Hot Rolling Research Articles

Natural convection and variable fluid properties of tangent hyperbolic nanofluid flow with Cattaneo-Christov theories and heat generation

The main aim behind this work is that we have to determine the enhancement that happens in thermal conductivity by using the Buongiorno model of nanofluid when the nanofluid particles are added to the tangent hyperbolic base fluid moving above the stretched surface. The viscosity of tangent hyperbolic nanofluid is assumed to be temperature-dependent. The modified form of the Fourier law of heat conduction motivated us; therefore, the Cattaneo-Christov heat and mass flux model is considered to observe its significance for heat and mass transport. The chemical reaction and heat generation are also considered to determine their influence on temperature and concentration gradients. This study is crucial because of its application in industrial manufacturing processes such as the coating of wire, the thinning of copper, the production of paper, photographic films, hot rolling, and the purification of crude oil. In electronic cooling systems, the efficient dissipation of heat in smartphones, computers, and data centers is critical to preventing overheating. Nanofluids, with their enhanced thermal properties, can significantly improve heat transfer rates, ensuring better performance, stability, and energy savings. The partial governing equations arising from fluid flow, mass, and heat transfer are transformed into ordinary differential equations via appropriate similarity variables. The obtained ordinary differential equations are solved numerically by using the Runge-Kutta Fehlberg method in the MATLAB software. The effects of the emerging parameters are represented through graphs. According to the results, the velocity profile upsurges due to the natural convection parameters and curvature parameter, while the power law index declines the velocity profile. As the Brownian motion coefficient rises, the concentration profile diminishes while the temperature profile increases. Both the concentration and temperature profiles increase for larger values of the thermophoresis parameter. The concentration profile declines for larger values of chemical reaction parameters, and enhancement happens in the temperature region.

Analysis of fatigue damage of hot rolling work rolls coupled with wear effect

During the hot rolling process, the work roll experiences cyclic contact stress due to the deformation of the strip steel, as well as thermal stress from periodic heating and cooling. The surface failure of the work roll results from the combined effects of wear and fatigue damage. This study proposes a comprehensive approach to analyzing coupled wear and fatigue damage using a method based on the Manson-Coffin equation, modified slope formula, and the Miner criterion. Finite element models were developed to simulate simplified heat transfer and thermal coupling, taking into account the actual rolling parameters and high-temperature material properties of the work roll. The evolution of the physical field of the work roll during the rolling process was analyzed. The analysis of these models revealed that the maximum strain on the work roll occurred at the rolling exit and was predominantly influenced by temperature. The effects of rolling speed and temperature on work roll strain varied, with fatigue damage being significantly reduced when wear was considered compared to scenarios where wear was not accounted for, under the same number of cycles.

Precipitation behavior of Al2CuLi, Al3Li and Al3Zr in A2060 aluminum-lithium alloys and mechanical behavior of their microinterfaces

The precipitated phase of Al-Li alloy is a major factor determining the properties of Al-Li alloy. Al2CuLi phase(T1 phase), Al3Li phase and Al3Zr phase are all important enhanced precipitated phases. In this paper, the properties of the matrix, the precipitated phase and the interface formed between each phase are calculated. The (111) crystal face of Al, (111) of Al3Li, (111) of Al3Zr, and (210) of Al2CuLi are the surfaces with the lowest surface energy of these phases. Al3Li/Al3Zr has the lowest interfacial energy (0.01961ev), so its thermodynamic stability is the best. The interface with the maximum bonding strength is the interface of Al3Zr/T1, and its adhesion work is 0.61878ev. A2060 aluminum-lithium alloy was thermally insulated at 580 °C for 2h and then hot rolled. After hot rolling, it was cooled to room temperature for cold rolling. Then the samples were treated with solid solution and aging, and different cooling methods were selected to obtain four kinds of samples: non-heat treatment, aging, air cooling and water quenching. It is found that the strength and hardness of Al-Li alloy are determined by the grain thickness of precipitated phase, and the ductility and hardness of Al-Li alloy are determined by the number of precipitated phase and the degree of dislocation density.

Influence of hot rolling on microstructure, mechanical properties, and martensitic transformation of TiNiCuNb shape memory alloy

TiNiCuNb shape memory alloys are a promising new class of materials with the potential to be applied as elastocaloric components. However, the mechanical processing of these alloys remains a challenge and new insights on this topic must enlighten the knowledge about this system. In this work, the effects of hot rolling on Ti46Ni38Cu10Nb6 alloy were investigated. The results showed that hot rolling leads to the increase of martensitic transformation temperatures and the formation of a matrix containing both B2 and B19 phases. The coarsening of the lamellar eutectic constituent was observed, and part of the β-Nb phase precipitated into the matrix after being dissolved due to hot work. Microstructural aspects and ultra-microhardness measurements suggest that dynamic recrystallization occurred during hot rolling.

Analyzing the permeability distribution of multilayered specimens using pulsed eddy-current testing with multi-scale 1D-ResNet

The mechanical properties of steel are determined by its microstructure, which is closely related to its permeability profile. In thermal processing, layered structures are formed in steel and different layers have different mechanical and magnetic properties. Therefore, it is crucial to propose a practical method to monitor the change of permeability profile along the depth, which can indicate the evolution of the microstructure of steel during thermal processing, such as hot rolling. This paper presents a method for determining the layered structure and permeability profile of the steel by using pulsed eddy current testing (PECT), which offers better penetration ability. An analytical model has been deduced for calculating the time-domain pulsed eddy current (PEC) response from a Hall sensor of a triple-layer conductor system based on the inverse Laplace transform. It is found the Tau (τ) curve is closely related to the permeability profile of the conductor. For the inverse solution, the Simultaneous Iterative Reconstruction Technique (SIRT) is utilized to determine the permeability profile of the multilayered specimens from the measured response. The approximate Jacobian matrix (sensitivity matrix) is obtained by the perturbation method based on the Tau curve. However, the permeability profile suffers from smoothing effect and sharp features are lost. Deep learning (DL) algorithm based on the Multi-Scale 1D-ResNet model is therefore introduced to address this issue. Numerical simulations and experiments have been performed to evaluate the proposed method for permeability profile estimation with various materials and thicknesses. The DL method can achieve an accurate estimation of the plate permeability profile with a relative error under 5%.

Achieving high strength in Mg-Gd-Ag-Zr alloy through heterogeneous microstructure with multimodal grain structure and hierarchical precipitates

The development of high-strength Magnesium (Mg) alloys is a key research focus due to their relatively low strength compared to other structural metals. In this paper, a high-strength Mg-13.4Gd-2.2Ag-0.4Zr wt% alloy is achieved by carefully designing a multimodal grain structure combined with hierarchical precipitates, using a processing route of hot rolling followed by aging. The multimodal grain structure, characterized by three distinct grain size distributions and a strong basal texture, arises from partial dynamic recrystallization during hot rolling. The hierarchical precipitates include microscale rod-like and particle-like β phase at grain boundaries, twins, and deformation bands, as well as nanoscale β phase precipitates (~63nm) dispersed within the grain interiors. The fully β precipitates also demonstrate a modified precipitation pathway, differing from the β' and γ'' nanoprecipitates observed in conventional Mg-Gd-Ag alloys. This unique microstructure results in an ultimate tensile strength of 447MPa, primarily attributable to the strong basal texture, hierarchical precipitates, hetero-deformation-induced (HDI) strengthening, and high dislocation density.

Modeling of Dynamic Recrystallization Kinetics of a High Strength Low Alloy Steel During Hot Rolling

Modeling of Dynamic Recrystallization Kinetics of a High Strength Low Alloy Steel During Hot Rolling

Interfacial microstructure and synergistic enhancement mechanism of symmetric gradient SiCp-reinforced aluminum matrix sandwich structure

Inspired by the biological sandwich structure to achieve excellent mechanical properties with both high strength and high ductility, the symmetric gradient silicon carbide particles (SiCp) reinforced aluminum (Al) composites, consisting of 10% SiCp/Al-3% SiCp/Al-Al-3% SiCp/Al-10% SiCp/Al, was fabricated using spark plasma sintering technology. The flat interface was achieved through hot rolling, significantly improving the bonding of interlayers. The differences in SiCp content among layers led to distinct evolution patterns in microstructure. In the pure Al layer, a notable continuous recrystallization mechanism was observed, while in the 3% SiCp/Al and 10% SiCp/Al layers, the recrystallization mechanism was nucleation-growth. The transmission electron microscope results indicated that the hindrance of dislocation motion at the interlayer interface and SiCp-Al interface enhanced the dislocation density, thereby improving its plastic deformation capability. On the other hand, the deflection and passivation of cracks at the interlayer interface significantly improves toughness. The differences intragranular strain among layers were most pronounced at the interlayer interfaces, leading to them becoming the stress concentration zone. Uncoordinated plastic deformation leads to sequential failure of layers, vertical cracks first occurred in the 10% SiCp/Al layer, then propagated towards the interlayer interface and the 3% SiCp/Al layer, respectively.

Pore coarsening mechanism during hot rolling induced by hydrogen gathering in Al-Mg alloy

A novel mechanism for pore coarsening during hot rolling was proposed that the hydrogen in the ingot, driven by non-uniform hydrostatic pressure, accumulates into the tortuous shrinkage cavities at the thickness center of the slab. High pressure hydrogen gas gradually changes the stomatal curvature and finally leads to pore coarsening.

Mechanism of homogenization temperature and time on Fe-containing phase transition in AA8014 aluminum alloy

The presence of coarse Fe-containing phases detrimentally affects the fracture toughness of 8xxx aluminum alloys, and their complete dissolution during homogenization is unattainable. Therefore, it is essential to determine the optimal homogenization temperature and time to facilitate particle breakup during hot rolling, necessitating the development of effective homogenization processes. This study systematically examines the effect of homogenization temperature and time on the transition of Fe-containing phases in AA8014 aluminum alloy using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The transition mechanisms of Fe-containing phases during homogenization were elucidated through first-principles calculations, thermodynamics, and kinetics calculations. Under homogenization conditions of 610–650 ℃/12 h and 630 ℃/1–20 h, the Al6(Fe,Mn) phase initially transforms into the α-Al12(Fe,Mn)3Si phase with a “micropore structure” via the reaction. Subsequently, the α-Al12(Fe,Mn)3Si phase transforms into the Al3(Fe,Mn) phase. First-principles calculations confirm the sequential stability enhancement of the Al6(Fe,Mn), α-Al12(Fe,Mn)3Si+6Al, and Al3(Fe,Mn) phases. Homogenization kinetics indicate an optimal homogenization time of 11.5 h at 630 ℃, rationalizing the observed phase transitions and homogenization treatment. This study provides a foundation for the manufacture of 8xxx series aluminum alloys.

Microstructure evolution by thermomechanical processing and high-temperature mechanical properties of HCP-high entropy alloys (HEAs)

The solid solution strengthening and deformation mechanisms of the hcp-high entropy alloys (HEAs) have not been elucidated yet because of the complexity introduced by the martensite structure, particularly in alloys undergoing phase transformation from bcc to hcp structures. This study attempted to fabricate an equiaxed hcp microstructure for TiZrHf, TiZrHfAl, and TiZrHfAlSc using the hot rolling process and subsequent heat treatment. The equiaxed hcp phase was successfully formed in TiZrHfAl, but the martensite structure remained in TiZrHf and TiZrHfAlSc. The 0.2 % proof stress at 400 and 600°C increased with the increase of the average atomic size misfit δ and the mixing entropy . The low activation volume and high-stress exponent of TiZrHfAl with equiaxed hcp phase at room temperature suggest minor obstacles such as cluster or short-range order inhibit the movement of dislocation and leading to the significant solid-solution strengthening. However, the effect diminished at 600 °C.

Ultrahigh strength – ductility in Ti–6Al–4V composites with high-activity graphene-induced in-situ TiC and coherent nanophases

Achieving ultra-high strength and ductility of titanium alloys possesses great potential for structural applications in the aerospace and military, yet there is a great challenge for breaking the trade-off barrier of these two properties. In this study, large elongation of ∼10 % and ultra-high tensile strengths of 1510 MPa were obtained in a titanium-based composite. We designed this superior composite based on nanoscale coherent αʹʹ precipitation within near-equiaxed β-Ti as well as micro-scale TiC network architectures along grain boundaries. These in-situ formed triangular αʹʹ coherent precipitates and TiC mainly contributed to the strengthening, while the extremely large elongation resulted from coherent β/αʹʹ interfaces and strain-induced coherent αʹʹ nanotwins. We demonstrated that this composite was easily fabricated using a simple powder metallurgy followed by a hot rolling process. This work can contribute to the design of duplex titanium-based composites as well as other structural materials with exceptional mechanical properties for broad applications.

Improving strength-ductility synergy of titanium matrix composites containing nitrogen via the introduction of intragranular nano-TiB

We prepared a titanium matrix composite (TMC) with added boron nitride nanosheets (BNNSs) for strength-ductility trade-off issues. The composite, characterized by in-situ nano-TiB intragranular distribution and trace nitrogen solid solution, was prepared using rapid hot press sintering (FHP) and short-duration hot rolling. During pre-rolling heat preservation, the diffusion of boron and nitrogen resulted in the intragranular distribution of nano-TiB and nitrogen solid solution. The nano-TiB demonstrated excellent load transfer, fracture suppression, and dislocation storage capabilities at both room and high temperatures. Coupled with the nitrogen solid solution, the composite exhibited a significant enhancement in strain hardening effect compared to the titanium matrix. The composite outperformed the titanium matrix in strength and ductility at both room and high temperatures, demonstrating a notable strength-ductility synergy. This work provides a reference for designing TMCs with excellent performance at both room and high temperatures.

Tribological Behavior of 316L Stainless Steel Fabricated Using Metal Extrusion Additive Manufacturing Under Dry and Simulated Body Fluid‐Lubricated Conditions

Herein, the tribological behavior of 316L stainless steel (SS) fabricated using metal extrusion additive manufacturing (MEAM) is investigated both under dry and simulated body fluid (SBF)‐lubricated conditions. The results and mechanisms are compared with those of 316L SS fabricated via selective laser melting (SLM) and hot rolling (HR). Under dry‐friction conditions, the 316L SS fabricated via MEAM shows inferior tribological performance compared with those fabricated via SLM and HR, primarily because of its lower initial hardness and better plasticity, which increase both abrasive and adhesive wear. Under SBF‐lubricated conditions, the tribological performance of the 316L SS fabricated via MEAM is comparable to that fabricated via HR and superior to that fabricated via SLM. The wear rate of the MEAM‐fabricated 316L SS is 16.8% and 3.2% lower than SLM‐ and HR‐fabricated, respectively. The numerous pores on 316L SS serve as traps for wear particles, which contribute to the reduction of three‐body wear. In terms of wear under SBF‐lubricated conditions, MEAM technology appears to be a promising method for the fabrication of customized 316L orthopedic implants.

Unveiling the Correlation among Microstructure, Texture, Slip System Activity, and Tensile Property in a Hot Rolled Ni Containing Medium‐Mn Steel

The microstructure–texture–tensile property relationships in a Ni‐containing medium‐Mn steel (Ni‐MMS), subjected to limited thermomechanical processing steps (i.e., hot forging and hot rolling), have been established in this study. The microstructure of the specimens hot rolled (HR) at 1173 (HR‐1173K) and 1373 K (HR‐1373K) exhibits ferrite and austenite phases. The austenite phase fraction in the HR‐1173K specimen is found to be higher than the HR‐1373K condition. The volume fraction of austenite to martensite transformation during tensile testing is also observed to be higher in the HR‐1173K specimen (≈13%) than the HR‐1373K condition (≈2%). This suggests the occurrence of more efficient transformation‐induced plasticity effect in the HR‐1173K specimen in comparison to the HR‐1373K condition, resulting in improved strength–ductility synergy in the former specimen. The smaller grain size of both the phases and higher fraction of twin boundaries as well the evolution of higher intensity γ‐fiber <111>//ND in the HR‐1173K specimen leads to better tensile properties. In addition, the overall activation of the primary slip systems (combination of face‐centered cubic and body‐centered cubic phases slip system), estimated through visco‐plastic self‐consistent simulation, is higher in HR‐1173K specimens, resulting in improved strain hardening response as compared to HR‐1373K one.

Slab assignment to non-identical reheat furnaces running in parallel mode

This article analyses a slab assignment problem for non-identical reheat furnaces in the steelmaking industry. We tackle the problem of assigning slabs to different types of reheat furnaces, a walking beam and a pusher type furnace. Furthermore, we need to determine the feed-in as well as the residence time for each slab. The aim is to (i) reduce the energy consumption, (ii) increase the production rate and (iii) the heating quality of the slabs which depends on the assigned furnace and to what extent the slabs are overheated. Moreover, the subsequent production stage (Hot Rolling Mill), needs to be synchronized with the furnaces which is essential for a smooth production. We specify the problem as a mixed integer optimization formulation that is solved with iterative parameter adjustment. Rapid convergence leads to a novel two-phase solution method that yields furnace schedules that are optimal for the adjusted parameter values in reasonable time. The results show that our proposed method performs better than an industry benchmark by increasing the production rate and increasing the reheating quality. Furthermore, the new generic problem formulation allows using standard software and can be applied to identical or non-identical furnaces highlighting its broad applicability across steel-making companies.

Novel Mn and Si alloyed complex phase steel for automotive applications

Automotive industries require materials with higher strength, plasticity and crashworthiness, aiming for 3rd generation of advanced high strength steels (AHSS) with medium Mn, Si and minor alloying elements. In this investigation, 3rd generation AHSS were synthesized using a vacuum arc melting furnace with manganese (Mn) and silicon (Si) as major alloying elements as well as minor additions such as Cr, Al, Ni, etc. The steels thus developed were characterized using FE-SEM, XRD, microhardness tester, universal testing machine (UTM) and 3-dimensional Atom Probe Tomography (APT). The alloy steels after casting and homogenization were subjected to hot rolling at 1100 °C, with rolling exit temperature 900 ± 50 °C. The FE-SEM micrographs in SE mode revealed a complex phase microstructure with martensite, ferrite, bainitic ferrite and retained austenite in the specimens obtained after rolling and air cooling. The microhardness of the developed alloys is found in the range of 395–502 VHN in the hot-rolled and air cooled condition of the specimen. The tensile strength of alloys was measured to be in the range of 1412–1614 MPa with elongation of 12.12 %–18.92 %. The analysis of fracture surfaces after tensile tests for developed alloys revealed that Alloy 1 (Fe-4Mn-1.5Si) had dimples indicating ductile fracture while Alloy 2 (Fe-6Mn-1.5Si) has a mixture of dimples and facets, and Alloy 3 (Fe-8Mn-1.5Si) has lower dimples but larger facets, confirming quasi-ductile fracture with a lower ductility limit of 12.12 %. Atom Probe Tomography was performed to study the complex phase structure at nanoscale through re-distribution of carbon and other alloying elements. 3D APT revealed the presence of very fine retained austenite film of thickness ∼4–5 nm and carbon content of 6–8 at.%. This complex phase microstructure obtained after hot rolling and normalizing is made of very fine bainitic ferrite with film type retained austenite providing TRIP effect, in addition martensite and ferrite resulting in high strength.

Evolution of Al2Cu Secondary Phase and Precipitation Strengthening of 2219 Al Alloy with Ultrasonic Melt Treatment, Hot Rolling, and Solution Aging

This study aims to clarify the combined effect of ultrasonic melt treatment (UST), hot rolling and solution aging (HRSA) on the evolution of the Al2Cu secondary phase in 2219 Al alloy toward the optimization of its mechanical properties for high‐performance structural applications. The results show that UST is beneficial for modifying the morphology and reducing the size of the secondary phase (by an average of 17.9%), and conducive to increasing the Cu content in the Al matrix (by an average of 37.5%) during solidification. The genetic effects of UST on the microstructure generated during HRSA result in denser and finer θ′/θ″ Al2Cu particles precipitating in the α‐Al matrix, with a 62.1% increase in the precipitates volume in the HRSA sample. Theoretical calculations confirm that precipitation strengthening is the predominant mechanism for strength improvement of 2219 Al alloy after UST and HRSA. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of the HRSA alloy without UST are 329, 214 MPa, and 11.9%, respectively, while these parameters are increased by 12.5% (to 370 MPa), 9.8% (to 235 MPa), and 17.6% (to 14.0%) for the UST alloy, respectively.

Effect of Subsequent Continued Heating After Hot Rolling on the Microstructures and Mechanical Properties of Hot-Rolled Super Ferritic Stainless Steels

Effect of Subsequent Continued Heating After Hot Rolling on the Microstructures and Mechanical Properties of Hot-Rolled Super Ferritic Stainless Steels

The Influence of the Hot-Rolling Temperature on the Microstructure and Mechanical Properties of Ti-Nb Microalloyed 21%Cr Ferritic Stainless Steel

Microalloying and heat treatment are essential processing techniques for ferritic stainless steel (FSS). Three different compositions of 21%Cr FSS with 0.28Ti, 0.21Ti + 0.05Nb, and 1.05Ti + 0.17Nb were prepared. The interaction effects of the Nb and Ti contents and hot-rolling annealing on the microstructure, mechanical properties, and precipitate phases of FSS were studied. The microstructure, crystal structure, and precipitation phase of steel at 930, 980, and 1030 °C with Ti-Nb microalloying were investigated using an optical microscope (OM), X-ray diffractometer (XRD), and scanning electron microscope (SEM). The room-temperature tensile properties, surface roughness, and hardness were tested separately. This study found that the composite addition of Ti and Nb had a dual effect of fine-grain strengthening and precipitation strengthening. The 1.05Ti + 0.17Nb steel specimen had a moderate grain size and the best uniformity after hot rolling at 980 °C. The tensile strength and elongation were 454 MPa and 34.2%, which achieved an optimal balance between strength and plasticity.