Hot Rolling Temperature Research Articles

Influence of Hot Consolidation Conditions and Cr-Alloying on Microstructure and Creep in New-Generation ODS Alloy at 1100 °C.

The coarse-grained new-generation Fe-Al-Y2O3-based oxide dispersion strengthened (ODS) alloys contain 5 vol.% homogeneously dispersed yttria nano-precipitates and exhibit very promising creep and oxidation resistance above 1000 °C. The alloy is prepared by the consolidation of mechanically alloyed powders via hot rolling followed by secondary recrystallization. The paper presents a systematic study of influence of rolling temperature on final microstructure and creep at 1100 °C for two grades (Fe-10Al-4Y2O3 and Fe-9Al-14Cr-4Y2O3 in wt%) of new-generation ODS alloys. The hot rolling temperatures exhibit a rather wide processing window and the influence of Cr-alloying on creep properties is evaluated as only slightly positive.

Influence of thermomechanical processing on microstructure, mechanical and strain hardening properties of single-phase Mg-4Li-0.5Ca alloy for structural application

The single-phase Mg- 4Li- 0.5Ca alloy was rolled at three different temperatures (250, 300 and 350 °C) and followed by annealing at 200 °C for 10 min. To evaluate the mechanical properties, the tensile test was conducted at a constant strain rate of 10−3 s−1. Factors influencing the tensile strength and strain hardening properties were assessed by microscopy, XRD and EBSD analysis. Besides, Kocks–Mecking plots (K-M) were used to determine the different stages of strain hardening exhibited by the variously processed Mg- 4Li- 0.5Ca alloy test specimens. The ultimate tensile strength has decreased as hot-rolling temperature increases with increased ductility. The strain hardening properties such as hardening capacity (Hc), strain hardening exponent (n) are increased significantly with an increase in hot rolling temperature and subsequent annealing.

Quench Temperature-Dependent Mechanical Properties During Nonisothermal Partitioning

The present study demonstrates the role of hot rolling and quench temperature in determining the mechanical properties of low alloy steel processed through quenching and nonisothermal partitioning (Q&P) route. The results indicate that the abrasive wear resistance does not show any significant variation with quench temperature. However, a reduction in tensile strength and an increase in charpy impact toughness and elongation is observed with increasing quench temperature. Interestingly, the retained austenite shows high thermal stability at sub-zero temperature. Furthermore, during deformation through the wear process, the retained austenite experiences the TRIP effect that leads to improvement in wear resistance. The incorporation of hot rolling prior to Q&P led to a significant improvement in strength, energy absorption capability and wear resistance due to a considerable refinement of the microstructural constituents.

Effect of Cr and W contents on Charpy impact properties of Fe–Cr–W oxide dispersion strengthened steels

In this study, the effects of Cr and W contents on the microstructure and Charpy impact properties of Fe–Cr–W oxide dispersion strengthened (ODS) steels were investigated. ODS steels were fabricated by mechanical alloying followed by hot-rolling and tempering, and Charpy impact tests were conducted at −40 °C in both longitudinal-transverse (LT) and longitudinal-short transverse (LS) orientations. The high contents of Cr and W induced a significant <110> fiber texture in the elongated ferritic/martensitic matrix, which was associated with the high stability of ferrite at the hot-rolling temperature. This anisotropic microstructure caused the texture-induced delamination perpendicular to the notch base for the LT orientation and parallel to the notch base for the LS orientation. Such delamination in the LT specimens increased the tendency for ductile fracture, thereby resulting in the enhanced fracture propagation energy in a Charpy impact test. For the LS specimens, however, the Charpy impact energy exhibited enormous scatter depending on the formation of secondary delamination and the degree of plastic bending of the un-notched ligament after primary fracture. When the contents of Cr and W were relatively low, the equiaxed and fine grain structure without preferred orientation was obtained by the dynamic recrystallization of high-temperature austenite during hot-rolling. With this microstructure, the steel offered a high resistance to crack initiation, but the crack was propagated abruptly along the grain boundary decorated with coarse carbide particles.

Surface transformation and interactions of iron oxide in glassy lubricant: An ab initio study

Density functional theory (DFT) calculation for full coverage (NaPO3)x glass on Fe2O3 (0001) surface, and ab initio molecular dynamics (AIMD) simulation for phosphate and iron/iron oxide clusters at high temperature in hot rolling of steel have been carried out to investigate the transformation of adsorbed oxide surface and the interaction of the oxide compound in the glass network. Among three main interlayer interactions, Fe-Oglass is the most dominant bond in the system with effect of weakening oxide surface topmost Fe-O bond. Osurface-P can be observed under compression conditions and Fe-P direct bonds occur in the combination of elevated temperatures, high exposure of iron and appearance of under-coordinated phosphorus. Fe atoms in Fe-P change their valence state adapting to the synergetic bonding. Na atoms from the glass network also play an important role in promoting the iron oxide deformation by generating O-terminated surfaces and reducing Fe-Osurface stability, even at normal temperatures.

Microstructural evolution and mechanical properties of hot-rolled Ti-30Zr-5Al-2.5Sn alloy with mixed α and α′ phases

Ti-30Zr-5Al-2.5Sn (TZAS, wt. %) is a novel α-type Ti-Zr based alloy. Herein, the effect of phase and microstructure evolution on mechanical properties of hot-rolled TZAS alloy with mixed α and α′ martensite phase were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and statistical analysis. The content of primary α phase decreased as the hot-rolling temperature increased from α to α+β region. When the rolling temperature increased to 875 °C, the predominant phase transformed from α phase to α′ martensite phase. The spheroidization degree of TZAS alloys increased with rolling temperature until 850 °C. As the rolling temperature increased from 775 °C to 825 °C, the yield strength gradually enhanced, attributing to the synergistic effect of grain-boundary strengthening, dislocation strengthening and second-phase strengthening from martensite. While, as further increase of rolling temperature, the coarsen primary α grains led to the decrease of yield strength. A peak yield strength of 1038 ± 26 MPa and total elongation of 14 ± 0.6% were obtained after rolling at 825 °C. One should note that work hardening was also a key factor for the alloys strengthening. Furthermore, the fracture mechanisms of studied alloys were also discussed in depth.

Patterns of changes in the plastic and deformation characteristics of rail steels alloyed with chromium in the temperature range of hot rolling

Based on the set of experimental studies for chromium rail steels of grades E76KhF, E76KhSF and E90KhAF, the basic laws governing the influence of hot rolling temperature on ductility and the regularities of temperature and strain rate influence in the temperature range of hot rolling on plastic deformation resistance are determined and scientifically substantiated. It was shown that for E76KhF steel at deformation temperatures of 1050 °C, a sharp decrease in ductility occurs due to the presence of cementite-type carbides (Fe, Mn, Cr)3C at the grain boundaries. For rail steels with a lower chromium content, the indicated ductility drop is not observed. It was established that an increase in the deformation temperature of rail steel E76KhSF causes a decrease in deformation resistance, and an increase in the strain rate significantly reduces this indicator. Also the fact that the deformation resistance decreases with distance from the surface to the central zone of continuously cast billets is established, which is due to an increase in grain size. Based on the obtained data, a new mode of rail rolling was developed in the conditions of the rail and beam workshop of EVRAZ ZSMK JSC, the introduction of which allowed the quality of the rails to be significantly improved as well as the technical and economic indicators of their production with an economic effect of approximately 120 million rubles/year.

Role of metal oxidation at high temperature

ABSTRACT Different cast steels (low-, medium- and high-carbon cast steel) converted into the wrought form by hot rolling and forging processes, the temperature of hot rolling and forging processes are kept 1000°C and then these cast and wrought steel samples prepared and subjected to high temperature oxidation in air under cyclic heating condition for 50 cycles, every cycle consisting of 1-h heating and 20-min cooling. Oxidation kinetics was established by thermo-gravimetric methods by measuring the weight changes at the end of each cycle. The oxidised samples with oxide-scaled surface were investigated for X-ray analysis, scanning electron microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDAX) . All the steel samples suffered oxidation attack in the air which resulted in intense spalling of the oxide scale. It is also observed that the high temperature oxidation rate is maximum for casted samples and is minimum for the rolled samples and for forged samples it lies between cast and rolled steel.

Effect of Niobium Addition on Microstructure and Mechanical Properties of Fe–7Al–0.35C Low-Density Steel

The present work reports the effect of niobium addition on a Fe–7wt.%Al–0.35wt.%C-based low-density steel. A hot rolling temperature of 1100 °C was selected to carry out rolling in the intercritical (ferrite + austenite) region. The phases formed on adding Nb were predicted by thermodynamic calculations using ThermoCalc. All the alloys exhibited a significant (20% or more) tensile elongation. Niobium addition also resulted in a significant increase in strength and hardness of the hot-rolled steel. About 80% increase in the yield strength is observed as the Nb content increases from 0.2 to 1.0 wt.%. Nb carbides present at rolling temperature resist grain growth and lead to improved mechanical properties. This study demonstrates the advantages of adding Nb to Fe–Al–C-based low-density steels. Earlier attempts to add Nb to low-density steels resulted in very low ductility. This may be related to their susceptibility to hydrogen embrittlement. Melting of high aluminum low-density steels in a controlled atmosphere may lead to a considerable improvement in mechanical properties. Further, it is also important to maintain a high C/Nb ratio to avoid the formation of Laves phases.

Sustainable development of the steel plate hot rolling technology due to energy-power process parameters justification

In order to ensure sustainable development of rolling production, technological processes were investigated using computer simulation, which allows us to examine a large amount of information regarding modes of reduction and energy consumption of metal treatment under pressure in order to determine rational values. Simulation of hot rolling process using DEFORM-3D software was performed to investigate energy parameters of treatment and to determine rational reduction modes. During investigation, objects were located in space, exact positioning of casting rollers respectively to workpiece was performed, and rheological model of deformable material was specified, where rigid-plastic environment was adopted. Mechanical properties of workpiece material were determined, low carbon steel was selected as material, reduction between casting rollers was specified, and friction coefficient between workpiece and rollers, which is equal to 0.3; contact interaction between casting rollers and workpiece was specified, hot rolling temperature was set to 1000°C. Finite element model of treated material was developed, displacement in deformation zone during hot rolling and vector field of metal movement were determined. Changes in force during treatment, deformation stress during rolling were determined. Changes of rolling force in deformation zone in course of time were determined. Distribution of active stress in deformation zone was investigated. Investigations allowed us to determine energy consumption of rolling process depending on reduction modes, which provided rational treatment modes.

Microstructure and Mechanical Properties of the Cold-Rolled Mg-14Li-1Zn Alloy after Hot Rolling

The as-cast Mg-14Li-1Zn alloy was hot rolled at different temperatures with the reduction of 50%, followed by cold rolling with the reduction of 80%. The effects of the hot rolling temperature on the microstructure and mechanical properties of the final specimens were investigated. The results show that the higher rolling temperature brings about a more homogeneous microstructure, which is favorable for the subsequent cold rolling. When the hot rolling temperature is 300°C, the final specimen possesses the highest tensile strength and hardness of 238 MPa and 67.7 HV, respectively. When the hot rolling temperature is 200°C, the final specimen possesses the highest elongation of 24.6%.

Effects of hot rolling temperature and aging on the second phase particles of Zr-Sn-Nb-Fe zirconium alloy

Abstract Various processes were used to prepare Zr-0.4Sn-1Nb-0.3Fe zirconium alloy plate samples, including hot rolling at 620,650,700℃ without aging and hot rolling at 700℃ after aging with 10 and 50 h at 480℃, respectively. The second phase particles (SPPs) of Zr-0.4Sn-1Nb-0.3Fe zirconium alloy were investigated by SEM and TEM. The results show that the mean diameter of SPPs is within 100 nm under different process conditions. Homogeneous and fine secondary phases distribute dispersively at 620℃, and most of these SPPs are Zr(Nb,Fe)2 with a C14 hexagonal close packed (HCP) structure. When hot rolling at 650℃, the β-Nb precipitates are also observed in addition to Zr(Nb,Fe)2 particles, and the distribution of SPPs is bunching and clustering. As the hot rolling temperature increases to 700℃, the SPPs present in a wide variety of sizes and non-uniform distribution, and the number of β-Nb particles increases. Aging prior to hot rolling is helpful to improve the uniform distribution of SPPs, as the aging time extends, the mean diameter of SPPs becomes larger. With the increase of hot rolling temperature, the average Nb/Fe ratio of Zr-Nb-Fe particles increases firstly and then decreases at the range of 620℃ to 700℃, aging processing leads to the further reduce of Nb/Fe ratio. Therefore, homogeneous and fine secondary phases distribute dispersively can be obtained when hot rolling at 620℃, which is beneficial to improve the combination property of zirconium alloys.

Increasing cold workability of Ti-6Al-4V alloy via thermo-mechanical processing: simulation and experiment

AbstractRolling temperature is thought to have a significant effect on the cold workability of Ti-6Al-4V alloy. To investigate the extent of this effect, four Ti-6Al-4V strips were hot rolled at different rolling temperatures in the range of 650–950 °C while other process parameters were invariant. The specimens revealed an increase in work hardening capacity with increase in rolling temperature, based on tensile and plane strain compression testing. After 10 % cold rolling, the same annealed samples exhibited propagation of edge cracks in specimens that had been hot rolled at 650, 750 and 850 °C while no cold rolling defect was found in the specimen hot rolled at 950 °C. The results of finite element method reveal that during cold rolling, the von Mises stress field is decreased as a result of increasing previous hot rolling temperature. In accordance with X-ray diffraction results, increasing previous hot rolling temperature is associated with lower lattice strain storage during subsequent cold rolling.

Application of a novel acrylamide copolymer containing highly hydrophobic comonomer as filtration control and rheology modifier additive in water-based drilling mud

Deep wells suffer from the instability and disintegration of natural polymers and other commonly used additives under high pressure and high temperature condition. As a result, serious problems such as hydraulic loss, stuck pipe, and high torque and drag are expected to take place which leads to a dramatic increase in cost and time. This study presents the functionality of a novel synthetic based acrylamide-styrene copolymer (SBASC) as a supersede additive for water-based drilling mud. First, the SBASC was synthesized using an emulsion polymerization process and its particle morphological and polymer chain structural properties were determined by Field Emission Scanning Electron Microscopy (FESEM) and Fourier- Transform Infrared Spectroscopy (FTIR), respectively. Then, the designated copolymer was added into a mud formulation which is applicable in oil and gas fields, and its performance in the mud was investigated with respect to filtration properties and rheological characteristics. In addition, the rheological characteristics and filtration behavior of drilling fluids containing SBASC were compared with those of a field applicable fluid that contained 9 g of HT starch which is a commercial natural polymer commonly used in drilling fluid industry. Furthermore, the thermal stability of SBASC was determined by conducting hot rolling and high pressure-high temperature (HP-HT) filtration tests. The obtained results confirmed that the addition of the copolymer enhances the rheological characteristics of the drilling fluid before and after aging at 121.1 °C. Moreover, the filtration behavior at both conditions was improved by introducing SBASC into the fluid, while the best performance was observed for the fluid containing 3 g of SBASC which shows 38.8% and 47.5% fluid loss reduction for HP-HT and LP-LT conditions, respectively. Furthermore, the solubility of SBASC in saline and fresh water is verified by demonstrating a promising solubility in high salinity water sample with different concentrations of a monovalent salt.

Synthesis of Oligomeric Silicone Surfactant and its Interfacial Properties

During the exploitation of low permeability gas-condensate reservoirs, the mud filtrate, acidizing liquid, and fracturing fluid invade the reservoir and condensate gas, severely reducing the permeability of the reservoirs due to increased capillary pressure and water wettability. For the current paper, an oligomeric silicone surfactant (OSSF) containing sulfonic acid groups was synthesized to improve the flowback of such fluids. The critical micelle mass concentration and critical surface tension were determined by equilibrium surface tension. The surface tension increased with the hot rolling temperature and decreased with the addition of NaCl, KCl, or CaCl2. When the concentration exceeded critical micelle mass concentration, a micelle was formed and its size increased with mass concentration. OSSF adsorption through solid–liquid surface changed the surface chemical composition of the cores and transferred the wettability of cores from water-wet to preferential gas-wet by decreasing the surface energy. At the same time, the increasing temperature led to a change in the adsorption isotherm of quartz sand from Langmuir type (L-type) to “double plateau” type (LS-type) in the OSSF solution. In addition, NaCl decreased the relative foam volume of OSSF while extending the half-life. OSSF decreased the initial foaming volume and stability of the induction period and accelerated sodium dodecyl benzene sulfonate (SDBS) formation.

Continuous cooling transformation diagrams of HSLA steel for seamless tubes production

The CCT and two DCCT diagrams were constructed for the HSLA steel containing Cr, V, Nb, and N microadditions, taking into account industrial processing parameters of this material in a seamless tubes rolling mill. The typical finish hot rolling temperature of 1173 K was used for the construction of the standard CCT diagram and the effect of previous austenite deformation at this temperature was evaluated in the DCCT diagram. Another DCCT diagram was developed after heating at 1553 K, followed by plastic deformation at 1173 K. The prior austenite grain size in the hot rolled material after heating at 1173 K was approx. 10 ?m, the heating of the as-cast material at 1553 K resulted in the prior austenite grain size over 200 ?m. The effect of the previous austenite deformation after low-temperature heating on the CCT diagram was negligible. The high-temperature heating showed a great influence on the austenite decomposition processes. The Ferrite-start temperature was significantly reduced at high cooling rates and the preferred decomposition of coarse grained austenite to acicular ferrite suppressed the bainite transformation at medium cooling rates. The developed DCCT diagrams can be used for the prediction of austenite decomposition products during the cooling of the seamless tubes from the finish rolling temperature. The CCT diagram can be utilized for the quality heat treatment of tubes.

An Integrated Model for Predicting Hierarchical Microstructure Evolution of Steel during Hot Rolling

A robust model for calculating the necessary process variables such as strain, strain rate and temperature in hot rolling of a steel plate or strip is presented in this paper. The applied approach includes a well-constructed velocity function in the deformation model that is validated using a commercial finite element solver. The developed microstructure model is then integrated into the process model and includes the most essential descriptions of restoration and austenite grain structure evolution phenomena during hot rolling. Furthermore, the concept of hierarchical grain structure evolution is described as a method track the evolution of un-recrystallized and recrystallized features of the microstructure throughout a given pass schedule. The most important outcome of this approach is that each grain size component is modelled separately based on its prior thermomechanical history. A computer implementation of these models called MICDEL is used together with a simulation example to demonstrate its capability of predicting process variables and austenite grain structure evolution in hot strip rolling of steel.

Microstructure, texture and mechanical properties of Ti-43Al-9V-0.2Y alloy hot-rolled at various temperatures

Using the hot-pack rolling method, β-solidifying Ti-43Al-9V-0.2Y alloy sheets were rolled (thickness reduction: 85%) within the α(α2) + β + γ ternary-phase region at temperatures ranging from 1100 °C to 1200 °C. The microstructure and texture evolution occurring during dynamic recrystallization of the γ phase and their effect on the mechanical properties were systematically investigated. After hot-rolling, residual lamellar structures of the as-forged TiAl alloy were completely broken down and the fraction of dynamically recrystallized grains increased significantly with increasing rolling temperature. Lower-temperature and higher-temperature rolling were conducive for dynamic-recrystallization nucleation and growth, respectively, of the γ grains. At 1100 °C, the precipitation of numerous fine (thickness: ∼200 nm) γ laths from the β-phase ribbon was accompanied by the emergence of γ twins in the new grains. The texture evolution was also strongly dependent on the hot-rolling temperature, as evidenced by the transformation of recrystallization textures into random deformation components when the temperature was increased to 1200 °C. Moreover, compared with those rolled at higher temperatures, the sheet hot-rolled at 1100 °C had a significantly higher tensile strength (ultimate tensile strength (UTS): 945 MPa, yield strength (YS): 840 MPa) at room temperature. A good combination of high strength (UTS: 550 MPa, YS: 480 MPa) and sufficient ductility (80%) of this alloy sheet was also achieved at 750 °C.

Studies on Bio-acceptability of Thermo-Mechanically Processed Mg-4Li-0.5Ca Alloy and Its Microstructural Correlation

In this study, in vitro corrosion behavior of rolled Mg-4Li-0.5Ca (wt.%) alloy at three temperatures (250, 300 and 350 °C) with 75% reduction and subsequent short annealing at 200 °C for 10 min was systematically investigated. Microstructural evaluation, Mg2Ca precipitation and defects like twins were characterized by an optical microscope, scanning electron microscope and x-ray diffraction. Micrographs reveal an increase in grain size and comparatively reduction in twins density population with an increase in hot rolling temperature and subsequent short annealing. In vitro corrosion tests like dynamic bio-corrosion immersion test, hydrogen evolution test and electrochemical linear polarization test were carried out in simulated body fluid. From in vitro corrosion tests, it is observed that the alloy rolled at 350 °C and subsequently short-annealed shows better bio-corrosion resistance than other hot-rolled and short-annealed alloys. This is due to low twins density and uniformly dispersed Mg2Ca compound throughout the matrix.

Crucial microstructural feature to determine the impact toughness of intercritically annealed medium-Mn steel with triplex-phase microstructure

We investigated the correlation between the impact toughness and microstructures of annealed Fe-8Mn-0.2C-3Al-1.3Si (wt.%) steel to identify the key microstructural feature determining the impact toughness of medium-Mn steel. The microstructural constituents were varied by changing the hot-rolling temperature in the range of 1000–1200 °C before intercritical annealing. The annealed steels exhibited a triplex-phase microstructure consisting of δ ferrite with coarse grains and an elongated structure along the rolling and transverse directions and nanolaminate α martensite plus γR retained austenite with ultrafine size. While the volume fraction of γR remained almost constant regardless of the hot-rolling temperature, the volume fraction of δ increased and that of α decreased with increase in the hot-rolling temperature. The average grain size for all phases increased with the hot-rolling temperature. The stability of γR decreased with the increase of the hot-rolling temperature owing to grain coarsening and a reduction in the Mn and C concentrations. A lower hot-rolling temperature resulted in improved impact toughness. We observed that deep parallel cracks formed and propagated along the δ interface decorated with Mn, ultimately causing a fracture. This result indicates that δ ferrite was the crucial factor determining the toughness among the existing phases, and the steels with a higher fraction of δ exhibited a lower impact toughness. The decrease of the retained austenite stability and the increase of the size of prior γ grains with increasing hot-rolling temperature were identified as other microstructural factors determining the impact toughness.