Recrystallization Temperature Research Articles

Effect of heating rate of final annealing stage on secondary recrystallization in grain-oriented silicon steel

A grain-oriented silicon steel sheet was manufactured by slab reheated at “medium temperature” and two-stage cold rolling method. The function of heating rate on secondary recrystallization in grain-oriented silicon steel was investigated. The results show that: compared with 30 °C/h heating rate, the initial temperature of the secondary recrystallization can increase by 10 °C at the heating rate of 20 °C/h. Furthermore, the temperature region of secondary recrystallization also extended either with the increased heating rate. Even though the inhibitors maintain AlN, complex precipitation of AlN and sulphide in both heating rate, the average diameter and Zener factor of inhibitors are distinct. Inhibitors in the route of 20 °C/h heating rate express stronger inhibition than that of 30 °C/h, and the average diameter and Zener factor are 17.519 nm and 3.925 × 10−4 nm−1, respectively. In addition, more Goss texture component and less γ-fiber texture ({111}//ND) component form at the heating rate of 30 °C/h than 20 °C/h at 1000 °C, but the final Goss texture component of 20 °C/h is greater than 30 °C/h. The average grain size of the final annealing sheets increased with the heating rate decreasing from 30 °C/h to 20 °C/h, and iron loss reduced by 0.05 W/Kg, the magnetic induction intensity increased by 0.025 T.

Constitutive Relationship for Hot Deformation of TB18 Titanium Alloy

In the present work, the hot deformation behavior of TB18 titanium alloy was investigated by isothermal hot compression tests with temperatures from 650 to 880°C and strain rates from 0.001 to 10 s−1. The flow curves after friction and temperature correction show that the peak stress decreased with the temperature increase and the strain rate decrease. Three typical characteristics of flow behavior indicate the dynamic softening behavior during hot deformation. At a strain rate of 0.001∼0.01 s−1, the flow stress continues to decrease as the strain rate increases after the flow stress reaches the peak stress; the flow softening mechanism is dynamic recovery and dynamic recrystallization at a lower temperature and dynamic recrystallization at a higher temperature. The discontinuous yielding phenomenon could be seen at a strain rate of 1 s−1, dynamic recrystallization took place in the β single‐phase zone, and flow localization bands were observed in the α + β two‐phase zone. At a higher strain rate of 10 s−1, the flow instabilities were referred to as the occurrence of flow localization by adiabatic heat. Constitutive equation considering the compensation of strain was also established, and the results show high accuracy to predict the flow stress with the correlation coefficient of 99.2% and the AARE of 6.1%, respectively.

Investigating the potential of FGMs through numerical minimization of thermal stresses

Functionally graded materials (FGMs) have the potential to reduce high stress concentrations near material interfaces. In the ITER divertor monoblock, this may be achieved by replacing the distinct W–Cu interface by an FGM, which gradually changes the coefficient of thermal expansion (CTE) from copper to tungsten. To assess the full potential of FGMs in improving the thermal and mechanical behavior, a first proof-of-principle study is performed in this paper to numerically optimize the tungsten volume fraction distribution of a W–Cu FGM based ITER monoblock for minimal thermal stresses using a simple thermal conduction model. We show that the optimizer can ensure that the temperature remains below the recrystallization temperature of tungsten and that it minimizes the chosen cost function, based on the fractional margin between the local temperature and melting temperature, in a computationally efficient way. Furthermore, the resulting design has a lower Von Mises stress measure at the original position of the W–Cu interface. However, a new material interface is introduced, which results in an additional undesired stress concentration. Future work should therefore aim at integrating a complete stress evaluation in the optimization method.

Physical and mechanical properties and structure of copper-based composite materials for diamond tools binder

The article describes the structure and physical and mechanical properties of dispersion-strengthened composite materials of Cu-Al-Ti-Sn-C-O system developed as a binder for making diamond tools for grinding composite materials and, in particular, hard alloys. It is shown that the materials under analysis have high thermal conductivity and recrystallization temperature values and are not inferior by mechanical properties to Cu-Sn system binders and, in particular, Cu-20 Sn binder widely used in the industry.

Development of copper dispersion-strengthened composite material with increased indexes of high-temperature strength and wear resistance for thermally loaded friction pairs

The article presents the chemical composition, technology and general properties of copper dispersion-strengthened composite material developed by the authors based on Cu-AlC-O system with increased indexes of high-temperature strength and wear resistance for parts of thermally loaded friction units and, first of all, for valve guides of highly forced internal combustion engines and plungers of die-casting machines. This material containing 0.9 wt % aluminum, 0.3 wt % carbon has recrystallization temperature of 1000 oC and has higher tribotechnical properties comparing with standard materials. In particular, the wear out intensity of the developed material is 2.9 lower comparing to gray cast iron Gh 1051, which is used for valve guides. At the same time, wear of coupled element is also became 2.8 times less. The technology of new material is based on the method of reactionary mechanical alloying in the attritor, which provided the material with dispersion-strengthened subgrain structure with γ -Al2O3 reinforcing nanodisperse particles.

Investigation of thermal stability of the structure and properties of ultra-fine-grained copper alloys obtained by ECAP

The paper describes the results of experimental studies of the effect of small chromium additives on the temperature of recrystallization (TR) of ultrafine-grained (UFG) copper obtained by equal channel angular pressing. Our investigation shows that the process of recrystallization in UFG CuCr copper alloys has a three-stage character - anomalous grain growth at annealing temperatures not exceeding the temperature of chromium particles(Tann<T1), “fixation” of grain boundaries by the released particles (T1⩽Tann<T2), and regular grain growth at higher temperatures (Tann⩾T2), when grain boundaries “detach” from particles of the second stage. It also shows that an increase in the chromium concentration in UFG copper by 0.3-0.5wt.% leads to a decrease in the temperature of the onset of the migration of grain boundaries T1 in the UFG copper by 40-60°C and an increase in temperature T2 to ∼ 400°C. We discovered that low-temperature pre-recrystallization annealing contributes to an increase in the thermal stability of the mechanical properties of CuCr alloys.

Alleviation of high-temperature oxidation and cracking of water-cooled roll for hot-rolling steel

Hot rolling is performed inside a heating furnace where the material is heated above its recrystallization temperature. As pinch rolls are located in this furnace and subjected to continuous high temperature, they are typically cooled with water to protect them from the harmful effects of the high atmospheric temperature. Despite cooling, cracks can develop on the surface of water-cooled rolls, which can result in fracture over time; further, high-temperature oxidation can cause the metal strip to stick to the roll, resulting in defects on the strip surface. To address these problems, we analyzed pinch rolls through mechanical stress, thermal stress, and high-temperature oxidation investigations with data measured from a production line in situ. Subsequently, solutions for improving the performance of the pinch rolls predicted from the calculations were applied to an actual hot rolling process.

Effects of Extrusion Processing on Microstructure of 7075Al Alloy in the Semi-solid State

A recrystallization and partial melting (RAP) process was introduced to prepare the semi-solid 7075 aluminum alloy used for thixoforming. In order to obtain an ideal semi-solid microstructure, a series of extrusion experiments were conducted to comparatively investigate the optimum extrusion process parameters. Commercial 7075Al alloy samples were frstly extruded with varying extrusion ratios below the recrystallization temperature followed by homogenization, then these samples were reheated to the semi-solid state and held in the range of 5 to 50 minutes. The experimental results show that varying process cause the difference in the deformation degree and microstructure for as-extruded samples, resulting in various semi-solid microstructure. It is verifed that the formation of equiaxed grains in semi-solid microstructure depends on recrystallization behavior of extruded samples during partial melting. Both relative high extrusion temperature and low extrusion ratio lead to high volume fraction of recrystallized area, thus entirely equiaxed solid grains in semi-solid 7075Al alloy samples can be obtained finally. In addition, Ostwald ripening was determined as the dominate coarsening mechanism of solid grains in semi-solid state for this 7075 Al alloy during the RAP route. The infuence of pre-deformation on recrystallization behavior of this 7075 Al alloy was discussed in detail.

Experimental investigation of the microstructural changes of tungsten monoblocks exposed to pulsed high heat loads

Abstract Extending the lifetime of tungsten based plasma facing components for future fusion reactors remains an everlasting challenge. In this work, the microstructure of tungsten monoblocks exposed to a few thousand cycles of combined pulsed heat loads of 10 and 20 MWm−2 (achieved via an electron beam) is thoroughly investigated. The heat exposure assisted surface roughening is observed to be significant. Build-up of thermal stresses in the monoblock results in severe geometrical distortions. The evolution of the microstructure of the tungsten monoblocks due to recrystallization is found to be substantial in the top 5.5 mm from the surface, and the relation between the recrystallization threshold and temperatures throughout the monoblock is investigated. Additionally, no traces of recrystallization-induced crack formation within the monoblock is observed. The recrystallization-induced microstructural evolution is investigated in terms of grain size, grain boundary distribution, and the recrystallization induced softening as determined from micro-hardness measurements. An adequate quantitative match between the changes in the microstructural features such as grain size, grain boundary character, and the related hardness is obtained. Moreover, the depth dependent microstructural recrystallized fraction in the monoblock is examined via hardness and EBSD measurements, and a comparison between the different methods is presented. The presence of a preferred crystal orientation of the recrystallized grains is observed and discussed in terms of the initial texture.

Effect of Heat Treatment Temperature on the Spinning Structure and Properties of a Cu-Sn Alloy.

A thin-walled copper (Cu)-tin (Sn) alloy cylinder was treated after spinning at 200-400°C for 0.5 h. The characteristics of the alloy microstructure under different temperatures were analyzed through electron back-scattered diffraction. The results were as follows. The grain size at 200-300°C decreases as the heat treatment temperature rises, but the grain size at 400°C increases. At 200-300°C, the microstructure primarily consists of deformed grains. It is found that the main reason for the formation of high-angle grain boundaries (HAGBs) is static recrystallization. For the grain boundary orientation differential, the low-angle sub-grain boundary gradually grows into the HAGB, and multiple annealing twin Σ9 boundaries appear. Grain orientation is generally random at any temperature range. The mechanical property test indicated that, at the upper critical recrystallization temperature of 300°C, the elongation of the Cu-Sn alloy gradually increases, and its yield strength and ultimate tensile strength rapidly decrease.

Microstructure and texture evolution and ring-tensile properties of recrystallized FeCrAl ODS cladding tubes

Oxide dispersion strengthened (ODS) FeCrAl ferritic steels are being developed as potential accident tolerance fuel cladding materials for the light water reactors (LWRs) due to significant improvement in steam oxidation by alumina forming scale and good mechanical properties up to high temperatures. In this study, the microstructural characteristics and tensile properties of the two FeCrAl ODS cladding tubes with different extrusion temperatures of 1100 °C and 1150 °C were investigated during processing conditions. While the hot extruded sample showed micron sized elongated grains with strong α-fiber in <110> texture, cold pilger rolling process change the microstructure to submicron/micron size grain structure along with texture evolution to both α-fiber (<110> texture) and γ-fiber ({111} texture) via crystalline rotations. Subsequently, final annealing resulted in evolution of microstructure to large grain recrystallized structure starting at recrystallization temperature of ~810–850 °C. Two distinct texture development happened in recrystallized cladding tubes, i.e., only large elongated grains of (110) <211> texture following extrusion temperature of 1100 °C; and two texture components of (110) <211> and {111} <112> following higher extrusion temperature of 1150 °C. The different texture development and retarding of recrystallization progress in 1100°C-extruded cladding tubes were attributed to higher distribution of oxide particles. Furthermore, the ring-tensile test properties of recrystallized FeCrAl ODS cladding tubes were evaluated in the temperature range of 25–800 °C and showed a very good combination of strength-ductility with a lower strength and higher ductility for 1150 °C extruded tube up to ~500 °C and opposite properties at higher temperatures.

Direct Observation via In Situ Heated Stage EBSD Analysis of Recrystallization of Phosphorous Deoxidised Copper in Unstrained and Strained Conditions

Recrystallization of phosphorous deoxidised copper used for strength critical applications at elevated temperatures was investigated by means of in situ heated stage EBSD analysis using a Gatan Murano heated stage mounted within a Carl Zeiss Sigma FEGSEM electron microscope. The influence of applied strain as the result of deformation within a Nakajima test as an analogue for industrial forming on the recrystallization temperature was investigated, the impact of increased heating rates on microstructural evolution was also investigated. Inverse pole figure plots combined with regions of reduction in local misorientations and variations in geometrically necessary dislocations were used to establish the point of recrystallization and the recrystallized fraction of the material. Recrystallization was observed to occur at temperatures as low as 130 °C in highly strained samples compared to around 300 °C within the annealed samples dependent upon heating rate. Increased heating rates were observed to produce a finer final grain structure but had little effect on presence of <111> 60° grain twins, which was influenced more by initial material condition.Graphic

Analytical model for estimating bending angle in laser bending of 304 stainless steel/Q235 carbon steel laminated plate

Compared with the single-component metal plate, the stainless steel-carbon steel laminated plate (SCLP) combines the stainless steel layer and the carbon steel layer with a special preparation technique. In order to estimate the bending angle of laminated plates accurately, it is of great significance to establish an analytical model. Based on the temperature gradient mechanism, the temperature distribution equation of the SCLP is established by the piecewise function. Then, the depth of the plastic zone is calculated by the recrystallization temperature according to the temperature distribution along the thickness direction of the SCLP. Moreover, by fitting the yield strength curves of stainless steel and carbon steel, the average compressive stress of the plastic zone is calculated through the integral method. By optimizing the calculation of the plastic depth and the average compressive stress in the plastic zone, the analytical model is established based on mechanical equilibrium equations. The experimental verification shows that the average error of bending angle using the proposed model is 9.95%, while Liu's model is 38.02%. The proposed model provides a calculation method for estimating the bending angle, which contributes to improving the accuracy of the analytical model in laser bending of SCLP.

Effect of heat treatment on the anisotropic microstructural and mechanical properties of Co–Cr–Mo alloys produced by selective laser melting

The purpose of this study was to evaluate the effect of heat treatment on the anisotropy of the microstructure and mechanical properties of cobalt–chromium–molybdenum (Co–Cr–Mo) alloys fabricated by selective laser melting (SLM). Dumbbell samples were fabricated with the axes deviating from the build direction by 0° (0°-sample), 45° (45°-sample), or 90° (90°-sample) and were subjected to heat treatment at various temperatures (750, 900, 1050, or 1150 °C) for 6 h. In samples heat-treated at 750, 900, and 1050 °C, the microstructures exhibited columnar grains with a <001> fiber texture along the build direction, the same as in the as-built state. The mechanical properties showed anisotropy; the 0.2% offset yield strengths (YS) of the 0°-samples were lower than those of the 90°-samples, and the elongations of the 0°-samples were significantly higher than those of the 45°- and 90°-samples. By contrast, in samples heated to 1150 °C for 6 h, the anisotropic columnar grains completely disappeared, and equiaxed grains with random orientations were found in all samples, indicating that recrystallization had occurred. Moreover, the specific microstructures and texture generated during SLM disappeared. Regarding tensile properties, the initially strong anisotropy exhibited by the as-SLM samples was significantly reduced. Thus, heat treatment at the recrystallization temperature produced uniform equiaxed grains with random texture, which contributed to reducing the mechanical anisotropy of the SLMed Co–Cr–Mo alloys.

Microstructure and mechanical properties of a low-carbon HDQ&P steel

ABSTRACTThe microstructure and mechanical properties of Fe-0.19C-1.46Mn-1.50Si, a low-carbon hot-rolling direct quenching and partitioning steel, were investigated, and particular emphasis was placed on the effects of the rolling temperature and the subsequent cooling method. Once rolling occurred above the recrystallization temperature, the grain size of prior austenite could be reduced from ∼88.2 to ∼11.8 μm. The corresponding packet and block sizes of martensite could be reduced from ∼17.6 to ∼4.3 μm and from ∼9.0 to ∼1.8 μm, respectively, after a typical two-step quenching and partitioning (Q&P) treatment following rolling immediately. Once rolling occurred below the recrystallization temperature, deformed prior austenite with a grain length and width of ∼150 and ∼60 μm, respectively, were obtained. Consequently, only the block size would be reduced to ∼1.9 μm. The volume fraction of retained austenite (RA), which was ∼11% in the specimens, was not significantly affected by the rolling temperature. Further, if the typical two-step Q&P treatment was replaced by air cooling after the rolled specimen was quenched to the martensitic start temperature, the volume fraction of RA in the specimen was reduced to ∼7.4%, and the corresponding carbon depletion degree in the martensitic matrix was decreased as well. Tension and impact tests indicated that the cooling method was more critical than the rolling temperature for determining the mechanical properties. The presence of sufficient amounts of RA and carbon depletion in the refined martensitic matrix contribute to the strong strain hardening and energy absorption capabilities of the steel together. As a result, rolling at a temperature that was slightly higher than the recrystallization temperature combined with the typical two-step Q&P treatment could be an optimized process to obtain excellent comprehensive mechanical properties. In particular, the ductile-to-brittle transition temperature (DBTT) could be reduced from −10°C to −30°C.

Effect of Reduction Ratio below Austenite Recrystallization Stop Temperature on Mechanical Properties of an API X70M PSL2 Line Pipe Steel

Steel grades having high toughness and high strength are required for line pipes since gas and oil should be transported through them at high pressures. Thermo-mechanically controlled rolling processes are used for increasing both toughness and strength at low temperatures since the line pipes are exposed to harsh climatic conditions at full length and rather severe service conditions. Various test methods such as Charpy, DWTT, CTOA have been used for measurement of toughness values of these steels and the results have been evaluated considering various criteria. In this study, thermo-mechanical rolling trials were performed at the temperature below the recrystallization temperature of austenite on an API X70M PSL2 grade steel, which is large scale used in the oil and natural gas line pipes, to increase the strength without sacrificing the toughness. Different reduction ratios were utilized and the effect of reduction ratios on mechanical properties and microstructures were investigated during the trials. It was observed that final grain size decreased and strength and toughness increased with increasing reduction ratio.

Investigation on metallurgical, tribological, hardness properties of spray deposited and warm rolled Al-18Pb, Al-22Pb alloys

Al-18Pb and Al-22Pb alloys were processed by a rapid solidification process known as the spray deposition technique. Gaussian or bell-shaped deposits were obtained at a pressure of 10 bar, nozzle to substrate distance of 423 mm and substrate inclination angle of 0°. Deposits obtained from both alloys were warm rolled at a recrystallization temperature of 395 °C. Microstructural analysis of deposits showed that Pb is equally distributed in the Al matrix with 60% thickness reduction. For both alloys, the decrease in thickness percentage resulted in the decrease of hardness values. Porosity was lower in spray deposits of Al-18Pb alloy than the corresponding one from Al-22Pb alloy due to the casting and rolling defects. When the Pb percentage is increased from 18 to 22 in Al-22Pb compared with Al-18Pb, the wear rate increases abnormally. The frequency of wear and coefficient of friction values of Al-22Pb alloy were also higher when compared with those of Al-18Pb alloy.

Influences of temperature and Sn-addition on microstructural evolution of Ag during FSW

ABSTRACTThe microstructural evolutions of pure Ag and Ag-0.75 wt-%Sn during rapid cooling friction stir welding (FSW) were examined. At the lower welding temperature of FSW conditions, the annealing twinning was highly suppressed and the microstructural evolution was dominated by the discontinuous dynamic recrystallisation (DDRX) via the high angle boundary (HAB) bulging. The fully recrystallised microstructure was remarkably finer than that formed through the frequent annealing twinning at the higher welding temperature. Moreover, the Sn-addition caused the HAB bulging due to the inhibition of dynamic recovery and decreased mobility of grain boundaries. With decreasing the ratio of the peak temperature to the recrystallisation temperature, the dominant grain refinement mechanism is implied to change from the annealing twinning to the DDRX.

The thermal stability of dispersion-strengthened tungsten as plasma-facing materials: a short review

One key challenge for the development of fusion energy is plasma-facing materials. Tungsten-based materials are promising candidates for plasma-facing components (PFCs) in the magnetic confinement nuclear fusion reactors because of their high melt temperature, high-thermal conductivity, high-thermal load resistance, low tritium retention, and low sputtering yield. In fusion reactors, PFCs are exposed to high-thermal flux, because there are some transient events such as plasma disruptions, edge-localized modes, and vertical displacement events (VDEs). Especially, in VDEs, a heat flux of 10–100 MW m−2 with duration of milliseconds-to-several seconds can induce recrystallization and then change the microstructure of tungsten-based plasma-facing materials, leading to instability of microstructures. Then, a significant degradation of material properties is caused such as a reduction of mechanical strength and fracture toughness, a rise in the ductile-to-brittle-transition temperature well, and decrease of irradiation/high-thermal load resistance. Therefore, many efforts were devoted to improve the thermal stability of tungsten-based materials as high as possible, such as oxide dispersion strengthening, carbide dispersion strengthening, and K bubbles dispersion strengthening. Here, the thermal stabilities of various dispersion-strengthened tungsten materials are reviewed by evaluating their recrystallization temperature and the corresponding hardness evolutions. In addition, the possible development trends are proposed.

Clinopyroxene episyenites in a Proterozoic rapakivi granite, SE Finland \u2014 recrystallization textures, mass transfer and implications for the petrology of A-type granite complexes

Na-metasomatic augite and aegirine-augite episyenites are hosted by subalkaline amphibole granites in the 1.644 Ga Suomenniemi rapakivi granite complex, southeastern Finland. In an examined drill core, episyenites are bordered by up to 50-cm-wide zones of Na-enriched augite-bearing granite in which alkali feldspar forms rims on plagioclase, and aggregates of augite and magnetite have formed by fluid-induced dehydration of hastingsite and biotite. In the episyenites, quartz has been partially removed, alkali feldspar (An<1Ab50Or50) and plagioclase have been partially recrystallized to granoblastic polygonal aggregates, and clinopyroxene (augite or aegirine-augite) has coarsened and been enriched in the aegirine component. Mass balance modeling implies addition of mainly Na, depletion of Si, F, Rb, Ba, Sr and 10–20% volume loss (by quartz dissolution) in the episyenitized zones in the drill core. Quartz-depletion and recrystallization may have been caused by several superimposed stages of alteration, probably related to voluminous dike- and A-type granite magmatism in the Suomenniemi area 10–15 m.y. after the emplacement of the Suomenniemi complex. Because of the coarse recrystallization textures and near-solidus recrystallization temperatures, distinguishing these fenite-like metasomatic rocks from igneous syenites is not trivial. In epizonal A-type granite complexes, high-temperature episyenites may be more common than currently thought.