , 30 – 33 ) and twinning [twinning-induced plasticity (TWIP)] ( 1 , 2 , 34 – 41 ) all lose their potency in UFG and NG structures ( 34 , 35 , 42 , 43 ).…”