Activation Energy Of Static Recrystallization Research Articles

Determination of Activation Energy For Static Re-Crystallization in Nb- Ti Low Carbon Micro Alloyed Steel

Data required for calculation the static re-crystallization kinetics have been evaluated from laboratory simulations. Series of two hit isothermal tests were conducted on high temperature torsion machine. These tests were conducted on four different temperatures and using inter-pass times between 0.5 and 5s with aim to investigate the influence of thermal activation on static re-crystallization. All tests were conducted on temperatures over TNR temperature, i.e. in temperature range in which all niobium is present only in solid solution. Method of evaluation of re-crystallization fraction was mechanical metallography, i.e. evaluation based on shape of each stress- strain curve. The fraction softening was calculated for all temperatures, together with avrami exponent, nA, and activation energy for re-crystallization, QSRX. Activation energy for static re-crystallization QSRX  281 KJ/mol and avrami exponent nA  1 determined in this work are in excellent agreement with previously reported data.

Micro-mechanism of static softening of high nitrogen austenitic stainless steel

The stress softening behavior and microstructure evolution of Mn18Cr18N steel remelted by electroslag remelting during the holding process were studied through two-pass hot compression tests with different parameters. The static recrystallization kinetics model of the steel was established by calculating the softening rate in two-pass hot compression, and the activation energy of static recrystallization was calculated to be 279.81 KJ/mol. Investigation of microstructural showed that the occurrence of complete static recrystallization needed sufficiently pre-strain and temperature. The static recrystallization was basically completed when compressed to a pre-strain 0.26 after holding 120 s with 1 s−1 at 1273 K. While the pre-strain was lowered to 0.18 requires a longer holding time of 320 s or a higher temperature of 1373 K to obtain complete static recrystallization. The EBSD analysis of the static recrystallization grain structure shows that the static recrystallization nucleation mechanism of this steel is mainly dominated by dislocation driven grain boundary migration, and few annealing twins are generated during the grain boundary migration process, promoting the fine homogenisation of the grains.

Determination of Activation Energy for Static Recrystallization in Al-Mg-Si Alloys with Different Zr Contents

In this study, activation energies required for the static recrystallization behavior during the annealing process after cold deformation of Al-Mg-Si alloy to which zirconium was added in various proportions were investigated. Depending on the zirconium content, the activation energies of the alloys were found and compared both experimentally and by calculation. For this purpose, alloys containing 0.1, 0.2 and 0.3 wt-% Zr were cold rolled after taking into solution and quenching. And then, the alloys were annealed at 375 °C and 500 °C for different annealing times. After the alloys were prepared metallographically, their grain structures were examined microscopically. Depending on the temperature, recrystallization-% was found by image analysis and experimental recrystallization-% curves were drawn. The time taken for recrystallization-50% to experimentally find the activation energy required for recrystallization to occur was found from the curves. These values were replaced in the relevant formulations and the required activation energy was experimentally found from the slope of the Arrhenius equation and the ln t50% and 1/T graph. In order to find the recrystallization-% by calculation, the nucleation rate and growth rate of the new recrystallized grains were found by image analysis. By substituting these values in Johnson-Mehl-Avrami equation, the calculated recrystallization-% curves of the alloys were found. From here, using the relevant equations, Arrhenius equation was passed and the activation energy was calculated from the slope of ln k and 1/T graph. The results showed that the activation energy increased with the increase of the zirconium ratio, and even the most effective zirconium ratio was between 0.1-0.2% by weight in increasing the activation energy. Therefore, this ratio should be considered in processes where recrystallization, which also affects other properties of the alloy, is not desired.

Static Recrystallization Behavior of Low-Carbon Nb-V-Microalloyed Forging Steel

Static recrystallization is a method of tailoring the microstructure and mechanical properties of steels, which is important for microalloyed forging steels as the hot deformation process significantly affects their mechanical properties. In this paper, the static recrystallization behavior of a low-carbon Nb-V-microalloyed forging steel was investigated by double-pass hot compression tests at deformation temperature of 800–1100 °C and interruption time of 1–1000 s. The static recrystallization fractions were determined using the 2% offset method. The static recrystallization activation energy and the static recrystallization critical temperature (SRCT) of the experimental steel were determined. When the deformation temperature was higher than the SRCT, the recrystallization fraction curve conformed to the Avrami equation. When the deformation temperature was below the SRCT, the recrystallization curve appeared to plateau, which was caused by strain-induced precipitation. Before and after the plateau, the static recrystallization kinetics still obeyed the Avrami equation.

Research on static recrystallization behaviour of pure molybdenum rods during forging

In this work, thermal compression experiment of pure molybdenum rods with sintered density of 9.7–9.8 g cm−3 were performed on the Gleeble-1500D thermal simulator. The double-pass vacuum high-temperature compression test was carried out in a deformation temperature of 1200 °C–1350 °C, a strain rate of 3 s−1 and an interval time of 10–500 s. The stress-strain curve was obtained and analysed. The static softening rate was calculated by the 2% compensation method of yield stress, and the curve of that was fitted. The results show that the softening rate is proportional to the interval time and the deformation temperature. The static recrystallization activation energy and critical temperature of pure molybdenum rod is 583.79 kJ mol−1 and 1365 °C, respectively. Besides, the static recrystallization kinetics model and grain growth model of pure molybdenum rod was established and microstructure evolution of molybdenum was analysed during the deformation process.

Static Recrystallization Behavior of Non-Quenched and Tempered Steel 38MnSiVS

Refinement and uniform austenite grains are essential to obtain excellent and homogenous properties for non-quenched and tempered steel, which is mainly affected by static recrystallization of the rolling process. Using the Gleeble-3500 thermal simulation test machine, 20% compression test was carried out for two passes at 850~1050 °C (interval of 50 °C) and different pass interval time conditions to study the static softening and recrystallization behavior of 38MnSiVS non-quenched and tempered steel during deformation process. The effects of strain rate, deformation temperature and interval time on static softening rate and austenite recrystallization fraction were analyzed. The results showed that the increase of deformation temperature and the increase of pass interval time had more significant impact on the static recrystallization volume fraction of 38MnSiVS steel, while the influence of strain rate was relatively smaller. When the deformation temperature was 950 °C or higher, the non-conditioning steel 38MnSiVS could undergo complete recrystallization, and partial recrystallization occurred in the temperature range of 850-950 °C. A static recrystallization volume fraction model of non-regulatory steel 38MnSiVS was established. The static recrystallization activation energy was 296.7 kJ·mol-1, and the static recrystallization volume fraction model had a relative error of 2%.

Some aspects of physical metallurgy of microalloyed steels

Some aspects of deformation, precipitation, and recrystallization behavior in medium carbon V-microalloyed and low carbon Nb/Ti-microalloyed steels are presented in the paper. Changes in microstructure are explained together with methods of quantification. The temperature of No-recrystallization (Tnr) is defined as a milestone to show the onset of retardation of recrystallization while the apparent activation energy for hot working shows the extent of this retardation. In the case of high cooling rates, this method is not sufficiently sensitive and Trl (recrystallization limit temperature) and Trs (recrystallization stop temperature) must be evaluated from softening data. Paper presented the possibility to estimate Tnr temperature on six stands finishing train at Hot Strip Mill in HBIS Iron and Steel Serbia, Smederevo as well as the activation energy for static recrystallization, QSRX, derived from Tnr temperatures.

Prediction of Post-deformation Recrystallization Kinetics in AISI 321 Austenitic Stainless Steel Using Double-Stage Hot Compression

In the present research, a series of double-stage hot compression tests were conducted in the temperature range of 950-1150 °C, strain rates in the range of 0.01-1 s−1, strain in the range of 0.1-0.3, and inter-pass time range of 3-100 s to evaluate the kinetics of the post-deformation recrystallization in AISI 321 austenitic stainless steel. An Avrami-type kinetics equation has been determined based on the obtained experimental data. Results show that the extent of post-deformation recrystallization increases with increase in inter-pass time, deformation temperature, pre-strain, and strain rate. The calculated activation energy for recrystallization (174 kJ/mol) is lower than the activation energy for static recrystallization of austenitic stainless steels. It is concluded that the both static and metadynamic recrystallization occurred during the inter-pass period. Also, the predicted softening fraction using the proposed kinetics equation agreed well with those obtained from experimental results.

Static recrystallization and grain growth behaviour of Al0.3CoCrFeNi high entropy alloy

Single phase Al0.3CoCrFeNi (Al0.3) FCC high entropy alloy (HEA) synthesized through arc melting was subjected to cold rolling and subsequent annealing to study its recrystallization and grain growth behaviour. For the as-cast alloy, only partial recrystallization was achieved after cold deformation followed by annealing at 800 and 900 °C, which was attributed to the pining effect of AlNi rich precipitates formed during annealing. The activation energy of static recrystallization (549 kJ/mol) for the as-cast Al0.3 HEA was significantly higher than that of conventional alloys due to the distorted lattice, sluggish diffusion and most importantly the interaction of AlNi rich precipitates with the recrystallization. Homogenization heat treatment on Al0.3 HEA increased the static recrystallization kinetics and was associated with the lower volume fraction of precipitates formed during annealing. An increased grain growth exponent (n ≈ 5) and activation energy (583 kJ/mol) compared with conventional alloys, particularly at low annealing temperatures, was observed for the Al0.3 HEA mainly due to the pinning effect of AlNi rich precipitates. Finally, through investigating the mechanical performance of the alloy after annealing in the precipitation-free (1050 and 1000 °C) and precipitation-containing (900 °C) temperature ranges, the relative contributions for grain boundary and precipitation strengthening were estimated for the annealed Al0.3 HEA.

Static Recrystallization Behavior of Z12CN13 Martensite Stainless Steel

In order to increase the hot workability and provide proper hot forming parameters of forging Z12CN13 martensite stainless steel for the simulation and production, the static recrystallization behavior has been studied by double-pass hot compression tests. The effects of deformation temperature, strain rate and inter-pass time on the static recrystallization fraction by the 2% offset method are extensively studied. The results indicate that increasing the inter-pass time and the deformation temperature as well as strain rate appropriately can increase the fraction of static recrystallization. At the temperature of 1050-1150 °C, inter-pass time of 30-100 s and strain rate of 0.1-5 s−1, the static recrystallization behavior is obvious. In addition, the kinetics of static recrystallization behavior of Z12CN13 steel has been established and the activation energy of static recrystallization is 173.030 kJ/mol. The substructure and precipitates have been studied by TEM. The results reveal that the nucleation mode is bulging at grain boundary. Undissolved precipitates such as MoNi3 and Fe3C have a retarding effect on the recrystallization kinetics. The effect is weaker than the accelerating effect of deformation temperature.

Kinetics of static recrystallization in the coarse-grained Fe–40 at.%Al–Zr–B alloy

The aim of works was to describe mathematically the kinetics of static recrystallization of the alloy type Fe–40at.%Al–Zr–B (with 24.6 Al–0.01 B–0.18 Zr–0.01 C in wt.%) with the coarse-grained structure. The microstructure of the laboratory castings made of this extremely brittle alloy was homogenized by hot rolling of the material in the protective capsules and by the long-term annealing at 1200°C. An initial microstructure with average grain size 0.77±0.27mm was obtained. Based on the isothermal plastic deformation tests and EBSD analysis, the static recrystallization kinetics of the prepared coarse-grained B2 iron aluminide after strain 0.20 was mathematically described. Recrystallized fraction depends on deformation/annealing temperature (900–1100°C) as well as on annealing time. The activation energy of static recrystallization was calculated as 255kJmol−1. Competition between dynamic recovery and static recrystallization was proved after strain 0.35 and annealing temperature 1100°C. Static recrystallization starts relatively easily in the studied alloy, but a very long-term annealing is quite necessary for the complete course of recrystallization. The mean size of recrystallized grains falls with the decreasing annealing temperature (0.47±0.15mm for temperature 1100°C, and 0.22±0.04mm for 900°C). Even at a temperature of 1200°C the annealing after deformation should last approx. 1min for obtaining the fully recrystallized microstructure. That is why the standard hot forming technologies should be combined by an interpass annealing in order to refine sufficiently the coarse grains.

The Static Recrystallization Behavior of Fe-Mn-Si-Al Series TWIP Steel

he softening and static recrystallization behavior of typical Fe-Mn-Si-Al series TWIP steel between high temperature deformation passes was investigated by two-pass hot compress deformation experiments on Gleeble-3500 thermal simulated test machine. The dynamic model of static recrystallization was built according to the experimental results. The investigation of the effects of deformation temperature, deformation rate and pre-deformation shows that deformation rate is the most effective parameter, and the increase of deformation and pre-deformation can also promote the static recrystallization. The calculated static recrystallization activation energy of TWIP steel is about 147kJ/mol through the dynamic equation built. The results of model predict conform to the experimental results.

Static Recrystallization Behavior of 316LN Austenitic Stainless Steel

The static recrystallization of 316LN austenitic stainless steel was studied by double-pass hot compression tests on a Gleeble-3500 thermomechanical simulator. The specimens were compressed at the deformation temperatures of 950, 1050, 1150 °C, strain rates of 0.01, 0.1, 1s−1, strains of 0.1, 0.15, 0.2, and intervals of 1 — 100 s. The results show that the volume fraction of static recrystallization of 316LN increases with the increase of deformation temperature, strain rate, strain and interval, which indicates that static recrystallization occurs easily under the conditions of higher deformation temperature, higher strain rate and larger strain. Deformation temperature has significant influence on static recrystallization of 316LN. The volume fraction of static recrystallization could easily reach 100% at higher deformation temperatures. By microstructure analysis, it can be concluded that the larger the volume fraction of static recrystallization, the more obvious the grain refinement. The static recrystallization activation energy of 317 882 J/mol and the exponent n of 0.46 were obtained. The static recrystallization kinetics was established. The predicted volume fraction of static recrystallization is in good agreement with the experimental results.

Multi-stage thermomechanical behavior of AISI 410 martensitic steel

The flow softening behavior of AISI 410 martensitic stainless steel was investigated by double hit compression tests in the temperature range of 950–1100°C and the strain rates of 0.01, 0.1, and 0.5s−1. The tests were conducted with delay times varying between 1 and 50s after achieving a strain of 0.1, 0.16 and 0.2 in the first stage. The fractional softening has been predicted by the offset stress method and the kinetic equations have been proposed to predict the static recrystallization behavior of hot deformed AISI 410 martensitic stainless steel. Experimental results indicate that the flow softening is a function of the inter-pass time for different strain rates and deformation temperatures. Using analytical approach, the static recrystallization activation energy and kinetics model was obtained and built. A good agreement between experimental results and predicted values of the model was achieved.

Strain-induced grain growth of cryomilled nanocrystalline Al in trimodal composites during forging

Abstract Grain growth of nanocrystalline aluminum ( nc Al) in trimodal Al metal-matrix-composites (MMCs) during hot forging was investigated. The nc Al phase formed through cryomilling of inert gas-atomized powders in liquid nitrogen has an average grain size down to 21 nm, exhibits excellent thermal stability. However, substantial grain growth of nc Al up to 63 nm was observed when the Al MMCs were thermo-mechanically processed even at relatively low temperatures. Grain growth of the cryomilled nc Al phase in trimodal Al MMCs after hot forging was documented with respect to temperature ranging from 175 °C to 287 °C, true strain ranging from 0.4 to 1.35 and strain rate ranging from 0.1 to 0.5 s −1 . Hollow cone dark field imaging technique was employed to provide statistically confident measurements of nc Al grain size that ranged from 21 to 63 nm. An increase in forging temperature and an increase in true strain were correlated with an increase in grain size of nc Al. Results were correlated to devise a phenomenological grain growth model for forging that takes strain, strain rate and temperature into consideration. Activation energy for the grain growth during thermo-mechanical hot-forging was determined to be 35 kJ/mol, approximately a quarter of activation energy for bulk diffusion of Al and a half of activation energy for static recrystallization.

Effects of Nb on Strain-Induced Precipitation of NbC and Static Recrystallization for High Nb Pipeline Steels

Strain-induced precipitation of complex carbonitrides and recrystallization for three high-Nb pipeline steels with different Nb and C content have been studied by using a stress relaxation technique and two-passes interrupted compression test. Sequentially, the PTT diagrams were obtained, and static recrystallization activation energy was calculated. Furthermore, the effects of Nb and C content on strain-induced NbC precipitation and static recrystallization were discussed. The results confirm the faster kinetics of precipitation and its retarded recrystallization in the case of higher Nb pipeline steel, and that the recrystallization is easier in low Nb pipeline steel in comparison to the case of high Nb steel. However, the effects of Nb on strain-induced precipitation and static recrystallization were associated with the Nb/C ratio. The precipitation start time (Ps) of strain-induced NbC is delayed in lower Nb/C ratio pipeline steel. It is suggested that the reduced supersaturation of Nb can result in the delay of precipitation of strain-induced NbC carbides forming in the low Nb/C ratio steel.

Effects of Rare Earths on the Austenite Recrystallization Behavior in X80 Pipeline Steel

In order to improve the effects of rare earths (RE) as microalloy on the recrystallization behavior in the high strength micro-alloyed steel, the X80 pipeline steels with different RE content were produced with a vacuum induction furnace, a series of hot torsion tests were performed under a range of deformation conditions, and the stress-strain curves were analyzed. The results showed that trace RE would improve the austenite recrystallization behavior. The activation energy of deformation and static recrystallization of the austenite in the X80 pipeline steel without RE additions were respectively 393 and 366 kJ/mol. When the RE addition was 0.0025 wt.%, the activation energy of deformation and static recrystallization were reduced by 33 and 29 kJ/mol respectively. But when the RE addition was increased to 0.0220 wt.%, RE would significantly inhibit the dynamic recrystallization of the austenite, the activation energy of deformation would be increased by 35 kJ/mol, but the activation energy of static recrystallization would reduce by 15 kJ/mol.

Static Recrystallization Kinetics Model After Hot Deformation of Low-Alloy Steel Q345B

The static recrystallization behavior of low-alloy steel Q345B during double pass hot compression deformation tests was investigated in the temperature range of 900–1000 C, the true strain range of 0. 15–0.25 and the interpass time range of 0.5–50 s on Gleeble-3500 thermo simulation machine. The results show that static recrystallization during the interpass time is observed. As the deformation temperature and strain increase, softening caused by static recrystallization is obvious. According to the analysis and calculation of thermo-simulation data, the static recrystallization activation energy was obtained and static recrystallization kinetics model was built. Finally, the error analysis of static recrystallization kinetics model proved that the model had good accuracy. Therefore, this model provides a theoretical basis for static recrystallization (SRX) and will contribute to the development of multipass hot rolling process, in order to control the rolling process more accurately.

The effect of Nb on recrystallization behavior of a Nb micro-alloyed steel

By the analysis of true stress–strain curves and the observation of microstructures at different deformation stages, the dynamic recrystallization (DRX) of a Nb micro-alloyed steel and a plain carbon steel is studied, and the critical stress and critical strain are determined under different deformation conditions. By the method of stress relaxation, the post-dynamic recrystallization of two steels is studied. The energy to induce recrystallization of austenite of Nb steel is higher than that of the plain carbon steel. The critical stress of DRX for Nb steel is higher than that for the carbon steel. The apparent activation energy of static recrystallization Q srx of Nb steel and the plain carbon steel is 318 and 231 kJ/mol, respectively. It is obvious that Nb in solid solution increases the value of apparent activation energy ( Q srx) dramatically. The precipitation and recrystallization are in competition because of stored deformation energy. The work shows that the ratios of ɛ p to ɛ c and that of ɛ * to ɛ c are 1.6 and 2.2, respectively, for the steels.

MODELING OF STATIC RECRYSTALLIZATION KINETICS OF Nb-BEARING STEELS

By using isothermal double hit compression tests and applying the 2% offset method, a new model was developed to predict the microstructural evolution of Nb-bearing steels at temperatures above and below the start temperature of strain-induced precipitation (T P ). The T P was developed as a function of true strain, initial austenite grain size and the Nb content. The activation energy of static recrystallization (Q rex ) was expressed as a function of the content of different alloy elements. It was found that Nb played the most important role in increasing the value of Q rex The microstructural observations and measurements confirmed the validity of the model developed in the present investigation.