Multi-pass Caliber Rolling Research Articles

Microstructural evolution and mechanical properties of pure zinc subjected to extrusion and caliber rolling

This study investigates the microstructural evolution and mechanical properties of pure zinc (Zn) during extrusion and multi-pass caliber rolling (CR). Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyses indicate that plastic deformation induces dynamic recrystallization (DRX), resulting in the formation of numerous low angle grain boundaries (LAGBs) and substructures. In particular, significant grain refinement (∼1.6 μm) is achieved with the texture deviating 30 ± 5° from the <0001> direction. The as-extruded pure Zn exhibits a yield strength (YS) of 130 MPa, an ultimate tensile strength (UTS) of 151 MPa, and an elongation (EL.) of 8.8 %, respectively. Subsequent caliber rolling significantly improved these mechanical properties (i.e., YS: 225 MPa; UTS: 301 MPa; EL.: 31%) due to the combined effect of grain refinement, dislocations and texture strengthening. In addition, the deformation mechanism shifts from an initial influence of both dislocations and twins to a predominance of dislocations alone.

Microstructural evolution and tensile property enhancement of low-cost Fe-24Mn-22Ni-12Cr medium-entropy alloy by cryogenic caliber rolling

High- and medium-entropy alloys (HEAs/MEAs) have been extensively developed over the last two decades owing to their superior mechanical performances from cryogenic to high temperatures. However, the high raw material costs of recently developed HEAs/MEAs limit their practical applications. In this study, we designed cost-effective Co-free, Fe-based MEAs based on thermodynamic calculations. To enhance the yield strength of the MEA, multi-pass caliber rolling, which has been recognized for improving the yield strength, was implemented at room and cryogenic temperatures. The yield strengths substantially improved from 229 MPa for the annealed specimen to 862 MPa for the sample caliber-rolled at cryogenic temperatures while maintaining good ductility. Based on the above findings, the effects of multi-pass caliber rolling at cryogenic temperatures on the microstructural evolution, mechanical properties, and deformation behavior are discussed.

Predicting the Effect of Processing Parameters on Caliber-Rolled Mg Alloys through Machine Learning

The multi-pass caliber rolling (MPCR) of Mg alloy has attracted much attention due to its engineering and manufacturing advantages. The MPCR process induces a unique microhardness variation, which has only been predicted using a finite element analysis thus far. This study employed machine learning as an alternative method of microhardness prediction for the first time. For this purpose, two machine-learning approaches were evaluated: the artificial neural network (ANN) approach and that aided by generative adversarial networks (GANs). These approaches predicted microhardness variation in the most difficult case (i.e., after the final-pass MPCR deformation). The machine-learning approaches provided a good prediction for the center area of the cross-section, because the prediction was relatively easy due to the small deviation in microhardness. In contrast, the ANN failed to anticipate the shifted hardness variation in the side sections, leading to a low predictability. Such an issue was effectively improved by integrating the GAN with the ANN.

Microstructure and mechanical properties of caliber rolled AlN/AZ91 composite

The multi-pass caliber rolling was applied to in-situ AlN/AZ91 composite rods, and the yield strength of 295.3 MPa, ultimate tensile strength of 384.7 MPa, fracture elongation of 12.3% and a good surface morphology were obtained under the reduction ratio of 78%. The results showed that the grains of the caliber rolled AlN/AZ91 composite rods were remarkably refined due to the occurrence of dynamic recrystallization (DRX), while the in-situ AlN reinforcements induced the nucleation of {101‾2} extension twins, and preferentially promoted the formation of extension twin-induced DRX before discontinuous DRX. Especially, twinning-induced DRX weakened the texture more effectively compared with discontinuous DRX. In addition, it was also found that the increased yield strength was mainly attributed to solid solution atoms, twinning-induced DRX, discontinuous DRX, high density dislocations and nano-sized γ-Mg17Al12 precipitates in the in-situ AlN/AZ91 composite rods, while the high ductility was mainly ascribed to grain size refinement, weakened texture and the activation of non-basal slip systems at room temperature.

Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

Ultrafine elongated grain (UFEG) structure with a strong <110>//rolling direction fiber texture was created for a 0.4%C-2%Si-1%Cr-1%Mo steel (mass%) through deformation of tempered martensite using multi-pass caliber rolling at 773 K with a rolling reduction of 78% (i.e. warm tempforming). Annealing of the warm tempformed steel at 843 K enhanced delamination toughening at lower temperatures without a significant loss of tensile strength at 1.8 GPa. It was suggested that delamination toughening was controlled through the precipitation of nanoscale Mo-rich precipitates in the UFEG structure.

Microstructural Evolution and Mechanical Properties of Pure Aluminum upon Multi-Pass Caliber Rolling.

The paper presents the microstructure and mechanical property of pure aluminum (Al) fabricated by multi-pass caliber rolling at room temperature. The finite element modeling (FEM) simulation was performed to explore the changes in rolling force, effective stress and strain, and temperature under various rolling passes. As the number of rolling passes increased, the overall temperature, effective stress, and strain gradually increased, while the maximum rolling force decreased. In addition, due to the dynamic recrystallization (DRX), the average grain size reduced from 1 mm to 14 µm with the increase in rolling passes. The dislocation density increased and it gradually evolved into the high-angle grain boundaries (HAGBs). Moreover, the initial cubic texture rotated to the brass component and finally changed to a mixture of Cube and Brass types. The highest tensile yield strength (TYS), ultimate tensile strength (UTS) and elongation (El.) of caliber rolled pure Al (116 MPa, 135 MPa, and 17%, respectively) can be achieved after 13 rolling passes, which mainly attributed to grain refinement.

Upsizing high-strength fail-safe steel through warm tempforming

Fail-safe (FS) steel is designed with enhanced fracture toughness through the crack deflection mechanism in an anisotropic microstructure. In this study, commercial boron (B)-bearing medium-carbon low-alloy steel bars with a cross-sectional area of 1390 mm2 were water-quenched and tempered at temperatures between 400 °C and 500 °C, followed by multi-pass caliber-rolling (i.e., warm tempforming). Tensile, Charpy V-notch (CVN) impact, and hydrogen embrittlement (HE) properties of the warm tempformed samples were investigated and compared with the rolling reductions of 45–92% to optimize the rolling conditions for upsizing the FS steel. Warm tempforming at 400 °C with a rolling reduction of 66% successfully produced an FS steel bar with a large cross-sectional area of 470 mm2. The evolution of a heterogeneous and anisotropic ultrafine-grained structure through the warm deformation of tempered martensite and pearlite generated an excellent combination of CVN toughness and HE resistance at the ultimate tensile strength of 1400 MPa. Delayed fracture resistance of the FS steels was also evaluated to be far superior to those of conventionally quenched and tempered steels, based on the balance between the HE susceptibility and hydrogen entry. Furthermore, it was observed that excessive warm tempforming to a rolling reduction of 92% tended to degrade the tensile elongation and HE resistance. The mechanism of the variations in mechanical properties during warm tempforming is discussed in association with the microstructural evolution.

Microstructural Evolution of Multi-Pass Caliber-Rolled Mg–Sn and Mg–Sn–Mn Alloys

Multi-pass caliber rolling has proven its vast potential for ultrafine-scale grain refinement and mass production of various metals. Nevertheless, the studies related to Mg alloys have primarily focused only on a few commercial materials, such as AZ31 and ZK60 Mg alloys. This is the first study to investigate caliber-rolled Mg–1Sn (TM10) and Mg–1Sn–1Mn (TM11) alloys. Specifically, this work aims to elucidate the microstructural characteristics of these alloys, including grain refinement, recrystallization, and texture development. Such features were discussed from the viewpoints of alloying effects (i.e., Sn and Mn) and mechanical effects (i.e., caliber-rolling strains). The combination of the addition of Mn and high-redundant strain results in effective grain refinement of the caliber-rolled TM11 Mg alloys. In addition, both TM10 and TM11 Mg alloys exhibit a unique split basal texture, wherein the basal poles are tilted in the plane normal to the rolling direction.

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

Our strategy is to enhance the fracture property of ultra-high-strength low-alloy steels with a yield strength of 1.4 GPa or over by arresting the propagation of brittle cracks in hierarchical, anisotropic, and ultrafine-grained structures. This provides a fail-safe design in addition to suppressing crack initiation. The present article reviews the strength, ductility, toughness, and delayed fracture resistance of ultra-high-strength low-alloy steels with ultrafine elongated grain structures processed by the deformation of tempered martensitic structures at elevated temperatures (referred to as warm tempforming). The evolution of heterogeneous microstructures during warm tempforming using multi-pass caliber rolling is discussed, as are the microstructural factors controlling the strength and fracture properties of warm tempformed steels. Furthermore, we apply warm tempformed steels with ultrafine elongated grain structures to the fabrication of ultra-high-strength bolts.

Effect of Multi-Pass Caliber Rolling on Dilute Extruded Mg-Bi-Ca Alloy

A Mg-1.32Bi-0.72Ca (BX11) alloy having bimodal grain structure was successfully prepared by a novel processing route of combining extrusion and three-pass caliber rolling. The first extruded and then caliber-rolled (E-CRed) alloy demonstrates a necklace-like grain structure with ultrafine grains formed around the microscale deformed grains, which is remarkably different from the uniform microstructure of the as-extruded alloy. In addition, the E-CRed BX11 alloy exhibits strong basal texture which is mainly original from the microscale deformed grains. Furthermore, the E-CRed BX11 alloy demonstrates excellent comprehensive mechanical properties, with an ultra-high yield strength of 351 MPa and a good elongation to failure of 13.2%. The significant strength improvement can be mainly attributed to the significant grain refinement and much stronger basal texture compared with the as-extruded sample.

Tailoring strength-ductility balance of caliber-rolled AZ31 Mg alloy through subsequent annealing

• Annealing effect was studied with respect to caliber-rolled AZ31 Mg alloys. • Low-temperature annealing gave rise to trade-off of strength and ductility. • High-temperature annealing led to simultaneous deterioration in strength and ductility. • The deterioration is attributed to a grain growth and resultant mechanical twinning. Recently, multi-pass caliber rolling has been shown to be effective for Mg alloys. This study investigated the effect of subsequent annealing on the mechanical properties of a caliber-rolled AZ31 Mg alloy to modulate the strength-ductility relationship. This annealing gave rise to different trends in mechanical properties depending on the temperature regime. Low-temperature annealing ( T ≤ 473 K) exhibited a typical trade-off relationship, where an increase in annealing temperature resulted in increased ductility but decreased strength and hardness. Such a heat treatment did not degrade the high strength-ductility balance of the caliber-rolled alloy, suggesting that the mechanical properties could be tailored for different potential applications. In contrast, high-temperature annealing ( T > 473 K) caused a simultaneous deterioration in strength, hardness, and ductility with increasing annealing temperature. These differences are discussed in terms of the varying microstructural features under the different investigated annealing regimes.

Improved tensile properties of AZ31 Mg alloy subjected to various caliber-rolling strains

Abstract A multi-pass caliber rolling has attracted attentions as an alternative to severe plastic deformation processes. The present study enhanced strength and ductility of AZ31 Mg alloy simultaneously through the application of caliber rolling. The improving trends in tensile properties were interpreted with various caliber-rolling strains. The oval/circular-shaped calibers imposed a high plastic strain at the center of cross-section, leading to effective grain refinement to submicron scale. This work also confirmed the texture randomizing effect of caliber rolling. Such microstructural evolutions gave rise to the fabrication of high-strength material. Moreover, the caliber-rolled AZ31 Mg alloys exhibited an improvement in ductility as compared to the as-received sheet-rolled material. This was discussed in terms of activation of non-basal slip systems and suppression of mechanical twinning. This study successfully proved the possibility of caliber rolling to produce a bulk Mg rod with enhanced tensile properties.

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

Our strategy to enhance fracture properties of ultra-high-strength low-alloy steel with a yield strength of 1.4 GPa or over is to arrest the propagation of brittle crack in a hierarchical, anisotropic and ultrafine grain structure designed to be fail-safe, in addition to suppressing the crack initiation. The present article reviews strength, ductility, toughness and delayed fracture resistance of ultra-high-strength low-alloy steel with an ultrafine elongated grain structure that was processed by deformation of a tempered martensitic structure at an elevated temperature (warm tempforming). The evolution of heterogenous microstructure during warm tempforming using multi-pass caliber rolling and the microstructural factors controlling the strength and the fracture properties of the warm tempformed steels are discussed. Furthermore, we introduce the application of the warm tempformed steel with an ultrafine elongated grain structure to ultra-high-strength bolt.

Microstructure and Mechanical Properties of Mg/Al Clad Bars with Ni Interlayer Processed by Compound Castings and Multi-Pass Caliber Rolling

Magnesium/aluminium clad bars were fabricated by compound casting and multi-pass warm caliber rolling. A Ni interlayer prepared using a plasma spraying process was inserted between the parent metals to improve the interfacial characteristics during the casting process, and the effect of caliber rolling on the evolution of the interfacial microstructure and mechanical properties of the Mg/Ni/Al composites was investigated. The results show that the formation of Mg-Al intermetallic phases was impeded effectively by the Ni interlayer and a typical AZ31/Ni/6061 multilayer structure with metallurgical bonding was formed during the compound casting process. In addition, an inhomogeneous strain distribution in the AZ31 and 6061 alloys were characterized during the rolling process. The AZ31 clad layer accommodated a larger proportion of the plastic strain during the initial passes, while the strain in the Mg core layer increased with increasing number of passes. The Ni interlayer fragmented during the rolling process, and transformed into the dispersed particles at the interface. Meanwhile, the fresh AZ31 and 6061 base alloys squeezed out and bonded together under the rolling force, and a well-bonded interface with no visible defects was formed.

Ultrafine-grained CoCrFeMnNi high-entropy alloy produced by cryogenic multi-pass caliber rolling

The ultrafine-grained (UFG) structure (∼100 nm) of CoCrFeMnNi high-entropy alloy was achieved using cryogenic multi-pass caliber rolling at 77 K to impose less deformation (ε = 1) compared to severe plastic deformation (SPD, ε > 4). Highly increased twinning activity at 77 K caused the grain interiors to fragment significantly, so UFG structure could be induced without imposing SPD. Intersected twin morphology and secondary twins played a key role in twinning-induced grain refinement to achieve UFG structure. The processed material showed an exceptional high yield strength of ∼1.5 GPa with a reasonable fracture elongation of ∼10% at room temperature.

Cryogenic Mechanical Properties of Warm Multi-Pass Caliber-Rolled Fine-Grained Titanium Alloys: Ti-6Al-4V (Normal and ELI Grades) and VT14

The effect of microstructural refinement and the β phase fraction, V β, on the mechanical properties at cryogenic temperatures (up to 20 K) of two commercially important aerospace titanium alloys: Ti-6Al-4V (normal as well as extra low interstitial grades) and VT14 was examined. Multi-pass caliber rolling in the temperature range of 973 K to 1223 K (700 °C to 950 °C) was employed to refine the microstructure, as V β was found to increase nonlinearly with the rolling temperature. Detailed microstructural characterization of the alloys after caliber rolling was carried out using optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscopy (TEM). Complete spheroidization of the primary α laths along with formation of bimodal microstructure occurred when the alloys are rolled at temperatures above 1123 K (850 °C). For rolling temperatures less than 1123 K (850 °C), complete fragmentation of the β phase with limited spheroidization of α laths was observed. The microstructural refinement due to caliber rolling was found to significantly enhance the strength with no penalty on ductility both at room and cryogenic temperatures. This was attributed to a complex interplay between microstructural refinement and reduced transformed β phase fraction. TEM suggests that the serrated stress–strain responses observed in the post-yield deformation regime of specimens tested at 20 K were due to the activation of $$ \left\{ {10\bar{1}2} \right\} $$ tensile twins.

Warm tempforming effect on the hydrogen embrittlement of 1.8-GPa-class ultra-high-strength low-alloy steel

Hydrogen embrittlement properties were investigated for 1.8-GPa-class ultra-high strength low-alloy steels by means of slow-strain-rate test of the pre-hydrogen-charged notched specimens, accelerated atmospheric corrosion test, and thermal desorption spectrometry. A Mo-bearing steel with a chemical composition of Fe-0.4C-2Si-1Cr-1Mo (mass%) was quenched and tempered at 773K for 1h and then deformed by multi-pass caliber rolling with a cumulative rolling reduction of 76% at 773K to create an ultrafine elongated grain structure with a strong <110>//rolling direction fiber texture. The warm tempformed (TF) sample was subsequently annealed for 1h to clarify the hydrogen trapping effect of nanoscale carbides relative to additive Mo. When the TF sample was annealed at 843K (TFA sample), the hydrogen absorption capacity was enhanced significantly through the formation of nanoscale Mo-rich precipitates in the matrix of ultrafine elongated grains. A high potential for hydrogen embrittlement resistance in an atmospheric corrosion environment was demonstrated in both the TF and TFA samples with an ultra-high tensile strength of 1.8GPa. The TF and TFA samples were much less susceptible to hydrogen embrittlement as compared to the tempered martensitic samples at an ultra-high tensile strength of 1.8GPa. The hydrogen trapping states and the high resistance to hydrogen embrittlement in the TF and TFA samples are discussed in association with the anisotropic, ultrafine grained structures with the nanoscale Mo-rich precipitates.

A thermomechanical process to achieve mechanical properties comparable to those of quenched-tempered medium-C steel

In quenching-tempering (QT), limiting factors such as hardenability, temper embrittlement, quenchant pollution, and quenching distortion and cracks have to be considered. In order to avoid these limitations, we propose a thermomechanical process to fabricate spheroidized cementite in ferrite matrix in a medium-C steel with mechanical properties that are comparable to QT, which is based on multi-pass caliber rolling at start rolling temperature (SRT) in two-phase α+γ region. In this study, the effect of the SRT (in the range from 720°C to 820°C) on microstructures, mechanical properties, and impact fracture behavior were investigated by using 45 steel as experimental material. Results indicate that the rolling can result in a fibrous “ferrite + pearlite” microstructure. If the SRT is at 740°C to 760°C, then the multi-sized ferrite grains with intensive α-fiber texture (<101>//RD) and the completely spheroidized cementite distributed in the fine ferrite grain region can be formed. The spheroidization of cementite is attributed to the deformation-induced divorced eutectoid transformation. The mechanical properties significantly exceeded the requirements of the Chinese National Standard GB/T 699−1999 for quenched-tempered 45 steel. When the SRT decreased from 780°C to 820°C to 720°C to 760°C, the Charpy impact absorbed energy (AKV) increased from approximately 50J to 100J, and the impact fracture behavior changes from dimple along with some splits into quasi-cleavage. This thermomechanical process is a potential alternative to QT of medium-C steels.

マルチパス溝ロール圧延加工によるAZ31合金の結晶組織制御

Energy saving is desired in development of transportation vehicles by adapting lightweight materials like fuel efficiency with magnesium alloys. However, magnesium has insufficient mechanical properties. Therefore grain refinement was conducted for AZ31 (Mg-3Al-1Zn-0.2Mn, by mass %) alloy by severe plastic working with caliber rolling to enhance its toughness and strength. The most suitable process in caliber rolling was elucidated, and the resultant mechanical properties were evaluated by quasi-static tensile test and impact three-point bending test. As a result, a strain distribution by FEM showed that multipass caliber rolling is the most suitable process. Tensile yield strength was increased to more than 270 MPa after the 12 pass rolling. The absorbed energy until a crack reached 0.4mm was increased by a factor of four from that of the initial as-cast state.

Delamination toughening assisted by phosphorus in medium-carbon low-alloy steels with ultrafine elongated grain structures

The effect of phosphorus (P) on delamination toughening was examined for 0.4%C–1%Cr–0.7%Mn–0.2%Mo steels (mass%) comprised of ultrafine elongated grain (UFEG) structures with strong <110>//rolling direction (RD) fiber textures. The UFEG structures evolved through the plastic deformation of tempered martensitic structures by multi-pass caliber rolling at a temperature of 773K (warm tempforming, WTF). The addition of P, up to 0.093% (mass%), had little influence on the evolution of the UFEG structure and the strength of the steels. Although the tensile ductility and upper-shelf energy showed a slight tendency to decrease as the P concentration increased from 0.001% to 0.093%, the delamination perpendicular to the notch orientation of the impact specimens was pronounced over a wider temperature range. As a result of delamination, the 0.093% P-doped steel exhibited a significant inverse temperature dependence of toughness at temperatures from 250K to 350K. The delamination toughening was dominated by the UFEG structure, and further assisted by the phosphorus segregation. It was considered that the formation of distinct P segregation bands, which presented a structure consisting of brittle and ductile layers, may be especially effective in accelerating delamination and improving toughness in the P-doped steel with an UFEG structure.