ND Texture Research Articles

Comparative study of microstructure and mechanical properties of cold rolled and annealed CoCrFeNi-MEA and CoCrFeNiMn-HEA fabricated by laser energy deposition

Equi-atomic quaternary CoCrFeNi Medium-entropy alloy (MEA) and quinary CoCrFeNiMn high-entropy alloy (HEA) are fabricated by laser energy deposition, followed by 5-pass cold rolling to total reduction of 70 % and annealing at temperatures of 600–1000 °C for 1 h. CoCrFeNi-MEA is severely cracked while CoCrFeNiMn- HEA is slightly cracked after cold rolling. Hardness of as deposited and fully recrystallized (heat treating temperature at 800–1000 °C) CoCrFeNi-MEAs are slightly higher than those of CoCrFeNiMn- HEAs, due to the larger atomic size misfit and lattice strain in CoCrFeNi-MEA than in CoCrFeNiMn-HEA. However, the higher microhardness of CoCrFeNiMn-HEAas-rolled than CoCrFeNi-MEAas-rolled is associated with the higher strain state in CoCrFeNiMn-HEAas-rolled than in CoCrFeNi-MEAas-rolled. With the increase of heat-treating temperature, microhardness of CoCrFeNi-MEA increases first and then decreases due to the precipitation hardening effect of Cr-rich (B2) particles in CoCrFeNi-MEAR-600. Microhardness of CoCrFeNiMn-HEA decreases with the increase of annealing temperature because of the weaker precipitation hardening effect of MnNi phase (L10) and Cr-rich particles (BCC) after annealing at 600 ℃ and higher temperatures. CoCrFeNi-MEAR-700 is much harder than CoCrFeNiMn-HEAR-700 because CoCrFeNi-MEAR-700 is partially recrystallized and CoCrFeNiMn-HEAR-700 is fully recrystallized. Strength behavior of the two alloys is consistent with microhardness behavior. {100}<110> texture component is acquired in both CoCrFeNi-MEAas-rolled and CoCrFeNiMn-HEAas-rolled. <111>//ND texture is observed in both alloys after annealing at 600 ℃. Orientation of recrystallized grains is random in both alloys. Size of recrystallized grains in CoCrFeNiMn-HEA is slightly larger than those in CoCrFeNi-MEA since homologous temperature (T/Tm) of CoCrFeNiMn-HEA is slightly higher than that of CoCrFeNi-MEA.

Hot Compression Behavior of 18Cr–11Mn–0.06Ni–0.19N High‐Mn Ultralow Nickel Duplex Stainless Steel under Large Deformation

To enhance the rolling production efficiency of high‐manganese low‐nickel duplex stainless steel (DSS) and optimize hot compression parameters, hot compression with a range of 0.01–10 s−1/850–1150 °C and deformations of 70% is used to investigate the hot deformation behavior of 18Cr–11Mn–0.06Ni–0.19 N DSS, which reveals the differences in the recrystallization mechanism of two phases and their thermoplastic properties. The results show that strain partitioning and softening occur first in the ferrite phase, with the austenite phase undergoing complex and incomplete softening. Most ferrite experiences continuous dynamic recrystallization and develops a &lt;001&gt;//ND texture when deformed at 0.1–10 s−1/950 °C, with higher temperatures facilitating the merging of high‐angle grain boundaries. A deformation‐induced phase transformation from δ to γ occurs in ferrite when deformed at 0.01 s−1/850–950 °C. However, austenite softening is dominated by discontinuous dynamic recrystallization, enhanced by twinning‐induced strain‐induced boundary migration when deformed at 0.1 s−1/950 °C; dynamic recovery controlled by dislocations is enhanced when deformed at 0.1 s−1/1150°C and 10 s−1/950 °C. A strain‐compensated constitutive model with an average absolute relative error value of 7.8% is established to better predict the flow stresses. Experimental DSS displays optimal hot workability in the parameter ranges of 0.1 s−1/950–1050 °C.

Dynamic Shear Texture Evolution during the Symmetric and Differential Speed Rolling of Al-Si-Mg Alloys Fabricated by Twin Roll Casting.

The effects of a reduction in area (RA) and the speed ratio between the top and bottom rolls on a shear strain and the crystallographic texture evolution of Al-Si-Mg (1.0%Si-0.6%Mg) aluminum alloys fabricated by twin roll casting (TRC) were comprehensively examined experimentally and through numerical predictions. Initial twin-roll casted strips had a texture gradient from the surface to the center. ⟨111⟩//ND textures were found in the surface layer, and weak rolling textures existed in the center of the strip. The distributions of shear and plane strain compression (PSC) textures varied with the RA and differential speed ratio. Strong shear textures including a rotated cube, {100}⟨011⟩, were obtained from both the symmetric and differential speed rolling processes. Symmetric rolling with a different reduction in area (SRDRA) produced shear textures mainly in the surface layer. Differential speed rolling (DSR) caused dynamic shear textures along the thickness direction, not limited to the surface. Based on the finite element method and crystal plasticity, the effects of different RA values, differential speed ratios, and friction coefficients on shear strain and texture evolution are discussed in detail. Loads measured from work rolls during DSR decreased with an increase in the speed ratio.

Electrochemical potential dependence of SCC initiation in X60 pipeline steel in near-neutral pH environment

Stress corrosion crack (SCC) in pipelines directly affects the long-term safety service and has a major impact on the continuity of oil and gas delivery. The near-neutral pH SCC propagation process has been widely reported in the past decades, while the crack initiation mechanism is rarely studied in-depth. Here, the crack initiation behavior of ×60 pipeline steel under different electrochemical potential levels was investigated by interrupted slow strain rate tensile testing (SSRT) and microstructural characterization. The experimental results show that the SCC initiation is dominated by hydrogen-facilitated anodic dissolution (AD) under the open circuit potential (OCP) environment, while it is by the hydrogen embrittlement (HE) under −1.1 and −1.2 VSCE cathodic potentials. All the SCC cracks in ×60 pipeline steel show transgranular features, pathing through the grains in different crystallographic orientations, which showed dependence on the electrochemical potential of the steel: initiation via slip-enhanced dissolution of {110}//ND or {112}//ND texture under OCP environment, but mostly by quasi-cleavage cracking of {100}//ND texture under −1.1 and −1.2 VSCE cathodic potentials.

Simultaneous improvement in strength and ductility of CT20 titanium alloy at cryogenic temperature

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of the CT20 alloy with a <-12-11>//ND texture were investigated. The CT20 alloy with equiaxed microstructure exhibits excellent mechanical properties with simultaneous increase in strength and elongation at cryogenic temperature. In current study, the initial <-12-11>//ND texture promotes basal slip actuation effectively and continuously increases Schmid factor (SF) of other slip systems to promote multiple slip. Cryogenic temperature weakens the deformation texture due to the promotion of multiple slip. Since the decrease of the stacking fault energy (SFE), more twins in number and variety nucleate at 77 K and promote multiple slip. It causes strong cryogenic twinning-induced plasticity (TWIP) effect. Grain refinement induces strong cryogenic dynamic Hall-Petch effect resulting in high strain-hardening rate (SHR) and strength. The yield strength (YS, ∼1052.67 MPa), ultimate tensile strength (UTS, ∼1102.51 MPa) and elongation (EL, ∼21.1 %) of the 77 K specimen are about 84.1 %, 69.1 % and 38.8 % higher than its counterpart at RT, respectively. In addition, cryogenic temperature changes the initiation location of cracks and promotes cracks initiation at grain boundaries homogeneously.

Insights into the dynamic impact behavior of intercritically annealed automotive-grade Fe–7Mn–4Al −0.18C steel

Recently, medium manganese steels (MMnS) have been developed due to their excellent strength and improved ductility to meet automotive manufacturer demands. However, research on the impact toughness of automobile parts developed from these steels needs considerable attention to meet safety standards. Therefore, the present investigation focuses on the effect of annealing time (30, 60 and 180 min) on the impact behavior of intercritically annealed (750 °C) Fe–7Mn–4Al-0.18C (wt. %) steel. The microstructure of intercritically annealed steel, as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), consists of blocky and lath-type reverted austenite (RA), fine intercritical ferrite (IF), lath-type martensite (M) and coarse elongated ferrite (EF). The impact toughness of the samples is evaluated at room temperature using a Zwick/Roell HIT450P Charpy impact machine. The sample annealed for 60 min absorbs the highest amount of impact energy among the three annealed samples. This is due to an increased volume fraction of RA, the transformation-induced plasticity (TRIP) effect, and an increase in the fraction of high angle grain boundaries (HAGBs). The microtexture analysis reveals that the presence of γ-fiber {111}//ND texture in ferrite and Rotated Goss texture {011} <011> in austenite contributes to the improved impact toughness in the specimen annealed for 60 min. The SEM fractographs of the sample annealed for 60 min exhibit crack branching and larger dimple size with inhomogeneous dimple distribution indicating higher energy absorption during crack initiation. Martensitic transformation nucleation sites are activated by a high volume fraction of RA in the sample annealed for 60 min, leading to increased impact toughness and the development of secondary cracks. In addition, the impact energy decreases when the sample annealed for 60 min is subjected to an impact test at temperatures lower than room temperature.

Gradient Recrystallization Behavior of a Moderate Warm-Rolled Non-Oriented Fe-6.5wt%Si Alloy

In Fe-Si alloy systems, the Fe-6.5wt%Si alloy shows low iron core losses and near-zero magnetostriction, thus having great potential for high-frequency applications. In this study, an Fe-6.5wt%Si alloy hot band was subjected to a moderate warm rolling with a thickness reduction of 40%, and then annealed at different temperatures. The recrystallization behavior was investigated using the EBSD technique. After the moderate warm rolling, the initial gradient structure of the hot band is inherited, leading to gradient recrystallization behaviors during the further annealing process. The sheet surface first densely nucleates and forms strong &lt;110&gt;//ND and {221}&lt;114&gt; textures. However, the &lt;110&gt;//ND and {221}&lt;114&gt; grains have fewer high-mobility and high-energy (20–45°) boundaries than the other oriented matrix grains, leading to insufficient growth advantages. In the center region, the recrystallization is slow, but the nuclei usually have larger sizes. The inheritance of the &lt;001&gt;//ND (θ-fiber) texture from the initial hot band appears. Some θ-fiber grains, which have easy-magnetized &lt;001&gt; axes lying in the sheet plane, preferentially nucleate in the strong α-fiber textured matrices and form a strong θ-fiber recrystallization texture in the center region.

Hydrogen embrittlement behavior in the nugget zone of friction stir welded X100 pipeline steel

Hydrogen-induced damage is an inevitable challenge in pipeline safety applications, especially, the fusion welded joints owing to microstructure heterogeneity caused by welding process. In this work, X100 pipeline steel was subjected to friction stir welding (FSW) at rotation rates of 300–600 rpm under water cooling, and the relationship among the microstructure, hydrogen diffusivity, and hydrogen embrittlement (HE) behavior of the nugget zone (NZ) were studied. The NZ at 600 rpm had the highest effective hydrogen diffusion coefficient (Deff) of 2.1 × 10−10 m2/s because of the highest dislocation density and lowest ratio of effective grain boundary. The Deff decreased with decreasing rotation rate due to the decrease of dislocation density and the increase of ratio of effective grain boundary, and the lowest Deff of 1.32 × 10−10 m2/s was obtained at 300 rpm. After hydrogen charging, the tensile strength of all specimens decreased slightly, while the elongation decreased significantly. As the rotation rate decreased, the elongation loss was obviously inhibited, and ultimately a lowest elongation loss of 31.8% was obtained at 300 rpm. The abovementioned excellent mechanical properties were attributed to the fine ferrite/martensite structure, low Deff, and strong {111}//ND texture dramatically inhibiting hydrogen-induced cracking initiation and propagation.

On the structure, mechanical behavior, and deformation mechanism of AZ91 magnesium alloy processed by symmetric and asymmetric rolling

In this study, the microstructural evolution, texture, and mechanical properties of AZ91 magnesium alloy rolled by symmetric and asymmetric rolling with 14%, 24% reduction, is presented. The study indicated that at identical deformation, the strength of the asymmetric rolled alloy was slightly greater than the symmetric rolled alloy, and the elongation was greatly enhanced because of finer grain size and weak {0001}//ND basal texture. The properties of the transverse direction (TD) samples are better than that in the rolling direction (RD), which is attributed to the TD samples having a {1¯1¯20}//TD texture. The TD sample by asymmetric rolled with a reduction of 24% had excellent mechanical properties with strength and elongation of 413 MPa and 5.08%, respectively, due to its fully recrystallized grains, the increase of {112¯3}//ND texture and favorable Schmid factor.

Effect of Rolling on Microstructure Evolution and Plastic Deformation Behavior of A473M Martensitic Stainless Steel

Herein, the surface of A473M martensitic stainless steel is strengthened by rolling processing technology. The microstructure evolution and plastic deformation behavior are characterized by electron backscatter diffraction (EBSD). The experimental results indicate that residual compressive stress will be formed on the surface of A473M steel after rolling, and the maximum value can reach 946 MPa. The surface roughness decreases significantly from 383 to 62.7 nm, which is only 1/5 of the matrix. The microstructure of the rolled samples is obviously refined, and &lt;101&gt;//ND texture is formed. The nanohardness of the hardened layer on the sample surface increases from 2.5 to 4.8 GPa, and the elastic modulus increases from 140 to 217 GPa. Compared with the matrix, the tensile strength and yield strength after rolling are increased by 40% and 22%, respectively. EBSD analysis indicates that the texture of the rolled samples after tensile changed from the &lt;101&gt;//TD direction of the matrix to the &lt;101&gt;//TD and &lt;111&gt;//RD directions.

Evaluation of texture weakening and microstructural evolution in an Fe–10Ni–7Mn martensitic steel severely deformed by six turns of high-pressure torsion

The effect of high-pressure torsion (HPT) on textural components and microstructural evolution of an Fe–10Ni–7Mn steel was investigated. Six turns of HPT, with a rotation rate of 1 rpm and with a pressure of 6.0 GPa, were applied to a solution annealed steel. Microstructural and textural evolution, including dislocation characteristics and grain size/misorientation measurements, were accomplished using electron backscatter diffraction (EBSD). The results showed that a fully martensitic structure, containing a high density of dislocations, was developed during the solution annealing stage and subsequently the application of six turns of HPT process converted the low-angle grain boundaries (LAGBs) of the solution annealed condition into high-angle grain boundaries (HAGBs). Thus, the sub-grain boundaries established in the solution annealed condition were altered into very sharp HAGBs. The grain size was also decreased from ∼ 25 μm in the solution annealed situation to ∼210 nm in the severely deformed condition of six-turn high-pressure torsion state. Yield strength, and tensile strength were increased from 765 MPa, and 840 MPa in the solution annealed case to 1890 MPa, and 2230 MPa in the six-turn HPT-processed sample, respectively. Under such a condition, ductility was decreased from 15.2% to 6.1% in the severely deformed state. Applying six turns of HPT developed a predominantly {111}//ND texture. However, the overall texture intensity of the HPT-processed sample was weakened to a value of about one-quarter of the as-quenched solution treated sample. This was related to dynamic recrystallization and grain subdivision as well as a dislocation density reduction in the HPT-processed sample. The texture components of strong Copper ({112}<111>), S ({123}<634>) and some average intensity Cube {100}<0001> were observed in the {100} pole figure in the solution annealed condition. As well, γ-fibre (<111>//ND) and β-fibre were seen in this condition. However, {110}<uvw> fibres were mostly developed in the six-turn sample with the texture components of E1{011‾}<111>, E2{01‾1}<111>, J1{01‾1}<2‾11>, J2+{11‾0}<1‾1‾2>, D2{1‾1‾2}<111> , D1{112‾}<111> and F {110}<001>. In addition, the Cu{112}⟨111⟩ component was significantly diminished. This weakened Cu{112}⟨111⟩ component would have caused enhancement of the mechanical properties, particularly the formability and toughness, as previously reported by the current authors. Finally, it was found that applying severe plastic deformation (SPD) in the form of HPT reduces the effect of martensitic texture in the solution treated steel.

Microstructure and Texture Evolution in Low Carbon and Low Alloy Steel during Warm Deformation.

Warm compression tests were carried out on low carbon and low alloy steel at temperatures of 600–850 °C and stain rates of 0.01–10 s−1. The evolution of microstructure and texture was studied using a scanning electron microscope and electron backscattered diffraction. The results indicated that cementite spheroidization occurred and greatly reduced at 750 °C due to a phase transformation. Dynamic recrystallization led to a transition from {112}<110> texture to {111}<112> texture. Below 800 °C, the intensity and variation of texture with deformation temperature is more significant than that above 800 °C. The contents of the {111}<110> texture and {111}<112> texture were equivalent above 800 °C, resulting in the better uniformity of γ-fiber texture. Nucleation of <110>//ND-oriented grains increased, leading to the strengthening of <110>//ND texture. Microstructure analysis revealed that the uniform and refined grains can be obtained after deformation at 800 °C and 850 °C. The texture variation reflected the fact that 800 °C was the critical value for temperature sensitivity of warm deformation. At a large strain rate, the lowest dislocation density appeared after deformation at 800 °C. Therefore, 800 °C is a suitable temperature for the warm forming application, where the investigated material is easy to deform and evolves into a uniform and refined microstructure.

Effect of deformation microstructures on hydrogen embrittlement sensitivity and failure mechanism of 304 austenitic stainless steel: the significant role of rolling temperature

Metastable austenitic stainless steels (ASSs) have excellent ductility but low strength, so that their usage as load-bearing components is significantly limited. Rolling is an effective method of increasing strength, whereas the effect of rolling temperature on microstructural evolution, the hydrogen embrittlement (HE) sensitivity and fracture mechanisms is still unclear. In present study, the effect of cold/warm rolling on detailed microstructural characteristics of 304 ASS was quantitatively investigated, and the corresponding HE sensitivity was evaluated via slow strain rate test (SSRT). The results suggest that cold-rolling led to high strength but poor plasticity and deteriorated HE sensitivity, while warm-rolled samples provided combination of high strength and ductility and also superior HE resistance. Compared with 18% α′-martensite in cold -rolled steel, warm-rolled specimens consisted of complete austenite, less twins and lower dislocation density，moreover, the favorable {112} ND and {110} ND textures replaced the harmful {001} ND texture. Based on in-situ EBSD observation during SSRT, the HE sensitivity was governed by the combined effect of pre-deformation microstructures and the dynamic microstructural evolution. Advanced method of time-of-flight secondary ion mass spectrometry was used to observe the distribution of hydrogen, and the hydrogen content of specimens was determined by the gas chromatograph thermal desorption analysis method. An exceedingly small amount of hydrogen entered the warm-rolled samples, while a large amount of hydrogen was trapped at grain boundaries of cold-rolled sample, leading to complete intergranular fracture. Therefore, warm rolling is an effective pathway for obtaining high combination of strength and ductility together with excellent HE sensitivity.

Effect of Multi-Pass Power Spinning on Microstructure Homogenization and Mechanical-Property Strengthening of Ti2AlNb-Based Alloy Using Welded Tube Blank.

Long seamless tubes of Ti2AlNb-based alloys are difficult to manufacture through conventional forming methods. In this study, a multi-pass power spinning process was first utilized to fabricate thin-walled tube of Ti-22Al-24Nb-0.5Mo alloy using welded thick tube blank, assisted by on-line electro-magnetic induction heating to maintain high spinning temperature during the whole spinning process. After six-pass hot power spinning at 950 ± 30 °C, the microhardness difference of BM (base metal), HAZ (heat affect zone) and FZ (fusion zone) became much smaller, and the microhardness fluctuation ΔHV dropped to 32 from 122 of the as-welded joint due to the phase composition and microstructure homogenization. The grain size of B2 phase was refined to 0.4/0.6 μm from 2.7/10.8 μm of the as-received BM/FZ, respectively. Meanwhile, the B2 phase <111>B2//ND texture of the as-received rolled sheet weakened during multi-pass spinning due to recrystallization, which co-existed with <001>B2//ND texture in final pass. The ultimate tensile strength in axial/tangential direction was increased to 1245/1299 MPa from 1206/1010 MPa of the as-received rolled sheet, respectively, mainly due to the effect of fine grain strengthening. This study provides an effective way to manufacture high-performance tubular workpieces with low cost and high efficiency.

Multiscale study on the dark-etching region due to rolling contact fatigue of 0.57C-bearing steel

The formation of a dark-etching region (DER) caused by rolling contact fatigue is a complicated phenomenon that is accompanied by macroscopic groove formation and hardness reduction, as well as microscopic texture development and carbon redistribution. To understand the mechanism of DER formation, this study employed a bearing steel with 0.57 wt% C and conducted in-depth characterisation of DER at different scales. While the accumulation of plastic strain within the material began at an early stage of the rolling cycles, DER and hardness reduction appeared only after 5×106 cycles. Inside the DER, a strong 〈111〉 // ND texture and a number of recrystallised cells developed, which indicated dynamic recrystallisation. Moreover, the carbon distribution changed when the DER was formed and its concentration in the matrix decreased as the number of rolling cycles increased, which was consistent with the results estimated by the dislocation-assisted tempering model. Based on these observations, it was suggested that the accumulation of plastic flow caused by repetitive rolling contacts enabled the carbon to redistribute from the matrix to carbides via dislocations and triggered recrystallisation. Hence, both carbide thickening and dynamic recrystallisation resulted in different etching behaviour and hardness reductions, which may result in the spalling of the bearing.

Microstructure and micro-texture evolution in rapidly solidified melt-spun Ni50Mn28Ga22 ribbons

Microstructure and texture play an important role in determining the magneto-mechanical properties of NiMnGa based Heusler alloys. The Ni50Mn28Ga22 melt-spun ribbons were prepared at wheel speeds of 1300 and 1600 RPM. The as-spun ribbons were annealed at different temperatures and for different time periods. X-ray phase analysis of the ribbons showed the presence of modulated structures, which was confirmed from the appearance of the three (202) peaks in almost all the 1300 RPM melt-spun and annealed ribbons. Phase analysis indicates that these twins (martensites) have both tetragonal and orthorhombic structures. Precipitates were observed along the grain boundaries and in the grain interior after annealing. Auger spectroscopy revealed that the precipitates were manganese-rich. TEM micrographs confirm that the annealed specimens have both 5 M and 7 M modulated structures, according to the satellite spots observed in the electron diffraction patterns. As-spun ribbons produced at 1300 and 1600 RPM had a predominantly 〈001〉 ‖ND fibre texture. 〈001〉 ‖ND fibre texture was also observed in the ribbons produced at 1300 RPM annealed at lower temperatures, such as 400 °C. 〈111〉 ‖ND texture was obtained in the melt-spun ribbons produced at 1300 RPM and annealed at 1000 °C for 5 h.

Thermomechanical Processing Map in Retaining {100}//ND texture via Strain-Induced Boundary Migration Recrystallization Mechanism

The feasibility of establishing thermomechanical conditions to promote {100}//ND fiber texture via strain-induced boundary migration (SIBM) recrystallization mechanism in a non-grain oriented (NGO) electrical steel was investigated. Single-hit uniaxial compression at various temperatures and strains has been applied on Fe-6 wt pct Si to establish the relationship between stored energy and the softening mechanisms. Recovery only and recrystallization by SIBM or by subgrain growth (SGG) have been observed depending on the stored energy level. A strong {100}//ND fiber recrystallization texture, i.e., 45 pct area fraction, was seen in the sample which was deformed to 0.2 strain at 650 °C and then annealed at 1000 °C for 15 minutes, whereas only 13 pct {100}//ND fiber component was observed after 0.4 strain at 500 °C followed by the same annealing treatment. By examining the same microstructural region before and after annealing via EBSD, it has been shown that {100}//ND textured recrystallized grains were formed adjacent to the {100}// ND textured deformed matrix. Low stored energy has been shown to favor the formation of {100}//ND texture recrystallized grains via SIBM recrystallization mechanism attributed to its slow recrystallization nucleation rate. The results from the deformation studies have been used to suggest a processing window map concept to define the recovery, SIBM, and SGG regions for the starting as-cast columnar microstructure.

Effects of Initial Precipitate on Shear Deformation during Asymmetric Rolling of Al-Mg-Si Alloy: Texture and Formability

Al-Mg-Si alloy was rolled asymmetrically at several temperatures to apply shear deformation, and the effects of the initial precipitate on shear deformation, texture evolution, formability, and plastic anisotropy were studied. Texture was analyzed using a EBSD, and the formability and plastic anisotropy of the specimen were evaluated using the value and value calculated from the plastic strain ratio (r-value) which was determined from the change in the length of the specimen during tensile deformation. Asymmetric rolling induces a larger equivalent strain than symmetric rolling, and the equivalent strain increases as the asymmetric rolling temperature increases. When a specimen with peak-aged initial precipitates was asymmetrically rolled, less shear deformation occurred at room temperature than in a solution-treated specimen without initial precipitates. In contrast, a larger shear deformation occurred at high temperatures (500°C). With asymmetric rolling at room temperature, the specimens without initial precipitates had higher formability and lower plasticity, while for asymmetric rolling at high temperature, the specimens with initial precipitates had higher formability and lower plastic anisotropy. This is due to the &lt;111&gt;//ND texture, such as {111}&lt;110&gt; and {111}&lt;112&gt; orientation that has similar and high r-values at 0°, 45°, and 90° to the rolling direction, developed by the shear deformation that occurred during asymmetric rolling.

Microstructure Evolution and Tempering Transformation Kinetics in a Secondary Hardened M50 Steel Subjected to Cold Ring Rolling

The microstructure evolution and tempering transformation kinetics of the M50 steel subjected to cold ring rolling (CRR) have been investigated. The results indicate that the brass R{110}<110> texture is weakened with the enhancement of the <111>//ND texture during CRR. Due to the increased low angle boundaries by CRR, the Ac1 temperature decreases while the carbon content and volume fraction of RA increase. During tempering, the activation energy of carbon atoms segregation and transition carbide precipitation decrease, while the activation energy of retained austenite (RA) decomposition increases after CRR. The kinetic analysis shows that the CRR is beneficial to the carbon atoms segregation during the beginning of tempering. Then, the CRR leads to the delay of the onset of transition carbide precipitation, but decreases the whole reaction time, which has been verified by the transmission electron microscopy (TEM) and hardness results. The lagging of transition carbide precipitation in the early stage is caused by the increased segregation trapping of carbon atoms, while the higher nucleation rate is responsible for the enhanced precipitation of transition carbide during the later stage. For the cementite formation, there are no significant changes in the predictive kinetics after the applied CRR. However, the kinetic transformation of RA decomposition is inhibited by the CRR, which is attributed to the higher carbon content and smaller grain size of RA. Additionally, the alloy carbides precipitation is also enhanced by the CRR process during secondary hardening.

Evolution of grain structure, texture and mechanical properties of a Mg–Zn–Zr alloy in bobbin friction stir welding

The evolutions of grain structure, microtexture and mechanical properties during bobbin friction stir welding of Mg-5.89 wt%Zn-0.61 wt%Zr alloy were investigated. The electron backscattered diffraction analyses revealed that the grain structure evolution was a complicated process dictated by continuous dynamic recrystallization but also involved geometrized effects of strain and {10–12} twinning. Local texture varied significantly from the parent metal to the weld nugget. With increased access to the weld nugget, the initial <0001>||ND texture gradually reoriented towards <0001>||TD and finally transformed into a near-<0001>||WD texture. Arising of the near-<0001>||WD texture was associated with the extensive continuous dynamic recrystallization and the reorientations of the recrystallized grains under the effect of shearing deformation introduced by the rotating stir probe. Microhardness distribution exhibited weak grain size dependence. Transverse tensile elongation of the joint was lower than that of the parent metal owing to strain localization in thermo-mechanically affect zone (TMAZ)/weld nugget zone (WNZ) interface region. Decomposition of β1' precipitates and texture evolutions in WNZ and TMAZ, as well as dislocations concentration and grain size mutation existed in the interface region corporately resulted in the inhomogeneous plastic deformation.