Multi-pass Hot Rolling Research Articles

The Influence of Multi-Pass Hot Rolling Parameters and Subsequent Heat Treatment on Microstructure and Mechanical Properties of Medium-Carbon Steel

The Influence of Multi-Pass Hot Rolling Parameters and Subsequent Heat Treatment on Microstructure and Mechanical Properties of Medium-Carbon Steel

Impact of hot rolling on the evolution of microstructure and mechanical properties of sintered commercially pure Ti compacts

While titanium (Ti) alloys offer significant advantages, such as high strength and corrosion resistance, their widespread utilization in various engineering sectors is hindered by their prohibitively high cost, which is attributed to expensive equipment and complex preparation processes. The present study centered on assessing the influence of multi-pass hot rolling, a commonly available industrial process, on the microstructure and mechanical properties of sintered powder metallurgy commercially pure Ti (cp-Ti). With increasing levels of accumulated deformation, the rolled materials exhibited a refined grain size, the formation of twins, and a reduced residual porosity, resulting in a tailored microstructure that enhanced the material's balance between strength and ductility. The ultimate tensile strength reached 574.8 MPa, with an elongation at break of 28.1%. The hardness peaked at 196.4 HV.

Hot Tensile Deformation Mechanism and Fracture Behavior of the ZW31/PMMC Laminate

In this work, a Mg-Zn-Y (ZW31) alloy with good plasticity was introduced into 10 μm 10 vol% SiCp/AZ91 composite materials (PMMCs) via the extrusion compound method, and then the ZW31/PMMC laminate was prepared via multi-pass hot rolling. The hot deformation mechanism and elevated temperature tensile fracture mechanism of ZW31/PMMC laminates were studied using the elevated temperature tensile test. The elevated temperature deformation mechanism is influenced by the strain rate. At low strain rates, grain boundary slip is the primary elevated temperature deformation mechanism of the ZW31/PMMC laminate. However, at high strain rates, the activation of pipeline diffusion is facilitated by the particle deformation zone (PDZ) in the PMMC layer with a high dislocation density, leading to the dominance of dislocation climbing as the main mechanism for elevated temperature deformation of the laminate. Additionally, the implementation of a ZW31/PMMC laminate structure effectively inhibits the initiation and propagation of cavities and microcracks within the laminate layer along the normal direction (ND) while simultaneously blunting crack tips via lattice dislocation emission toward the ZW31 layer. Upon cracking of the PMMC layer, stress concentration occurs in the fracture area of the ZW31 layer, ultimately resulting in necking-induced detachment.

The rolling schedule of Zircaloy-4 strip during multi-schedule and multi-pass hot rolling process

The rolling schedule of Zircaloy-4 strip during multi-schedule and multi-pass hot rolling process

The effect of rolling temperature on the microstructure and properties of multi pass rolled 7A04 aluminum alloy

The current research on 7-series aluminum alloys mainly focuses on solid solution and aging treatments, as well as the flow stress during the deformation process. There are limited researches on the influence of thermal deformation temperature on the microstructure and properties of the aluminum alloy during multi-pass hot rolling process. In this study, the as-cast 7A04 aluminum alloy was subjected to homogenization treatment, followed by multi-pass hot rolling. The effects of different deformation parameters on dislocation density were analyzed. Microstructural characterization of the deformed alloy was performed using optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and micro-hardness tester. The optimal microstructure of the deformed alloy was selected based on the size of recrystallization. Subsequently, the Deform–3D finite element simulation software was used to analyze the multi-pass hot rolling process. The influence of deformation parameters on the uniformity of equivalent strain distribution within the samples was investigated. The results showed that at the deformation temperature of 430 °C, a significant amount of recrystallized microstructure appeared in the alloy, resulting in the lowest dislocation density and a significant reduction in the quantity of coarse precipitates. Finite element numerical simulation revealed that the deformation temperature had a certain influence on the uniformity of strain distribution within the alloy. However, this influence was mostly eliminated when the deformation temperature exceeded 380 °C. Meanwhile, the distribution of strain within the alloy was found to be related to the temperature distribution.

Simultaneous enhancement of strength and ductility in friction stir welded AZ31 alloy via multi-pass hot-rolling and subsequent annealing

Friction stir welding (FSW) is a new solid-state joining process for joining light metals, such as magnesium (Mg) alloys. However, the texture-induced softening mechanism (in stir zone, SZ) tends to cause the worsening of mechanical properties in FSW Mg alloys. In this work, multi-pass hot-rolling and subsequent annealing is used to ameliorate the FSW AZ31 alloy plate. The results show that multi-pass hot-rolling leads to the c-axes of most grains in the SZ approximately perpendicular to the normal direction (ND) transforming into these almost parallel to the ND, accompanied with multiple twin types. After subsequent annealing, twins, as nucleation sites, promote the formation of new grains with off-basal texture, resulting in the weak basal texture. Compared with the FSW plate and the initial plate, the rolled-annealed FSW plate exhibits a relatively uniform hardness distribution and a “strength-ductility” synergy, which are mainly attributed to an appropriate texture feature and a homogeneous grain structure. This work provides a new idea for the development of new high-performance FSW Mg alloys.

Evolution of interface microstructure of rolled Al-Mg composite plate implanted with Er powder

Al-Mg composite plates has excellent mechanical properties and corrosion resistance, but the existence of hard and brittle phases at its interface greatly hinders its application and promotion. In this study, we reported for the first time that the formation of hard and brittle phase at the interface of Al-Mg composite plate was inhibited by implanting Er powder at the interface and multi-pass hot rolling process. The results show that the implantation of Er powder can effectively inhibit the formation of intermetallic compounds (IMC) at the interface of Al-Mg composite plates. Specifically, at the interface of Al-Mg composite plate without Er, there is 5–8 μm discontinuous IMC. But there is only 0.2 μm polycrystalline mixed structure at the interface of the Al-Mg composite plate with Er implantation. Meanwhile, compared with Al-Mg composite plate without Er, the implantation of Er can enhance the interface peeling strength of Al-Mg composite plates. Therefore, this provides a new idea for inhibiting the formation of IMC at Al-Mg interface and preparing advanced Al-Mg composites.

Interface Microstructure and Properties of Vacuum-Hot-Rolled 55#/316L Clad Rebars

The existing process for the preparation of cladded rebars is too complicated for large-scale industrial production. Therefore, this paper proposes a 55#/316L rebar preparation method based on vacuum hot rolling. The microstructure and mechanical properties of the composite interface of the rebar, along with the connecting technique, were studied using transmission electron microscopy, X-ray diffraction, and Vickers hardness testing. The obtained results showed that the minimum thickness of the 55#/316L rebar cladding was 0.25 mm, which was twice that of the M 329M/M 329-11 design standard used in the United States of America. Due to the diffusion of carbon, large numbers of second-phase particles were precipitated on the stainless-steel side, which resulted in intergranular chromium depletion. After multi-pass hot rolling, the minimum bonding strength of the composite interface reached 316.58 MPa, which was considerably higher than the specified value of 210 MPa. In addition, we designed three different types of rebar connection joints: sleeve, groove-welded, and bar-welded. According to the tensile test, the bar-welded joint had higher yield strength (385 MPa) and tensile strength (665 MPa) than the base rebar (376.6 MPa and 655 MPa), as well as a very high corrosion resistance.

Effects of rolling deformation on microstructure orientations and tensile properties of TiB/(TA15-Si) composites

To explore the orientation evolution and interfacial characteristics under the β-phase region, rolling deformation with different reduction ratios of 40– 90% was carried out by hot-pressing sintering and multi-pass hot rolling on a series of TiB whiskers reinforced Ti-6.5Al-2Zr-1Mo-1 V-0.3Si (TiB/(TA15-Si)). As rolling deformation increased, the matrix exhibited slight refining and distortion within lamella α + β, and a stronger T-type α texture was gradually formed. A portion of Burgers Orientation Relation (BOR) between parent β and α phases gradually disappeared due to a decrease in rolling temperature and post deformation after phase transformation. Meanwhile, TiB rotated and presented an intenser orientation of {100} 〈010〉. Silicides heterogeneously precipitated along the α/β phase boundaries both near and away from TiB. Silicide/matrix remained fine interfaces owing to resolution and reprecipitation. Finally, the ultimate strengths at room temperature were monotonously improved with the increase of deformation due to strong work hardening. And an anisotropy of tensile properties was found under large deformation. The composite tensioned along the transverse direction (TD) can exhibit higher strength and lower ductility due to mutual competition of TD strengthening by T-type texture and RD strengthening by TiB distribution, especially at 600 °C. The fracture paths of as-rolled composites were discussed in detail. • Matrix gradually formed an intenser T-type α texture mainly inherited from β by BOR. • TiB can form an obvious orientation of {100}<010 > but have a minor proportion of OR. • Most silicide/matrix interfaces possessed orientation relations in the β-rolled composites. • The ultrahigh ultimate strength of 1505 MPa was obtained in the 90%-rolled composite. • Composites along TD exhibited higher strength and lower ductility especially at 600 °C.

Microstructure evolution and recrystallization of Ti-44.5Al-3.8Nb-1Mo-0.2B alloy with different initial microstructure during hot pack rolling

Ti-44.5Al-3.8Nb-1Mo-0.2B alloy (TNM) sheets were prepared by hot rolling, and the effect of the initial microstructure on the process was discussed in this work. The as-received TNM alloy billets with nearly and fully lamellar structures were prepared by forging and casting processes (named M1 and M2), respectively. For the as-rolled sheets from M1, the fraction of recrystallization increased gradually with the decrease of reduction per pass based on GOS analysis. Compared with M1, M2 required a larger deformation to achieve complete recrystallization. Meanwhile, the as-rolled sheets from M2 possessed a smaller grain size than that from M1. In addition, the γ-DRX behavior during the multi-pass hot rolling was discussed, and the DDRX was found to play the dominant role in this process. The phase transformation of β/β0 → α occurred in the 1200 °C rolling process. It was presumed that this transformation was promoted by increasing the rolling temperature, therefore, the volume fraction of the β0 phase decreased. The α2 lath decomposed gradually with the increasing of rolling temperature from 1200 °C to 1250 °C, simultaneously, the combination of the adjacent γ laths resulted in the coarsening of γ lath.

Effect of hot rolling process parameters on the microstructure and mechanical properties of continuously cooled low-carbon high-strength low-alloy (HSLA) steel

Abstract In this work, high-strength low-alloy (HSLA) steel with 0.22 wt% carbon was produced in laboratory scale and hot rolled with a total deformation of 42% via 4, 5, or 6 passes. After multipass hot rolling process, samples were examined either in as-rolled (AR) or as-rolled and heat-treated (ARH) conditions. The results indicated that microstructural and mechanical properties of HSLA steels are influenced by hot rolling conditions for both cases. It was observed that strength values in AR samples have a tendency to increase with increment in rolling pass number. In contrast to AR samples, it was seen that the mechanical properties were slightly decreased in ARH samples that were austenitized at 1150 °C for 45 min and then cooled in still air. Microstructural investigations showed that finer precipitates in AR samples are obviously more than that of ARH samples, as an evidence for higher strength results by precipitation hardening. In addition to precipitation strengthening, refinement of lath bainite and amount of blocky martensite/austenite in AR samples favor the increase in strength.

Precipitation behavior of second phases and mechanical property of Fe–Cr–Al–Mo–Nb/Ta/Zr alloy during aging at 1073 K

The precipitation behavior of second phases and mechanical property of Fe–13.5Cr–4.7Al–2.1Mo–0.5Nb–0.8Ta–0.2Zr (wt.%) alloy was investigated in the present study. Alloy ingots were fabricated by vacuum arc melting and multi-pass hot rolling, then solid-solutionized at 1473 K for 2 h and aged at 1073 K for 0–24 h. In the initial aging process, the precipitated phase were mainly composed of spherical Laves Fe2M (M = Nb, Ta, Zr) and Fe23Zr6 particles. With increasing the aging time, the morphology of Laves phase particles changed gradually from the spherical shape to short-rod shape, and then to granular shape. While the Fe23Zr6 particles still remain spherical during the whole aging process. It is closely related to the lattice misfit between precipitated phase and the BCC matrix, in which the lattice misfit of ε = 1.3% between Fe2M and BCC is remarkably larger than that (ε = 0.2%) between Fe23Zr6 and BCC, leading to a significant change in Fe2M particles. Moreover, the morphology of Fe2M particles in solutionized-aged state is also different from that in rolled-aged state. Consequently, the yield strength (σYS = 410 MPa) of the solutionized-aged alloy is much lower than that (σYS = 560 MPa) of the rolled-aged alloy, which is ascribed to that the strengthening contribution (σor = 48 MPa) induced by short-rod particles is less than that (σor = 153 MPa) of spherical particles.

Minimizing thickness variation in monolithic U-10Mo fuel foil and Zr interlayer during hot rolling: A microstructure-based finite element method analysis

Low-enriched uranium alloyed with 10 wt. % molybdenum (U-10Mo) has been identified as a promising alternative to highly enriched uranium fuel for the United States’ high performance research reactors. The monolithic U-10Mo fuel plate consists of a metallic U-10Mo fuel foil with a 25 µm Zr interlayer and a relatively thick cladding of aluminum alloy 6061. The Zr interlayer is typically applied during the hot co-rolling process, and this process dictates the uniformity of the Zr interlayer. Thickness variation observed in the U-10Mo and Zr interlayer has been attributed to several sources: the initial grain size of the U-10Mo castings, can materials, rolling temperature, inhomogeneous molybdenum content, and porosity in the cast U-10Mo. This thickness variation limits the ability to meet the dimensional specification; thus, a better understanding of the factors causing the nonuniform thickness is needed. In this work, we used a novel, microstructure-based finite element method to model the hot rolling process to address these concerns. Grain microstructures in U-10Mo were tessellated and explicitly considered in the finite element model. Each grain was assigned a random material property to mimic the grain strength variations induced by different grain orientations. Simulations were performed using six steel can thicknesses, four grain sizes, and with or without a Zr interlayer to investigate the influences of those variables on the thickness nonuniformity. The simulation results showed that a thinner steel can and finer U-10Mo grain size reduce thickness variations in both the U-10Mo fuel foil and Zr interlayer. The direct findings from the simulations and analysis can be used to optimize the hot rolling schedule, reduce fabrication defects, and meet the dimensional specifications. The proposed microstructure-based finite element model can be also coupled with experimental microstructure characterization data, images, and models to simulate multi-pass hot rolling.

Improving the ductility of Mg-2.5Nd-0.5Zn-0.5Zr alloy by multi-pass hot rolling

Fine-grained, high-strength and high-ductility Mg-2.5Nd-0.5Zn-0.5Zr alloy sheets were prepared by multi-pass hot rolling with ultimate tensile strength of 311.9 MPa, yield strength of 272.4 MPa, elongation of 17.1%, and the average grain size of 4.25 μm. After multi-pass hot rolling, all plates showed the characteristics of bimodal rolling direction-tilt texture (with the basal poles tilting at about ±15–20° form normal direction towards rolling direction). With the increase of rolling passes, the basal texture strength decreased gradually, which was 9.5 (1st pass), 7.5 (2nd pass) and 5.4 (3rd pass), respectively. The ductility improvement was the result of the interaction of texture weakening, basal slip and non-basal slip actuation.

EBSD characterization of Al7075/graphene nanoplates/carbon nanotubes composites processed through post-deformation annealing

The effects of the post-deformation annealing on the microstructural evolution of hot rolled Al7075 matrix composites reinforced with CNTs and GNPs were investigated. The multi-pass hot rolling was applied on the stir cast samples. Annealing was then applied to the composites at 450 °C for 4 h. Microstructural evolution was examined by SEM, EDS, and EBSD techniques. EBSD data showed that the addition of 0.87 vol.% (GNPs + CNTs) significantly inhibited the occurrence of recrystallization. Also, in the composite with 0.96 vol.% CNTs, recrystallization was partially inhibited. Whereas, in composites with 0.92 vol.% of GNPs, the occurrence of recrystallization through particle stimulated nucleation (PSN) mechanism was significantly accelerated. The volume fraction of recrystallized grains depends significantly on the occurrence of PSN in the presence of reinforcements. The intensity and type of the main components of the texture as well as the FCC fibers depend on the type of reinforcement.

Achieving prominent strengthening efficiency of graphene nanosheets in Al matrix composites by hybrid deformation

Achieving uniform reinforcement dispersion and strong interfacial bonding remains challenging to increase the strengthening efficiency in advanced metal matrix composites (MMCs). In this work, we report the prominent strengthening efficiency in graphene nanosheet reinforced Al matrix (GNS/Al) composites fabricated via hybrid deformation combining hot extrusion and multi-pass hot rolling (MPHR). Results show that most GNS-rich zones in extruded GNS/Al composites were eliminated by MPHR, leading to an even layer-distribution of GNSs aligning along the Al grains, which initiates grain recrystallization and promotes dislocation accumulation for a high strain hardening of the composites. Moreover, the shear stress induced by MPHR was revealed to exfoliate overlapped GNSs to attach with Al and enhance the formation of boundary-like defects/disorders at the edge of GNSs, which promotes Al–C interdiffusion and generates the typically infiltrated Al-GNS interfaces featured by transition zones. Such unique interface structure exhibits a high interfacial shear strength, enabling the effective load transfer between GNSs and Al. It is confirmed that the fine distribution of GNS and robust Al-GNS interfacial cohesion contribute to the remarkable strengthening efficiency of GNSs. The present work paves a new way to disperse GNSs and tune interface structures for enhancing mechanical performance of Al matrix composites.

Multi-Scale Modeling of Microstructure Evolution during Multi-Pass Hot-Rolling and Cooling Process.

In this work, a 6-pass hot-rolling process followed by air cooling is studied by means of a coupled multi-scale simulation approach. The finite element method (FEM) is utilized to obtain macroscale thermomechanical parameters including temperature and strain rate. The microstructure evolution during the recrystallization and austenite (γ) to ferrite (α) transformation is simulated by a mesoscale cellular automaton (CA) model. The solute drag effect is included in the CA model to take into account the influence of manganese on the γ/α interface migration. The driving force for α-phase nucleation and growth also involves the contribution of the deformation stored energy inherited from hot-rolling. The simulation renders a clear visualization of the evolving grain structure during a multi-pass hot-rolling process. The variations of the nonuniform, deformation-stored energy field and carbon concentration field are also reproduced. A detailed analysis demonstrates how the parameters, including strain rate, grain size, temperature, and inter-pass time, influence the different mechanisms of recrystallization. Grain refinement induced by recrystallization and the γ→α phase transformation is also quantified. The simulated final α-fraction and the average α-grain size agree reasonably well with the experimental microstructure.

Hot Deformation Behavior and Hot Rolling Properties of a Nano-Y2O3 Addition Near-α Titanium Alloy

The hot deformation behavior and hot rolling based on the hot processing map of a nano-Y2O3 addition near-α titanium alloy were investigated. The isothermal compression tests were conducted at various deformation temperatures (950⁠–1070 °C) and strain rates (0.001–1 s−1), up to a true strain of 1.2. The flow stress was strongly dependent on deformation temperature and strain rate, decreasing with increased temperature and decreased strain rate. The average activation energy was 657.8 kJ/mol and 405.9 kJ/mol in (α + β) and β region, respectively. The high activation energy and peak stress were contributed to the Y2O3 particles and refractory elements comparing with other alloys and composites. The deformation mechanisms in the (α + β) region were dynamic recovery and spheroidization of α phase, while the β phase field was mainly controlled by the dynamic recrystallization and dynamic recovery of β grains. Moreover, the constitutive equation based on Norton–Hoff equation and hot processing map were also obtained. Through the optimal processing window determined by the hot processing map at true strains of 0.2, 0.4 and 0.6, the alloy sheet with multi-pass hot rolling (1050 °C/0.03–1 s−1) was received directly from the as-cast alloy. The ultimate tensile strength and yield strength of the alloy sheet were 1168 MPa and 1091 MPa at room temperature, and 642 MPa and 535 MPa at 650 °C, respectively, which performs some advantages in current research.

Enhanced ductility of Mg–1Zn–0.2Zr alloy with dilute Ca addition achieved by activation of non-basal slip and twinning

Wrought Mg–Zn–Zr alloys with a strong basal texture usually exhibit highly anisotropic plastic behavior, resulting in premature fracture during deformation at room temperature. In the present study, we prepared a Mg–1Zn–0.2Zr (ZK10) alloy sheet by multi-pass hot rolling and annealing, tailoring the basal texture and reducing the plastic anisotropy with the addition of dilute Ca. Microstructural characterizations of the tensile-deformed alloys show that pyramidal <c+a> slip and 101¯2 twinning are more easily formed in the Ca-containing alloy compared with those in the ZK10 alloy. The weakened basal texture involving Ca addition leads to promoted activation of 101¯2 twinning, without significant impact on the Schmid factor distribution of pyramidal <c+a> slip. Simulation results of the visco-plasticity self-consistent model further indicate that Ca reduces the ratio of critical resolved shear stress for pyramidal <c+a> slip and 101¯2 twinning versus basal <a> slip, leading to a significant improvement in ductility. This work may provide a new strategy to develop wrought Mg alloys with enhanced ductility.

Effect of hot rolling on microstructure and tribology behaviors of Ti−50.8Ni alloy

Abstract We link different microstructures to tribological behaviors of Ti−50.8Ni (mole fraction, %) in reciprocating mode at room temperature (20 °C). Hot-rolled alloys with B2 phase exhibit lower coefficient of friction and wear rate compared to the ones with B19′. Stress-induced martensitic transformation occurs during sliding. However, multi-pass hot rolling weakens the wear resistance. In this study, microstructures were characterized through electron backscatter diffraction and transmission electron microscopy (EBSD/TEM). From the concept of energy conservation, the effects of weak intensity of hot-rolled textures on the wear resistance are minimal. Based on the result that the alloy with a higher portion of coincidence site lattice boundaries shows lower martensitic start transformation temperature in the DSC curves than that with higher KAM values, the delay on B2-B19′ transformation from {112}B2 twins outweighs dislocations. Moreover, widely distributed small-angle grain boundaries owing to dynamic recovery improve the wear resistance effectively compared to those that are well-recrystallized.