Annealed State Research Articles

Microstructure and mechanical properties of the as-cast and annealed CoNiV-based MEAs with Al addition

Lattice distortion, which is intended to increase the yield strengths of alloys, is central to alloy design. This study focuses on investigating the close connection between microstructure and mechanical properties of (CoNiV)97Al3 medium-entropy alloys (MEAs) in the as-cast and annealed states. The grain size and phase composition of the alloys were optimized by combining the large deformation cold-rolling and high temperature annealing treatment, and the toughening mechanism of the alloys was evolved. After annealing at 900 and 950°C, a small amount of diffuse B2 phase appears within the alloy, which is able to strengthen the alloy to obtain high yield strength. Since intermetallic compounds such as Ni3Al are extremely unstable, they will decompose during annealing at higher temperature (1000°C), the alloy transforms into a single FCC phase. Therefore, the as-cast and annealed (CoNiV)97Al3 alloy exhibited excellent mechanical properties, including yield strengths of 0.8–1.1 GPa, ultimate tensile strengths of 1.05–1.7 GPa, and an optimal elongation of 36.7 %. Combined with the mechanical properties and microstructure of the as-cast and annealed (CoNiV)97Al3 MEAs, the alloy strengthening was mainly attributed to the synergistic effect of dislocations, solid solution phases, and B2 brittle precipitated phases, while the good ductility was mainly due to the annealing twins. Thus, harmonizing multiple strength/toughness mechanisms can lead to a more optimal alloy strength–plasticity equilibrium point.

Research on the ultra-low temperature tensile deformation mechanism of Al-Mg-Si alloys in different heat treatment states

The susceptibility of Al-Mg-Si alloy to cracking during room temperature large plastic deformation poses a significant obstacle to its widespread application. Cryogenic temperature forming of aluminum alloys has emerged as a prominent research topic. However, the precise mechanisms underlying the enhancement of aluminum alloy plasticity in different states remain elusive. In order to elucidate this matter, a series of uniaxial tensile experiments were conducted on Al-Mg-Si alloy featuring diverse initial states, under varying temperature conditions. The results show that when the deformation temperature is reduced from 25℃ to −196℃, the tensile strength and elongation of the wrought material are increased by 48 MPa and 5.42 %, and the tensile strength and elongation of the annealed material are increased by 118 MPa and 5.65 %. In contrast, while the T4 state sample exhibited a significant improvement in tensile strength (103 MPa), no substantial enhancement in elongation was observed. This disparity can be primarily attributed to the absence of second-phase precipitation in the as-forged and annealed states. As the temperature decreased, the critical shear stress increased, resulting in increased resistance to deformation. Consequently, an increased degree of lattice rotation and activation of dislocations in various slip systems ensued, thereby improving the deformation uniformity. The formation of initial microvoids predominantly occurred close to grain boundaries. Therefore, compared with room temperature deformation, low temperature deformation caused by the accumulation of dislocations and hole sprouting concentrated at a single location was less likely. As a result, the dislocation distribution was more uniform and fracture was less likely to occur. Conversely, in the T4 state, the aging process resulted in the precipitation of a substantial amount of the soluble second phase (Mg5Si6). Consequently, microvoid nucleation transpired at the phase boundaries, leading to an elevated tensile strength. However, because of the increased dislocation hindrance when the deformation temperature was lowered, no significant enhancement in plasticity was observed.

Effect of Machining Parameters on the Surface Roughness of Hot Die Steel

H13 tool steel is frequently used in hot work dies, hot forging, hot extrusion, and mold materials for casting ferrous and nonferrous materials. Surface roughness is of key importance in case of dies and moulds, as it insures the finish of the final product. After studying the work done by the researchers in field of machining and its impact over surface roughness, it was found that machining behaviour of H13 steel at the annealed state is not being studied. The surface finish obtained during turning of H13 steel are not studied on a greater scale, so the present study includes the analysis of finish (surface roughness) generated. Turning operation is carried out on the CNC machine at dry condition with an aim to find systematically the effect on surface roughness by distinct machining variables like feed rate, depth of cut and speed. RSM model using Box Behnken design is used to predict the roughness developed during turning of annealed H13 steel using carbide tool. It was found that feed rate and the depth of cut have a direct relation with the surface finish and the value of surface roughness increases with increase in these parameters. On the other side, cutting speed has a less impact over the surface roughness & is inversely related.

Microstructure evolution and mechanical properties of NiAlCrFeMo high entropy superalloy after different annealing treatment

A novel NiAlCrFeMo high entropy superalloy was prepared using the vacuum arc melting method, followed by annealing at 800 °C, 1000 °C, and 1200 °C for 10 h. The microstructural characteristics and mechanical properties of the alloy after annealing were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Vickers hardness testing, and high-temperature tensile testing. The results indicate that the as-cast alloy consists of dendritic γ+γ′ phases and interdendritic B2-type β phase, with hemispherical α-Cr phases present within the β phase. Compared to the as-cast status, the volume fraction of the β phase in the annealed state increased from 18.52 % to 26.13 %. Notably, at 800 °C/10h, acicular γp’ phases precipitated within the β phase. The alloy exhibited varying degrees of improvement in both strength and ductility after annealing. The specimen annealed at 800 °C/10h showed the highest strength (σYS = 181.06 MPa) and good ductility (εEI = 12.45 %), with strength increasing by approximately 13.10 % compared to the as-cast status. This improvement is attributed to the coarsening of the α-Cr phase, the transformation in γ′ morphology, and the precipitation of acicular γp’ phase. At 1200 °C/10h, all precipitates dissolved into the matrix, resulting in the lowest strength (σYS = 134.08 MPa) and the highest ductility (εEI = 15.54 %).

Process parameters selection for multi-layer friction surfacing of 7075 aluminium alloy

The effect of deposition parameters on the microstructure and mechanical properties are studied in multi-layer friction surfacing of 7075 aluminium alloy. These multi-layer structures were successfully manufactured after a parametric study which allows the generation of a deposition window, including an interface quality comparison. A higher rotational speed leads to a larger grain sizes. The coarse precipitates size and volume fraction decrease along the build direction in correlation with the thermal cycles’ profile. The top layer has a higher hardness after deposition, while bottom layers are in annealed state due to the growth of the strengthening phases. Fracture surface analysis revealed that transversal cracks are due to interlayer decohesion and that voids nucleated on the coarse precipitates.

A single-phase Nb25Ti35V5Zr35 refractory high-entropy alloy with excellent strength-ductility synergy

Refractory high entropy alloys (RHEAs) are promising candidates for high-temperature structural materials due to their excellent high-temperature performance. However, the room-temperature brittleness of most alloys results in poor plastic formability, thereby limiting their engineering applications. In this study, Nb25Ti35V5Zr35 alloy with cold-rollability was developed, and its phase stability, tensile mechanical properties, elastic properties, strengthening mechanism, and deformation mechanism were investigated by combining experiments, CALPHAD, DFT and molecular statics (MS) methods. The results demonstrate that Nb25Ti35V5Zr35 alloy possesses good phase stability, with both the as-cast and annealed states maintaining a single-phase BCC structure without undergoing phase transformation. The tensile yield strength of the alloy reaches its peak at 1152 MPa in the cold-rolled condition, while its annealed state exhibits an optimal balance of strength and plasticity, with a yield strength of 836 MPa and an elongation of 22.45 %, respectively. Solid solution strengthening is the primary source of its high strength, with V and Zr playing key roles in this strengthening mechanism. Dislocation slip plays a dominant role in plastic deformation. Additionally, compared to traditional BCC alloys, the significance of edge dislocations in the deformation process is notably enhanced, with the {112} plane serving as the preferred slip plane for dislocations. DFT results indicate that the alloy exhibits significant anisotropy in both Young's modulus and shear modulus. This work contributes to understanding the material properties of the Nb25Ti35V5Zr35 alloy and provides a reference for the design of new ductile RHEAs.

Microstructural evolution and mechanical properties of maraging steel by additive manufacturing

Laser powder bed fusion (LPBF) is a revolutionary and innovative technology that provides advanced technical support for the forming of parts with high precision and complex structures. In this work, a new type of Fe-Ni-Mo-Ti-Al-Y cobalt-free maraging steel was successfully fabricated by LPBF. The additive manufacturing parameters and the microstructural evolution of cobalt-free maraging steel under different heat treatment parameters were systematically studied. The results show that the parts without cracks and close to complete density can be fabricated under a wide LPBF process window. The dislocation cell with 500 nm in the printing state makes the material have good plasticity. After post-heat treatment, the preferred orientation of LPBF maraging steel is reduced, but the typical characteristics of molten pool and cellular structure in maraging steel disappeared, which is the result of local composition and microstructure homogenization. The elongation of LPBF maraging steel in solution annealed state is higher than that in as-printed state, which is due to the reduction of dislocation density and grain coarsening. However, after direct aging, due to the formation of nano-sized Ni3(Ti, Mo) precipitates in the matrix, the mechanical properties of the material were effectively enhanced, and the tensile strength increases from ∼1.1 GPa in as-printed state to ∼1.6 GPa in aging state. In contrast, the corrosion resistance of as-printed maraging steel is higher and comparable to that of traditional cobalt-containing maraging steel. However, the corrosion resistance of LPBF maraging steel after being aged is reduced, which is due to the existence of precipitates and dislocations. This study provides a theoretical reference for the composition design and strengthening mechanism of LPBF cobalt-free maraging steel.

Formation, thermal stability and soft magnetic properties of Fe-Co-B-Si amorphous alloys with ultrahigh saturation magnetic induction of 2.0 T

This paper studies the influence of metallic element composition on the formation ability, thermal stability and magnetic properties of melt-spun (Fe1-xCox)B15–19Si1 (x =0.2–0.4) amorphous alloy ribbons. The maximum metal concentration at which an amorphous phase is formed during melt spinning has been determined in conjunction with the metal content dependence of crystallization processes and crystallized phases. The amorphous (Fe0.8Co0.2)84B15Si1 alloy with the highest metal content in an optimally annealed state exhibits an extremely high saturation induction (MS) of 2.0 T, low coercive force of 7.6 A m−1, high effective permeability of 13500 at 1 kHz and low core losses of 5.5 W kg−1 at 100 mT and 19.7 W kg−1 at 200 mT at 10 kHz which have not been simultaneously obtained for all kinds of soft magnetic materials up to date. The replacement of Fe with Co significantly increases the Curie temperature of the amorphous phase, resulting in very high thermal stability of the high MS alloys. The combination of excellent soft magnetic properties with ultrahigh MS value makes them candidates for use in highly loaded high-speed electric motors capable of operating at temperatures up to 473 K.

Effect of ultrasonic assisted-ECAP processing on the microstructure, mechanical properties, and fluoride-induced corrosion performance of pure titanium

The influence of the ultrasonic assisted equal channel angular pressing (UA-ECAP) process on the microstructural characteristics, mechanical properties, and fluoride-induced corrosion behavior of grade 2 commercially pure titanium (CP-Ti) is investigated. The UA-ECAP process, particularly in the first pass, induces the formation of twins and slip bands. Continued slip band activity leads to non-equilibrium structures and ultrafine grains in subsequent passes. Mechanical properties analyses show hardness progression from 147 HV (annealed state) to 233 HV (3-pass UA-ECAPed) and yield strength increase from 465 MPa to 765 MPa with elongation reduction from 24.6 % to 16.6 %. Fluoride-induced corrosion of various samples in 1 wt% HF solution is investigated through electrochemical and immersion tests. After 28 days of immersion, the 3-pass UA-ECAPed sample exhibits a corrosion rate around half that of the annealed one and lower than other UA-ECAPed samples. Microscopic observations of corroded samples reveal the 3-pass UA-ECAPed sample's film is denser and more uniform, as compared with the other samples. Glow discharge optical emission spectroscopy (GDOES) confirms the corrosion films on all samples consist of an outer region rich in oxygen/fluorine and an inner region rich in oxygen; however, the film exists on the 3-pass UA-ECAPed sample exhibits over twice thicker than other samples and with higher contribution of oxygen in it as well. A proposed physical model is provided to explain the 3-pass ECAP sample's enhanced corrosion resistance.

Research on the deformation behavior of pure zinc fabricated by forward extrusion and composite extrusion

Zinc and its alloys are biomedical biodegradable materials with broad application prospects. In this paper, commercially pure zinc bars were subjected to two different types of extrusion treatments, forward extrusion (FE) and composite extrusion (CE), at 120°C to study the changes in microstructure and mechanical properties. Compared to the virgin annealed state of pure zinc, the yield strength of CE decreased significantly from 73.67 MPa to 40.87 MPa, while the elongation of FE increased markedly from 9.23 % to 59 %. The anomalous phenomenon of decreasing strength and increasing ductility of extruded pure zinc is significantly different from that of extruded zinc and magnesium alloys. To investigate the reason for this anomaly, a detailed study of the microstructure evolution of pure zinc under three processing states was carried out using EBSD. Grain growth and texture weakening lead to a loss of strength, whereas the increase in ductility after extrusion is attributed to the activation of more slip systems.

Modeling and investigation of combined processes of casting, rolling, and extrusion to produce electrical wire from alloys Al–Zr system

The results of modeling and research of casting, rolling, and extrusion processes for producing wire from Al–Zr system alloys and determining its physical and mechanical properties have been presented. When implementing combined processes for processing aluminum alloys, the number of operations is significantly reduced, productivity and yield are increased. As a result of the conducted research, the influence of alloy preparation modes and their chemical composition on the physical, mechanical and electrical properties of longish semifinished products from Al–Zr system alloys obtained by combined rolling-extrusion (CRE) and ingotless rolling-extrusion (IRE) methods were investigated. The simulation of the CRE process for one of these alloys of the system was carried out in the DEFORM 3D software package using data on its rheological properties obtained by the hot torsion method. Based on the modeling results, the optimal modes for conducting experimental studies were selected. The features of metal forming were experimentally studied, the temperature-velocity and technological parameters of combined processing were found, as well as the properties of cast billets, including those obtained using an electromagnetic mold (EMM). The results of experimental studies of the CRE and IRE processes suggest that it is possible to obtain longish deformed semifinished products from alloys Al–Zr system with a level of physical, mechanical and electrical properties that meet international standards. At all technological stages, including drawing, the structure of the metal was studied, and data on the physical and mechanical properties of hot-extruded rods and wire in cold-deformed and annealed states was obtained. The heat resistance of wire made from the investigated alloys was studied and it was found that after testing at a temperature of 280 °C and a holding time of 1 h, it satisfies the requirements of the AT3 type standard with a maximum permissible long-term operating temperature of 210 °C. Recommendations are given for industrial implementation; alloys containing 0.15–0.20% zirconium and 0.10–0.15% iron are recommended for the manufacture of AT1 type wire without heat treatment, as well as 0.25–0.30% Zr and 0.2–0.25% Fe for AT3 wire type with heat treatment.

Supramolecular structure and physiochemical properties of annealed maize starches: Effect of starch granule-associated surface and channel proteins

To investigate the effect of starch granule-associated surface and channel proteins (GSCP) on starch during annealing, normal maize starch (NMS) and waxy maize starch (WMS) were subjected to protease treatment then annealing for 0–36 h to study changes in structural and physicochemical properties. The removal of GSCP accelerated the rate of increase in granule size of NMS during annealing. XRD results showed that annealing initially decreases the crystalline order of starch granules, but with prolonged annealing, the relative crystallinity increases. Also, GSCP removal decreases the rate of reduction in relative crystallinity during annealing. The lamellar structure of starch becomes compact in the initial state of annealing. With extended annealing time, the rearrangement of the microcrystalline structure may result in a decrease in compactness. The dual treatment increased the thickness of crystalline lamellae (dc), and the removal of GSCP advanced the change of lamellar structure during annealing. From pasting results, the rigidity of swollen starch was reduced after GSCP removal, while it increased with annealing time for NMS. This study adopted a GSCP removal method that had minimal impact on the structure of starch granules, providing novel information about the role of GSCP in the annealing of maize starch.

Unveiling a common phase transition pathway of high-density amorphous ices through time-resolved x-ray scattering.

Here, we investigate the hypothesis that despite the existence of at least two high-density amorphous ices, only one high-density liquid state exists in water. We prepared a very-high-density amorphous ice (VHDA) sample and rapidly increased its temperature to around 205 ± 10K using laser-induced isochoric heating. This temperature falls within the so-called "no-man's land" well above the glass-liquid transition, wherein the IR laser pulse creates a metastable liquid state. Subsequently, this high-density liquid (HDL) state of water decompresses over time, and we examined the time-dependent structural changes using short x-ray pulses from a free electron laser. We observed a liquid-liquid transition to low-density liquid water (LDL) over time scales ranging from 20ns to 3 μs, consistent with previous experimental results using expanded high-density amorphous ice (eHDA) as the initial state. In addition, the resulting LDL derived both from VHDA and eHDA displays similar density and degree of inhomogeneity. Our observation supports the idea that regardless of the initial annealing states of the high-density amorphous ices, the same HDL and final LDL states are reached at temperatures around 205K.

Unveiling dual crystallization peaks in Zn2P2O7 glass: Insights into stability, nucleation, and growth kinetics

This study reports on the successful synthesis of Zn2P2O7 glass using the conventional melt-quenching method. The state of the material has been investigated using X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC), to verify its amorphous and glassy state with the onset of two distinct crystallization peaks. These peaks were indicative of the transition to α-Zn2P2O7 and γ-Zn2P2O7 phases during the annealing process, a finding that was supported by Fourier-transform infrared spectroscopy (FTIR) analysis. This marked the inaugural occasion where the stabilization of both Zn2P2O7 phases from their respective annealed glassy state was achieved. The crystallization kinetics and associated parameters of Zn2P2O7 glass were deeply delved into, with various models including Kissinger, Ozawa, and the Matusita-Sakka approach. The applied models elucidate the mechanisms of growth and nucleation within the glass matrix. This kinetic study provided valuable insights into the crystallization process, revealing that α-Zn2P2O7 is both kinetically and thermally more stable than the γ-phase. However, it is less thermodynamically stable compared to the γ-phase. Besides, the study of phase transformations and crystallization kinetics was enhanced by the analysis of the Avrami index.

Effect of rare earth element Y content on microstructure, magnetic properties, and electrochemical properties of the as-annealed FeCoNiAl0.2Yx high-entropy alloys

FeCoNi high-entropy alloy (HEA) is widely used in the aerospace and chemical industry. However, the strength and corrosion resistance of the alloy still need to be improved. In this paper, FeCoNiAl0.2Yx (x = 0, 0.05, 0.1, 0.2, and 0.3 in mole ratio) high entropy alloys with different contents of rare earth (RE) element yttrium (Y) were prepared by the vacuum arc melting method, and then the alloys were subjected to annealing treatment at 800 °C/2h. The microstructure, hardness, magnetism, and corrosion performance of FeCoNiAl0.2Yx HEAs in the annealed state with different contents of element Y were analyzed. The results show that the annealed FeCoNiAl0.2Yx HEAs without the addition of element Y and after the addition of element Y both were composed of a face-centered cubic phase. The alloy showed a dendritic structure inside. The element Y was solidly dissolved in the alloys to refine the microstructure of the alloys, and the dendrites were gradually refined with the addition of Y. The Y element caused the phenomenon of lattice distortion inside the alloys, which led to the increase in the alloys’ hardness. The alloy with x = 0.2 showed the greatest exchange of magnetic atoms and the alloy with x = 0.05 showed the lowest coercivity. The alloy with x = 0.1 showed the lowest self-corrosion current density, the broadest passivation zone, the densest dendrites, the smallest grain spacing, and the weakest tendency for intergranular corrosion. The present study shows that the introduction of element Y improves the microstructural morphology, hardness, magnetism, and corrosion properties of FeCoNiAl0.2Yx HEAs in the annealed state.

Strengthening and Toughening of ZG25SiMn2CrB Steel without Tempering Brittleness via Electropulsing Treatment.

High-strength low-alloy steels are widely used, but their traditional heat-treatment process is complex, energy-intensive, and makes it difficult to fully exploit the material's potential. In this paper, the electropulsing processing technology was applied to the quenching and tempering process of ZG25SiMn2CrB steel. Through microstructural characterization and mechanical property testing, the influence of electropulsing on the solid-state phase transition process of annealing steel was systematically studied. The heating process of the specimen with the annealing state (initial state) is the diffusion-type transition. As the discharge time increased, the microstructure gradually transformed from ferrite/pearlitic to slate martensite. Optimal mechanical properties and fine microstructure were achieved after quenching at 500 ms. The steel subjected to rapid tempering with 160 ms electropulsing exhibited good, comprehensive mechanical properties (tensile strength 1609 MPa, yield strength 1401.27 MPa, elongation 11.63%, and hardness 48.68 HRC). These favorable mechanical properties are attributed to the coupled impact of thermal and non-thermal effects induced by high-density pulse current. Specifically, the thermal effect provides the thermodynamic conditions for phase transformation, while the non-thermal effect reduces the nucleation barrier of austenite, which increases the nucleation rate during instantaneous heating, and the following rapid cooling suppresses the growth of austenite grains. Additionally, the fine microstructure prevents the occurrence of temper brittleness.

Anelasticity of Mg-Mn and Mg-Gd alloys

Anelastic relaxation at sub-resonance frequency (from 0.01 to 100 Hz), temperature (from 0 to 450°C) and amplitude (ε0 from 5×10−5 to 10−3) range in binary Mg-0.8 wt%Mn (0.36 at%) and Mg-2 wt%Gd (0.31 at%) in as-extruded and annealed states was experimentally studied and analyzed, to characterize acting thermally activated and structural relaxation effects. Activation parameters for thermally activated anelastic effect and structural studies suggest that it is the grain boundary relaxation with dominating large angle boundaries, while the high-temperature background is mainly controlled by dislocations sliding. Pseudo peak at ∼290 °C (Mg-Mn) and ∼410 °C (Mg-Gd) is the result of the recrystallization process in the as-extruded samples, which indicates that the addition of Gd restricts the recrystallization of Mg compared with the addition of Mn. Analysis of amplitude dependencies of internal friction in the frames of Granato and Lücke approach suggests higher density of movable dislocations in as-extruded Mg-Mn alloy.

The Influence of Mo Content and Annealing on the Oxidation Behavior of Arc‐Melted Cr–xMo–8Si Alloys

The influence of Mo (10–40 at%) additions to Cr–8 at%Si is systematically studied by analyzing arc‐melted alloys in the as‐cast and annealed state. The oxidation resistance is tested by thermogravimetric analysis (TGA) at 1200 °C in air for up to 100 h. Samples are characterized by X‐ray diffraction, scanning electron microscopy, and wavelength‐dispersive X‐ray spectroscopy. The studied Cr–xMo–8Si alloy series shows a beneficial effect of Mo on the corrosion behavior. For all of the investigated Mo contents, no nitridation is observed and the oxide scale adhesion is improved. An increased amount of intermetallic A15 phase leads to the formation of a SiO2 scale beneath the Cr2O3 layer during high‐temperature exposure. The internal SiO2 layer inhibits further internal oxidation of the A15 phase. Uniform size and distribution of A15, benefits the formation of a duplex oxide scale. Cr–25Mo–8 at%Si, shows the most promising oxidation behavior. The TGA data follows the paralinear law, with both the growth rate, kp, and volatilization rate, kv, of Cr2O3 being reduced by adding 10–25 at% Mo. A binary Cr/Mo–Si phase diagram is generated in order to determine accurate annealing conditions and estimate the stability range of the metastable σ phase.

Enhanced high-temperature ductility without strength drop in a lean Co Ni-based superalloy

The conventional Ni-based IN738LC superalloy series are typically hardened by a fine distribution of closely spaced fine and coarse Ni3(Al, Ti)-type L12 ordered γ' precipitates, which is formed by solid-state nucleation and growth in the disordered γ matrix. However, outstanding high-temperature mechanical performance requires a high amount (∼9 wt%) of Co, which is the alloy's most expensive adding element. Here, we report a compositionally modified IN738LC alloy with a 50% reduction in Co content and a 20% increase in comparatively cheaper Mo content. This compositional modification caused more γ' precipitates with uniform distribution than those in the conventional counterpart subjected to the same heat treatments. The modified superalloy showed a twofold increase in high-temperature (750 °C) tensile elongation while maintaining the conventional one's strength (∼1.1 GPa) at the temperature. This remarkable ductility gain, while no loss in strength, was predominantly attributed to a transition in the high-temperature deformation mechanism, i.e., from multiple intersecting slip bands-indued stress localization for the conventional IN738LC alloy to unidirectional microtwins for the modified IN738LC material. More Mo and less Co contents could drive more coherent γ' precipitates in the annealed state and the high density of microtwins in the deformed state, resulting in stress delocalization and enhanced ductility at comparable strength. The findings of this study have significant implications for the development of cost-effective, strong, and ductile superalloys for high-temperature applications.

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.