Global iron and steel making industries generate immense number of by-products, among which few are already being utilized for the generation of high value products, while few are still struggling to gather a good market space. Waste utilization is the major concern for every industrial maker. In this context, iron powder which holds immense market in applications like powder metallurgy (PM) parts, welding electrodes, advanced oxidative agents for water treatment, food fortifying agents, metal injection moulding, catalysts, fuels etc., can now be a novel outcome from steel industry by-products. Iron powder can be manufactured by various techniques like reduction, atomization, electrolysis, etc., resulting in fine particles of various morphologies ranging from spherical to irregular shapes and low to high purity. The application of these iron powders is depended on the process, quality and purity of the desired product.
Only a few models for estimating electrical conductivity of molten slag have been developed, which are limited to systems with certain types of components. In this study, a new method for estimating the electrical conductivity of molten slag through neural network calculations is proposed and is compared with previous estimation approaches. The present estimation approach can reproduce the electrical conductivity of molten slag composed of SiO2, CaO, MgO, MnO, Al2O3, FeO, Fe2O3, and Na2O to an uncertainty of 30%. We found that the neural network calculation is applicable to various kinds of molten slag over wider mole fraction and temperature ranges than conventional models.
For increase of sinter productivity, it is important to design sinter mixture granulation.
Moisture is indispensable for granulation as a binder between raw material particles. Once granulation is completed, moisture is dispensable during sintering because moisture vaporization is endothermic reaction.
Based on the above-mentioned view, a process of drying the granules after granulation with high moisture examined for sintering productivity by use of sinter pot test.
The main results obtained are described as follows:
(1) Drying in conjunction with high moisture granulation is effective to increase flame front speed with maintaining sintering yield;
(2) Increasing flame front speed is due to shorten the time to evaporate moisture in the wet zone of sintering packed bed in addition to increasing permeability of sintering packed bed. This effect is also evaluated and proved based on calculation of moisture transition in and out of sintering packed bed;
(3) Maintaining sintering yield is due to higher heat generation in sintering packed bed caused by higher coke combustion efficiency in addition to lower moisture concentration of sinter mixture.
(4) Collapse of granules in case of drying after granulation is avoided till the critical moisture, that is defined as the one left in the mix after higher moisture granulation makes granules to keep shape easy due to higher moisture quantity on the surface of granules.
Improvement of sinter productivity at high moisture granulation and dry treatment.
Graphite morphology and the liquid flow behaviour in lower part of blast furnace show a close relationship to the interfacial energy between iron and graphite. In this study, molecular dynamics simulations were employed to explore the position preference of an anti-spheroidizing element (such as oxygen atom) in melt cast iron as well as its influence on the iron/graphite interfacial energy. First, our results showed that oxygen atoms were more favorably adsorbed on the prism plane of graphite than on the basal plane. Second, MD study revealed that the adsorbed oxygen atoms would influence the wettability between molten iron and graphite prism plane, leading to a significant change in interfacial energy. For instance, the interfacial energy decreased with increasing number of adsorbed oxygen atoms.
The mechanical properties of iron ore pellets are of central importance to guarantee good productivity in direct reduction plants. Besides the generation of fines during handling, mechanical degradation resulting from forces produced inside the furnace are detrimental to the performance of these reactors, since they can lead to the generation of clusters, and also because they impact negatively the permeability of the charge to the flow of reducing gases. The present work analyzed the effect of different degrees of reduction on the mechanical properties of direct reduction iron ore pellets so as to estimate the proportion of fines generated inside a direct reduction furnace. As such, tests have been performed with unreduced, as well as iron ore pellets that were subjected to different degrees of reduction, with the aim of analyzing their mechanical properties, including microhardness, cold compression strength, mass loss in drop tests as well as pore size distributions. From these results, a parameter of a model of mass loss due to surface breakage was estimated, which demonstrated their greater amenability to breakage as reduction progressed. A combination of these results to simulations using the Discrete Element Method of a direct reduction furnace made it possible to estimate in 5.7% the percentage of fines generated in the furnace.
Direct reduction behavior and dynamic characteristics of oxidized pellets under the 75%H2-25%N2 atmosphere at 760, 900, 1000°C are studied in this paper. 500 g oxidized pellets in the size of 10–12.5 mm are reduced by gas with the flow rate of 12 L·min−1 for 1 hour. Weight loss during reduction was recorded and the model of un-reacted core was adopted for dynamic analysis. Morphology of metalized pellets was analyzed through optical microscope and scanning electron microscope. Compressive strength and degradation index were also detected. Results showed that both the reduction degree and reaction rate increased with the increasing temperature. The reduction rate was controlled by chemical reaction with the apparent activation energy of 40.954 kJ·mol−1. The chemical reaction resistance could be effectively reduced through appropriately raising the temperature. However, the effectiveness was weakened with the further increase of temperature. The reaction rate constant at 900°C was 0.025 m·s−1, which was slightly lower compared with reduction kinetics under pure hydrogen. The compressive strength decreased with the increasing temperature, and amounts of holes and cracks were observed at higher temperature. Reduction degradation behavior of pellets under this atmosphere was not obvious.
The evolution mechanism of non-metallic inclusions in Al-killed, Ti-bearing 11Cr stainless steel with Ca treatment was investigated by industrial trials and thermodynamic calculation. The morphology, composition, and size distribution of inclusions in steel specimens were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The alloy addition and calcium contents in steel significantly influenced the characteristics of inclusions according to the present study. After the addition of Al, there were mainly alumina-rich inclusions in steel. With the titanium addition after calcium treatment, three types of inclusions were formed: irregular MgO–Al2O3–TiOx inclusion, spherical CaO–MgO–Al2O3–TiOx inclusion, and irregular dual phase Ti-containing inclusion. At the end of LF refining process, solid calcium titanates inclusions were formed due to the high calcium content in steel. The evolution of these inclusions was consistent with thermodynamic calculation, which indicated that the compositions of inclusions in steel specimens after the addition of titanium were mostly located in Al2O3–TiOx stable phase. Based on the characteristics of inclusions in steel and thermodynamic calculation, calcium could reduce the stability of spinel and strongly modify solid alumina and Al2O3–TiOx inclusions to form liquid oxides or solid calcium titanates. At the same time, the effects of calcium content in Al-killed, Ti-bearing 11Cr molten steel on the formation of inclusions were discussed through the coupling of thermodynamics calculation and experimental results.
Bimetallic composite roll has been given more and more attentions because of its superiority in playing the advantages performance of the internal and external materials at the same time. In the present study, a 2D quasi-steady state mathematical model of the electroslag cladding technology for producing bimetallic composite roll was developed by the Fluent software with the UDS and UDF function. Characteristics of the electromagnetic field, flow field and temperature field of the composite roll system have been numerically simulated and the laboratory scale experiments with the different power supply circuits were also developed to provide a verification of the mathematical models. The results indicate that: simulation results of the temperature distribution in the composite roll were well verified by the corresponding experiments. With the using of current supplying mold (CSM®), the improved conductive circuit is more beneficial to improve the distributions of current density and Joule heat in the slag pool and keep the high temperature zone away from the roll core surface than the conventional conductive circuit. On one hand, it makes the roll core be no longer as a pole of the electroslag process and the temperature adjustment of the slag pool become more flexible. On the other hand, it leads to a partial micro-melting of the roll core surface which is beneficial to form a metallurgical bonding and effectively avoid the mechanical mixing of the liquid metal between the roll core and composite layer, so, it can improve the comprehensive performance of bimetallic composite roll.
Schematic diagram of the electroslag cladding method with the (a) electrodes→roll core and (b) electrodes→mold conductive circuit for producing composite roll. (Online version in color.)
Mistral Desolvation (MD), a sample introduction method for Inductively Coupled Plasma (ICP)-Atomic Emission Spectroscopy (AES) and Mass Spectrometry (MS), provides sensitivity enhancement over 5 times compared to conventional sample introduction method. Some groups have been proposed different mechanisms of sensitivity enhancement by MD, e.g. inhibition of poly-atomic ion generation derived from solvent, influence of the change of plasma condition, and improvement of sample transportation efficiency in plasma. However, uniform understanding has not been obtained.
In this paper, we have identified the dominant factor of a sensitivity enhancement by MD and examined application to chemical analysis of steel samples. It was found that the MD method provided a decrease of 100–250 K plasma temperature, which led to sensitivity loss. On the other hand, sample transportation efficiency was improved by a factor of 4.7 times owing to an increase in the sum of small droplets. This improvement was comparable to fivefold sensitivity enhancement. Thus, it was concluded that the dominant factor of sensitivity enhancement achieved by the MD method was improvement of sample transportation efficiency with decreasing droplet size.
Besides, the steel certified reference materials have analyzed by MD-ICP-AES. It was found that almost tenth amount of sample consumption and almost 3-fold sensitivity improvement could be achieved, the analyzed value corresponded exactly to certificated value. Thus, in case of a little amount of sample for chemical analysis, for example, sampling from a defected part or a corroded part, this method can be useful due to the high sensitivity and the small sample consumption.
Effect of heating temperature of MD process for droplet size distribution and introduction efficiency. (a) Droplet size distribution upon heating temperature of MD process (b) Results of sample introduction efficiency. ■, 298 K; △, 413 K.
Analysis techniques for quantifying crystal structures of mineral phases and their fractions in iron ore sinters have been developed using the Rietveld analysis of X-ray diffraction patterns and applied to iron ore sinters of different mechanical strength, which were prepared by laboratory-scale sinter pot testing. The Rietveld analysis successfully determined the phase fractions and structural parameters for co-existing phases such as hematite (α-Fe2O3), magnetite (Fe3O4), multi-component calcium ferrites or silico-ferrite of calcium, and aluminum (SFCA:Ca2(Ca,Fe,Al)6(Fe,Al,Si)6O20 and SFCA-I:Ca3(Ca,Fe)(Fe,Al)16O28) and other minor phases. The strength of the iron ore sinter correlated with the quantity of magnetite and not simply with that of the calcium ferrites determined by this method. The lattice constants of calcium ferrites differed among the specimens; moreover, no clear difference was observed among iron oxide phases. These results show that the Rietveld analysis provides crucial information for controlling the sintering process and suggests the phase fractions.
To understand the γ→α transformation and control the carbon contents among the phases involved is most important in the design of high-strength and high-ductility low carbon steels. Using a previously-developed field emission-electron probe microanalyzer (FE-EPMA) which is able to suppress hydrocarbon contamination to a very low level, the carbon concentrations at γ/α interfaces and within the austenite were analyzed in Fe-xC-2.0Si-yMn (x=0.15 or 0.20, y=1.5 or 2.0 in mass%) steels isothermally transformed at 750°C and 800°C. The paraequilibrium (PE) model gives a good accounting of carbon enrichment in the 1.5 mass% Mn steel held for 15 s, whereas the NPLE/PLE transition model of local equilibrium gives a much better accounting in the 2.0 mass% Mn steel than PE. However, the interfacial carbon concentration agrees with the composition shown by the NPLE/PLE transition line in both alloys when annealed for 1800 s. In the 1.5 mass% Mn steel, the carbon concentration at the interface in austenite seems to have shifted from PE to NPLE during annealing.
This paper presents our latest studies on the effects of coiling temperature on the microstructure, precipitation behavior, and mechanical properties of an Nb–Ti microalloyed steel produced by endless strip processing (ESP) and coiled at different temperatures. The amounts of soluble elements were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The microstructure and precipitates were analyzed using SEM, EBSD, TEM, and electrolytic dissolution and filtration tests. The results revealed that large amounts of microalloying elements were still in solution before coiling. As the coiling temperature decreased from 600°C to 560°C, the content of acicular ferrites (AF) increased and the average ferritic grain size was refined from 2.01 µm to 1.29 µm, the yield strength and tensile strength of the tested steel increased by 22 MPa and 20 MPa, respectively, under the effect of microstructural strengthening. As the coiling temperature increased from 600°C to 640°C, the mass fraction of precipitates increased from 0.083% to 0.110% and the percentage of fine precipitates (smaller than 18 nm) increased from 12.2% to 14.7%; the intense precipitation strengthening effect increased the yield strength and tensile strength by 35 MPa and 42 MPa, respectively. Therefore, as the coiling temperature decreased from 640°C to 560°C, the strength of the tested steel decreased first and then increased while the elongation decreased steadily from 18.9% to 14.1% due to the increasing content of AF.
Leveling is a process used to minimize the plate defects including flatness imperfections and uniformity of internal stress in the plate industry. It plays an important role in delivering the desired material properties and product standards required. This paper presents a new analytical method for the curvature analysis of plate during the leveling process. The explicit expressions of the curvature integration model were derived in detail by an assumption of ignoring the residuals stress superimposed effect (IRSSE). The curvature analysis procedure was given about how to choose different expression to build the explicit curvature integration equations which were solved with fsolve function in Matlab. The contact angles and bending curvatures could be firstly analyzed in 0.7–0.8 second even though with random initial values. Then, they were initialized to the procedure by considering the residual stress effect and it only needed 3–4 seconds in 2 iteration steps to get the final solution. It was found that the result by IRSSE is close enough to the solution of the method by considering residual stress effect (CRSSE). The curvature and trajectory distribution by IRSSE and CRSSE just reflects on the last leveling areas because of the residual stress accumulative error effect. The analytical methods by IRSSE and CRSSE have the advantage of iteration speed and solution accuracy, respectively. Therefore, the proposed combined method is potential to the future roller intermeshes optimization research.
Since voids in a billet or an ingot are detrimental under tensile stress, they are closed by forging or rolling through a combination of collapse and contraction. In plane-strain forging or rolling, a cylindrical void or through-hole was found experimentally as well as analytically to be closed as the effective strain at the center of the void reached a certain value. In the present investigation, this finding was further examined for transverse forging, axial rolling and axial forging, in which the void was elongated or shortened in length. Since strain as well as stress components in length were irrelevant to a description of cross sectional changes, a concept of the planar effective strain and the planar hydrostatic stress was introduced. As a result, void closure on cross section was able to be predicted by the planar effective strain and the normalized planar hydrostatic stress at the center of the cross section, which were obtained from an analysis of non-void model. However, there were two exceptions; one was the case in which the planar hydrostatic stress was positive in sign and the other was the axial forging in which the void never collapsed on cross section.
The weld appearance, microstructures and mechanical properties of plasma arc welded joints of ultra-high strength steel and aluminum alloy were studied. The weld appearance was improved when the single bevel groove was used. The steel-aluminum joint is divided into weld zone, bond zone and interface zone. The welds with Al–Cu and Al–Si fillers consist mainly of α-Al + Al2Cu and α-Al + Si, respectively. The interface zone has a double-layer structure, the Fe2Al5 layer at steel side and the Fe4Al13 layer at aluminum weld side. The interface IMC layer is the weakest region in the joint and its evolution process has been summarized. The welding current and filler wire composition have great effects on the interface layer and joint properties. With the increase of welding current, the interface layer thickness increased and the crack appeared in the interface layer when the welding current exceeded 100 A. The joint strength with Al–Si and Al–Cu fillers can reach 62 MPa and 118 MPa respectively at the welding current of 90 A. It is favorable to use Al–Cu filler and welding current of 90 A for improving mechanical properties of the steel-aluminum joint.
The effect of Si on the oxidation resistance of high purity Nb containing 19% Cr ferritic stainless steels has been investigated by means of isothermal heating at temperatures up to 1273 K in air and, the structures of the scale and scale/metal interface were investigated with FE-SEM and FE-TEM. The results are as follows:
Si improved the oxidation resistance, as reported in previous studies. The Si addition of about 0.1% improved the limit temperature of the oxidation resistance more than 100 K. The presence of an amorphous SiO2 layer was found in the interface between the Cr2O3 scale and the metal. This layer might act as an oxidation resistance barrier. In the Si-free steel, a NbO2 layer formed under the Cr2O3 scale, and the Fe2Nb- free region formed beneath the surface. On the other hand, when Si was added, the formation of NbO2 layer was suppressed. In case of 1%Si, no NbO2 layer formed and the Fe2Nb-free region was eliminated. In addition, Fe particles were present in the Cr2O3 scale in the Si-added steel.
The mechanical properties of as-quenched and tempered steels are affected by austenitizing temperature. The present work has investigated the effect of austenitizing temperature on martensitic microstructure, carbide precipitates and mechanical properties of 30NiCrMoV12 alloy steel for the axle of high-speed train. The martensitic microstructure and carbide precipitates were studied using OM, FE-SEM, TEM, EBSD and EDS. Thermodynamic calculation of equilibrium precipitation were carried out by Thermo-Calc software. The results showed that the prior austenite grains, martensitic packets, blocks and laths were coarsening with increasing austenitizing temperature. Besides, with increasing austenitizing temperature, after tempering the amount of large size carbides precipitated at martensitic lath boundaries decreased while the amount of small size carbides precipitated in matrix increased. Meanwhile, phase transformation from M23C6 to M7C3 during tempering was enhanced with increasing austenitizing temperature. Coarse grains and wide martensitic laths were beneficial to reducing the amount of strip-like M23C6 carbides precipitated at martensitic lath boundaries due to the reduction of boundary area and thereby obtaining more fine precipitates in matrix. The strength and impact toughness could be improved to a certain extent by refining carbides in tempered steel with higher austenitizing temperature. However, the degree of favorable influence on impact toughness resulting from refining carbides was lower than the negative effect from coarse martensitic structures. Therefore, the toughness is deteriorated and the strength is improved with increasing austenitizing temperature.
Dual-phase (DP) steel sheets composed of soft ferrite and hard martensite phases are typical advanced high strength steel sheets applicable to a variety of automobile parts. The crystallite texture of steel sheets is an important factor which influences the press formability. However, the texture of the martensite itself in DP steel sheets has not been discussed, since the texture was generally measured by the X-ray diffraction method, which does not distinguish the texture of martensite from that of ferrite. The objective of this study is to investigate the texture evolution behavior of each compromising phase; especially the martensite phase, in DP steel sheets by a newly-developed analysis method using Electron Back-Scatter Diffraction (EBSD). The chemical composition of the steel used was 0.088%C-1.23%Si-2.29%Mn-0.093%Ti (mass%). The two sequent annealing was conducted, changing the second annealing temperature, both in the intercrtical region and in the γ single-phase region. The obtained DP microstructures were controlled to have the same volume fraction of martensite of approximately 40%. The overall texture including martensite after the intercritical annealing was similar to the texture before 2nd-annealing, while the texture after the γ single-phase annealing became weak. The new analysis technique using OIM clearly revealed that the discriminate textures from only martensite were close to, but slightly weaker than those of ferrite under the two annealing conditions.
New ferritic heat-resistant steels with high nitrogen content were prototyped and their microstructures and mechanical properties at high temperature were evaluated. The addition of 0.3 mass% N into ferritic steels was achieved without the formation of blowholes by applying pressurized melting methods under an atmosphere of up to 4.0 MPa. The high-nitrogen ferritic heat-resistant steels contained several kinds of nitrides within the lath martensitic structure. V-rich coarse particles were identified as crystallized MN. Fine VN or Cr2N particles were precipitated on the martensitic grain boundaries such as prior-austenite grain boundary, packet boundary, block boundary and lath boundary depending on the V content. The martensitic structure of the high-nitrogen steels contained a hierarchical microstructure including martensitic laths, blocks, packets, and prior-austenitic grains. These martensitic structures satisfied the Kurdjumov–Sachs relationship as with conventional carbon steel. The creep strengths of the prototyped steels were comparable with those of Gr. 91 steel, albeit lower than those of Gr. 92. Additional precipitates other than nitrides are required for further strengthening of the developed steels.
The tensile properties and mechanical stability of retained austenite in a low alloy steel were evaluated at low temperatures. Transformation-induced plasticity introduced a good balance of strength and ductility at the temperatures from 193 K to 293 K. A high work-hardening rate in the initial stage of deformation and strengthening of the ferrite matrix by lowering the temperature were responsible for the good balance. The higher work-hardening rate at low temperatures was enhanced by the stress-induced transformation of retained austenite. At 0.1 strain over a temperature range from 193 K to 293 K, the retained austenite near a zone normal to <111> was mechanically stable, where not only mechanical stability but also deformability in the retained austenite and austenite grain rotation with ferrite matrix strongly affected the martensitic transformation in the steel. On the other hand, at 77 K, almost all of the retained austenite was transformed to martensite regardless of its orientation because of its low phase stability.
Stainless steel has shown potential as a catalytic material in bulk form. However, it only becomes active in an aqueous acidic environment and elevated temperatures. This study aims to produce stainless steel nanoparticles that have high photocatalytic activity in a neutral medium and at room temperature and to elucidate the photocatalytic activity mechanism of the nanoparticles. Spherical, photocatalytic nanoparticles called “nanoballs” were synthesized by the submerged glow-discharge method. Stainless steel SUS316L grade wire was used as the cathode, platinum mesh was used as the anode while the electrolyte was potassium carbonate. The nanoballs were obtained after centrifuging and washing with water. The physical characteristics of the photocatalytic nanoballs were analysed by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. The nanoballs were mixed with methylene blue and irradiated with ultraviolet light for the evaluation of photocatalytic reaction. The photodecomposition samples were determined using UV-vis spectrometry. The by-products of the photodecomposition were evaluated using mass spectrometry. The results show that stainless steel nanoballs have photocatalytic activity when irridiated with ultraviolet light at room temperature. Submerged glow-discharge plasma method can synthesize nanoparticles rapidly using only metal wires as the electrode.
Experiments were carried out in a slag cleaning electric furnace to reduce magnetite in copper smelting slag using petro-diesel or biodiesel produced from waste cooking oil, and the reduction effects using the two reducing agents were compared. The pyrolysis experiments of petro-diesel and biodiesel were carried out in a fixed bed reactor to study their pyrolysis characteristics and explore the reduction mechanism of magnetite in copper smelting slag. The experimental results showed that the primary crystalline phases in copper smelting slag were magnetite [Fe3O4] and silicate. And the content of fayalite [Fe2SiO4] increased while the magnetite [Fe3O4] decreased after reduction by petro-diesel and biodiesel. In the process of copper smelting slag reduction, the petro-diesel and biodiesel firstly cracked into coke, H2, CO and CH4, and then reacted with the magnetite in the slag. The reduction effect of biodiesel was better than petro-diesel because more reducing gases can be generated through pyrolysis of biodiesel, and its price should be much lower than petro-diesel. Therefore, magnetite reduction in copper smelting slag using biodiesel produced from waste cooking oil should be recognized as an economical and environment-friendly process for waste management and application.
The removal of iron-containing dross particles and recovery of zinc from galvanizing dross by super-gravity separation was investigated using a model Zn–Fe–Al alloy. After super-gravity separation, the high purity molten zinc went through the filter, while the residue mainly consisting of dross particles was intercepted by the filter and separated from the molten zinc. The effects of gravity coefficient and separating temperature on zinc recovery and iron removal were investigated. The preliminary results show the super-gravity separation is a promising method of recovering zinc from galvanizing dross.
Cho and Kim1) proposed a simple model for predicting the amount of mix steel generated during ladle changes involving different steel grades in the same tundish. The authors solved the equations of the model numerically and validated their model for two different tundishes. This model has the advantage of having only one parameter, which should be calibrated for each tundish. In the present work, general analytical solutions were deduced for the Cho and Kim model. The solutions obtained are dependent on a single variable. This variable allows easy identification of the optimum operating parameters for the ladle change as it is illustrated by an application example. This work also investigated the meaning of the parameter of the Cho and Kim model in terms of chemical reactor theory.
The effect of instrumental correction on X-ray line profile analysis was discussed in cold rolled low carbon ferritic steel. It was confirmed that the effect of instrumental broadening is underestimated by utilizing Gaussian correction in comparison with Voigt correction. The values of micro-strain, which were evaluated by the recently developed direct fitting method, were overestimated slightly in Gaussian correction. As a result, the following equations were established in the relation between micro-strain (ε) and dislocation density (ρ) for each case: