Warm Rolling Process Research Articles

Stepwise warm rolling for synergistic strength and ductility enhancement in heterolamellar medium-Mn steel

Medium manganese steel represents a promising third-generation advanced high-strength steel. However, achieving excellent plasticity in high-yield-strength medium manganese steel remains challenging, particularly with lower alloying element contents. In this study, we employed an innovative stepwise warm rolling process on 5Mn medium manganese steel, developing a heterolamellar microstructure along the rolling direction. The resulting steel exhibited a yield strength exceeding 1.5 GPa while maintaining a uniform elongation of approximately 29%. The high yield strength is attributed to fine lamellar grains with high dislocation density, while the excellent uniform elongation is due to the synergistic effect of multiple plastic deformation mechanisms, which promoted prolonged strain hardening and delayed the onset of necking. These mechanisms include hetero-deformation induced (HDI) hardening generated during the early deformation of the heterolamellar structure, transformation induced plasticity (TRIP) effect-induced work hardening, and delamination cracking that alleviates interface strain concentration and delays material failure. Collectively, these mechanisms enabled the material to achieve an exceptionally high product of yield strength and uniform elongation of 45 GPa·%. This work provides new insights into the design of high-strength, ductile medium manganese steels, advancing the application of high-performance medium manganese steels.

The influence of Zn addition on the microstructure and mechanical and corrosion properties of warm rolled Al[sbnd]Mg alloys containing Er and Zr

The effects of a minor Zn addition on the mechanical and corrosion properties and microstructure of a high Mg content AlMg alloy containing Er and Zr in the warm-rolled state were studied using tensile test, nitric acid mass loss test (NAMLT), exfoliation corrosion susceptibility test (ASSET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The tensile test results showed that the 0.58 wt% Zn addition to the Al-Mg-Er-Zr alloy increased the yield strength from 297 to 351 MPa and tensile strength from 416 to 445 MPa, but decreased the elongation from 13.3 % to 12.5 %. The NAMLT and ASSET results showed that the two warm rolled alloys were initially in the stabilization state, but the Al-Mg-Er-Zr alloy without Zn added became sensitized severely after the accelerated sensitization annealing (ASA) at 100 °C. The Zn addition improved the intergranular corrosion (IGC) resistance and exfoliation corrosion (EC) resistance significantly. The TEM results showed that, for the Al-Mg-Er-Zr alloy, there were Al3(Er,Zr) phase particles in the matrix and β (Al3Mg2) phase particles separated from each other at the grain boundary. After the ASA treatment, more β phase particles were precipitated and covered the grain boundary completely. For the Al-Mg-Zn-Er- Zr alloy, another nanoscale T (Al32(Mg, Zn)49) phase was precipitated in the matrix, and there were no grain boundary phase particles observed at the grain boundary, because the precipitation of T phase consumed the supersaturated Mg in the matrix, thus suppressing the formation of grain boundary phase particles during the ASA treatment and resulting in a good corrosion resistance. The strengthening effect of the Zn addition was mainly due to the formation of T phase particles during the warm rolling process.

Achieving unexpected strength and ductility synergies in heterogeneous metastable lamellar steels

High-strength steel with excellent ductility is pivotal for the formability and safety of critical structural components. Here, a heterogeneous metastable lamellar steel, composed of alternating lamellar ferrite and austenite aligned with the rolling direction, was developed through an innovative combination of warm rolling and immediate annealing processes. This novel design overcomes the strength-ductility trade-off, achieving high ultimate tensile strength (∼1.2 GPa) and excellent uniform elongation (∼78%), pushing the product of ultimate tensile strength and uniform elongation to an ultra-high level (> 90 GPa %). The high tensile strength is attributed to ultrafine lamellar grains and significant work hardening induced by the hetero-deformation and transformation-induced plasticity (TRIP) effect. The exceptional ductility is a result of the synergy of multiple plasticity mechanisms, including (i) the inherent plastic deformation ability of lamellar microstructure and the hetero-deformation-induced hardening in the early deformation period, (ii) the persistent TRIP effect induced by the lamellar austenite with high mechanical stability and the elimination of strain localization caused by prolonged strain hardening due to the coordinated deformation of lamellar austenite and ferrite in the middle deformation period, and (iii) delamination cracking in the late deformation period. This approach adopted in current work offers a straightforward and economically feasible pathway for fabricating advanced high-strength steel with superior performance.

Enhancing strength-ductility synergy in low-Mn lightweight steel by large-deformed warm rolling and flash annealing

The presence of δ-ferrite makes it challenging to achieve higher strength-ductility in low-Mn lightweight steels. In this study, a large deformation warm rolling process was used to construct a precursor enriched with Mn, nano-precipitations, ultra-fine grains, and high-density dislocations. The subsequent flash annealing process not only promotes the formation of multi-heterogeneous structures but also refines and reduces δ-ferrite while increasing the ultrafine-grained hard phase martensite. Additionally, this process enhances the retention of retained austenite, whose ultrafine grains contribute to improved mechanical stability. The synergistic effect of multiple strengthening mechanisms enables low-Mn lightweight steel to achieve outstanding comprehensive mechanical properties, with a tensile strength of 1423 MPa and a total elongation of 23.0 %.

Excellent combination of strength and ductility in austenitic lightweight steel achieved by warm rolling process

In this study, warm rolling was applied to Fe–28Mn–11Al–1C–5Ni (wt.%) austenitic lightweight steel, which realized the higher dislocation density and finer dislocation-cell structures, achieving a better mechanical properties with ∼2.0 GPa of yield strength and ∼6.8 % of total elongation than cold rolling in the same conditions. In the subsequent partial recrystallization condition, the numerous dislocations and substructures existed in warm rolled steel provide more heterogeneous nucleation sites for grain refinement, resulting in the ultrafine-sized austenite and B2 with the size of 0.36 μm and 0.24 μm, respectively. Combined with grain refinement strengthening, solid solution strengthening, precipitation strengthening, and dislocation strengthening in the unrecrystallized austenite, the present steel shows an ultimate tensile strength of 1734 MPa, a uniform elongation of 21.7 % and a specific tensile strength of 267 MPa g−1 cm3. Such an excellent combination of strength and ductility induced by simple warm rolling and annealing is much better than previously reported for lightweight steels.

Achieving an ultrahigh yield strength of 1.5 GPa in warm-rolled lightweight steel via synergistic multiplication of precipitation and dislocations

The microstructural evolution and tensile property of a Fe-18Mn-8Al-1C-5Ni (wt%) lightweight steel subjected to warm-rolling and subsequent aging treatment have been investigated. During the warm rolling process, dislocations-induced precipitates further hinders movement of dislocations, resulting in the synergistic multiplication of dislocations and B2 particles. Additionally, shear bands observed within the grains also induce the formation of B2 particles. Subsequent aging facilitates the precipitation of coherent κ-carbides within the matrix, with their its size and volume fraction increasing as dislocation density rises. The newly designed warm-rolled and aged steel exhibits a remarkable ultrahigh strength (yield strength of 1537 MPa and tensile strength of 1632 MPa) and a total elongation of 11.29%. Such superior tensile property not only surpass those of other hot rolled lightweight steels strengthened by B2 and/or κ-carbides but also exceed those of the steels subjected to additional cold rolling. This advancement is expected to expand the applications of B2-strengthened steels in response to an increasing demand for lightweight constructions.

Designing the heterogeneous microstructure via a direct warm rolling process to synergistically enhance the strength-ductility in a medium Mn steel

This work introduced a facile method for fabricating heterostructures in a medium Mn steel via a direct warm rolling process. The heavy warm rolling promoted the transformation of metastable austenite (∼12.2 vol%) into hard domain α’ martensite, which formed a heterogeneous microstructure with the untransformed γ (soft domain). After 600 °C re-annealing, the hard domain α’ re-reversed to α + γ, and the heterostructure disappeared. Compared to the homogeneous structure, the heterostructure exhibited the synergistic enhancement of strength-ductility (yield strength (YS): 782 → 1113 MPa; ultimate tensile strength (UTS): 1099 → 1304 MPa; total elongation (TEL): 20.8 % → 21.7 %). Quantitative analysis showed that the heterogeneous deformation induced (HDI) strengthening (∼261 MPa) was the primary contributor to the increased ΔYS (782 → 1113 MPa) value, rather than the traditional strengthening mechanisms. Transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effect were the main deformation mechanisms of both homogeneous/heterogeneous structures. However, compared to the homogeneous microstructure, the heterogeneous structure possessed the more pronounced TRIP and HDI hardening effects as well as L-C locks, the cooperative effect of these three factors further improved the strain hardening ability to break through the strength-ductility trade-off dilemma.

Heterogeneous Multi-Phase Grains Improving the Strength-Ductility Balance in Warm-Rolled Fe-18Mn-3Ti Steel.

The thermal properties, microstructure, and mechanical properties of Fe-18Mn-3Ti (wt%) were investigated, focusing on the effects of different heat-treatment processes. Results revealed that the 450 °C warm-rolling sample (450 WR) exhibited promising mechanical properties. Specifically, this sample displayed a yield strength of 988 MPa, an ultimate tensile strength of 1052 MPa, and total elongation of 15.49%. Consequently, a favorable strength-ductility balance was achieved. The strain-hardening ability surpassed that of the cold rolling sample (CR). Microstructure analysis indicated the simultaneous occurrence of dynamic equilibrium between grain deformation and re-crystallization because of the co-influence of thermal and strain in the warm rolling process. This desirable mechanical property was attributed to the presence of a multi-phase (α-martensite, austenite, and ε-martensite) and heterogeneous microstructure. The improvement of ultimate tensile strength was based on grain refinement, grain co-deformation, and the transformation-induced plasticity (TRIP) effect in the early stage of plastic deformation (stage Ⅰ). The improvement of ultimate elongation (TEL) was ascribed to the TRIP effect in the middle stage of plastic deformation (stage Ⅱ).

Realization of strength-ductility balance of 10 Mn-steel by tailoring symbiosis microstructure

Medium Mn steel is considered as a third-generation advanced high-strength steel. However, the bottle-neck problems of excessive strength and insufficient plasticity seriously limited its development. In this study, a warm rolling process was employed to refine grains and acquire high-density dislocations. Subsequently, a quenching-tempering process was employed to prepare a symbiosis microstructure containing multi-phase structures and double precipitates (κ- and V-carbides). On the premise of providing a gigapascal-level yield strength, the introduction of multi-phase structures activated various deformation mechanisms during the straining and contributed to a tensile strength of 1777 MPa and total elongation of 14.1 % in sample W500. In sample W700, the high-density dislocations in martensite gradually passed through the austenite/martensite interfaces and entered the neighboring austenite, enhancing the coordinated deformation capacity of martensite. Sample W700 exhibited a total elongation of 21.8 % and tensile strength of 1468 MPa. Combined with a microstructure analysis during the interrupted tensile deformation, the influences of martensite transformation, dislocation motion, double precipitates, and deformation twins on the work hardening and ductility are discussed in detail.

A new perspective on Lüders band formation in medium-Mn steels based on Lüders-strain-rate and dislocation evolution

Propagating Lüders bands with pronounced strain localization are often observed in medium-Mn transformation-induced plasticity (TRIP) steels, which adversely limits the application of such alloys in engineering structures. The present work aims to understand this phenomenon from a dislocation-based perspective, with a focus on the specific role of dislocation multiplication. The material studied is a typical dual-phase medium-Mn steel with a ferrite matrix and a second phase of retained austenite. A warm-rolling process was used as a pre-straining approach to adjust the microstructure of the material, such that materials with two different microstructural states can be obtained: as-received material and pre-strained material. They show distinct differences in initial dislocation density. Stress-controlled rather than conventional strain-controlled tensile testing was adopted, which allowed the Lüders band to develop in an unconstrained manner. In this way, the intrinsic Lüders-strain-rate can be obtained. The results show that the Lüders band-related mechanical parameters, including Lüders strain, Lüders-strain-rate and yield stress drop, all depend on the initial microstructure state and the dislocation evolution process during Lüders band formation. In particular, Lüders-strain-rate is a critical microstructure-sensitive factor. It is closely related to the dislocation multiplication in the formation of Lüders band, which can be characterized and quantified using scanning transmission electron microscope and synchrotron X-ray diffraction. Finally, a quantitative relationship between Lüders-strain-rate and dislocation multiplication rate is established, which allows providing a better understanding of the exceptional Lüders band phenomenon in medium-Mn steels.

Strain-induced grain evolution of pure nickel under warm power torsional rolling process

Strain-induced grain evolution of pure nickel under warm power torsional rolling process

A strong and ductile ferrite-based lightweight steel manufactured via high-temperature warm rolling process

A trade-off between strength and ductility is unavoidable in ferrite-based lightweight steels due to the presence of δ-ferrite, and improving the properties of such steels requires precise control of the retained austenite and the complete mobilization of multiple strengthening mechanisms. In this study, we obtain a ferrite-based lightweight steel with the chemical composition Fe-0.3C-2.8Mn-3.5Al-0.5Cr-0.2V by adopting a higher temperature warm rolling process, endowing the best comprehensive properties. The results demonstrate that multi-scale heterogeneous microstructures are built without additional recrystallization annealing under the higher temperature (>700 °C) warm rolling process. Meanwhile, a large amount of retained austenite, higher dislocation density and strain-induced vanadium carbide precipitation were obtained through the warm rolling process. As warm rolling refines austenite grains, Mn and Cr are further diffused and enriched, enhancing the chemical stability of the retained austenite. After low-temperature tempering, this warm-rolled steel shows excellent comprehensive properties, including a tensile strength of 1140 MPa and elongation of 30%. The enhanced strength-ductility is attributed to the higher stability of retained austenite, stable maintenance of dislocation density and the pinning effect of precipitation relative to dislocation lines. Furthermore, a stronger discontinuous yielding behavior of the warm-rolled and tempered steel was obtained, enhancing the overall strain.

Evolution Behaviors of Inclusions in Warm‐Rolled L605 Thin‐Walled Tubes and Their Effects on Machinability

This paper investigates the evolution behaviors of inclusions in the warm rolling process of L605 thin‐walled tubes and analyzes their influencing mechanism. Homogeneous spherical and irregular SiO2–Al2O3–Cr2O3(MnO + CaO) inclusions are observed in the cast tubes. After warm rolling, the homogeneous inclusions are changed into heterogeneous spherical ones with gray‐colored (Al2O3)‐rich phase and dark‐colored (SiO2)‐rich phase and Cr2O3(MnO + CaO)‐rich phase due to different deformability of various inclusions under the combined effects of diameter reduction and wall pressure. As the rolling times of tubes increases, large‐sized inclusions are crushed continuously, and the average size of the inclusions gradually decreases. At the same time, the number density of inclusions presents a first increasing and then decreasing trend. It is estimated that the critical size of the inclusions that are hard to further crack in warm rolling is about 0.5 μm. Meanwhile, the inclusions would lead to stress concentration at the positions near large‐sized irregular inclusions, causing cracks and penetrating defects. The simulation results show that the stress near the outer diameter of the inclusions is twice that in the middle and the changes of stress in the 30 μm inclusions and nearby areas exhibit a significant increase compared to the small‐sized 2 μm inclusions.

Outstanding high-temperature strength-ductility combination in inconel 718 alloy by warm rolling and simplified aging treatment

In the present study, a comparative study was conducted with the cold-rolled Inconel 718 alloy and warm-rolled Inconel 718 alloy. The influences of deformation process and aging treatment on microstructure evolution and tensile properties of Inconel 718 alloy were investigated. The results showed that some fresh recrystallized grains can be observed in the warm-rolled and subsequent aged samples, resulting in refined microstructures of the warm-rolled and aged samples. Besides, the warm rolling process can accelerate the precipitation of γ" strengthening phase. The peak hardness (∼560 H V) of the warm-rolled sample was obtained after aging at 720 °C for 2 h, which far exceeded that of cold-rolled Inconel 718 alloy even aged for 8 h (∼520 H V). According to the TEM analysis, the fraction and size of γ" particles of the warm-rolled sample after 2 h aging were about 10.3% and 5.9 nm, which was higher than the cold-rolled sample with the same aging treatment (7.6% and 2.9 nm). Moreover, most of the γ" particles in the warm-rolled sample after simplified aging was nearly spherical, rather than the disk-shaped in the traditional two-stage aging Inconel 718 alloy. Compared with cold-rolled and aged materials, the warm-rolled alloy after aging exhibited superior mechanical properties. When deformed at 650 °C, the tensile strength and elongation of warm-rolled samples after aging treatment were 1247.6 MPa and 18.7%, while the corresponding values of cold-rolled samples after aging were 1162.5 MPa and 13.6%. The excellent strength-ductility combination of Inconel 718 alloy was linked with refined grains, numerous modified precipitates, and partial recrystallized structure with great dislocation density and many dislocation cells. As a result, warm rolling may provide an effective way to simplify the traditional 18 h two-stage aging to just 2 h single-stage aging treatment, and meanwhile, to improve the mechanical properties of Inconel 718 alloy.

Microstructure evolution during the heavy warm rolling of a nickel aluminum bronze

Nickel aluminum bronze (NAB) alloys quenched after rolling to different reduction ratios were used to investigate the microstructure evolution during the heavy warm rolling (HWR) process. The results demonstrate that the average grain size continuously declines as rolling progresses while the dislocation density steadily increases. As a result of Widmanstatten and eutectoid transformation, the β phases are almost entirely transformed into α phases. Simultaneously, different types of k phases also rapidly precipitate from the matrix. After HWR, the microstructure comprises coarse-grained Widmanstatten α phases, ultrafine-grained eutectoid structures, and many types of k phases dispersedly distributed on the matrix. There is no noticeable texture due to the formation of numerous equiaxed α grains generated by eutectoid transformation. As the reduction ratio increases, the increasing dislocation lines gradually become entangled, eventually forming many dislocation cells. The precise statistics of the precipitates' size, position, and area fraction manifest that the newly generated k phases during rolling are primarily distributed in the region of eutectoid structures, and their size is typically below 50 nm. The improvement of the mechanical properties is attributed to the increase of dislocation density and nano precipitates as well as the continuous microstructure refinement. Based on the accurate characterization of microstructures, the phase transformation kinetics during rolling influenced by combined thermo-mechanical effects are holistically described.

Quantitative Analysis of Yield Strength in V-Alloying Medium Manganese Steel under Different Processes

In the present study, Fe-0.2C-1.2Si-10.3Mn-3.4Al-0.33V multiphase steels were prepared by two different processing including intercritical annealing and warm rolling plus heat treatment. The microstructure changes induced by working processes and their effects on mechanical properties were investigated. By establishing the yield strength contribution model of each phase, the contribution of various strengthening mechanisms to the yield strength of each phase is calculated. The calculated results suggest that warm rolling plus heat treatment process improves the grain boundary strengthening, solid solution strengthening, precipitation strengthening and dislocation strengthening of each phase, and improves the yield strength.

Warm Rolled Temperature Effect on Microstructure and Mechanical Properties of 18Mn/40Si2CrMo Multilayer Composite Steel

In order to obtain a good strength-plastic/toughness match relationship, 18Mn/40Si2CrMo multilayer composite steels were successfully fabricated by a vacuum hot rolling and warm rolling process in this paper. The effects of different warm rolling temperatures (400–600 °C) on the microstructure and mechanical properties of the multilayer composite steel were systematically investigated. The result shows that the warm rolling process reduces thickness of the interfacial diffusion layer, which improves the interfacial bonding strength of multilayer composite steel. With the increase of warm rolling temperature, the total elongation (TEL) increases but ultimate tensile strength (UTS) decreases. The multilayer composite steel with a warm temperature of 500 °C achieves the balance of strength and plastic of which the UTS and TEL are 1.7 GPa and 12.5%, respectively. This is due to the high work-hardening ability of deformation twins of the 18Mn layer and the precipitates nanoscale carbides of the 40Si2CrMo layer to obscure the dislocation movement.

Microstructure Evolution Mechanism of Ultra-Thin Dual Phase Magnesium-Lithium Alloy during Asymmetric Warm Rolling.

Magnesium–lithium alloy is the lightest metal alloy material so far, and the ultra-thin plate is also one of the main trends in the future development of Mg-Li alloy. In order to explore how to prepare LZ91 ultra-thin Mg-Li alloy, this topic adopts the combination of the finite element method (FEM) and visco-plastic self-consistent (VPSC) calculation, electron back-scattered diffraction (EBSD) and tensile experiment, and uses the asymmetric warm rolling process to realize the processing of ultra-thin LZ91 Mg-Li alloy plate with a thickness of 0.25 mm. The experimental results show that the maximum basal texture strengths of 1 mm initial plate and 0.25 mm ultra-thin rolled plate are 36.02 mud and 29.19 mud, respectively. The asymmetric warm rolling process not only reduces the basal texture strength but also significantly refines the grains. The tensile strength and yield strength of 0.25 mm ultra-thin rolled plate along the rolling direction reached 206.8 MPa and 138.4 MPa, respectively. This has a positive effect on the mechanical properties of subsequent materials. VPSC results show that the base slip is the main factor in Mg-Li alloy asymmetric warm rolling, and a large number of tensile twinning are initiated due to the coordinated deformation of the body-centered cubic (BCC) phase, which is beneficial to improve the plastic deformation capacity of Mg-Li alloy.

Recrystallization Behavior of Warm Rolling and Cold Rolling Cr-Ti-B Steel during Annealing

To study the nucleation and recrystallization behavior of deformation bands, shear bands and grain boundaries during the recrystallization process, a heat treatment test was carried out on Cr-Ti-B low-carbon steel after warm rolling and cold rolling. The results show that recrystallization occurs preferentially in shear bands and grain boundaries. The γ deformation texture can be enhanced and the Goss texture can be weakened during the warm rolling and subsequent cold rolling process. Recrystallization of the deformation bands was observed, but the nucleation time of recrystallization in the deformation band is much slower than that in the shear band and grain boundary.

Microstructural evolution and strain hardening behavior of a novel two-stage warm rolled ultra-high strength medium Mn steel with heterogeneous structures

A heterostructured medium Mn steel with duplex phases (ferrite and austenite) and multiple morphologies (lath-typed and granular) is fabricated by a novel two-stage warm rolling process and subsequent intercritical annealing. The obtained sample exhibits excellent mechanical properties with the yield strength and ultimate tensile strength of 905 MPa and 1320 MPa, respectively, and the total elongation of 45.6%, the mechanical properties are higher than those of the hot rolled samples and the one-stage warm rolled samples. The microstructural evolution during the two-stage warm rolling process and annealing are characterized and the strain partitioning behavior of the material is investigated. It is indicated that the outstanding mechanical properties and the strain hardening ability rely on the combination of the transformation induced plasticity (TRIP) effect and the hetero-deformation induced (HDI) hardening.