Static Recrystallization Behavior Research Articles

Static Recrystallization Behavior and Twin Formation Mechanism of Fe–Mn–Cr–N Steel During Medium Temperature Annealing

Static Recrystallization Behavior and Twin Formation Mechanism of Fe–Mn–Cr–N Steel During Medium Temperature Annealing

Effect of withdrawal rate on the microstructure and static recrystallization behavior of Ni-based single crystal superalloy

Effect of withdrawal rate on the microstructure and static recrystallization behavior of Ni-based single crystal superalloy

Effects of Fe addition on the mechanical and corrosive properties of biomedical Co-Cr-W-Ni alloys for balloon-expandable stents

Co-20Cr-15W-10Ni (mass%, CCWN) alloy is extensively used as a platform material for balloon-expandable stents. In this study, the mechanical properties of CCWN alloy are improved following the addition of Fe, and the effects of Fe addition on the mechanical and corrosive properties of the alloy are investigated. As-cast specimens were fabricated by adding pure Fe to a commercially available CCWN alloy (base alloy) such that the resulting alloys contained 4, 6, and 8 mass% Fe. The as-cast specimens were subjected to homogenization heat treatment at 1523 K for 7.2 ks and then hot-forged at 1473 K (as-forged specimens). The as-forged specimens were cold-rolled at a reduction rate of 30% and heat-treated at 1473 K for 300 s (recrystallized specimens). The matrix of the recrystallized base- and Fe-containing alloys consisted of a single γ (face-centered cubic)-phase. The Fe-added alloys revealed precipitates composed of the η-phase (M6X-M12X-type phase, M: metallic element, X: C and/or N). The average grain size of the recrystallized base and Fe-added alloy specimens was approximately 34 μm and the amount of added Fe had no significant effect on the static recrystallization behavior of the resulting alloys. Alloys containing 6 mass% or more Fe showed improvements in strength and ductility compared with the base alloy. When the Fe-added alloys were compared, their strength decreased whereas their ductility increased when the added Fe increased. Because Fe acts as a γ-phase-stabilizing element for Co, Fe addition increases the stacking fault energy of the base alloy, resulting in the formation of the ε (hexagonal close-packed)-phase owing to the suppression of strain-induced martensitic transformation (SIMT), and improvements in ductility. No deterioration in corrosion resistance was observed following the addition of up to 8 mass% Fe to the base alloy. Based on these results, the addition of Fe to CCWN alloy may be considered an effective method to improve its mechanical properties, especially ductility, without impairing its corrosion resistance. The results of this study will be useful for the future development of Ni-free Co-Cr alloys for next-generation, small-diameter stents.

Investigation of constitutive models and microstructure evolution during hot deformation and solution treatment of Al–Zn–Mg–Cu alloy

In this paper, isothermal thermal compression tests were carried out on Al–Zn–Mg–Cu alloys at varying deformation temperatures (360°C∼440°C) and strain rates (0.001s−1∼10s−1) using a Gleeble-3500C thermal simulation tester. Based on the true strain stress data obtained from the tests, the flow behavior of Al–Zn–Mg–Cu alloys during thermal deformation was investigated. Through a comprehensive consideration of deformation temperature, strain rate, and strain compensation, a high-precision constitutive model was established. Additionally, the specimens subjected to hot compression were further treated with solution annealing for different durations (0 h–2 h) to investigate the static recrystallization (SRX) behavior and the associated microstructural evolution of the alloy during the solution treatment process. Electron Backscatter Diffraction (EBSD) was employed to characterize the microstructure evolution of Al–Zn–Mg–Cu alloy under various deformation and solution treatment conditions. The EBSD data were further processed and analyzed using the MTEX toolbox. The results revealed that dynamic recovery (DRV) is the predominant softening mechanism during the deformation process, accompanied by a small amount of dynamic recrystallization (DRX). The dynamically recrystallized grains exhibit a random crystallographic orientation. Further investigation showed that low temperature and high strain rate conditions are unfavorable for the occurrence of dynamic recovery and dynamic recrystallization during the thermomechanical processing. However, dislocations accumulated during deformation provided sufficient stored energy for the growth of static recrystallized grains during subsequent solution treatment, with static recrystallized grains predominantly forming at grain boundaries.

Regulating the grain refinement and rolling properties of coarse-crystalline Mg-Zn-Gd-Ca-Mn alloy through multi-pass cold rolling and annealing

The newly developed Mg–Zn-RE (rare earth) alloy sheet shows significant prospects for 3C applications due to its superior room-temperature malleability compared to the commercial AZ31 alloy. However, the casting ingots of these alloys often exhibit coarse grains due to low alloying element content and the absence of the grain-refining element Zr, making them susceptible to significant cracking while hot-rolling. This study applies a multi-pass cold rolling technique with minimal reduction to a cast Mg–Zn-Gd-system alloy characterized by coarse grains, followed by a static annealing process to enhance its rolling capability. The impact of cold rolling and annealing temperatures on microstructure, plastic deformation mechanism, and static recrystallization (SRX) behavior were studied. It was found that multi-pass cold rolling with minimal decrease promoted the generation of more twins and slip lines, resulting in more uniform deformation and a substantial accumulated rolling strain of 10 %. Consequently, the significant accumulated strain, coupled with stress concentration at positions such as grain boundaries, twin boundaries, and dislocation tangles, acted as nucleation sites for complete static recrystallization at a specific annealing temperature of 375 °C. As a result, the coarse cast grains were successfully refined from 400 μm to 37 μm. Fortunately, this improvement has significantly enhanced the hot-rolling qualities, removing fractures throughout the process. This advancement not only enables industrial-scale rolling but also enhances production efficiency.

Effects of Crystal Orientation and External Stress on the Static Recrystallization Behavior of an Ni-Based Single-Crystal Superalloy.

The deformation mechanism and static recrystallization (SRX) behavior of an Ni-based single-crystal superalloy are investigated. Indentation tests were performed to investigate the effects of crystal orientation and external stress on SRX behavior. Following solution heat treatment, the depth of the SRX layer below the indentation increases with a deviation angle (β) from the [001] orientation. The slip analysis indicates that an increased deviation angle leads to an increase in the resolved shear stress on the slip plane and a decrease in the number of active slip systems. In addition, the variation pattern of the SRX layer depth with the deviation angle is consistent for different external stresses. The depth of the SRX layer also increases with external stress. The coarse γ' phases and residual γ/γ' eutectics obviously enhance the pinning effects on the expansion of recrystallized grain boundaries, resulting in slower growth rates of the recrystallized grains in interdendritic regions than those in dendrite core regions.

Static recrystallization behavior and strengthening mechanism of a single-phase Cu–18Ni–17Zn alloy

The microstructural evolution and recrystallization behavior of a single-phase Cu–18Ni–17Zn alloy during annealing has been investigated. The strengthening effects of the solute atom concentration, grain size, and recrystallized volume fraction have also been studied. The results have shown that the difference in yield strengths for the fully recrystallized samples mainly depended on the grain boundary strengthening effect. This is attributed to a constant (∼41 MPa) solid-solution strengthening contribution in the completely recrystallized Cu–18Ni–17Zn alloy. When compared with pure copper, this alloy exhibited a high Hall-Petch constant (∼0.36 MPa m1/2), which is due to the higher grain boundary interface energy. A discontinuous recrystallization occurred in the alloy in the temperature range 400 °C–500 °C. Furthermore, the yield strength was linearly correlated to the recrystallized volume fraction in the partial recrystallized samples. Moreover, the addition of Ni and Zn increased the recrystallization temperature and slowed the recrystallization kinetics. The activation energy for the recrystallization was estimated as 92.6 ± 5.1 kJ/mol in the cold-rolled Cu–Ni–Zn alloy, which indicates that the grain boundary migration during recrystallization was mainly controlled by diffusion along the grain boundaries. In addition, the recrystallized grains preferentially nucleated at shear bands with high strain energies in the Cu–Ni–Zn alloy during annealing. As the regions of shear banding were completely consumed, new recrystallized nuclei formed at the grain corners. The limited number of nucleation sites resulted in a low Avrami exponent value that ranged from 0.41 to 0.61.

Static recrystallization behavior of biomedical Co-29Cr-6Mo-0.16 N alloy with negative stacking fault energy

Static recrystallization (SRX) behavior of Co-29Cr-6Mo-0.16 N (CCMN) alloy subjected to a prior compression to 30% at room temperature and a subsequent annealing at 1000 °C was ex-situ observed by using an electron backscatter diffraction (EBSD). Ascribed to the large negative stacking fault energy of the alloy at room temperature, it was found that the microstructure of alloy compressed at room temperature is characterized by plenty of intersected strain-induced martensitic transformation (SIMT) ε phase bands with a mean interval of 2–3 μm, which divided the parent grains into fine pieces surrounded by high angle boundaries (HABs). The static recrystallization of CCMN alloy in the subsequent annealing at 1000 °C takes place in terms of transient transition of the HABs into Σ3n boundaries and reorientation of new grains.

Effect of nitrogen content on the static recrystallization and precipitation behaviors of vanadium–titanium microalloyed steels

Abstract Double compression tests were performed on vanadium–titanium microalloyed steels with different nitrogen contents by using a Gleeble-3800 thermo-mechanical simulator to study the softening behaviors of the deformed austenite during different time intervals between the two passes. The static recrystallization fractions were calculated by the stress offset method and static recrystallization diagrams for the tested steels were obtained. The effects of deformation temperature and interval time on the softening behaviors were analyzed. Especially, the effect of nitrogen on the softening behaviors of the tested steels is discussed in detail. The results showed that the softening behaviors of the tested steels with various nitrogen contents are different. As far as the steel with low nitrogen content is concerned, the softening fraction increases monotonically with increasing time interval, and higher temperature can promote the static recrystallization. However, with more nitrogen added into vanadium–titanium microalloyed steel, precipitated particles of vanadium titanium carbonitride can be observed in the tested steel at the temperature of 850 °C or 800 °C, which leads to the formation of plateaus on the softening curves. An increase in nitrogen content in the steel is favorable for vanadium titanium carbonitride precipitation, which leads to a stronger prohibition of static recrystallization and a longer plateau on the softening curves. Moreover, the precipitated particles in the tested steel will not play an inhibition role in static recrystallization until the nitrogen content in the steel reaches a critical value.

Interaction between phase transformation and static recrystallization during annealing of rolled TC18 titanium alloy

TC18 titanium alloy was subjected to hot rolling at 840 °C, followed by annealing experiments at 830, 860, and 890 °C for different time lengths. The effects of annealing temperature and time on phase transformation and static recrystallization (SRX) behavior, as well as the interaction between phase transformation and SRX, were studied. The results showed that at the low annealing temperature of 830 °C, the microstructure underwent β → α phase transformation and α grain growth with the increase of annealing time, and the SRX of β phase proceeded through subgrain nucleation mechanism induced by α particles. At the middle annealing temperature (860 °C), the α → β phase transformation occurred before the SRX of β phase, and the SRX of β phase was dominated by the grain boundary (GB) bulge mechanism. Meanwhile, the reduction of α phase content accelerated the SRX rate and grain growth. As the annealing temperature (890 °C) exceeded the β transus temperature, the α phase completely transformed to the β phase, and the SRX of the β phase proceeded with a very fast grain growth rate. In addition, the interaction between phase transformation and SRX affected the distribution of α particles. The large-sized α particles (830 °C) were located at the triple GB junction and hindered the SRX β grain growth, while smaller α particles (860 °C) were bypassed by β GB and dispersed within the SRX β grains.

The influence of Mo addition on static recrystallization and grain growth behaviour in CoNiFeMn system subjected to prior deformation

The influence of Mo addition on static recrystallization and grain growth behaviour in CoNiFeMn system subjected to prior deformation

Effect of Oxygen on Static Recrystallization Behaviors of Biomedical Ti-Nb-Zr Alloys

Titanium alloys that are used in biomedical applications must possess biocompatibility and a low elastic modulus so that they protect host bone tissue without causing stress shielding. As the elastic modulus of beta Ti alloys is close to that of bone (10–30 GPa), these alloys are considered potential orthopedic implant materials. The elastic modulus of the single β-phase Ti-39Nb-6Zr (TNZ40) alloy is approximately 40 GPa, whereas the strength is lower than that of other types of Ti alloys. Interstitial oxygen in a Ti matrix is well known to improve the matrix strength by solid-solution hardening. The desired mechanical properties can be optimized using a thermo-mechanical procedure to maintain a low elastic modulus. In order to enhance the strength, TNZ40 alloys were fabricated with different amounts of oxygen. The TNZ-0.16O and TNZ-0.26O alloys were cold swaged into 11 mm diameter bars, subjected to solution treatment at 900 °C and 950 °C for 2 h, and furnace-cooled to room temperature. As a result, recrystallized grains were clearly observed in the β matrix. The TNZ-0.26O alloy that was cold-worked by swaging followed by solution treatment at 900 °C exhibited the best mechanical properties (Vickers hardness: 247 HV, ultimate tensile strength: 777 MPa, elongation at rupture: 18.6%, and compressive strength: 1187 MPa). This study reports the effects of oxygen content on the recrystallization behavior and mechanical properties of these alloys.

The Performance of Niobium-Microalloying Ultra-High-Strength Bridge Cable Steel during Hot Rolling.

This study focuses on exploring the effects of niobium (Nb)-microalloying on the properties of steel for ultra-high-strength bridge cables during hot-rolling processes. We employed a combination of dual-pass compression tests, stress-strain curve analysis, and Electron Backscatter Diffraction (EBSD) techniques to investigate the influence of Nb-microalloying on the static recrystallization behavior and grain size of the steel. The key findings reveal that Nb-microalloying effectively inhibits static recrystallization, particularly at higher temperatures, significantly reducing the volume fraction of recrystallized grains, resulting in a finer grain size and enhanced deformation resistance. Secondly, at a deformation temperature of 975 °C, Nb-containing steel exhibited finer grain sizes compared to Nb-free steel when held for 10 to 50 s; however, the grain size growth accelerated when the hold time exceeded 50 s, likely linked to the increased deformation resistance induced by Nb. Lastly, this research proposes optimal hot-rolling process parameters for new bridge cable steel, recommending specific finishing rolling temperatures and inter-pass times for both Nb-containing and Nb-free steels during the roughing and finishing stages. This study suggests optimal hot-rolling parameters for both Nb-containing and Nb-free steels, providing essential insights for improving hot-rolling and microalloying processes in high-carbon steels for bridge cables.

Evolution of static recrystallization microstructure caused by residual strain of an Al-richen Ni-based single crystal superalloy

Recrystallization has a devastating effect on the service process of single crystal superalloys (SX). This study mainly investigated the static recrystallization (SRX) behavior of an as-cast high Al content nickel-based SX under local or global deformation at room temperature, as well as heat treatment at various temperatures. The microstructural evolution was observed under different conditions using electron back scatter diffraction (EBSD), which was employed to determine the SRX threshold. The results indicated that the critical SRX temperature exceeds 1260 °C, and the critical plastic strain is greater than 5 %. In particular, the characteristic of the higher SRX tendency in the interdendritic region (IDR) of the as-cast SX was discovered, which was attributed to the phenomenon that the IDR with lower deformation resistance was prone to significant plastic accumulation and the bulk γ' could be the nucleation substrate of the SRX. Furthermore, with the increase in heat treatment temperature, there are certain changes in the morphology characteristics of re-precipitated γ' in the vicinity of the SRX grain boundary with a higher migration rate. This is mainly attributed to the decrease in the internal subcooling of the bulk γ' phase and the increase in the concentration of γ' forming elements at the grain boundary front.

Effect of Zr on static recrystallization of deformed austenite and strain-induced precipitation in Ti microalloyed steel

The static recrystallization and strain-induced precipitation behavior of Ti and Ti-Zr low carbon microalloyed steels were studied through isothermal stress relaxation experiments at different deformation temperatures (875–1025 °C). The precipitation kinetic curves of microalloyed carbides were obtained, and the effect of Zr on the precipitation kinetics of microalloyed carbides was analyzed. Two static recrystallization kinetic models were established, and the activation energies for static recrystallization of Ti steel and Ti-Zr steel were calculated to be 312.44 and 246.59 kJ/mol, respectively. The results indicate that the addition of Zr lowers the nose point temperature of the precipitation–time–temperature curve, shortens the incubation period for the nucleation of precipitates, promotes the nucleation of strain-induced precipitates in Ti microalloyed steel, and reduces the coarsening rate of precipitates particles by an order of magnitude. In addition, the addition of Zr also advances the end time of static recrystallization of deformed austenite, inhibits the growth of static recrystallization austenite grains in Ti steel during the isothermal process, and makes the austenite grains finer and more uniform.

Re-dissolution behavior of secondary phases and mechanical response of CNT/2024Al composites

Heat treatment is one of the most effective strategies for regulating microstructure and enhancing the mechanical properties of aluminum matrix composites. In this work, the effects of solution treatment on the static recrystallization behavior, characteristics of secondary phases dissolving, and mechanical response of carbon nanotubes reinforced aluminum matrix composites (CNT/2024Al) were systematically investigated using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). Since plenty of deformation stored energy in as-extruded composites is consumed, the residual energy is insufficient to induce static recrystallization during solution treatment. Besides, various interfacial phases aggregated around the Al2Cu phases, which reduced the effective contact area between the Al2Cu phases and matrix, and severely hindered the dissolution process of the Al2Cu phases. The yield strength, tensile strength, and elongation of as-solution treated composites were 23.2%, 44.9%, and 23.0% higher than those of as-extruded composites, respectively. The enhanced yield strength is attributed to solid solution strengthening induced by the dissolution of secondary phases, thermal mismatch strengthening, and the strengthening originating from the formation of Al4C3 phases.

Influence of Ca addition on the dynamic and static recrystallization behavior of direct extruded flat profiles of Mg-Y-Zn alloy

This paper investigates the influence of addition of Ca in a Y-Zn-containing magnesium alloy on the dynamic and static recrystallization behaviors and reveals the formation mechanism of the quadrupole texture during thermomechanical processing. Direct extrusion of flat bands has been conducted at various process conditions to study the difference between the two alloys WZ10 and WZX100 in terms of microstructure and texture development. It can be shown that, Ca addition promotes the DRX of WZ10 alloy. During additional heat treatment, the absence of Y segregation at the grain boundaries and the associated lack of solute drag to the boundary mobility leads to a pronounced grain growth during SRX in WZX100 alloy. Furthermore, it is shown that the addition of Ca to Y-Zn is not beneficial in terms of formability. It is demonstrated that alloying elements can have different effects depending on the recrystallization mechanisms. Partially recrystallized microstructure is a prerequisite at the as-extruded status to form the quadrupole texture and during subsequent annealing, which stands for high formability.

Influence of carbon content on static recrystallization behavior of 50% cold-rolled Fe-18Mn-9Cr-2Al-xC steels

Recrystallization behavior during annealing at various temperatures was investigated for 50% cold-rolled Fe-18Mn-9Cr-2Al-xC steels with C contents varying between 0 and 0.5 wt%. Nucleation of recrystallization occurred near randomly in the carbon-free steel, whereas increasing the carbon contents promoted preferential nucleation at carbides formed along the grain boundaries through the particle stimulated nucleation mechanism. New grains in the carbon-free steel grow freely at the expense of deformed grains until the end of recrystallization during which migration of recrystallization front was blocked by the elongated δ-ferrites. For the carbon-added steels, on the other hand, (Cr,Mn)23C6 carbides and FeAl intermetallics formed during annealing and pre-existing carbides at grain boundaries pinned the recrystallization front, and thereby suppressing the growth of new grains and developing a distinct necklace structure. Recrystallization of the carbon-added steels completed only after carbides were dissolved at higher temperatures around 900 °C. It is noteworthy that it is not the carbon atom itself in solid solution but carbides that promotes nucleation of recrystallization and subsequently suppressed growth of new grains. It was also found that tensile properties of the cold-rolled steels restored nearly to those prior to cold rolling, i.e., in as-annealed state. It is concluded that recrystallization kinetics, special distribution of new grains, and texture of the cold-rolled Fe-18Mn-9Cr-2Al-xC steels are significantly affected by the carbon contents. In addition, restoration of tensile properties of cold-rolled steels by recrystallization suggests that many repetitive thermomechanical processing are applicable to the steels for forming into a desire shape.

Investigating the Static Recrystallization Behavior of 22MnB5 Manganese–Boron Steel through Stress Relaxation Analysis

A constitutive model was developed to characterize the static recrystallization (SRX) and evolution of the grain size of the industrially relevant press-hardening steel, 22MnB5, subsequent to the hot forming of sheet metal. Isothermal stress relaxation tests were conducted using the BAEHR 805 A/D thermomechanical simulator, encompassing a temperature range of 950 to 1050 °C, prestrain levels ranging from 0.01 to 0.1, and strain rates spanning from 0.01 to 0.8 s−1. The results obtained from the isothermal stress relaxation tests facilitated the formulation of an Avrami equation-based model, which aptly describes the kinetics of SRX in relation to the temperature, prestrain, and strain rate. Notably, an increase in temperature led to accelerated recrystallization kinetics, signifying temperature-dependent behavior. When the temperature increased from 950 to 1050 °C, the recrystallization time was reduced to approximately one-third. Additionally, the prestrain exhibited a positive influence on the acceleration of SRX kinetics. A quintupling of the prestrain from 0.01 to 0.05 resulted in a reduction of the static recrystallization duration to approximately one-fifth. Among the parameters studied, the strain rate had the least impact on the SRX kinetics, as doubling the strain rate from 0.01 to 0.8 only resulted in a halving of the recrystallization duration. Moreover, an analysis of the microstructural evolution in response to the forming parameters was undertaken. While the grain-size investigation post-isothermal stress relaxation tests provided results in line with the SRX kinetics calculations, the observed effects were comparatively subdued. Furthermore, a comprehensive examination was conducted using electron backscatter diffraction (EBSD) analysis, aiming to explore the effects of specific stress relaxation states on the morphology of martensite. The findings reveal fully recrystallized globulitic microstructures, characterized by relatively minor differences among them.

Static recrystallization behaviors and mechanisms of 7Mo super-austenitic stainless steel with undissolved sigma precipitates during double-stage hot deformation

Static recrystallization behaviors and mechanisms of 7Mo super-austenitic stainless steel with undissolved sigma precipitates during double-stage hot deformation