The equilibrium phase relations of molten Si–Fe, Si–Ni, and Si–Fe–Cr alloys saturated with either silicon carbide (SiC) or graphite, which are candidates for the solvent for rapid solution growth of SiC, have been investigated. The measured carbon solubilities at 2073 K were 0.19–6.6 mol% for the Si–(24.1–70.1) mol% Fe, 0.061–5.2 mol% for Si–(30.0–85.0) mol% Ni, and 1.1–3.9 mol% for Si–(50−x) mol% Fe–x mol% Cr (x = 10.4–40.1) alloys. A quasi-chemical model that assumes that the carbon atoms are introduced into the interstitial sites of the Si–Fe, Si–Ni, and Si–Fe–Cr solvents and obstruct the bonding between solvent atoms was used to evaluate the activity coefficient of carbon in each alloy. The estimation reproduced the trends of the measured carbon solubilities fairly well. However, the estimation using the sub-regular solution model often overestimated the carbon solubilities. Thus, the carbon behavior in molten silicon–transition metal alloys is well described by the quasi-chemical model.
In this work, a comparison between CO reactivity of lumps and briquettes made of two different binder and three different raw materials is presented. Experimental results on the prereduction behavior of such materials in 70% CO and 30% CO2 atmosphere, heating rate of 0,17 K/s (10°C/min) at temperatures up to 1100°C are discussed. It was shown that briquettes presented higher CO reactivity, especially those whose molasses was the binder which had the highest reactivity. Level of oxygen also played an important role in CO reactivity. Comilog and Urucum with the highest oxygen level had highest reactivity while Assmang with the lowest oxygen level had the lowest reactivity between the raw materials. Porosity was a key variable to explain CO reactivity. Molasses briquettes had the highest porosity and the highest CO reactivity followed by bentonite briquettes and lumps.
The estimation of interaction parameters in liquid iron is strongly demanded due to the difficulty of their measurements and its time consuming for enormous combinations of target solute elements in liquid iron. Therefore, several estimation models have been developed so far. In this study, the interaction parameters between metal elements and/or metalloid elements in liquid Fe are estimated by neural network computation in order to improve the estimation accuracy. The input parameters used in the neural network computation are assessed by lateral inhibition learning. The estimation results by nerural network computation with the assessed parameters reasonably agree with the recommended values in the literature.
Expansion of the system for thermodynamic parameters in liquid iron is expected for the improvement in iron & steelmaking processes. The development of their calculation method is one of the issues for its realization. In the present work, we proposed a calculation method for an activity coefficient of solute in infinite dilute liquid iron to element i, γοi, based on the surface tension of binary liquid Fe alloys. It was found that the estimated values by our proposed method agree with recommended literature data.
The interaction coefficient between Al and Sn in molten iron containing high Al was measured using a chemical equilibrium technique. A molten Fe–Al alloy was equilibrated with a molten Ag–Sn alloy in an Al2O3 crucible at 1823 K. The interaction coefficient of Sn and Al in Fe–Al alloys was measured to be = −3.18 while varying the concentration of Al in a range from 0.01–0.17 in mole fraction. The influence of Sn on the deoxidation equilibrium of Al and O was estimated using the above interaction coefficient. The results indicate that under a constant Al concentration, a contamination of several percent of Sn slightly raises the O concentration in high Al steel.
Energy efficiency is fundamental in the steel industry. Latent heat storage (LHS) systems with phase change materials (PCM) are attractive technologies for the recovery and utilization of heat, especially for the development of high-temperature thermal energy storage system. This paper describes fabrication of LHS pellets for high-temperature applications using metallic microencapsulated PCM (MEPCM). The LHS pellets consist of Al–Si PCM parts and an Al2O3 matrix. The pellets were fabricated by mixing MEPCM with sinterable alumina. The powder mixture was then pelletized and sintered at different pressures and atmospheric conditions, respectively. Some MEPCM in the pellets remained spherical after being sintered at 1000°C, a high-temperature condition above the PCM melting temperature. All fabricated pellets exhibited latent heat of PCM at the melting point of the PCM, about 577°C. The maximum value of latent heat was 73.5 J g−1. This was observed for the LHS pellet pelletized at 20 MPa and sintered under O2 atmosphere. Therefore, this study presents a great material for high-temperature thermal energy storage systems in the steel industry.
Phase change materials (PCM) have great application potential in the field of thermal energy storage (TES). However, most PCM have low thermal conductivity, which limits the TES efficiency. In this paper, a novel method employing oscillating heat pipe (OHP) to enhance the heat transfer performance of latent heat TES system was investigated. OHPs with different turns, inner dimeters and wall thickness were designed, manufactured and tested. Thermal performance of TES system enhanced by embedded OHPs were tested. The influence of turn number, inner dimeters and wall thickness of OHPs on the heat transfer performance of paraffin were investigated. The results show that the prepared OHPs have high heat transfer performance. The time of the thermal storage process for the paraffin based TES coupled with OHP (Di=3 mm, Do=4 mm, 4 turns) is 38.45% shorter than that without OHP. Therefore, the OHPs can effectively improve the heat transfer rate inside paraffin in the thermal storage process.
Complex section products have significant lightweight and functional characteristics, and the twin-roll casting (TRC) is characterized by high efficiency and short flow. Hence, the TRC process for fabricating complex section products combines both advantages and will have a broader market demand and application prospect. In this paper, the research progress in recent years is reviewed, and novel TRC processes are divided into three categories according to the product section characteristics, namely transverse variable profiled strip, longitudinal variable profiled strip, and circular section products. The essence of the TRC process of complex section products is to change the steady-state characteristics in time series and the uniform characteristics in spatial distribution into transient or nonuniform. The technical principle, deformation characteristics, influence mechanism, are systematically analyzed. The current challenges and future directions of the TRC process are discussed.
The melt structure with fluorine addition has been investigated using molecular dynamics (MD) simulation for the CaO–SiO2–CaF2 and CaO–Al2O3–CaF2 ternary slag system. By analyzing the coordination number of the network framework, the results indicate that the structure of Si–O tetrahedron is more stable than the structure of Al–O tetrahedron. F− ions are dominantly coordinated with Ca2+, there is a dynamic equilibrium between Ca2+ and the coordination anions (O2− and F−) in both systems, and the total coordination number (CN) is maintained between 6 and 7. The analysis of the distribution of oxygen types demonstrates the degree of polymerization (DOP) of network structure in CaO–SiO2–CaF2 system is lower than that in CaO–Al2O3–CaF2 system. Although the addition of CaF2 can lower the viscosity of both slag systems, the microscopic reasons for that are completely different: in CaO–SiO2–CaF2 system, CaF2 actually acts as network diluent, and creates the space where particles can move longer. But in CaO–Al2O3–CaF2 system, CaF2 can depolymerize the network structure of the melt.
To improve vanadium leaching and yield rates during wet vanadium extraction processes, the crystallization behavior and growth mechanism of spinel crystals in vanadium-containing slags were investigated by the mathematical models and high temperature experiments. The results show that the suitable temperature range for spinel crystallization was 1473–1573 K. And the spinels’ crystallization abilities were ranked FeCr2O4 → FeV2O4 → Fe2TiO4. Although the concentration of chromium in the vanadium-containing slags was relatively low, the crystallization rate of all spinel crystals was greatly affected by the chromium spinels. The distribution of spinel diameters differed under the actual smelting condition, with the most common diameter range being 10–15 µm. In addition, the mean diameter and volume fraction of spinels increased with prolonging holding time and decreasing temperature in the actual smelting temperature range. Spinel crystals grew rapidly with time at 1623 K, the mean crystal diameter changed from 15.0 µm at 0 min to 24.9 µm at 60 min. And the mean diameter and volume fraction of spinels treated at 1523 K for 30 min were 28.1 µm and 46.3%, respectively. The mean diameter and volume fraction of spinel crystals increased with prolonging holding time and by decreasing the temperature in the actual smelting temperature range (1573–1673 K). Thus, the remaining slag process is beneficial to spinels growth in industrial vanadium-extraction process.
SFC (Sillico-Ferrite of Calcium) is a kind of simplified SFCA (Sillico-Ferrite of Calcium and Aluminum) with no Al2O3. SFC and SFCA are believed to be the most desirable bonding phase in sinter. In order to better understand the fundamentals of the reduction of SFC, a series of experiments on the SFC reduction were carried out in the present work, including phase equilibria tested by XRD, morphology tested by SEM-EDS, and reduction pathway under the different CO/CO2 mixture gas at 1000°C. The experimental results indicated, (1) in the case of CO = 20% and 40%, most of Fe2O3 in SFC was reduced to FeO. The equilibrium phases were FeO, CaO·Fe2O3, and CaO·SiO2. (2) In the case of CO = 60%, CaO·Fe2O3 was reduced to generate FeO and 2CaO·Fe2O3. The equilibrium phases were FeO, 2CaO·Fe2O3, and CaO·SiO2. (3) In the case of CO = 80% and 90%, FeO was reduced to Fe, and 2CaO·Fe2O3 was reduced to generate Fe and CaO. The equilibrium phases were Fe, CaO, and CaO·SiO2. The findings from this work may provide guidelines for the improvement of sintering production and blast furnace performances.
The oxidation induration process of Hongge vanadium titanomagnetite pellets (HVTMP) with different amounts of CaO was investigated. This research forms part of an ongoing study on a novel and clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite. The results revealed that the compressive strength of HVTMP could be enhanced by adding only 1% CaO because of the formation of fine grains and homogenous microstructures. However, a further increase in CaO decreased the compressive strength. Excessive amounts of CaO decreased the grain size but increased the porosity, impeding the oxidation induration process of HVTMP. An increase in CaO slightly influenced the phase compositions but largely reduced their peak intensities. An innovative index, namely induration degree, was proposed to directly estimate the induration behavior of HVTMP. A schematic diagram was presented to clearly describe the induration mechanism of HVTMP with different amounts of added CaO.
Using hydrogen as a reducing agent for iron production has been the focus of several studies due to its environmental potential. The aim of this work is to study the influence of H2–H2O content in the gas phase on the reduction of acid iron ore pellets under simulated blast furnace conditions. Temperature and gas compositions for the experiments were determined with multi-point vertical probes in an industrial blast furnace. The results of the reduction tests show that higher temperatures and H2 content increase the rate and extent of reduction. For all the gas and temperature combinations, morphological, mineralogical, and microstructure changes were observed using different characterization techniques. Microscopy images reveal that H2–H2O, in the gas phase, has a positive influence on reduction, with metallic iron forming at the pellet’s periphery and core at lower temperatures compared to CO–CO2–N2 reducing gas. Porosity and surface area changes were determined using a gas pycnometer and the BET method. The results indicate that increasing the reduction temperatures and H2 content results in greater porosity and a larger surface area. Moreover, carbon deposition did not take place, even at lower temperatures. A rate minimum was detected for pellets reduced at 800°C, probably due to metallic iron formation, hindering the diffusion of reducing gases through the product iron layer.
As an innovative route to mitigating CO2 emissions in ironmaking, increasing the hydrogen reduction in a blast furnace is promising. One possible method is the shaft injection or blast tuyere injection of coke oven gas (COG) with its hydrogen concentration enhanced by steam-reforming methane and tar. Therefore, the reduction behavior of sintered ores in a blast furnace by injecting reformed COG was investigated using a softening-melting tester and counter-current reaction simulator (BIS). The shaft injection of reformed COG promoted the reduction and improved the permeability of the ore layer, particularly in the wall area of the blast furnace. An injection rate larger than 200 Nm3/t-HM was required for reformed COG for a limiting intermediate distribution ratio of injection gas lower than 20% in a large blast furnace. Unchanged shaft temperature and increased hydrogen reduction were observed during the shaft injection of hot reformed COG in the BIS test. The water-gas shift reaction below the temperature of the thermal reserve zone was insignificant even for the shaft injection of reformed COG. As for tuyere injection, direct reduction was decreased by increasing the injection rate of reformed COG from tuyere. The injection of COG with or without reforming from tuyere reduced the carbon consumption of the blast furnace by 10 kg/t-HM. The influence of the composition of COG on carbon consumption was insignificant. Direct observation of hydrogen reduction revealed a decrease in flooding molten slag in the upper coke layer during reduction, thus explaining the improved permeability of the ore layers.
Changes in gas composition during the shaft injection of reformed COG. (a); (H2·CO2)/(H2O·CO), (b); H2 utilization, (c); CO utilization. (Online version in color.)
For achieving high sinter yield and quality, various technologies are being implemented and developed to control the heat pattern during the sintering reaction. Further improvements in these technologies necessitate detailed time-course profiles of temperature at all sinter-bed heights; however, no technique has yet been reported for determining the temperature distribution in the top layers of the sinter bed at high spatial and time resolutions. Herein, detailed heat patterns in these layers were visualized by a newly developed pot test apparatus having ~300-mm sinter-bed height. The developed apparatus demonstrated the effect of ignition time on heat patterns during combustion and immediately after ignition. Ignition times of 30, 60, and 90 s demonstrated that the high-temperature holding time increased with an increase in ignition time, and this effect is more evident in the top layer. All parameters, including high-temperature holding time, flue gas composition, and sinter yield, suggest that a longer ignition time intensified coke combustion in the top half layer. The developed technique to measure the temperature in the top layer will quantitatively clarify the effect of segregation or ignition condition on the heat pattern in the top layer.
Argon bubbles are usually injected into steel continuous casting mold to prevent the clogging of submerged entry nozzle (SEN), but some bubbles may be entrapped to form defects in the final slab. In order to provide a reference for improving the quality of steel, a mathematical model based on the Eulerian-Lagrangian approach with advanced bubble break-up and coalescence models was established to study the effect of operation conditions on bubble distribution in a steel continuous casting mold. A bubble break-up model based on a daughter bubble fraction, which is suitable for the continuous casting system, was considered. The mathematic model was validated by comparing of the size and number of captured bubbles with the plant measurements of previous work. The result shows that argon gas injection has obvious effect on the flow pattern in the upper recirculation zone of the mold. In the upper recirculation zone, the bubbles mean diameter decreases and the bubble number increases with increasing casting speed, and both of the bubble size and number increase with the increase of gas flow rate. From the result, it can be found that the number and diameter of bubbles arriving at the advancing solidified shell region increase with increasing casting speed. In addition, the increase of gas flow rate causes more bubbles arriving at the advancing solidified shell region, but has little effect on the size of bubbles.
Transmission electron microscopy (TEM) is a powerful tool for analyzing fine precipitates because it can measure the size of the precipitates directly. In contrast, small angle X-ray scattering (SAXS) can observe much larger volumes and yield statistical quantitative results. However, the consistency between results obtained by SAXS and TEM has not been well investigated, especially in the case of precipitates having anisotropic shapes. In this study, the quantitative capability of SAXS was investigated by comparing SAXS and TEM results for TiC precipitates contained in high-strength steel. Samples with various size distributions of TiC precipitates were prepared. The average size, number density and volume fraction of TiC were obtained by SAXS analysis of these samples using a sphere or a disk form factor. Regardless of the form factor, the average size and volume fraction were almost the same, whereas the number density differed by one order of magnitude. The average size of TiC precipitates measured by SAXS analysis was consistent with that obtained by TEM. Since it is considered that the difference in number density depending on the form factor is attributed to an error due to the overestimation of the size distribution width, the average number density was defined to correct for this. The average number density calculated from the results using both form factors agreed well and were reasonable. It was found that using a sphere form factor with good convergence is effective for obtaining average information concerning the precipitates.
Roller chains are commonly used to transmit mechanical power in many kinds of machineries for wide industrial fields. Roller chain manufactures are doing a lot of efforts to improve the wear resistance through conventional real chain type wear testing with huge amount of time and cost. In this study, a new wear testing machine is developed to evaluate wear amounts more efficiently without using main chain components such as inner plate, outer plate and roller. The results show that the nearly same amounts of wear rate and wear status can be obtained between the newly developed wear testing machine and the conventional machine. It may be concluded that the newly developed wear testing has sufficient reproducibility and can be used more conveniently for investing roller chains compared to the conventional wear testing machine.
In this study, a new generation automobile Medium-Mn steel (0.1C-5Mn-Fe) was welded by fiber laser and regional thermal cycle experiment was performed on a thermo-mechanical simulator. The microstructure, microhardness, and tensile properties of both base metal (BM) and simulated heat-affected zone (HAZ) were investigated. The results show that the peak temperature (PT) of different regions in HAZ results in differences of microstructure and mechanical properties. The microstructural analysis indicates that BM is comprised of an ultrafine-grained (UFG) duplex microstructure of ferrite and austenite. The change of PT has significant influence on microstructure and mechanical properties of HAZ. At the PT of 1350°C, the microstructure consists mainly of martensite and austenite film. At the PT of 900°C, the microstructure consists mainly of martensite packet with high density dislocations. At the PT of 700°C, the microstructure corresponding to the inter-critical HAZ (ICHAZ) consists of ferrite, austenite, and carbides. At the PT of 500°C, the microstructure corresponding to the sub-critical HAZ (SCHAZ) consists of ferrite and austenite. The volume fraction of austenite and ferrite increased sharply and the content of martensite decreased with decreasing PT. Tensile strength and yield strength decreased with decreasing PT due to martensite content reduction. Static toughness of ICHAZ is 343.4 MJ/m3 due to good balance of ductility and strength of metastable austenite. CGHAZ has the lowest static toughness of 196.4 MJ/m3 due to the lower ductility for martensite.
M2052 is a famous high damping Mn–Cu alloys with good strength, but lack of well corrosion and wear resistance. In this study, we expect to enhance the wear and corrosion resistance of M2052 damping alloys by electroless plating Ni–P coating. Successfully, a high phosphorus amorphous Ni–P coating with thickness about 15 µm plated on M2052 substrate. After electroless plating Ni–P coating, the roughness of samples surface decreased and the microhardness increased. Thus, the coated sample featured better wear resistance, and attributed to adhesive wear mechanism. By contrast, the friction coefficients of uncoated samples presented a high value with great fluctuations, which due to low hardness, high roughness, and easier to be oxidized. This leads to the dominant wear mechanisms are abrasive and corrosive wears. Ni–P coating significantly improved the corrosion resistance, because it has lower Icorr, higher Ecorr, and higher impedance than M2052 substrate. Surface morphologies after electrochemical tests were also observed: the uncoated samples had been corroded severely with a fibrous corrosion product layer dispersing cracks and pits. However, coated samples had not been corroded and remains intact. Furthermore, Mott–Schottky plots inferred that the sample surface after plating Ni–P coating performed an excellent passivation behavior in NaCl solution.
The room temperature (RT) ductility of ferritic Fe–Al–Ni-based alloys containing B2-type NiAl precipitates was improved by the refinement of the matrix. The microstructure and tensile properties of Fe–Al–Ni–Cr–Mo–Mn alloys after annealing at 1223 K followed by air cooling were investigated focusing on Mn content. The matrix of the alloy containing 4 at% Mn consists of coarse equiaxed α (bcc) grains and fine grain regions composed of the α and γ (fcc) grains. Fine grain regions are formed through the phase transformation between the α and γ phases during annealing and air cooling. In the heat treatment process, the precipitation of (FeCr)2Mo Laves phase is effective in the refinement of the matrix grains due to grain boundary pinning effect. The alloy with fine grain regions in the matrix exhibits not only large elongation (approximately 14.7%) at RT but also high strength, compared with modified 9Cr-1Mo and 316 stainless steels in the temperature range from RT to 973 K. The fine grain regions which are fractured by ductile fracture mode are responsible for the large ductility of the alloy at RT. Moreover, the high strength of the alloy at high temperatures is attributed to the high stability of the NiAl precipitates at 973 K.
Gypsum waste, with CaSO4·2H2O as the main ingredient, decomposed into SO2(g) at a proper temperature, according to previous research. It could sulfurize SnO2 to SnS(g) in the presence of C or CO(g), based on which a method of roasting with gypsum waste (CaSO4·2H2O) for removing Sn from Sn-bearing iron concentrates was put forward in this paper. In addition, a traditional curing agent, FeS2, was introduced and comparatively studied. With FeS2 used as the curing agent for tin sulfurization and removal, the FeS generated from the FeS2 decomposition played a major role through its transformation to SO2(g) and COS(g) in mixed gases of 35 vol.%CO and 65 vol.%CO2. Besides, the COS(g) had a better sulfurization effect on tin than SO2(g). The ‘S’ from gypsum waste (CaSO4·2H2O) was mainly transformed into FeS and Ca3Fe4S3O6 upon roasting with tin-bearing iron concentrate in mixed gases of 35 vol.%CO and 65 vol.%CO2, both of which could sulfurize Sn(l) to SnS(g) also through their transformation to SO2(g) and COS(g). The amount of sulfur added by CaSO4·2H2O could be decreased compared with that added by FeS2 due to the higher utilization efficiency of ‘S’ in CaSO4·2H2O. This process realized the cyclic utilization of gypsum waste, Sn effective removal and the iron pre-reduction from tin-bearing iron concentrate.