E-martensitic Transformation Research Articles

Mn vaporization control and stress-induced martensite transformation in high-manganese steel welds under different laser keyhole conditions

Vaporization modeling of high-Mn steel during laser welding, along with the effects of Mn vaporization on the tensile properties at room and cryogenic temperatures, were investigated for various laser defocusing (LD) conditions. The LD10 exhibited a full penetration keyhole, while LD20 showed a partial penetration keyhole. The vaporization modeling based on computational fluid dynamics (CFD) analysis confirmed that a significant Mn flux occurred in LD20, which corresponded with the most substantial loss of Mn observed in the partially penetrated weld. The room temperature tensile testing showed a slight increase in the yield strength and a minor reduction in tensile elongation for LD20, which could be attributed to the stress-induced ε-martensitic transformation. In cryogenic tensile testing, LD20 exhibited a higher yield strength with more martensitic transformation, including some stress-induced α′-martensitic transformation observed. Through the vaporisztion modeling, significant Mn vaporization in LD20 was found to decrease the stacking fault energy, which enhanced stress-induced martensite transformation and yielding stress during tensile deformation at 110 and 298 K.

Correlation of austenite grain size with ε-/α′-martensitic transformation and mechanical properties in a high-manganese damping steel

One of the core studies on low stacking fault energy (SFE) high-manganese steel is to maintain excellent damping capacity while achieving high strength and toughness. The austenite grain size (AGS) in high-Mn steel affects its SFE and even the strength-plasticity and damping capacity of the steel, but the detailed mechanism related to martensitic transformation has not been clarified. In this study, Fe-17Mn high-Mn damping steel is used as the material to obtain austenite grains of different sizes by controlling the cold rolling and annealing processes. By using in-situ tensile testing, damping capacity testing, and various microscopic analytical techniques, the influence of AGS on the thermal/deformation induced martensitic transformation, work hardening behavior, mechanical properties and damping capacity of the steel is mainly studied. The results indicate that the refinement of austenite grain increases the SFE of high-Mn damping steel and reduces the amount of thermal induced ε-martensite (εth) and stacking faults (SFs). The deformation induced martensitic transformations (DIMTs) in high-Mn damping steel during tensile deformation include γ→εD, εth→α′ and εD→α′ transformation. The deformation induced ε-martensitic transformation is more helpful to improve the work hardening rate than deformation induced α′-martensitic transformation. Due to the concentration of strain partitioning at grain boundaries, twin boundaries and phase boundaries, refinement of austenite grain can promote deformation induced ε-martensitic transformation and improve the steel strength. However, excessively small austenite grains can suppress deformation induced α′-martensitic transformation leading to a significant decrease in elongation. Under the synergetic effects of grain refinement strengthening and multiple martensitic transformations, when the average AGS is about 4.0 μm, the steel has high strength and high plasticity, with a tensile strength of 919 MPa, a yield strength of 518 MPa and an elongation of 46.4 %. The product of tensile strength and elongation is up to 42.6 GPa·%. At low or high strain amplitudes, the damping capacity of this steel shows an opposite trend with the refinement of AGS. The damping capacity of the steel gradually increases with grain refinement at low strain amplitudes of 0.01 %–0.065 %, mainly due to the reduction of the content of weak pinning points. At high strain amplitudes of 0.065 %–0.1 %, the damping capacity of the steel gradually decreases for the reduction of damping sources with the refinement of grain size.

Effect of Co-content on microstructure, phases, and mechanical properties of laser additive manufactured Cox(CrNi)100-x alloy

This study describes the combination of mechanical properties of the CoCrNi medium entropy alloy system by tailoring its non-equiatomic compositions. The Laser Directed Energy Deposition (LDED) based Additive Manufacturing (AM) technique is deployed to fabricate the Cox(CrNi)100-x (x=40, 50, 60) alloy system. All compositions exhibit the formation of solidification substructures, with the refinement of subgrain size correlated with an increase in Co-content. The Co40 alloy exhibited a single-phase FCC structure, while Co50 (3.1 % ε-martensite) and Co60 (53.6 % ε-martensite) exhibited dual FCC+HCP structure during deposition. The combined effect of dislocation slip, deformation twinning, and deformation-induced HCP ε-martensite transformation strengthened the Co40 alloy during deformation. However, the Transformation-Induced Plasticity effect (TRIP) resulted in greater HCP ε-martensite transformation during deformation. Due to limited slip systems in the HCP structure, the Co60 alloy showed lower strength. The TRIP effect is highly dominant in Co60 alloy due to the prevalent HCP phase fraction in the initial samples. This led to stress concentration at FCC grain boundaries and ε-martensite, resulting in early failure of the alloy. With the increase in Co-content, the deformation mechanism changed from dislocation slip to deformation twinning to HCP ε-martensitic transformation. The LDED-built Cox(CrNi)100-x alloy system showed a good combination of strength and ductility. The study suggests that additive manufacturing is an easier and more suitable technique for obtaining compositions with the desired combination of mechanical properties.

Atomic-scale understanding of twin intersection rotation and ε-martensite transformation in a high Mn twinning-induced plasticity steel

Twin intersections have been reported to significantly impact on macroscopic properties by relaxing localized stress concentration and accommodating strain. Here the atomic-scale structural characterization of the twin intersection region in a deformed high Mn twinning-induced plasticity (TWIP) steel was conducted using high-resolution transmission electron microscopy. Detailed microstructural features were revealed at the twin intersection region, including twin intersection rotation, low angle grain boundary and ε-martensite. The twin intersections were observed to preserve the face-centered cubic structure, which exhibits deviation angles of ∼0–15o with respect to the barrier twin depending on the localized stress concentration. Interestingly, the ε-martensite was observed in the vicinity of the twin intersection, which shows a wedge shape, distinct from the usual plate-like deformation-induced martensite. Therefore, we identified here a novel stress relaxation mechanism at the twin intersection region. Based on the detailed microstructural characterization of the twin interaction region at the atomic scale, the fundamental dislocation mechanisms of twin transmission and interaction were discussed. The research thus advances the understanding of twin intersection rotation and ε-martensite transformation by twin-twin interactions.

Investigations on austenite stability and martensitic transformation kinetics of a medium Mn steel under different strain states

Martensitic transformation has received wide attention due to its significant role in improving mechanical properties of medium Mn steels. In this paper, three typical strain states in sheet metal forming, uniaxial tension, biaxial tension and plane strain states, were selected to investigate the effect of the strain state on martensitic transformation of a medium Mn steel at room temperature. The experimental results show that the austenite stability of the medium Mn steel is seriously strain state dependent. The sample deformed under the plane strain state exhibits the lowest austenite stability, while it progressively increases for biaxial tension and uniaxial tension states. The microstructural evolution and the strain partitioning behavior of the material are characterized. It is indicated that the strains in austenite under different deformation modes are quite different even though the overall deformation conditions are similar, which leads to different transformation rates of γ → α’ transformation. Besides, the ε-martensitic transformation that only generates under the plane strain state further decreases the austenite stability. A strain state dependent α’-martensitic transformation kinetics law is proposed that incorporates the effect of the stress triaxiality and Lode angle parameter, which provides a reasonable prediction of γ → α’ transformation in the medium Mn steel over a wide range of strain states.

Effect of Cobalt Addition on the Evolution of Austenite and ε-Martensitic Transformation during Loading of 201 Stainless Steel

Effect of Cobalt Addition on the Evolution of Austenite and ε-Martensitic Transformation during Loading of 201 Stainless Steel

A new route to achieve high strength and high ductility compositions in Cr-Co-Ni-based medium-entropy alloys: A predictive model connecting theoretical calculations and experimental measurements

A new route to achieve high strength and high ductility compositions in the Cr-Co-Ni medium entropy alloys (MEAs) is proposed, by controlling the solid solution hardening parameter (Mean Square Atomic Displacement, MSAD) and twinning propensity parameter (Stacking Fault Energy, SFE), respectively. The MSAD is calculated to increase with the increase in the Cr content and with the increase in the Ni/Co ratio at high Cr concentrations, while the SFE is calculated to decrease with the increase in the Cr content and with the increase in the Co/Ni ratio at high Cr concentrations. In experiment, the strength at 0 K (derived from the temperature dependence of yield stress) increases as the Cr content increases and/or as the Ni content increases for a given high Cr content, so that a linear correlation is found between the yield strength at 0 K and MSAD. The SFE also decreases as the Cr content increases and as the Co content increases for a given high Cr content. However, while the tensile elongation increases with the decrease in SFE down to SFE values of 10–12 mJ/m2, it abruptly decreases once the SFE decreases below this value due to a change in major deformation mode from deformation twinning to deformation-induced ε-martensite transformation. Based on the established connection between the theoretical calculation and experimental measurement, outstanding combinations of strength and ductility are predicted and experimentally confirmed at high Cr compositions and at a bit Ni-rich side of the Co/Ni equi-composition line. The proposed composition (around 45Cr-20Co-35Ni) exhibits a greater 0 K strength and a superior 77 K tensile ductility by 32 % and 13 %, respectively, compared to those of the equiatomic Cr-Co-Ni alloy.

The synergistic effect of grain refinement and precipitation strengthening on mechanical properties and dry sliding wear behavior of medium manganese steels

The hot rolled medium manganese Ti-bearing and Ti-free steels were solution treated at 1000 ℃ and then aged at 500, 550 and 600 ℃, respectively. The results showed that Ti-bearing steel had refined grain size but higher hardness than Ti-free steel. Moreover, Ti-bearing steel exhibited a superior impact toughness than Ti-free steel, especially when the samples were aged at 500 ℃, which was attributed to the homogeneous distribution of Ti(C, N) precipitates and alloyed cementite in the matrix. In addition, the Ti-bearing steel aged at 500 ℃ exhibited the best wear resistance despite its lower initial hardness, which was primarily attributed to the significant work hardening achieved by ε-martensitic transformation and mechanical twins during wear deformation.

Correlation between microstructure and shape memory properties in an Fe-9.5Ni-6.5Mn dual phase steel developed by intercritical annealing and subsequent ageing

Research was conducted to investigate the shape memory properties related to the microstructure in an Fe-9.5Ni-6.5Mn (wt.%) dual phase steel developed by intercritical annealing and subsequent ageing. Electron back scattering diffraction (EBSD) analysis and high resolution transmission electron microscope (HRTEM) images revealed that the microstructure of the initial steel in the solution-annealed condition was a typical lath α′-martensite with a high density of dislocations. During the intercritical annealing treatment of the solution-annealed steel at 590 °C in the ferritic-austenitic (α+γ) two-phase region for various annealing times, a part of α′-martensite transformed to the reversed γ-austenite with a difusionless shear nature, resulting in the development of a dual-phase (α′+γ) steel. Also, subsequent ageing treatment of the intercritically annealed steel at 480 °C for 3.6 ks led to formation of the nanoscale θ-NiMn precipitates in the dual-phase microstructure. The experimental results indicated a maximum shape recovery of ∼55% at 1% pre-strain for the intercritically annealed steel for 1.8 ks, followed by subsequent ageing. The presence of austenite phase reinforced by precipitates in the dual-phase steel was the main reason for appearance the shape recovery. In addition, the existence of isolated stacking faults in the reversed austenite region after straining confirmed that the occurrence of the austenite to ε-martensite transformation (γ→ε) under loading and the reverse transformation (ε→γ) upon heating are the main causes of the shape memory effect in the studied steel.

Influence of hydrogen on deformation and fracture mechanisms in austenitic steel types

In the present work, the hydrogen/material interaction with two austenitic steel types, created via a completely different alloying strategy, is investigated. The two steels include 304L austenitic stainless steel (ASS) and 18Mn-0.6C twinning-induced plasticity (TWIP) steel. Constant extension rate tensile tests are performed to evaluate the influence of hydrogen on the deformation and fracture mechanisms. A reference condition without hydrogen is compared to a seven days electrochemically hydrogen precharged condition. 304L ASS shows transformation to α’-martensite without hydrogen, while hydrogen increases the α’-martensite fraction and additionally enables the transformation to ε-martensite. The fracture surface has a transgranular, quasi-cleavage appearance. The TWIP steel shows deformation twinning without hydrogen, while abundant ε-martensite transformation is observed in the presence of hydrogen. The fracture type is intergranular due to the high cracking sensitivity of the grain boundaries.

Transformation-induced plasticity via γ → ε → α’ and γ → ε → γ martensitic transformations in Fe–15Mn–10Cr–8Ni–4Si alloy

Transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) are key mechanisms for achieving excellent strength–ductility in advanced high-strength steels (AHSSs). The Fe–15Mn–10Cr–8Ni–4Si alloy is an austenitic steel that exhibits high plastic fatigue durability due to reversible bidirectional γ→ε→γ martensitic transformation under push–pull cyclic loadings. In addition to the fatigue property, the Fe–15Mn–10Cr–8Ni–4Si alloy exhibits good strength–ductility balance (where the product of strength and ductility is 51.4 GPa%). In particular, its total elongation of 77% is comparable to those of TWIP steels. To elucidate the underlying mechanism for the TRIP-enhanced ductility, this study reports on the tensile deformation microstructure. The post-fracture microstructure is a γ-ε-α′ triple-phase structure that includes a significant amount of deformation-induced ε-martensite, whereas the frequency of γ-twinning was very limited. In addition to sluggish strain-induced ε-martensitic transformation (ε-TRIP), two-stage γ→ε→α′ martensitic transformation (two-stage TRIP) and bidirectional γ→ε→γ transformation (B-TRIP) under monotonic tensile loading were uniquely observed at intersections of the ε-martensite variants. The tensile property and microstructure of the Fe–15Mn–10Cr–8Ni–4Si alloy (where the Gibbs free energy difference ΔGγ→ε between γ-austenite and ε-martensite is −65.0 J/mol) are compared with those of the Fe–30Mn–(6−x)Si–xAl (x = 0, 1, 2, 3, 4, 5, 6 wt%) alloy system, with different ΔGγ→ε (−276.5–417.5 J/mol) resulting in different plastic deformation mechanisms (martensitic transformations or twinning). The three TRIP mechanisms with different transformation paths, i.e., γ→ε, ε→α’, and the reverse ε→γ, in the Fe–15Mn–10Cr–8Ni–4Si alloy are then discussed in terms of their contributions to its excellent ductility, which is comparable to that produced by TWIP.

Hydrogen-Induced Martensitic Transformation and Twinning in Fe45Mn35Cr10Co10

Hydrogen embrittlement can occur in steels with metastable phases, due to activation of the hydrogen-enhanced decohesion mechanism upon transformation. Meanwhile, recent investigations suggest that alloys undergoing ε-martensite transformation may exhibit resistance to hydrogen embrittlement. To better understand hydrogen effects in these alloys, we investigate the hydrogen-induced microstructural transformations in a metastable Fe45Mn35Co10Cr10 alloy. To this end, we electrochemically charge unstrained samples, quantify the hydrogen evolution by thermal desorption spectroscopy, and observe microstructural transformations by scanning electron microscopy techniques. Through these analyses, we find that the hydrogen-induced ε-martensite formation is dependent on the crystallographic orientation of the austenite grains, and takes place preferentially along Σ3 boundaries. Further charging of hydrogen induces extension twinning within the martensite. We examine the microstructural factors influencing these transformations to better understand the hydrogen-microstructure interactions.Graphical Abstract

Transformation plasticity in high strength, ductile ultrafine-grained FeMn alloy processed by heavy ausforming

The mechanisms contributing to the excellent mechanical properties of the ultrafine-grained (UFG) Fe-23 wt.%Mn alloy processed by heavy ausforming are unraveled based on detailed characterization analysis and modelling. The UFG microstructure is fully austenitic after the heavy ausforming step involving a 90% rolling reduction; while the material quenched from the coarse-grained (CG) austenite consists of epsilon (ε)-martensite and austenite. The UFG Fe23Mn alloy shows a high strain-hardening capacity which leads to a much higher true uniform elongation (0.33) and true tensile strength (1330 MPa) than the CG counterpart (0.17 and 950 MPa, respectively). The high ductility of the heavily-ausformed microstructure with no subsequent annealing step contradicts the general trend of UFG alloys produced by severe plastic deformation. In addition, a ductile fracture mode with improved resistance to damage initiation in the UFG microstructure contrasts with the brittleness of the CG counterpart. Therefore, the UFG Fe23Mn alloy exhibits a high combination of strength, resistance to plastic localization and resistance to cracking. This superior mechanical performance is attributed to the gradual deformation-induced ε-martensitic transformation and to the large plastic co-deformation of the UFG ε-martensite, in which twinning is suppressed at the expense of the activation of non-basal <c+a> slip. A mean-field micromechanical model is used to analyze the contribution of the phase transformation to plasticity, and to further rationalize the mechanical response of the UFG ε-martensite. This finding provides new insight into the effects of microstructural scale on the mechanical behavior of this class of transformation-induced plasticity (TRIP)-assisted alloys.

Stacking fault energy and fcc→hcp transformation driving force in Fe-Mn-C-Cr-Si high manganese steels and experimental investigation

In order to improve the strength and work hardening capacity of high manganese steel, the effects of alloying elements on the stacking fault energy (SFE) and driving force of fcc→hcp transformation in Fe-Mn-C-Cr-Si high manganese steels were explored in detail. Based on the thermodynamic calculations, the Fe-0.6C-15Mn-(4,6)Cr-(0,3)Si (wt.%) steels were prepared to investigate the microstructure and mechanical properties. The calculated results show that the Cr reduces the SFE of Fe-C-Mn-Cr high Mn steels linearly and the reduction rate of SFE is greater as the C content increasing. With increasing the Si concentration, the SFE of Fe-C-Mn-Si steels decreases when the Mn content is higher than 18 wt.%. However, when carbon content is less than 1 wt.% and Mn content less than 18 wt.%, the SFE reaches to a maximum value and then declines with the increase of Si content. The combined effect of Cr and Si on the SFE of Fe-C-Mn-Si-Cr steels appears the similar behaviors to that of Si. Generally, the value of driving force, of fcc→hcp transformation in Fe-Mn-C-2Cr-Si (wt.%) steels increases with the increase of C and Mn and decreases with the Si content increasing. However, for 0.6 wt.% C and 7 wt.% Mn steels, the value of first increases and then decreases with the increase of Si content. The results of tensile test indicated that the Fe-15Mn-0.6C-6Cr-3Si (wt.%) high manganese steel demonstrates a better combination of the ultimate strength of 987 MPa, yield strength of 470 MPa, fracture elongation of 41.5% and high work hardening capacity because of the ε-martensitic transformation caused by the great (large negative value) and low SFE under stress.

Evolution of microstructure and deformation behavior in Al–Ni added medium-Mn steel processed through intercritical / cold rolling and annealing

In the present work, the effect of intercritical annealing on Fe–8Mn–4Al-3.5Ni-0.8Si-0.25C (wt.%) medium-Mn steel, processed through two different processing routes viz. intercritical rolling (IR) and cold rolling (CR), has been studied. The microstructure, mechanical properties, austenite stability and deformation behavior of the steel, after intercritical annealing (IA) at different temperatures (760, 800 and 840 °C), has been investigated. It has been observed that different rolling regimes (intercritical rolling and cold rolling) give rise to distinct variation in the grain structure owing to different recrystallization behavior during intercritical annealing. The IR-annealed samples showed a mixture of lath and equiaxed grains while the CR-annealed samples showed mostly equiaxed grain morphology. Due to extensive recrystallization in CR-annealed samples, a higher fraction of retained austenite was formed, as compared to IR-annealed samples. The yield strength (YS) and ultimate tensile strength (UTS) was found to be higher for IR-annealed samples, as compared to CR-annealed samples, at all annealing temperatures. However, a high elongation (EL) of 57 % with (UTS x %El) product of 47.7 GPa% was obtained in CR sample, annealed at 800 °C. The mechanical stability of retained austenite was found to influence the work hardening behavior of the annealed samples. The CR-annealed samples exhibited strain-induced transformation to α′-martensite, as compared to ε-martensite transformation in IR-annealed samples. A sustained three-stage strain hardening behavior during deformation, comprising combined TWIP and discontinuous TRIP effect, led to excellent strength-ductility combination in CR sample annealed at 800 °C.

Correlation between microstructure evolution and mechanical response in a moderately low stacking-fault-energy austenitic Fe–Mn–Si–Al alloy during low-cycle fatigue deformation

Through in-depth microstructural and mechanical characterization, a mechanism for low-cycle fatigue (LCF) deformation of an Fe-30.7Mn-4.3Si-1.8Al (in wt%) austenitic transformation-induced-plasticity (TRIP) steel at a total strain range of 2% was investigated. The LCF deformation of the steel was performed through two main deformation modes which were planar slip of Shockley partials, and ε-martensitic transformation and its reverse transformation. The varying significance of each deformation mode as well as the relevance between the two modes determined the microstructures evolved during fatigue deformation and resulted in a four-stage cyclic hardening behavior. With increasing fatigue cycles, the LCF deformation was dominated sequentially by the multiplication of partial dislocations, development of slip bands, reversible ε-martensitic transformation, and formation of more thick and crossed ε-martensite along with enhancement of planar dislocation slip, thus generating the characteristic deformation stages of primary cyclic hardening, cyclic softening, cyclic saturation, and secondary cyclic hardening correspondingly. In general, the superior LCF resistance of the steel was attributed to appreciably high plasticity reversibility during the entire fatigue deformation which was caused by reversible planar dislocation slip and ε-martensitic transformation.

Strain rate sensitivity of hydrogen-assisted ε-martensitic transformation and associated hydrogen embrittlement in high-Mn steel

This study presents the degree of promotion of deformation-induced γ−ε martensitic transformation by hydrogen charging and the associated fracture behavior at various strain rates ranging from 10−5 to 10−2 s−1. A decrease in the strain rate from 10−2 to 10−5 s−1 promotes the deformation-induced γ−ε martensitic transformation regardless of hydrogen charging (65%→82% in area fraction for uncharged specimens, 68%→84% for hydrogen-charged specimens). Hydrogen charging, which provides 11.7 mass ppm hydrogen concentration, further promotes the γ−ε martensitic transformation. However, the degree of promotion of the transformation by hydrogen is insensitive to the strain rate. Corresponding to the promotion of the γ−ε martensitic transformation, the hydrogen embrittlement susceptibility increases with a decrease in the strain rate. For instance, the elongation of the hydrogen-charged specimens decreases from 36 to 32% by decreasing strain rate from 10−2 to 10−5 s−1. Hydrogen uptake deteriorates the resistance to crack initiation and propagation. Furthermore, the primary effect of the decrease in strain rate on hydrogen embrittlement is the acceleration of the crack propagation. In addition to the promotion of γ−ε martensitic transformation, a decrease in the strain rate in the presence of hydrogen may cause hydrogen localization at the crack tip, which assists brittle-like martensite cracking.

Effect of the γ→ε Phase Transition on Transformation-Induced Plasticity (TRIP) of Nickel-Free High Nitrogen Steel at Low Temperatures

The deformation behavior, mechanical properties, and microstructure of Fe-Cr-Mn-0.53%N austenitic stainless steel were studied at a temperature range of 77 up to 293 K. The dynamics of the steel elongation were non-monotonic with a maximum at 240–273 K, when peaks of both static atom displacements from their equilibrium positions in austenite and residual stresses in the tensile load direction were observed. The results of X-ray diffraction analysis confirmed that the only stress-induced γ→ε-martensite transformation occurred upon deformation (no traces of the γ→α′ one was found). In this case, the volume fraction of ε-martensite was about 2–3%. These transformation-induced plasticity (TRIP) patterns were discussed in terms of changes in the phase composition of steel as the root cause.

The effect of austenite grain size on deformation mechanism of Fe–17Mn steel

Abstract The transition of deformation mechanism from transformation-induced plasticity (TRIP) to twinning-induced plasticity (TWIP) was investigated in a viewpoint of γ-austenite grain size (AGS) using Fe–17Mn steel. When the AGS decreased from 51.72 μm to 0.75 μm, the apparent stacking fault energy (SFE) value increased from 10.8 mJ/m2 to 23.4 mJ/m2. The transition of deformation mechanism from TRIP to TWIP occurred at the late stage of tensile strain in ultrafine-grained specimens with high apparent SFE values (>23.1 mJ/m2). This result matches well with the fact that a critical AGS for the transition of deformation mechanism is ~0.52 μm, which was calculated from the relationships between AGS and critical resolved shear stresses for mechanical twinning (τtwin) and e-martensitic transformation (τe-mart). UFG specimens with the AGSs below 1.12 μm exhibited a two-step rise at the stage II of strain hardening rate curves due to active mechanical twinning and possessed high tensile strength without a great loss of elongation.

Awakening the metastability of an interstitial high entropy alloy via severe deformation

The metastability of a typical non-equiatomic FeMnCoCr high-entropy alloy (HEA) system was demonstrated to be dormant upon co-doping with C and N interstitials, i.e., displacive γ-ε phase transformation disappears during tensile deformation. Interestingly, we found in the present study that the displacive phase transformation prevails again in the C-N co-doped HEA upon severe deformation via cold-rolling. The generation of ε-phase lamellae is found to be motivated by strain localization which facilitates the formation of shear bands. Such highly concentrated strains significantly intensify the local elastic fields to neighboring γ matrix and finally eke out the driving force to overcome the interstitials-enhanced energy barrier of ε-martensite transformation. The results suggest that the suppressed phase metastability is awakened, which inspires efforts to tune the phase metastability via modifying the strain state during alloy processing and gives new insights into the development of HEAs with desirable phase stability and mechanical properties.