End Of Recrystallization Research Articles

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.

Tailoring the microstructure and mechanical properties of AISI 316L austenitic stainless steel via cold rolling and reversion annealing

Tensile properties of cold rolled AISI 316L stainless steel after full reversion of martensite to austenite, recrystallization of retained austenite, and grain growth were studied at 850, 950, and 1050 °C. At higher temperatures, it was found that the kinetics of the reversion and recrystallization processes enhance but coarser grain sizes will be obtained at the end of recrystallization. At 1050 °C, appreciable grain growth was observed after the completion of the recrystallization process, which was not the case for a low temperature of 850 °C. At the stage of full recrystallization, by decreasing the annealing temperature, the yield stress (YS) and the ultimate tensile strength (UTS) values increased and total elongation decreased, which was related to the grain size strengthening by the Hall-Petch law. However, the Hall-Petch slope for the UTS was found to be much smaller than that of YS, which reveals that YS has greater grain size dependency. The latter was ascribed to the improved work-hardening behavior and enhanced transformation-induced plasticity (TRIP) effect by coarsening of grain size. To obtain high-strength and ductile steel with tensile toughness higher than 300 MJ/m3 and yield ratio of ∼0.5, the average grain size of ∼3 μm was found to be desirable.

Prediction of Austenite Flow Stresses During Steel Hot Deformation Strengthened with Interphase Nanosize Carbide Precipitates

A model is developed for austenite flow stress dynamics during hot deformation that makes it possible to construct stress-strain curves at different temperatures, and strain rate in relation to steel chemical composition. The model is verified on the basis of independent published data and good convergence of the results obtained is demonstrated. Stress calculations are performed using the model during hot rolling for steel strengthened due to a system of titanium carbide interphase precipitates. The effect of adding titanium and molybdenum on temperature for the end of recrystallization is established.

Modelling of uniaxially pre-strained and annealed AZ31 magnesium sheet based on microstructural considerations

Material deformation at room temperature and subsequent thermal aspects are analyzed at the microstructural level to understand the uniaxial deformation behavior of AZ31 magnesium sheet from pre-straining and annealing (PSA) process. The sheet is pre-strained in uniaxial tension to various strains by conducting interrupted tests and its uniaxial stress-strain responses are obtained. The pre-strained specimens are then annealed at different temperatures and times and then reloaded in uniaxial tension to obtain their post-anneal stress-strain response up to large strains. Pre and post-annealing mechanical responses are analyzed and correlated with static recovery, grain recrystallization and growth kinetics from annealing. Experimental results are utilized to develop and validate a microstructure-based model to capture the room temperature mechanical and grain-level responses of AZ31 sheet from the PSA process. The model incorporates the effect of recovery on the recrystallization kinetics, as well as non-constant nucleation and growth behavior in order to predict the grain size at the end of recrystallization and within the grain growth stage. In addition, the mechanical properties of PSA materials are predicted by considering the resulting microstructure as a composite of un-recrystallized, recrystallized and coarsened grain regions and by employing the rule of mixture.

Thermo-mechanical factors influencing annealing twin development in nickel during recrystallization

The effects of prior stored energy level, annealing temperature, heating velocity, and initial grain size on annealing twin development during static recrystallization of commercially pure nickel (99.999 %) are investigated. The twin content (measured as the twin boundary density or as the number of twins per grain) at the end of recrystallization is shown to be primarily influenced by the prior stored energy level and by the initial grain size, but the effects of heating rate and the annealing temperature are negligible. Taken together, the results are consistent with a new proposition that roughness of the recrystallization front promotes the formation of annealing twins during recrystallization.

Kinetics of Recrystallization and Grain Growth of Cold Rolled TWIP Steel

Hot rolled, laboratory-cast, TWIP steel samples (5.4 mm thick) of 22% Mn - 0.6% C (in mass-%) were cold rolled to different reductions (from 40 % to 70 %) and subsequently isothermally annealed for various times at temperatures ranging from 450º C to 1100º C. The evolution of recrystallization and grain growth was followed by control of the softening kinetics complemented by metallographic, OIM and microtexture observations. A map of the recovery, recrystallization and grain growth in the temperature-time space was obtained. In all instances, the grain size at the end of recrystallization was very fine, D ≤ 2 µm and larger grain sizes were the result of grain growth. A range of grain sizes 2 µm ≤ D ≤ 50 µm was covered by the grain growth experiments. A phenomenological grain growth equation that is useful for the annealing control of this steel was derived from the measurements.

Texture evolution during the recrystallization of a warm-rolled low-carbon steel

The texture changes taking place during the recrystallization of a warm-rolled low-carbon steel were examined using electron backscattered diffraction. The deformation textures of the warm-rolled material are similar in shape to those of cold-rolled materials, but are somewhat more intense. The recrystallization textures resemble the deformation textures but with a more extended α fibre that includes the {1 1 3}〈4 7 1〉 orientation; the γ fibre extends to the {5 5 4}〈2 2 5〉 orientation. These two orientations are related to the {1 1 2}〈1 1 0〉 deformed grains by near 26° rotations about selected 〈1 1 0〉 axes. Nevertheless, both orientations appear in the early stages of recrystallization, an observation that does not support the oriented growth theory. The {1 1 1}〈 h k l〉 orientations are the first to recrystallize while the α fibre is present until the end of recrystallization. It is finally consumed by all types of grains as well as by subgrain coalescence. The similarities in the growth rates for the {1 1 1}〈 h k l〉 and random orientations and the late disappearance of the α fibre suggest that recrystallization takes place according to the high stored energy oriented nucleation concept.

Effect of prestrain and deformation temperature on the recrystallization behavior of steels microalloyed with niobium

The evolution of microstructure during the hot working of steels microalloyed with Nb is governed by the recrystallization kinetics of austenite and the recrystallization-precipitation interaction. The present study focuses on the effects of prestrain and deformation temperature on the rectrystallization behavior in these steels. The extent of recrystallization is characterized by a softening parameter calculated from a series of interrupted plane strain compression tests carried out at different deformation temperatures and strain levels. The results indicate that at low temperatures, softening is caused by static recovery, while at higher temperatures, static recrystallization is the predominant mechanism. The recrystallization-stop temperature (T 5pct) and the recrystallization-limit temperature (T 95pct), marking the beginning and end of recrystallization, respectively, are determined as a function of strain. In order to achieve a homogeneous microstructure, finish rolling should be carried out outside the window of partial recrystallization (T 5pct<T<T 95pct), as determined in this study. The Nb(CN) precipitation kinetics have been calculated using a model proposed in an earlier work, and these results are used to estimate the precipitate pinning force under the given processing conditions. Based on these estimations, a criterion has been proposed to predict the onset of recrystallization. The predicted results are found to be in reasonably good agreement with the experimental measurements.

Recovery and recrystallization of copper during stress relaxation after hot compression

The kinetics of recovery and recrystallization of ETP copper undergoing stress relaxation was studied after high temperature compression and torsion. Two groups of specimens were strained to a common interruption stress: the first at 450°C, 1.8 × 10 −3s −1 and the second at 540°C, 9.3 × 10 −2s −1. A third group was tested in both compression and torsion at 450°C, 1.8 × 10 −1 s −1. After straining to 0.15, the samples were stress-relaxed or load-free annealed at the deformation temperature. The progress of restoration was followed by mechanical and metallographic methods. Recovery and recrystallization occurred under both relaxation and load-free annealing conditions. The former followed an exponential law and the latter the Mehl-Avrami relationship. The rates of recovery and recrystallization during relaxation were lower and higher, respectively, than during load-free annealing. Plastic flow in stress relaxation, by generating some degree of hardening, retards or offsets recovery, which in turn enhances recrystallization. The stress relaxation curve can be used to determine approximately the amount of softening and the onset and end of recrystallization.

Recrystallization Mechanism in Carbon Steels

A systematic study of the recrystallization mechanisms in carbon steels has been undertaken. The microstructures (martensite, pearlite, tempered martensite containing Fe3C—particles of various sizes) of the starting-point specimens were prepared in a preliminary heat-treatment experiment. For each of the specimens, the start, progress and end of recrystallization were followed up by means of optical and electron microscopes as well as hardness measurements. Various recrystallization mechanisms were observed, and each was seen to have correlation with a particular starting-point microstructure.

Recrystallization Mechanism in Carbon Steels

A systematic study of the recrystallization mechanisms in carbon steels has been undertaken. The microstructures (martensite, pearlite, tempered martensite containing Fe3C—particles of various sizes) of the starting-point specimens were prepared in a preliminary heat-treatment experiment. For each of the specimens, the start, progress and end of recrystallization were followed up by means of optical and electron microscopes as well as hardness measurements. Various recrystallization mechanisms were observed, and each was seen to have correlation with a particular starting-point microstructure.

The relation between the polygonization and recrystallization of nickel

The recrystallization temperatures of 99·85% and 99·997% pure nickel were determined. It was found that up to a deformation of about 20% the temperature drop at the beginning and end of recrystallization was very steep and then much more gradual and linear. The greater the deformation and purity of the metal, the smaller was the degree of polygonization of the deformed material in which nucleation took place. It was also found that the growth rate of grains is slowed down at isothermic annealing. These phenomena are considered in relation to the non-uniformity of deformation and the decrease in the density of vacancies, produced in the process of deformation.

Growth of recrystallization nuclei in rapidly heated L62 brass

1. One of the criteria for estimating the recrystallization capacity of a material is the recrystallization temperature, determined by the temperature of the beginning of primary recrystallization, the range of temperatures in which it occurs, and the degree of recrystallization in this range. 2. From the experimental data we constructed a three-dimensional diagram of the recrystaltization of L62 brass with 30–60% prior strain during induction heating at rates of 100–2000 degrees/sec. 3. An increase of the heating rate promotes intense refinement of the structure toward the end of primary recrystallization. At the same time, beginning at heating rates of 100–250 degrees/sec, further increase of the heating rate up to 2000 degrees/sec has little effect on the final grain size resulting from primary recrystallization of brass at all the degrees of prior cold working investigated. 4. On heating at rates above 400–500 degrees/sec and rapid cooling the primary recrystallization is completed at higher temperatures. The temperature of the end of recrystallization does not depend on the cooling rate if the cooling rate is at least double the heating rate.

Effect of rolling conditions on the recrystallization and strength of nickel under stress at high temperatures

1. The temperatures of the beginning and the end of recrystallization of nickel rolled at 800 and 900°C and quenched are 100° higher than those of nickel rolled at 20°C (swaged 25%). These conditions decrease the recrystallization rate at 600°C, and thus increase the heat resistance of nickel. 2. In nickel rolled at high temperatures with subsequent quenching as well as in nickel rolled at 20°C, the heat resistance at 600°C in vacuum (σ=10 kg/mm2) is higher than the heat resistance of annealed nickel. The time preceding rupture and the time required for 1% elongation increase even when the tests are made at the recrystallization temperature. 3. The recrystallization of rolled nickel at 600°C prevents elongation of the samples at the beginning of the test.

EFFECT OF ROLLING REDUCTION ON THE RECRYSTALLIZATION TEMPERATURE OF PURE ALUMINIUMS

The recrystallization temperatures of high-purity (99.998%, 99.992%, 99.9%) and commercial pure aluminiums (99.6%) were studied after cold rolling by following the variation of hardness and microstructure in the course of annealing.It was found that the recrystallization temperature of 99.998% Al decreases proportionally to its reduction but those of aluminiums less than 99.992% purity become constant at the reduction of about 60%. The end temperature of recrystallization of 99.95% Al was the highest in the heavy reduction over 80%, but in the case of lighter reduction (20-30%) that of 99.6% Al was the highest. It was ascertained again that there exists a maximum point in recrystallization temperatures of pure aluminums between 99.9% and 99.99% purity in the heavy reduction.The temperature range between beginning and end of recrystallization is remarkablly wide as such as 180°C in 99.998% Al, but those of 99.9 and 99.6% Al are very narrow as 50°-60° in the heavy reduction.Furthermore, it was found the beginning temperature of recrystallization in 99.998% was 40°C in the heavy reduction as such as 95%, then it suggests to begin to recrystallize even at room temperature after heavy rolling.