Intermediate Annealing Treatment Research Articles

Microstructural and textural evolution of double stage cold rolled non-grain oriented electrical steel

Non-grain oriented electrical steels (NGOES) are typically used in electric applications with rotating magnetic fields and thus essential for the production of electric motors. The increasing number of electric vehicles results in a growing demand for electrical steel sheets used in the stacked laminations of rotor and stator components. E-mobility applications require the best possible magnetic properties for optimum performance and efficiency, especially at high frequencies. In addition, increased mechanical strength is necessary to withstand the centrifugal forces resulting from high revolution speeds. Chemical composition, microstructure and crystallographic texture strongly influence the magnetic properties, whereas the mechanical properties are mainly affected by the chemical composition and grain size. Optimizing the texture is a possible method for improving the magnetic properties without significantly compromising the mechanical strength. In this work a special processing route for the production of 3.25% Si NGOES sample material has been studied, using laboratory cold rolling and annealing facilities. Compared to the classical processing route of single stage cold rolling and annealing, this alternative method involves two cold rolling steps with an intermediate annealing treatment between the first and second rolling sequence and a final annealing treatment after the second rolling step. The samples were produced with different intermediate thicknesses, changing the amount of cold rolling deformation of each sample variation. The degree of deformation affects the recrystallization and grain growth behavior and thus the resulting microstructure and texture. The microstructural and textural evolution was investigated in the hot rolled, intermediate annealed and final annealed state using electron backscatter diffraction (EBSD). Finished samples were additionally examined using magnetic testing and tensile testing. The results indicate a correlation between the intermediate thickness and the final grain size of the steel samples. Furthermore, the highly grain size dependent mechanical strength and magnetic losses are influenced. EBSD-data were used to interpret the texture and to calculate a parameter describing the magnetic quality of the texture. The results show a strong improvement of magnetically favorable texture components along with increasing intermediate thickness, enabling significantly better polarization values in rolling direction and transversal direction. However, anisotropy of the magnetic properties increases as well due to the textural changes.

Optimization of Intermediate Annealing Treatment Duration for ABS Resin Plating Using UV Irradiation as A Pre-Treatment

Optimization of Intermediate Annealing Treatment Duration for ABS Resin Plating Using UV Irradiation as A Pre-Treatment

Effect of hot rolling finishing temperature and intermediate annealing on the microstructure, texture evolution, and comprehensive properties of Al-Mg-Si alloy

The effect of varying hot rolling finishing temperature and the application of intermediate annealing on the microstructure, texture evolution, and mechanical properties—including forming, hemming, and roping properties—of Al-Mg-Si alloy sheets was systematically investigated. The hot-rolled plate with a higher rolling finishing temperature exhibits a significantly higher volume fraction of Cube texture which is readily retained and inherited to the final state microstructure. A substantial quantity of Mg2Si particles can also be observed in this plate, while the amount notably decreases at lower rolling finishing temperatures. These large quantities of Mg2Si hinder the PSN effect, subsequently encouraging Cube texture and hindering CubeND texture formation during solute solution. Following intermediate annealing, Ostwald ripening mechanism leads to finer Mg2Si particles dissolve while the coarser Mg2Si continue to grow, reducing the obstruction to the PSN effect. The T4P sheets without intermediate annealing exhibit a significant volume fraction of Goss texture. Goss texture can be effectively minimized by applying intermediate annealing process and thus almost disappears in T4P sheets that undergo intermediate annealing. Cube texture proved advantageous for hemming processes but detrimental to both formability and roping performance; thus, it should be modulated within an optimal range. On the other hand, Goss texture negatively impacted all mechanical properties and should be minimized or eliminated. Optimal comprehensive properties can be achieved by lowering the hot rolling finishing temperature and implementing a suitable intermediate annealing treatment.

Intermediate annealing treatment as an effective tool for suppression of abnormal grain growth at longitudinal weld of 2196 Al–Cu–Li profile

The longitudinal weld of extrusion profiles will form dramatic abnormal grain growth (AGG) during solution treatment, leading to performance deterioration. A modified heat treatment method, i.e., an intermediate annealing treatment (IAT) was inserted into standard T6 treatment was proposed in this paper to alleviate AGG of longitudinal weld. 2196 Al–Cu–Li profiles with longitudinal weld were subjected to IAT with different parameters, and the grain growth behavior and microstructure evolution of them were studied. The processing window of IAT was determined as 450 °C/0–60 h and 475 °C/0–6 h and some parameters in between, the reasonable IAT temperature is below solution treatment about 50 °C. IAT at 450 °C/24 h is the most noticeable parameter for the suppression of AGG, a narrow AGG area formed during this IAT, and the fine grains surrounded AGG area exhibited continuous uniform coarsening, leading to releasing of sub-grain boundary energy and decreasing of driving force for AGG by 50%. Besides, many secondary phases formed during IAT and work as pinning particles, hence the width of AGG area in this sample reduced 90% compared to that of T6 samples, and the tensile strength increased about 20 MPa and the elongation increased by 42%.

Optimization in strength-ductility of Mg-Gd-Y-Zn-Zr alloy processed by upsetting-extrusion combined with intermediate thermo-mechanical treatment (ITMT)

In this work, the effects of intermediate annealing and intermediate annealing subsequent aging treatment on the second phase precipitation, dynamic recrystallization (DRX) behavior, and mechanical properties of Mg-9Gd-4Y–2Zn-0.5Zr (wt.%) alloy were comparatively studied. The results showed that the one-pass upsetting-extrusion (UE) deformation intermediate annealing treatment sample (UAE) exhibited the highest dynamic recrystallized (DRXed) grains number fraction and the largest average DRXed grain size, which was mainly attributed to the precipitation of a large number of β-Mg5RE phases (>1 μm) at the grain boundaries (GBs) and within unDRXed grains after annealing treatment. These β-Mg5RE phases promoted DRX through particle-stimulated nucleation (PSN) mechanism during subsequent extrusion process. However, the lack of the pinning effect of the fine second phase precipitations led to the growth of DRXed grains. The DRXed grains of the deformation intermediate annealing subsequent peak-aging treatment sample (UAAE) were significantly smaller than the UAE sample. This is mainly due to the fact that the densely distributed prismatic β′ phases precipitated by the peak-aging treatment were rapidly transformed into nano-scale β-Mg5RE phases and pinned at the DRXed grain boundaries to inhibit the growth of the DRXed grains during the subsequent extrusion process. The ultimate tensile strength (UTS) and failure elongation (EL) of the UAAE sample were 274 MPa and 14.3%, respectively, 4.2% and 85.7% higher than those of the UE sample, showing excellent strength-ductility synergy. The randomly oriented fine DRXed grains, coarse unDRXed grains with high-density dislocations and substructures, and nano-scale β-Mg5RE particles were co-contribute to the strength-ductility synergy.

Influence of intermediate annealing temperature on the microstructure and texture of double stage cold rolled non-grain oriented electrical steel

Non-grain oriented electrical steels (NGOES) are commonly used as stacked laminations of rotors and stators in electrical vehicles. In order to achieve the best performance and efficiency for the motor, NGOES need the best possible magnetic properties of high polarization and low magnetic losses. Two important aspects influencing these magnetic properties are the grain size and the crystallographic texture of the material. Grain size and texture of the finished steel strongly depend on the production route and the processing parameters. Another important aspect besides the magnetic properties is the mechanical strength, which is needed to withstand the centrifugal forces, accounted with high rotational speed in high frequency applications. In this work a special processing route for the production of 3.25% Si NGOES sample material has been studied, using laboratory cold rolling and annealing facilities. Compared to the classical processing route of cold rolling and annealing, this alternative method involves two cold rolling steps with an intermediate annealing treatment between the first and second rolling step and a final annealing treatment after the second rolling sequence. The samples were heat treated at different intermediate and final annealing temperatures, influencing the recrystallization and grain growth behavior and thus the resulting microstructure and texture. Finished samples were examined using magnetic testing, tensile testing, light imaging microscopy and by electron backscatter diffraction (EBSD). The results indicate a correlation between the two annealing treatments (intermediate and final) and the final grain size of the steel samples. Furthermore the highly grain size dependent magnetic losses are influenced. EBSD-data was used to interpret the texture and to calculate a parameter describing the magnetic quality of the texture. The results show a strong improvement of magnetically favorable texture components along with increasing intermediate annealing temperatures, enabling significantly better magnetic properties.

Thermomechanical treatments for a dual phase cast high entropy alloy

Thermomechanical treatments modify the cast microstructure of a dual phase hypoeutectic high entropy alloy. The as-cast microstructure consists of an FCC matrix and a BCC eutectic phase forming a semi-continuous network. The as-cast material is subjected to various thermomechanical treatments: I) hot compression; II) hot compression with strain rate jumps; III) multi-stage hot compression with intermediate stages of isothermal soaking; IV) hot compression followed by annealing. The material recovers rapidly after the strain rate jump and no dependence of the yield stress on the previous deformation step is observed. Much of the stress relaxation occurs within seconds during the hold for the multi-stage tests. A steady-state stress is reached for the first holding cycle, while progressively slower softening is observed for later holding cycles. The eutectic BCC phase fragments during hot deformation, while discontinuous dynamic recrystallisation associated with the formation of Σ3 occurs in the FCC phase. Precipitates are formed at high temperatures and pin the high-angle grain boundary motion. The rotation of the eutectic BCC phase and the precipitates during plastic deformation also promotes local lattice rotation of the FCC phase. As a result, a fine and intricate substructure is formed in the interdendritic spaces. Complete recrystallisation is not achieved during either hot deformation or annealing, suggesting that practical grain refinement of the investigated alloy would only be achieved at larger strains or a combination of larger deformations and intermediate annealing treatments.

Body-thorough ultrahigh strength and ductility of austenitic 316L stainless steel by industry-applicable 3-axis stress-released impact

Austenitic stainless steel (SS) has been seeking a decent strength to match its other exceptional advantages such as remarkable corrosion resistance, antioxidant activity and good formability. High-strain-rate deformation techniques that are effective in strengthening SS surfaces, disappointingly, bring high risk of fracturing when applied to strengthen a bulk SS part. We demonstrate that a 3-axis room-temperature impact with intermediate annealing treatment can consistently promote the strength of bulk 316L SS to an unprecedented high level while posing no fracturing danger to the bulk SS. The impacts from multiple directions enable the smallest nanograins and a high volume of the thinnest twins in the sample, and in the meantime they inhibit the formation of martensite phase. The annealing treatment not only induces element segregation in the SS, which adds extra strengthening to the already significant grain/twin boundary strengthening, but also recovers the capability of the SS in storing dislocations upon deformation. Consequently, the 316L SS achieves an excellent ductility on the basis of the extraordinarily high strength. The steel also has a surprisingly low degree of hardness anisotropy, enhancing its applicability in complicated loading environments. Moreover, the novel process is realized with industry instruments and applicable for industries.

Effect of Annealing Temperature on the Interfacial Microstructure and Bonding Strength of Cu/Al Clad Sheets with a Stainless Steel Interlayer.

To explore the influence of annealing temperatures on the interfacial structure and peeling strength of Cu/Al clad sheets with a 304 stainless steel foil interlayer, an intermediate annealing treatment was performed at temperatures of 450 °C, 550 °C, and 600 °C, separately. The experimental results indicate that the interfacial atomic diffusion is significantly enhanced by increasing the intermediate annealing temperature. The average peeling strength of the clad sheets annealed at 550 °C can reach 34.3 N/mm and the crack propagation is along the steel/Cu interface, Cu-Al intermetallic compounds layer, and Al matrix. However, after high-temperature annealing treatment (600 °C), the liquid phase is formed at the bonding interface and the clear Cu/steel/Al interface is replaced by the chaotic composite interfaces. The clad sheet broke completely in the unduly thick intermetallic compounds layer, resulting in a sharp decrease in the interfacial bonding strength.

Effect of antimony addition and asymmetric cold rolling on the texture and magnetic properties of a 1.2% Si steel

This paper investigates the effect of antimony on the microstructure, texture, and magnetic properties of a 1.2 wt% Si steel sheet produced by asymmetric cold rolling. First, the specimens were cast with three different antimony percentages, and after homogenization and hot rolling, they were subjected to an intermediate annealing treatment at 1150 °C for 30 min. The sheet thickness was then reduced to 1 mm using an asymmetric cold rolling process with 80% thickness reduction and finally, the final annealing treatment was performed at 1000 °C for 3 min. The results indicated that increasing antimony improved the texture parameter by increasing the intensity of the θ-fiber. Antimony also accelerated the formation and density of shear bands. Additionally, Cube components nucleated predominantly in shear bands, enhancing the desired texture in the microstructure. Texture evolution affected the magnetic properties of the specimens such that the sample containing 0.026 wt% Sb exhibiting the lowest coercivity and remanence compared to the sample devoid of antimony. It seems that asymmetric rolling has a good interaction with antimony to improve the magnetic properties of low silicon steels.

A route to produce toughened acicular ferrite with equivalent hardness as martensite: The combined effect of elements segregation and pre-transformed allotriomorphic ferrite

Acicular ferrite (AF) is a universal occurrence during the welding of steel. In this study, when heat treatment of intermediate annealing after austenitization was adopted, AF was obtained in the quenching process (−100 °C/s). The transformed AF has significantly higher toughness with no loss in hardness compared to martensite, which was also obtained at a cooling rate of −100 °C/s. The experimental and calculated results showed that film-like allotriomorphic ferrite are generated and high levels of boron (B) and molybdenum (Mo) segregation occur before transformation. These two effects inhibit the nucleation of bainitic ferrite (BF) and promote AF nucleation of inclusions. The segregation of B mainly occurred during the cooling process from austenitizing temperature to intermediate annealing temperature via the nonequilibrium mechanism, and the Mo segregation could be enhanced during intermediate annealing treatment by the generation of allotriomorphic ferrite.

Enhancing the performance and stability of carbon-based CsPbI2Br perovskite solar cells via tetrabutylammonium iodide surface passivation

All-inorganic carbon-based perovskite solar cells (C-PSCs) with CsPbI2Br as photosensitizer have attracted great attention due to their low cost, high efficiency, and good stability. However, the CsPbI2Br film prepared by the solution method usually has many defects, which reduces the charge extraction rate and photoelectric performance. In this paper, intermediate gradient annealing and antisolvent ethyl acetate treatment are combined to prepare CsPbI2Br films with good crystallinity and few voids. The surface of the obtained CsPbI2Br film is then treated using tetrabutylammonium iodide (TBAI), which can interact with the Pb-I framework to passivate defect states and extend the carrier lifetime. Finally, the champion power conversion efficiency (PCE) of the optimized C-PSCs with a structure of FTO/SnO2/CsPbI2Br/carbon electrode prepared in the air reach 12.29%. At the same time, TBAI molecules also effectively enhance the stability of the PSCs, and the unencapsulated device can still maintain 90% of the initial efficiency after 300 h of storage in an ambient air atmosphere with a relative humidity of 20%-30%. This work provides a simple and effective strategy for the preparation of cheap, high-performance, and stable all-inorganic C-PSCs under atmospheric conditions, and also increases the feasibility of PSCs commercialization.

Influence of Intermediate Annealing Treatment on the Kinetics of Bainitic Transformation in X37CrMoV5-1 Steel.

Intermediate annealing treatment (IAT) is a new process that accelerates the bainitic transformation in steels. This stimulation is crucial, especially in the prolonged production of nanobainitic steels. Among other recognised methods, it seems to be an effective and economical process. However, there are very few research works in this area. The objective of this study was to collate microstructural changes caused by IAT with differences in the kinetics of the subsequent bainitic transformation in the X37CrMoV5-1 tool steel. Differential dilatometry, LM and SEM microscopic observations, EDS and XRD analysis, and computer simulations were used to investigate the effect of IAT on the kinetics of bainitic transformation. The study has revealed that introducing an additional isothermal heating stage immediately after austenitising significantly affects the kinetics of bainitic transformation—it can accelerate or suppress it. The type and strength of the effect depends on the concentration, distribution, and morphology of the precipitations that occurred during IAT.

Effects of yttrium addition on microstructure and mechanical properties of Inconel 718 alloy produced by sub-rapid solidification

In order to improve the mechanical properties of Inconel 718 alloy produced by sub-rapid solidification, the yttrium (Y) element was added during casting. One alloy with 0.1% weight Y content (0.1Y) and a reference alloy without Y addition (0Y) were produced, which involved homogenization, cold rolling, intermediate annealing, and aging treatment. The influences of Y addition on the microstructure and mechanical properties of Inconel 718 alloy were examined. Due to the precipitation of Ni3Y and Ni17Y2 particles, 0.1Y alloy exhibited a refined grain size and a lower recrystallization fraction. The average grain size of 0Y homogenized sample and 0.1Y homogenized sample were about 50.8 μm and 29.5 μm, respectively. Besides, a higher fraction of δ phase precipitated in the 0.1Y annealed sample, including a large amount of granular or short-rod shape δ phases and a small amount of needle-like δ phases. The area fraction of δ phase in the 0.1Y annealed sample was ~10.45%. However, the area fraction of δ phase in the 0Y annealed sample was lower (~7.93%), and needle-like δ phase was hardly observed under this condition. Compared with 0Y alloy, 0.1Y alloy showed better tensile properties. The 0.1Y alloy after aging treatment exhibited an excellent combination of ultimate tensile strength (~1400 MPa), and total elongation (~20%) when deformed at room temperature.

Preparation of a Cube-Textured Ni-7at.%W Based Template Used for Coated Conductors

Although Ni-W substrate with high W content (>5at.%) substrates have been developed successfully, the quality of cube texture and grain boundary, as well as extensive applications in coated conductors should be further improved. In the present work, once intermediate annealing treatment (IAT) at 500°C for 2 h has been employed to optimize the deformation and recrystallization textures in Ni-7at.%W (Ni7W) substrates. As a result, competitive high cube texture content (2Zr2O7 (GZO) buffer layer with strong cube texture and high-quality surface deposited successfully on the Ni7W substrate using the chemical solution deposition method, demonstrating the advanced GZO/Ni7W template is promising for coated conductors.

The Effect of Asymmetry on Strain Distribution, Microstructure and Texture of Multilayer Aluminum Composites Formed by Roll-Bonding

AA1050/AA7050 multilayered composite sheets with a proportion of 1:1 were produced by Accumulative Roll Bonding (ARB) and Asymmetric Accumulative Roll-Bonding (AARB), using up to 8 cycles and intermediate annealing treatments at 500°C. The main purpose was to produce one composite sheet with high strength and moderate ductility, taking advantage of the mechanical properties of these aluminum alloys. Microstructural features were investigated in order to evaluate the potential to achieve a refined microstructure and the development of structural patterns. The strain distributions as a function of friction and asymmetry were simulated by finite element analysis. Texture was evaluated by X-ray diffraction and electron backscatter diffraction. A continuous layer pattern was obtained by ARB, up to 6 cycles but after 8 cycles shear bands fragmented the harder layers. In the early AARB cycles, the bending and necking of the AA7050 layers yielded a wavy-pattern. The shear strain in the AARB process has a strong influence on achieving a wavy-pattern, more than the flow stress differences of the alloys in the composite. Shear texture increased with the degree of the layers’ discontinuity. Different sources of shear contributed to the formation of microstructural patterns: the shear due to asymmetry, the frictional shear at roll-sheet interface and at the central layer interface and the shear at the layers’ interface. In addition, the ARB process achieved a better interfacial adhesion at the middle interface and higher strength and elongation than the AARB process.

Improved tensile strength and electrical conductivity in Cu–Cr–Zr alloys by controlling the precipitation behavior through severe warm rolling

A Cu–Cr–Zr alloy was subjected to severe warm rolling, and the effects of processing temperature and strain on the precipitation and microstructures were systematically studied. The results show that the nucleation and growth of precipitates interact with the deformation-induced defects, and therefore, the distribution precipitates vary with the different warm rolling processes. This leads to a significant impact on mechanical and electrical properties. In detail, the size of the precipitates is coarser, but the number density is lower as the applied strain (after each annealing treatment) and temperature are higher. And therefore, the UTS is lower, but the electrical conductivity is higher in rolled sheets under higher strain and temperature. Moreover, the present process could improve the comprehensive properties of Cu–Cr–Zr alloys, and an excellent combination of high UTS of 586 MPa and good electrical conductivity of 78.2%IACS was achieved in the sample of RRA ~ 723 K. (The sample was subjected to intermediate annealing treatment at 723 K between each of two rolling passes.)

Texture evolution and mechanical properties of Al–Mg–Si alloys at different intermediate annealing temperatures

Intermediate annealing treatment produces different effects on the state of particles in Al–Mg–Si alloy sheets, thereby affecting their recrystallization textures and formability. To improve the formability of the sheets, the effects of different intermediate annealing temperatures on the texture evolution and mechanical properties of these sheets for automotive applications were studied using optical microscope (OM), scanning electron microscope (SEM) and tensile tests. The results reveal that intermediate annealing temperature has a significant influence on the recrystallization textures and average plastic strain ratio (r). After solution treatment, all the alloy sheets possess similar recrystallization texture components comprising of cubeND {100} and P {011} orientations, whereas a characteristic strong cube-oriented {100} texture is observed only in the alloy annealed at a temperature of 380 °C. However, in comparison with the alloy not annealed, and the alloy annealed at 550 °C, the alloy annealed at 380 °C possesses a lower average r value. Furthermore, the relationship between textures and r value was analyzed by using the Taylor full constraints model in this study.

Grain refinement and enhanced precipitation of Cu–Cr–Zr induced by hot rolling with intermediate annealing treatment

A new process of hot rolling with intermediate annealing is developed to increase the strength and electric conductivity of the Cu-1Cr-0.1 Zr (wt.%) alloy. The process can refine the crystalline structure and accelerate the speed of precipitation simultaneously, and a combination of high ultimate tensile strength of 522 MPa, excellent electrical conductivity of 81.9 IACS% has been achieved. The results show the higher strain rate and temperature, the higher speed of precipitation. In addition, the microstructure and property of the strip processed by HR-6˜723 K is non-uniform through the thickness, and the top layer with ˜0.2 mm thickness shows a higher tensile strength and electrical conductivity than that of the overall rolled sheet.

Annealing on Anisotropy and Mechanical Properties of an Al-Mg-Si Alloy

Intermediate annealing on anisotropy and mechanical properties of an Al-0.78Mg-0.90Si-0.65Zn-0.16Cu (wt. %) alloy was investigated by tensile test, optical microscope (OM) and electron back-scattered diffraction (EBSD). The results indicated that alloy sheet displayed various microstructure after without intermediate annealing, intermediate annealing treatment at 350°C for 2 h, 450°C for 2 h and 500°C for 5 min. Compared with the alloy without intermediate annealing, the alloy exhibited equiaxed grain with 35.0µm after annealing at 500°C for 5 min, grain orientation of the alloy was distributed randomly, and plastic strain ratio value of 45° direction was more than 0.6. The anisotropy of the sheet was significantly reduced. Annealing at 500°C for 5 min was suitable for the production process of automobile body sheets.