A new SiO2–CaO–MgO–Fe2O3 system ceramics, namely pyroxene ceramics in this paper, was put forward for efficiently utilizing the steel slag. The prepared ceramic with 30 wt% of steel slag has excellent properties with flexural strength of 107 MPa and water absorption rate of 0.045%. Microstructure evolution in the new system ceramics was studied by X-ray diffractometry and scanning electron microscopy. High content CaO in this system contributes to crystallization in low temperature. Diopside (CaMgSi2O6) formed at temperature below 800°C, and was predominant at approximately 1000°C before densification. The main phases of pyroxene have not changed except the solution of ions of Fe2+/Fe3+, Al3+, Mn2+, Ti4+ and so on. Melting of iron-rich andradite, Fe2O3 and RO (solution of FeO, MgO, MnO etc.) phases at temperature between 1100°C to 1180°C promoted liquid sintering and densification process. The crystallization process at temperature between 700°C to 1100°C is prior to the densification process at temperature between 1150°C to 1220°C, and the formed crystals played an important role of framework during the densification process. Sole interlocking pyroxene phases and less glass phase in the final ceramic are contributed to its excellent mechanical performances.
A theoretical model for predicting the electrical capacitance of various materials was developed by taking into account geometrical configurations of crucible and rod electrodes. The calculated results were in good agreement with the corresponding measurement data obtained at room temperature (20°C) for liquid materials with known relative permittivity. The measured capacitances of aqueous suspensions containing oxide powders with various grain sizes and relative permittivity values systematically decreased at room temperature with increases in their volume fractions regardless of the sizes of the dispersed solid phases and matched the results obtained from the proposed capacitance prediction model combined with Lichtenecker’s equation for calculating the relative permittivity of dual-phases mixtures. In addition, the validity of the proposed model for predicting capacitances of supercooled oxide melt suspensions was tested at elevated temperatures (above 1300°C). The observed decrease in capacitance for silicate melts with known crystallinities estimated from the corresponding phase diagrams was consistent with the data predicted by the proposed capacitance model combined with Nielsen’s equation instead of Lichtenecker’s equation due to the large differences in relative permittivity between the utilized oxide melts and the solid phases.
The effect of TiO2 on the liquids zone and apparent viscosity of SiO2-CaO-8wt%MgO-14wt%Al2O3 system were studied in the present work. At fixed CaO/SiO2 between 0.5 and 1.3, higher TiO2 content decrease the slag viscosity indicating that TiO2 additions up to 50 wt.% behaved as a viscosity-decrease agent by loosening the silicate network structure. The free running temperature increase at TiO2 content from 10 wt.% to 30 wt.%. At fixed TiO2 content of 20, 30 and 40 wt.%, increasing the CaO/SiO2 resulted in lower viscosity due to the depolymerization of the structure. Four different viscosity models were discussed and two of them were employed to predict the viscosity and found that the Urbain’s Model agrees well with experimental data at high viscosity (4–12 dPa·s) and the KCC’s Model agrees well with experimental data at a lower viscosity (0–4 dPa·s).
The investigations of concentrating iron, slag and britholite-(Ce,La,Pr,Nd) from gaseous reduced Bayan Obo ore were conducted at 1473 K in a super gravitational field. The results showed that iron grains concentrated at the bottom area along super gravitational direction, whereas the gangue formed the slag in the upper area along the opposite direction, as well as the REEs enriched into britholite-(Ce,La,Pr,Nd) with a typical hexagonal structure and concentrated in the bottom slag. Moreover, the effects of gravity coefficient on both iron-slag separation and the concentration of REEs precipitates were investigated further.
Steel industries need to increase the use of low-rank coals in coke making since coking coals have been depleting and the price of coking coal has been increasing. In this study we propose to pretreat low-rank coals in non-polar solvent such as 1-methylnaphthalene below 400°C for converting them to a substitute for coking coals. The proposed method was found to be effective in deoxygenating low-rank coals significantly while suppressing cross-linking or polymerization reactions which often accompany deoxygenation reactions. The amount of low-molecular-weight compounds formed in the solvent-treated coals was comparable to that existing in coking coals. Coking tests utilizing the solvent-treated coals suggested that the solvent-treated coals can be substitutes for slightly-coking coals in coke making process.
The relative effects of gibbsite, kaolinite and aluminous goethite as alumina sources on the thermal stability, concentrations and formation mechanisms of silico-ferrite of calcium and aluminium (SFCA and SFCA-I) iron ore sinter bonding phases, was investigated using in situ X-ray diffraction. Iron ore containing gibbsite as the primary source of alumina is less likely to form high quality sinter due to the lower reactivity of the alumina leading to low amounts of SFCA-I and SFCA bonding phases being generated. Sintering of this ore is likely to require higher fuel as higher temperatures are required to generate the bonding phases. Alumina in the form of kaolinite or aluminous goethite, however, produced larger amounts of both SFCA-I and SFCA and at lower temperatures. Use of kaolinite resulted in the formation of a highly reactive gehlenite intermediate phase that maximised the formation of SFCA-I, the matrix phase that imparts high strength and good reducibility characteristics to sinter. Iron ore containing aluminous goethite also generated SFCA bonding phases however the difference in the reaction mechanism between kaolinite and aluminous goethite containing ore led to less SFCA-I being formed overall. These findings give some insight into why sintering investigations using Australian ores with kaolinite tend to show less impact on sinter quality than the more widely reported alumina studies involving gibbsite-rich ores.
This paper presents a comprehensive study on the behaviors of titanium compounds generated in the blast furnace (BF) hearth during the vanadium titano-magnetite smelting by the dissection method combined with experimental and theoretical analysis. The results show that considerable titanium compounds are formed in the eroded furnace wall below the taphole level. The phases of titanium compounds consist of Ti(C,N) crystals, slag phase and liquid iron. The phase of Ti(C,N) crystals are mainly TiC0.3N0.7. The formation mechanism of titanium compounds is revealed. It is found that the Ti(C,N) phase is formed within hot metal, while the slag phase originates from the interaction between the mineral in coke and final slag in the BF hearth. Furthermore, the slag is confirmed present in the low part of the BF hearth. The thermal conductivity of the titanium compounds in the hearth is determined as 11.98 W/m/K by analyzing the thermodynamic and heat transfer characteristics of the compounds. This prediction is in satisfactory agreement with the measurement.
We commercialized Reactive Coke Agglomerate (RCA), a cement-bonded pellet to decrease the thermal reserve zone temperature for the reduction of the reducing agent rate of blast furnaces. To achieve a high productivity of supplying RCA to large blast furnaces, a rapid curing process of RCA using steam was investigated. We obtained rapid curing of RCA within 18 h by combining primary curing for 12 h and stream curing at 80°C for 5 h subsequently with drying for 1 h. This combination provided sufficient strength to an RCA product when compared with the strength obtained after conventional yard curing, which requires a long curing time of 14 days. Plant trials revealed that a longer primary curing time was required because of the non-homogeneity of thermal conditions. Nevertheless, the curing period could be shortened by 12.5 days with drying and 9 days without drying. Mineralogy and morphology of hardened cement in RCA after rapid curing were investigated. XRD and thermal analysis revealed that the basic mineral composition of cement after rapid curing was comparable with that after conventional yard curing. In plant tests, during rapid curing, hydration and microstructural evolution of cement in RCA were accelerated by steam curing. RCA involving the steam curing process has been implemented in Oita works and it has been helping in a stable operation of two large blast furnaces under a low RAR.
Production flow sheet of RCA implemented in Oita works.
A considerable amount of works were focused on the formation mechanism of calcium ferrite phases during the iron ore sintering process, especially under various O2 content atmospheres at temperatures higher than 1100°C. But little attention has been paid on reactions between CaO and iron oxides in CO–CO2 atmospheres at lower temperatures. In this study, the solid state reaction mechanisms between CaO and Fe3O4 under CO–CO2 atmospheres at 800°C–1100°C were revealed by using XRD, VSM, etc. The results indicated that Ca2Fe2O5 was easily formed under 5–50 vol% CO/(CO+CO2) atmosphere above 850°C via the reaction of 6CaO + 2Fe3O4 +CO2 = 3Ca2Fe2O5 + CO and the reaction would be promoted with increasing the roasting temperature. In the CO–CO2 atmosphere, Fe3O4 is easily oxidized to Fe2O3 in the presence of CaO because CO2 components act as oxidative medium for the oxidation of Fe2+ to Fe3+.
A thermodynamic model was developed to predict slag–steel–inclusion reactions of 304 stainless steels. The dissolved aluminum in the steel, the sulfur distribution ratio and the composition of inclusions equilibrated with varying slags were predicted using the current model. The model can also be widely used to predict the liquid fraction of inclusions. For Al-killed 304 stainless steels, the optimized composition of CaO–Al2O3–SiO2–MgO slags is proposed to modify solid Al2O3 inclusions to liquid CaO–Al2O3–MgO at 1873 K. For Si-Mn-killed 304 stainless steels, the optimized composition of CaO-SiO2-MgO-Al2O3-20%CaF2 slags is suggested to suppress the formation of Al2O3–MgO in SiO2–CaO–MnO–MgO–Al2O3 inclusions and lower their melting temperatures.
The idea of twin-roll casting (TRC) was first patented by Sir Henry Bessemer in 1857. Development of the TRC process took more than 100 years and now it is commercialized for production of both ferrous and non-ferrous alloys particularly for some special steels. The process has significantly lower energy consumption and pollution compared to conventional processes and some other benefits as well as some limitations. This overview explains the history and principles of TRC for steels. Moreover, the utilization of TRC for different categories of steels and the following microstructural and mechanical properties is discussed in details.
A new creep straightening casting curve that continuous casting slab can be straightened by full using of high-temperature creep property was proposed in this paper. The basic arc segment is cancelled in the new curve so that length of the straightening area can be extended and time of creep behavior can be increased significantly. In order to maximize the use of high-temperature creep property, various curvilinear equations with different changing rate of curvature were studied. The distance from solidifying front of slab at 1200°C is confirmed by finite element method. The strain rate at different locations which is beneath the center of inner arc surface were calculated when temperature is 1200°C. Uniaxial tensile tests of Q345C were carried out in order to obtain yield strength and minimum creep strain rate. It is concluded that the strain rate in the straightening area of new curve was less than minimum creep strain rate under yield strength at 1200°C. Therefore, strain rate can be below minimum creep strain rate on new creep straightening curve so that deformation of slabs depended on creep behavior only comes true. Continuous casting slab is straightened by means of creep strain so as to reduce the straightening strain and strain rate substantially. Internal cracks of slab caused by straightening could be effectively avoided, and the quality of the slab could be improved.
Effect of a weak transverse magnetic field (B ≤ 0.7 T) on the microstructures in directionally solidified Zn-2.2 at.% Cu peritectic alloy has been investigated experimentally. The results indicate that the magnetic field causes the formation of a transition from the primary dendrite to peritectic phase, macrosegregation of the Cu solute in the primary dendrite, a change in the volume fraction of the primary phase, and the refinement of the primary dendrite. Furthermore, energy dispersive spectrometer (EDS) analysis reveals that the magnetic field increases the Cu solute content in the solid and front of the solid/liquid interface. The Seebeck voltage near the solid/liquid interface in directionally solidified Zn-2.2 at.% Cu alloy at various growth speeds is measured in situ, and the result shows that a thermoelectric current exists near the solid/liquid interface. The thermoelectric magnetic convection (TEMC) in the liquid under the magnetic field is numerically simulated, and the result reveals that a unidirectional TEMC forms in the liquid near the solid/liquid interface during directional solidification under the transverse magnetic field. The modification of the microstructures in directionally solidified Zn-2.2 at.% Cu alloy under the transverse magnetic field should be attributed to the TEMC driven solute transport.
The transient three-dimensional (3D) full-coupled multi-physical fields in the Electroslag-Remelting (ESR) process with the vibrating and traditional electrodes have been compared in this paper. A mathematical model for simultaneously predicting the electromagnetic phenomenon, heat transfer, two phase flow and solidification has been established in the ESR furnace. Especially, the Joule heating and electromagnetic force are calculated by self-developed program based on the magnetohydrodynamic (MHD) model. The effects of the vibrating modes, such as horizontal and vertical vibration, on the heat transfer and MHD two-phase flow as well as solidification are clarified. The results indicate that the melting rating can be increased in the ESR process with vibrating electrode. The small-scale factory experiments are conducted and a reasonable agreement between the experimental observations and numerical results is obtained. The variation of temperature distribution dominated by the dropping behavior of the metal droplets is ordered and periodic. Particularly, the distinct variation of temperature distribution occurs beneath the bottom tip of the electrode. The horizontal vibrating ESR process can generate smaller metal droplets, which provide less energy (heat plus momentum) into the metal pool, constitute a shallower pool and a lower average temperature gradient. Moreover, with the increasing amplitude or frequency, the average temperature gradients for both cases decrease.
The wetting effect of melt puddle between nozzle and chilling wheel in the planar-flow melt-spinning process was simulated numerically. A two-dimensional model was developed for the puddle in which the inertial force, viscosity, surface tension, wettability, and heat transfer with phase transformation were incorporated. The wetting conditions include the static contact angle between the puddle and nozzle and the dynamic contact angle between the puddle and chill wheel, and their influence on the puddle shape, ribbon thickness and air-pocket frequency were evaluated. Results show that the puddle shape was affected significantly by the wetting condition on the nozzle surface rather than that on the wheel surface. The contact condition between the puddle and nozzle must be non-wetting in order to reach a steady puddle shape rapidly. On the other hand, a wetting contact condition is preferable between the puddle and wheel surface to reduce the amount of air entrainment and lower the air-pocket frequency on the ribbon surface.
Development of accurate soft sensors for online quality prediction (e.g., silicon content) in an industrial blast furnace is a difficult task. A novel just-in-time-learning (JITL) prediction approach using adaptive feature-weighting for similar samples is developed. First, a dual-objective joint-optimization framework is proposed to introduce both input and output information into the model. Then, a suitable similarity criterion with feature weighting strategy is formulated, which is not considered in conventional JITL methods. Moreover, the trade-off parameter in the joint-optimization problem can be chosen automatically, without the time-consuming cross-validation procedure. The proposed method is applied to online predict the silicon content in an industrial blast furnace in China. Compared with other JITL-based soft sensors, better prediction performance has been obtained.
Parity plot based of assay values against the prediction values of the silicon content in the test set using the adaptive weighting JLSSVR and traditional JLSSVR soft sensor models.
Depletion of the high quality ores around the world has forced ferronickel producers to extract metal values from low-grade ore bodies with significant amounts of impurities. Under this condition, maintaining alloy quality is of utmost importance for the smelters; however still, accessibility of a reliable sulphide capacity model for FeNi refining processes is an issue. Many of the current models, such as those incorporating optical basicity, have proven to be erroneous and unreliable for wide ranges of composition and temperature. These models are typically developed and tested without a proper validation method thus allowing for great correlations which may not fare well with the introduction of new data. Models built from fundamental thermodynamic data perform much better in predicting sulphide capacities but are not only complicated to formulate but also too complicated to be used by operators on a day to day basis as multitude of inputs are needed. Hence, development of a reliable model based on fundamentals, which can also be directly used by plant operators is very much demanded by the industry. In the current study, an artificial neural network (ANN) approach has been used to predict sulphide capacities of slag compositions in the CaO–SiO2–Al2O3–MgO system with an objective to be used in ferronickel refining processes. The resulting models are evaluated on: 1) coefficient of multiple determination (R2), 2) correlation strength (r), 3) root mean square error (RMSE) and 4) computation speed. The ANN based model has shown to be superior in predicting sulphide capacities to current models.
An approach to a class-specific and shared dictionary learning (CDSDL) for sparse representation is proposed to classify surface defects of steel sheet. The proposed CDSDL algorithm is modelled as a unified objective function, covering reconstructive error, sparse and discriminative promotion constraints. With the high-quality dictionary, the compact, reconstructive and discriminative feature representation of an image can be extracted. Then the classification can be efficiently performed by discriminative information obtained from the reconstructive error or the sparse vector. Based on a dataset of surface images captured from a practical steel production line, the CDSDL algorithm is carried out to verify its effectiveness. Experimental results indicate that the CDSDL algorithm is more effective in classifying surface defects of steel sheet than other algorithms.
In the steel works, direct observation of the internal states of many processes, such as the blast furnace, is difficult. Automation of such processes based on process visualization is an urgent issue. Because the number of sensors is limited, the state estimation utilizing partial sensor information is necessary. We developed a technique which visualizes the entire temperature distribution of a shaft furnace by means of the particle filter, which combines the sensor information and a nonlinear model calculation. This state estimation was incorporated in the heat pattern control logic based on future prediction, in which the estimated heat pattern is set as the initial condition. The control logic was implemented in a ferro-coke pilot plant. As a result, the control accuracy of 10°C was achieved. Furthermore, the operational condition was adjusted based on the correlation between the estimated heat pattern and the product strength. In consequence, the product strength improved by 0.5 points (Drum Index 150/15 mm, DI15015).
The aim of this research was to predict the residual liquid distribution during laser beam welding at different welding speeds using Multi-phase field modeling to investigate the solidification cracking phenomenon. The calculated secondary dendrite arm spacing and primary dendrite tip radius were compared with experimental values and Kurz–Giovanola–Trivedi modeling. The effect of calculation parameters, such as interfacial mobility and anisotropy of interfacial mobility, on lengths of the residual liquid distribution composed of residual liquid connecting with the molten pool (LP) and film-dot (LFD) regions was evaluated quantitatively. The length of each region increased with increasing interfacial mobility. The lengths of LP and LFD increased and decreased, respectively, with increasing anisotropy of interfacial mobility and finally both remained constant. An adjustment of the calculation parameters using experimental results yielded the lengths of the residual liquid distribution that were nearly the same as that of the fracture surface of a solidification crack. The residual liquid distribution could be predicted from verification with experimental results and calculated parameter optimization at a high cooling rate.
The current research status and main drawbacks of underwater welding are briefly summarized. A novel welding torch is proposed to overcome the problems and issues. The design details and working principle are introduced. A series of welding experiments are conducted, obtaining nearly defect-free joints. The experimental results indicate that the innovative methodology achieves a higher welding speed and better welding stability than conventional underwater welding. The feasibility and superiority of the innovative methodology are verified. An optimal database and corresponding weld bead diagrams are presented for direct employment in subsequent research.
In this work, the effects of gas composition, elapsed time of reaction and temperature during annealing on scale removability were investigated for a (3.2 wt.% Si) non-grain oriented electrical steel, and the results were discussed from the viewpoint of oxide morphology.
The annealing tests were carried out under conditions similar to those of industrial annealing operations. For this purpose, steel samples with their original as-received tertiary scale were annealed over the temperature range 900–1000°C in O2–CO2–H2O–Ar–N2 and N2–H2 gas mixtures and in pure N2. After annealing, oxide/steel samples were cooled in air and some were water quenched to study the effect of thermal shock on oxide scale removability. During the annealing tests, four types of oxide scales were observed: oxide scale without idiomorphic growth (Type I), oxide scale with idiomorphic growth (Type II), neutral scale (Type III) and reduced scale (Type IV). The experiments showed that the annealing atmosphere, annealing time, temperature and cooling media influence the morphology and removability of oxide. In general, the experiments indicated that a reducing atmosphere during annealing and water cooling at the end of annealing are the ideal conditions for oxide removal.
Water under a film of paint in corroded steels was visualized using thermal neutrons at the RIKEN-accelerator-based compact neutron source. Two painted plate samples made of normal steel and corrosion-resistant alloy steel were prepared. Both were scratched on the painted surface and then subjected to a cyclic corrosion test to generate blisters caused by under-film corrosion. They were soaked in water for 2 h and then removed from the water. Time dependences of the water distribution in the under-film corrosion were observed using the neutron transmission imaging method for the first time. The alloy sample contained less water than the sample made of normal steel and the water in the alloy escaped from the sample more rapidly than that in the normal steel. We also evaluate the corrosion resistance performance of the painted steel sample.
Time dependence of the water distributions. The colors indicate the estimated water thickness at each pixel.
Torsion simulations of plate rolling were carried out on an X70 steel at 900°C; pass strains of 0.4 and a strain rate of 1 s−1 were employed together with interpass times of 1.0 s, 10.0 s, 20.0 s and 30.0 s. The mean flow stresses (MFS`s) applicable to each pass were calculated by integration of the individual flow curves. These decreased with pass number, indicating that both dynamic transformation and dynamic recrystallization were taking place during straining. The critical strains for the initiation of dynamic transformation were determined by double differentiation and fell in the range 4–5% from the second to the last pass. The volume fraction of dynamically formed ferrite retained after a simulated rolling pass decreased with interpass time. This was due to the increased amount of ferrite retransformed into austenite during the longer interpass times. The forward transformation is considered to occur displacively while the retransformation into austenite during holding takes place by a diffusional mechanism.
The hydrogen trapping sites of commercial 20CrMo steel samples with electrochemically charged hydrogen were characterized by thermoelectric power (TEP) and scanning Kelvin probe force microscope (SKPFM). A surface potential drop of about 190 mV was found for the globular MnS inclusion and 150 mV for the elongated one due to the hydrogen absorption of MnS inclusions. Similar to thermal desorption measurement, TEP is a potential method in analyzing hydrogen traps of solid solution, dislocations and irreversible traps. The fracture morphology and hydrogen induced cracking can be explained by combined hydrogen embrittlement mechanisms. Although hydrogen induced cracks are found to initiate at the elongated inclusions, only longitudinal cracks were observed in this study which is not detrimental to the embrittlement.
The rupture time of the tungsten-alloyed steel is much shorter than that of the molybdenum-alloyed steel. The fracture mode of the former steel is typically intergranular, but the latter steel shows a mixed fracture mode of intergranular and ductile. The shorter rupture time of the tungsten-alloyed steel is due to the active carbide formation reaction of tungsten in ferrite which depletes carbon within the matrix; the resulting higher segregation concentration of phosphorus at GCIs and carbide-free PAGBs. The longer rupture time of the other steel arises from two factors: the molybdenum segregated at the interfaces as a grain boundary strengthener; the repulsive segregation between carbon and phosphorus which repels phosphorus from the interfaces and produces the lower segregation concentration of phosphorus.
The work hardening behavior and the change in the dislocation density of lath martensite at strain levels of less than 15% under uniaxial tensile loading were investigated. It was clarified that the work hardening rate and the multiplication of dislocation become more prominent as the solute carbon content increases. The change in the mobile dislocation density during deformation was evaluated by studying dynamic strain aging behavior, and it was found that the annihilation of mobile dislocations becomes slower at a higher carbon content. The findings were further examined by a modified Kocks-Mecking-Estrin model proposed in order to explicitly clarify the changes in the mobile and sessile dislocation densities during deformation. From the model-based analysis, it is also suggested that the solute carbon retards the formation of dislocation cells by reducing the mobility of dislocations. These findings were also corresponded well with the observation of the dislocation structure using a transmission electron microscope.
Blast furnace (BF) slag has been recycled in the construction industry mainly as cement and concrete. However, in the past few years, recycling conditions have changed and other recycled materials have become dominant; thus, new applications for BF slag need to be considered. In this study, we first reviewed applications in which BF slag was treated by hydrothermal reactions. Under hydrothermal conditions, tobermorite (Ca5Si6O16(OH)2·4H2O) was formed from BF slag. This tobermorite, which was produced in a CaO–SiO2–H2O system, was used as the main binding mineral in autoclaved lightweight concrete (ALC), and the corresponding ALC exhibited excellent properties in terms of heat insulation and lightness.
Next, in the present study, the utilization of BF slag in the ALC manufacturing process as an alternative raw material was evaluated based on the environmental impacts associated with its use. Specifically, the environmental impact was evaluated with life cycle inventory (LCI) data for the resulting CO2 emissions. The LCI data for ALC prepared with BF slag were compared with LCA data for other conventional production processes, and the results showed that the ALC prepared with recycled BF slag had lower levels of CO2 emissions than the other processes that were evaluated.
Special steel materials, including alloy steel and stainless steel, are among the most widely utilized materials in our society. Many kinds of metals other than iron accompany the special steel materials. Therefore, to achieve sustainable metals use in the steel industry, it is important to untangle the logistics of special steel materials in society. In conventional material flow analysis (MFA) studies based on a top-down approach, primary inputs of materials into industries tend to be regarded as “end use” of material. However, materials are often traded between industries or even exported as intermediate or final products to foreign countries. In this study, discrepancies in requirements for materials between their primary and final versions are revealed by means of a waste input-output MFA (WIO-MFA) model for special steel materials made in Japan in 2005. The result shows that only 45% of the primary demand is domestically consumed as finished product because exports of products such as automobiles and machinery contain significant amounts of special steel materials. In addition, non-negligible inter-industrial transactions are observed. The results imply a need for the careful accounting and precise understanding of material usages, and their sustainable management is crucial.