Recrystallization Period Research Articles

Advanced microstructural path modeling of primary recrystallization in aluminum alloys AA5182 and AA5657

AbstractWhen analyzing recrystallization kinetics data, it is extremely important to use a model, which has appropriate assumptions for nucleation and growth, including spatial distribution of nuclei, nucleation rate, growth rate, and directionality. In the present work, we reveal how advanced microstructural path modeling (MPM) can successfully fit kinetics data for the complex recrystallization of two different industrial aluminum alloys. Simpler models have failed to fit the data over the entire recrystallization period. The new model allows for spatially clustered nucleation and for different growth rates in different sample directions, whereby the grains evolve with an aspect ratio different from 1. Based on the MPM analysis, the specific nucleation and growth parameters as well as the recrystallized grain sizes are deduced, and the recrystallization characteristics of the two alloys are compared. The work demonstrates the power of quantitative metallography and the wealth of recrystallization information that may be obtained from MPM modeling of such stereological data.

СТРОЕНИЕ СНЕЖНОЙ ТОЛЩИ НА КОЛЬСКОМ ПОЛУОСТРОВЕ

In 2016–2019, the structure of the snow thickness in the northern and central parts of the Kola Peninsula (from the Barents Sea to the Khibiny Mountains) was studied in tundra, forest-tundra, taiga, high–altitude Arctic and other landscapes during the periods of maximum recrystallization of the snow (February–April) and initial snow accumulation (October). 37 borings were made in the snow thicknesses. 399 snow layers of different ages and genesis were examined. In the total, 399 measurements of the density, porosity, structure of snow (size and shape of ice crystals) and texture (orientation of crystals and pores) of snow layers, 413 measurements of temperature at the contacts between snow layers, 46 measurements of the temporary resistance of the layer to rupture, 27 measurements of the time resistance to compression, 119 measurements of the resistance of the snow layer to horizontal sounding (with a cross-shaped tip that allows taking into account the anisotropy of the snow layer) were performed. The percentage of crystals of different classes of shapes in the layer was determined. It was found that the Kola Peninsula has a high rate of evolution of the snow thickness. Even in multi-snow winters (including the landscapes of high-altitude Arctic deserts in Khibiny and Monche-tundra) in March, up to 90% of the snow thickness is made up of snow layers with a columnar and fibrous texture, composed of ice crystals of semi-skeletal and skeletal classes of shapes with a diameters of up to 4 mm. These patterns of the evolution are typical for the Arctic and Subarctic (confirmed by studies on the Yamal Peninsula, in the lower reaches of the Northern Dvina River and in Karelia). Values of the strength characteristics of the snow layer (time resistance to rupture, resistance to compression, and to horizontal sounding with regard for the anisotropy of the snow layer texture) are the lower, the higher the content of crystals in the layer of the highest stages of evolution (skeletal) and the more developed the texture of the layer. The lowest values of strength characteristics were observed in snow layers with a fibrous texture.

Petrochronology of Wadi Tayin Metamorphic Sole Metasediment, With Implications for the Thermal and Tectonic Evolution of the Samail Ophiolite (Oman/UAE)

AbstractOphiolite metamorphic soles preserve important records of ophiolite emplacement, but there have been few detailed investigations into their non‐mafic portions. We present new thermobarometric and petrochronologic data from a metasediment and mafic restite in the upper Wadi Tayin sole exposure in the Samail (Oman‐UAE) Ophiolite. Thermodynamic modeling suggests metasedimentary garnet nucleation at ~4 kb, ~550°C and final growth at 7.5 ± 1.2 kbar, 665 ± 32°C, occurring by 93.0 ± 0.5 Ma (Lu‐Hf isochron). Zircon U‐Pb dates of 106.9 ± 2.3 (detrital) and 98.7 ± 1.7 to 94.1 ± 1.6 Ma (metamorphic) bracket the initiation of metamorphism, and monazite U‐Pb dates from ~97–89 Ma suggest a lengthy period of growth or recrystallization. A mafic titanite U‐Pb age of 92.2 ± 1.8 Ma records the earliest possible juxtaposition of high‐ and lower‐grade sole rocks. These and other data suggest that (i) the Wadi Tayin sole preserves an inverted metamorphic, metasomatic, and age gradient,(ii) metasediment metamorphism occurred during, or soon after, crystallization of the overlying ophiolite (≤96.5 Ma); and (iii) sole metasediments define a thermal gradient continuous with hotter, higher‐P amphibolites. Some of these data conflict with existing models for sole formation, and we propose several hypotheses to explain them. Cooling of the sole below Ar closure by ~92 Ma suggests that strain rapidly partitioned away from the sole, leading to large‐scale, thin‐skinned thrust emplacement of the ophiolite >100 km across the continental margin and the late, cool underthrusting of the continental margin.

Characterization of hot deformation behavior of 30Si2MnCrMoVE low-alloying ultra-high-strength steel by constitutive equations and processing maps

Isothermal compression tests of as-forged 30Si2MnCrMoVE low-alloying ultra-high-strength steel were carried out on a Gleeble 3500 thermal simulator at the deformation temperatures of 950–1150 °C and strain rates of 0.01–10 s−1. Based on the classical stress–dislocation density relationship and the kinematics of the dynamic recrystallization, the constitutive equations of the work hardening dynamical recovery period and dynamical recrystallization period were developed by using the work hardening curve and Avrami equation, which shows good agreement with the experimental value. Processing maps at the strain of 0.90 were constructed based on dynamic material model and were analyzed combined with microstructure observation under different conditions. The optimum parameter based on the processing maps was obtained and verified by a supplementary experiment. The power dissipation maps and instability maps at strains of 0.05–0.90 were also constructed, and the evolution law was analyzed in detail. The established constitutive equation and hot processing maps can provide some guidance for hot working process.

Physically-Based Constitutive Modelling of As-Cast CL70 Steel for Hot Deformation

In order to conduct numerical simulation of plasticity forming and confirm the processing parameters of heat deformation for as-cast CL70 steel, the hot deformation behaviors of as-cast CL70 steel were studied by isothermal compression tests which used a Gleeble-1500D thermal mechanical simulation tester for the deformation temperatures ranging from 1173 to 1523 K and the strain rates ranging from 0.001 to 1 s−1. Flow stress curves of the steel were obtained under high temperature. The flow stress constitutive models of the work hardening-dynamical recovery period and dynamical recrystallization period were established for as-cast CL70 steel. In work hardening-dynamic recovery period, the flow stress was predicted by employing the evolution rule of dislocation density in the constitutive model. In dynamic recrystallization period, the flow stress after the critical strain was predicted by employing the dynamic recrystallization kinetics in the constitutive model. To improve the prediction accuracy of the model, the dynamic recovery coefficient is modified in the traditional physically-based constitutive model. The results indicate that the proposed physically-based constitutive model has high accuracy in predicting the flow stress under hot deformation for as-cast CL70 steel.

New age constraints on the Lan Sang gneiss complex, Thailand, and the timing of activity of the Mae Ping shear zone from in-situ and depth-profile zircon and monazite U-Th-Pb geochronology

The Mae Ping shear zone (MPSZ) is one of four major strike-slip systems in Thailand and a key structural element in some models of the Cenozoic tectonic evolution of Southeast Asia. In northwestern Thailand, the MPSZ exposes a ∼5-km-wide core of intensely deformed high-grade metamorphic and minor undeformed magmatic rocks, the Lan Sang gneiss complex (LSGC). Despite previous efforts to determine the chronology of the LSGC and, ultimately, the MPSZ, the evolution of this gneiss complex remains incompletely resolved. Here we present new zircon and monazite U-(Th-)Pb LA-(MC-)ICP-MS ages and whole-rock geochemical analyses from three peraluminous, high-K (meta)igneous granitic rocks (augen gneiss, sheared granodiorite, undeformed subvolcanic dike) of the LSGC. Our zircon U-Pb dating suggests that the granitic protolith of the augen gneiss intruded metasedimentary basement of Sibumasu as early as ∼235–220 Ma. Zircon rim and monazite U-(Th-)Pb ages from the same sample attest to periods of metamorphic recrystallization and overgrowth in the Late Triassic-Early Jurassic, Early Cretaceous and Eocene. The latter event had started by ∼45 Ma and culminated in partial melting of the basement gneisses and the intrusion of granodiorite magma into the LSGC at ∼35 Ma, contemporaneous with ductile deformation along the MPSZ. A late undeformed subvolcanic dike that crosscuts the mylonitic fabric of the calc-silicate and marble core of the MPSZ, dated in this study at ∼22 Ma, may indicate that ductile shearing had ceased by that time. Thus, our study provides the first evidence for Late Eocene-Early Miocene magmatism in the LSGC.

Crystal Chemistry and Geochronology of Thorium-Rich Monazite from Kovela Granitic Complex, Southern Finland

Abundant porphyritic granites, including Grt-bearing and Bt-bearing porphyritic granites, and porphyritic potash-feldspar granite (trondhjemite-granitic composition) are widely distributed within the Kovela granitic complex Southern Finland, which associated with monazite-bearing dikes (strong trondhjemite composition). The investigated monazite-bearing dikes are dominated by a quartz + K-feldspar + plagioclase + biotite + garnet + monazite assemblage. The monazite forms complexly zoned subhedral to euhedral crystals variable in size (100 - 1500 μm in diameter) characterized by high Th content. The chemical zoning characterised as: 1) concentric, 2) patchy, and 3) intergrowth-like. Textural evidence suggests that these accessory minerals crystallized at an early magmatic stage, as they are commonly associated with clusters of the observed variations in their chemical composition are largely explained by the huttonite exchange , and subordinately by the cheralite exchange with proportions of huttonite (ThSiO4) and cheralite [CaTh(PO4)2] up to 20.4% and 9.8%, respectively. Textural evidence suggests that these monazites and associated Th-rich minerals (huttonite/thorite) crystallized at an early magmatic stage, rather than metamorphic origin. The total lanthanide and actinide contents in monazite and host dikes are strongly correlated. Mineral compositions applied to calculate P-T crystallization conditions using different approaches reveal a temperature range of 700°C - 820°C and pressure 3 - 6 kbars for the garnet-biotite geothermometry. P-T pseudo-section analyses calculated using THERMOCALC software for the bulk compositions of suitable rock types, constrain the PT conditions of garnet growth equilibration within the range of 5 - 6 kbars and 760°C - 770°C respectively. Empirical calculations and pseudo-section approaches indicate a clockwise P-T path for the rocks of the studied area. 207Pb/206Pb dating of monazite by LA-MC-ICPMS revealed a recrystallization period at around 1860 - 1840 Ma. These ages are related to the tectonic-thermal event associated with the intense crustal melting and intra-orogenic intrusions, constraining the youngest time limit for metamorphic processes in the Kovela granitic complex.

Constitutive modeling and critical strain of dynamic recrystallization in SA508Gr.4N steel for advanced pressure vessel materials

Using a Gleeble–1500D thermal–mechanical simulator, the hot-deformation behavior and critical strain in the dynamic recrystallization of SA508Gr.4N steel were investigated by compression tests from 1050 to 1250 °C with strain rates from 0.001 to 0.1 s−1. Stress–strain curves were fitted by a nonlinear fitting method. Based on these tests, the flow stress constitutive equations of the work-hardening dynamical recovery period and dynamical recrystallization period were established for SA508Gr.4N steel. The stress–strain curves of SA508Gr.4N steel predicted by the established models are in a good agreement with the experimental ones. Curves of lnθ − e and − ∂(lnθ)/∂e − e (where θ is the work-hardening rate and e is true strain) were plotted from experimental data. A critical strain (ec) and a peak strain (ep) of dynamic recrystallization were obtained and exhibited a linear relationship, i.e., ec = 0.386ep. The predicted model of ec could be described by the equation of ec = 1.604 × 10−3Z0.127.

STABILITY OF SUPERCOOLING SOLUTIONS OF CRYSTALLIZATION SYSTEMS IN CLASSICAL THEORY OF NEW PHASE FORMATION

Theoretical and experimental evaluations of crystallization systems solutions stability to overcooling were summarized. The general regulariries of the kinetics of the crystallization process are discussed from the standpoint of the classical theory of the formation and growth of new-phase particles. During the analysis of the process of periodic homogeneous crystallization kinetic diagram, three characteristic periods were revealed: the period of resistance to supercooling, the period of crystal growth, and the period of recrystallization. The nature of the processes determining the duration of the characteristic periods has been established. The applicability of the mathematical apparatus of the new phase formation classical theory for calculating the basic and particular functionals of the crystallization system is substantiated. Relations are given that make it possible to calculate the main and particular functionals of the crystallization system stability for supercooling. The analysis of crystallization system category influence on the magnitude of limit supercooling and periodic homogenous crystallization induction period extreme was made. Parameters of the resistance to supercooling of supersaturated aqueous solutions of inorganic and organic substances certain classes under periodic homogeneous crystallization are presented. Conclusions are drawn regarding the position of the main and particular functionals extrema of the crystallization system. The correctness of the conclusions is confirmed by an analysis of the experimental data on the crystallization kinetics of a number of inorganic and organic substances from aqueous and aqueous-organic solvents. On the example of periodic homogeneous crystallization process of the vitamin B1 thiamin bromide from the water-ethanol solution, a complete series of the crystallization system main and particular functionals extremum positions the are constructed. The regularities of the influence of the organic component concentration in a binary solvent on the stability functionals of the crystallization system are noted.Forcitation:Slivchenko E.S., Samarskiy A.P., Isaev V.N., Blinichev V.N. Stability of supercooling solutions of crystallization systems in classical theory of new phase formation. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 5. P. 88-93.

Geochemistry of speleothems affected by aragonite to calcite recrystallization – Potential inheritance from the precursor mineral

Formerly aragonite speleothems recrystallized to calcite result from solutions subsaturated in aragonite and supersaturated in calcite that infiltrate into the speleothem through the interconnected porosity. In most cases, the crystal replacement takes place through a thin solution film. This diagenetic process can occur under open or semi-closed geochemical conditions. Thus, secondary calcite crystals record the composition of the fluid at the time of diagenesis affected by calcite partition coefficients and fractionation factors (open system) or partly inherit the composition of the primary aragonite (semi-closed system). So, whether or not recrystallized aragonite speleothems can record reliable geochemical signals from the time of speleothem primary deposition still is an open debate. We studied a stalagmite from Eagle Cave (Spain) predominantly composed of secondary calcite that replaced aragonite, although a core of primary aragonite extending 45mm along the growth direction was preserved at the base of the sample. We obtained Mg and Sr compositional maps, paired U–Th dating and δ18O and δ13C profiles across the diagenetic front. Additionally, two parallel isotope records were obtained along the speleothem growth direction in the aragonite and calcite sectors. Our results support that recrystallization of this speleothem took place in open system conditions for δ18O, δ13C, Mg and Sr, but in semi-closed system conditions for U and Th. The recrystallization of this sample took place during one or several events, likely after the Younger Dryas as a result of climate change influencing drip water composition. Based on compositional zoned patterns, we suggest that the advance of diagenetic fronts in this speleothem had an average rate of 50±45μm/yr. Such recrystallization rate can transform any aragonite speleothem into calcite within a few centuries. We suggest that the volume of water interacting with the speleothem at the time of recrystallization is of critical importance for inheritance of different elements. The volume of solution is controlled by (1) the discharge of water passing through the sample and (2) the lapse time between aragonite dissolution and calcite precipitation. Hydrology and hydrochemistry of the interacting solution, together with the mineralogy and texture of the speleothem are the essential controls for the diagenesis of the speleothem. Recrystallization of aragonite speleothems does not follow stratigraphical levels of the sample but occurs along sites with preferential flow paths in any sector of the speleothem. In these cases the relationship between age and distance from base is not preserved. However, alternation of periods of recrystallization with periods of aragonite precipitation causing speleothem accretion can result in recrystallized speleothems with coherent distance from the base-age relationship. Thus, early diagenesis of speleothems affected by seasonal or inter-annual oscillation of drip waters supersaturated and subsaturated in aragonite may provide best-scenario conditions for dating and preservation of paleoenvironmental records along recrystallized speleothems. However, even in this scenario, the variable discharge and the diagenetic rate control the geochemical inheritance from the primary aragonite crystals.

CaCO3 recrystallization in saline and alkaline soils

Are desert ecosystems a stable sink for atmospheric CO2? Although the uptake of atmospheric CO2 by soil during the nighttime is detected in deserts and some semi-deserts, the underlying mechanisms remain elusive. In order to determine the factors affecting the CO2 fluxes into soil and to reveal the relationship between CO2 fluxes and carbonate formation and recrystallization in saline and alkaline soils, four soils with contrasting salinity from two sites, Aksu and Yingbazar, along the Tarim River were analysed. Soils were incubated in 14CO2 labelled atmosphere for 90days at three CO2 concentrations: 0.04%, 0.4% and 4%. The 14C activity was measured in soil water and air, as well as in carbonates after 2, 14 and 90days. The 14C incorporation in CaCO3 increased with corresponding 14C decrease remaining in the CO2. The highest 14C incorporation into CaCO3 (54%) was observed in the Yingbazar saline soil. The carbonate recrystallization rates increased logarithmically (r2>0.97) with the CO2 concentration. The average carbonate recrystallization rate from three sampling times was highest in the Yingbazar saline soil under 4% CO2 (8.45×10−6day−1) and lowest in the Aksu alkaline soil under 0.04% CO2 (0.03×10−6day−1). The average carbonate recrystallization rate increased with electric conductivity (corresponding to soil salinity) but decreased with pH (R2=0.99 for 4% CO2). The alkaline soils incorporated less 14C into CaCO3 than the saline soils. At the highest CO2 concentration of 4%, the full recrystallization period of the remaining primary carbonates was 10- to 100-fold shorter than at the lower CO2 concentrations. Therefore, besides soil chemical parameters (e.g. pH, CaCO3 content), CO2 concentration (respiration of microorganisms and roots) is an important factor for CaCO3 recrystallization and formation of pedogenic carbonates in desert soils. It is the most important factor for CaCO3 recrystallization and so, for the formation of pedogenic carbonates.

Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Araçuaí Orogen, Brazil

The Capelinha Formation (Macaubas Group) consists of a lower quartzitic unit with metamafic intercalations and an upper metapelitic sequence. It occurs in a complex tectono-metamorphic sector of the Aracuai orogen, where post-collisional collapse-related structures superimposed collisional structures. The garnet-bearing assemblages started crystallization in the collisional deformation stage that formed the main regional foliation around 570 Ma. Garnet porphyroblasts display a well-developed growth zonation of Fe-Mg-Ca-Mn and show, from core to rim, increasing almandine and pyrope contents in contrast with decreasing grossular and spessartine contents. Mineral relations and microstructures provide criteria for local equilibria and a structurally controlled application of geothermobarometers based on cation exchange and net transfer reactions. The P-T values calculated from cores to rims of garnets, aligned along clockwise trends, resulted in increasing temperatures (from 500 oC up to 620 oC) under decompression conditions (from 8.0 kbar to 4.5 kbar). The Th-U-Pb dating of homogeneous monazites by electron microprobe revealed a recrystallization period at around 490 - 480 Ma. These ages can be related to the tectono-thermal event associated with the gravitational collapse, constraining the youngest time limit for metamorphic processes in the Aracuai orogen.

Study on constitutive modeling and processing maps for hot deformation of medium carbon Cr–Ni–Mo alloyed steel

The hot deformation behavior of medium carbon Cr–Ni–Mo alloyed steel 34CrNiMo was studied in the wide temperature range of 900–1150°C and the strain rate of 0.002–5s−1. The thermo-mechanical analysis using Thermo-Calc software indicates austenite is the main phase during hot compression, which has a high occurrence tendency of DRX because of low stacking fault energy of such a phase. Constitutive equations for flow stress were developed by using the work hardening curve for the work hardening and dynamic recovery period and Avrami equation for the dynamic recrystallization period. All the factors in the equations can be illustrated in terms of Zener–Hollomon parameter. Besides, processing maps based on dynamic material model at the strains of 0.2, 0.4, 0.6, 0.8 and 1.0 were established. The concluded optimum hot working parameters are at 950–1100°C & 0.01–0.2s−1 and 1100–1150°C & 0.01–5s−1.

Does continental crust transform during eclogite facies metamorphism?

AbstractEclogites within exhumed continental collision zones indicate regional burial to depths of at least 60 km, and often more than 100 km in the coesite‐stable, ultra‐high pressure (UHP) eclogite facies. Garnet, omphacitic pyroxene, high‐Si mica, kyanite ± coesite should grow at the expense of low‐P minerals in most felsic compositions, if equilibrium obtained at these conditions. The quartzofeldspathic rocks that comprise the bulk of eclogite facies terranes, however, contain mainly amphibolite facies, plagioclase‐bearing assemblages. To what extent these lower‐P minerals persisted metastably during (U)HP metamorphism, or whether they grew afterwards, reflects closely upon crustal parameters such as density, strength and seismic character. The Nordfjord area in western Norway offers a detailed view into a large crustal section that was subducted into the eclogite facies. The degree of transformation in typical pelite, paragneiss, granitic and granodioritic gneiss was assessed by modelling the equilibrium assemblage, comparing it with existing parageneses in these rocks and using U/Th–Pb zircon geochronology from laser ablation ICPMS to establish the history of mineral growth. U–Pb dates define a period of zircon recrystallization and new growth accompanying burial and metamorphism lasting from 430 to 400 Ma. Eclogite facies mafic rock (~2 vol.% of crust) is the most transformed composition and records the ambient peak conditions. Rare garnet‐bearing pelitic rocks (<10 vol.% of crust) preserve a mostly prograde mineral evolution to near‐peak conditions; REE concentrations in zircon indicate that garnet was present after 425 Ma and feldspar broke down after 410 Ma. Felsic gneiss – by far the most abundant rock type – is dominated by quartz + biotite + feldspar, but minor zoisite/epidote, phengitic white mica, garnet and rutile point to a prograde HP overprint. Relict textures indicate that much of the microstructural framework of plagioclase, K‐feldspar, and perhaps biotite, persisted through at least 25 Ma of burial, and ultimately UHP metamorphism. The signature reaction of the eclogite facies in felsic rocks – jadeite/omphacite growth from plagioclase – cannot be deduced from the presence of pyroxene or its breakdown products. We conclude that prograde dehydration in orthogneiss leads to fluid absent conditions, impeding equilibration beyond ~high‐P amphibolite facies.

RETRACTED-Effect of electropulsing treatment on the microstructure, texture, and mechanical properties of cold-rolled Ti–6Al–4V alloy

Abstract

Direct physical evidence of dolomite recrystallization

AbstractThe possibility of recrystallization is a long‐standing barrier to deciphering the genetic origin of dolomites. There is often uncertainty regarding whether or not characteristics of ancient dolomites are primary or the consequence of later recrystallization unrelated to the original dolomitization event. Results from 65 new high‐temperature dolomite synthesis experiments (1 m, 1·0 Mg/Ca ratio solutions at 218°C) demonstrate dolomite recrystallization affecting stoichiometry, cation ordering and nanometre‐scale surface texture. The data support a model of dolomitization that proceeds by a series of four unique phases of replacement and recrystallization, which occur by various dissolution–precipitation reactions. During the first phase (induction period), no dolomite forms despite favourable conditions. The second phase (replacement period) occurs when Ca‐rich dolomite products, with a low degree of cation ordering, rapidly replace calcite reactants. During the replacement period, dolomite stoichiometry and the degree of cation ordering remain constant, and all dolomite crystal surfaces are covered by nanometre‐scale growth mounds. The third phase (primary recrystallization period), which occurs in the experiments between 97% and 100% dolomite, is characterized by a reduced replacement rate but concurrent increases in dolomite stoichiometry and cation ordering. The end of the primary recrystallization period is marked by dolomite crystal growth surfaces that are covered by flat, laterally extensive layers. The fourth phase of the reaction (secondary recrystallization period) occurs when all calcite is consumed and is characterized by stoichiometric dolomite with layers as well as a continued increase in the degree of cation ordering with time. Inferences of recrystallization, in natural dolomite, based on cation order or stoichiometry of dolomite, usually depend on assumptions about the precursor dolomite subjected to recrystallization. If it is assumed that the experimental evidence presented here is applicable to natural, low‐temperature dolomites, then the presence of mounds is direct evidence of a lack of recrystallization and the presence of layers is direct evidence of recrystallization.

Constitutive Modeling for Elevated Temperature Flow Behavior of 30Cr2Ni4MoV Ultra-super-critical Rotor Steel

In order to perform numerical simulation of forging and determine the hot deformation processing parameters for 30Cr2Ni4MoV steel, the compressive deformation behaviors of 30Cr2Ni4MoV steel were investigated at the temperatures from 970 to 1270 °C and strain rates from 0. 001 to 0. 1 s−1 on a Gleeble-3500 thermo-mechanical simulator. The flow stress constitutive equations of the work hardening-dynamical recovery period and dynamical recrys-tallization period were established for 30Cr2Ni4MoV steel. The stress-strain curves of 30Cr2Ni4MoV steel predicted by the proposed model well agreed with experimental results, which confirmed that the proposed equations can be used to determine the hot deformation processing parameters for 30Cr2Ni4MoV steel.

High Temperature Deformation Behavior of 4340 Steel: Activation Energy Calculation and Modeling of Flow Response

The 4340 steel is extensively utilized in several industries including automotive and aerospace for manufacturing a large number of structural components. Due to the importance of thermo-mechanical processing in the production of steels, the dynamic recrystallization (DRX) characteristics of 4340 steel were investigated. Namely, hot compression tests on 4340 steel have been performed in a temperature range of 900–1200 °C and a strain rate range of 0. 01–1 s−1 and the strain of up to 0. 9. The resulting flow stress curves show the occurrence of dynamic recrystallization. The flow stress values decrease with the increase of deformation temperature and the decrease of strain rate. The microstructure of 4340 steel after deformation has been studied and it is suggested that the evolution of DRX grain structures can be accompanied by considerable migration of grain boundaries. The constitutive equations were developed to model the hot deformation behavior. Finally based on the classical stress-dislocation relations and the kinematics of the dynamic recrystallization; the flow stress constitutive equations for the dynamic recovery period and dynamic recrystallization period were derived for 4340 steel, respectively. The validity of the model was demonstrated by demonstrating the experimental data with the numerical results with reasonable agreement.

Effect of Electric Current on Microstructural Evolution in a Cold-Rolled 3% Si Steel

The effect of electric current pulse (ECP) treatment on grain orientation in a cold-rolled Fe­3%Si steel was investigated in this study. Results showed that the recrystallized nuclei preferred to form along the current direction in the primary period of recrystallization. The theoretical analysis revealed that the anisotropic nucleation orientation was ascribed to the different dislocation mobility derived from the electron wind force during the passing of electric current. Hence, the ECP treatment should be a special and effective method to control the nucleation orientation, and the present work is of great technological and physical importance. [doi:10.2320/matertrans.M2011272]

Modeling of Mechanical Characteristics in Hot Deformation of 4130 Steel

AbstractIn this investigation, hot compression tests were performed at 900 °C − 1100 °C and strain rate of 0.001 − 0.1 s−1 to study hot deformation behavior and flow stress model of 4130 steel. Based on the classical stress–dislocation relations and the kinematics of the dynamic recrystallization, the flow stress constitutive equations of the work hardening‐dynamical recovery period and dynamical recrystallization period were established for 4130 steel, respectively. The validity of the model was demonstrated by comparing the experimental data with the numerical results. The agreement of this comparison is quite reasonable.