Experimental investigations are carried out on mixing time in a water bath agitated by side gas injection with an L-shaped lance. The mixing time is measured using an electrical conductivity sensor and an aqueous KCl solution as a tracer. Particular attention is paid to bath agitation under the conditions that any kinds of swirl motions of a bubbling jet do not appear. An empirical equation is proposed for the mixing time as a function of the gas flow rate, bath diameter, bath depth, and the physical properties of water by referring to a previously proposed empirical equation for mixing time in a bath agitated by J-shaped top lance gas injection. The equation is compared with an empirical equation proposed for a bath in the presence of a swirl motion of the deep-water wave type.
Aiming at the direct production of Ti–Fe alloy, its direct electrowinning has been attempted in a CaF2–CaO–TiO2–FeO bath by using a direct-current electro-slag remelting unit. The experiments were carried out in the slag where the molar ratio of CaO to TiO2 was fixed as 1.5, and the influence of the molar ratio of FeO to TiO2 was mainly investigated. The experimental results proved that Ti–Fe alloy in liquid could be obtained at the limiting bath compositional range. At the molar ratio of FeO to TiO2 was 0.90, both the Ti content in the deposit and the cathodic current efficiency were the best under the conditions in this study; the Ti content reached about 50 wt%, and the cathodic current efficiency also did about 50% at best.
The real and imaginary parts of the relative complex permittivity (εr' and εr") were measured in the ranges of X-band frequencies (8.2 to 12.4 GHz) and between 1 and 10 GHz for graphite, carbon black and coal powders at room temperature so as to clarify the relation between the complex permittivities of carbonaceous materials and their characteristics, i.e., graphitization, porosity (i.e., specific surface area) and ash contained in coals. It is found that the complex permittivities increase with increasing crystallite size and specific surface area. It is also found that the dependency of the permittivities on the ash content seems be negligible within the range of the ash content in the present study.
The high temperature oxidizing-chloridizing roasting is one of useful methods to separate nonferrous metals from pyrite cinder and metallurgy slag. However, as one kind of main nonferrous metals in pyrite cinder and metallurgy slag, the occurrence of zinc is complicated and its chlorination behavior is not demonstrated. In the present study, chlorination behaviors of ZnO, ZnS and ZnFe2O4 at the temperature range of 1025–1175°C in air by simulating the chloridizing roasting process of pyrite cinder and metallurgy slag have been investigated. It is shown that ZnS and ZnO is much easier to remove, ZnFe2O4 is refractory to remove because of the presence of gangues. If enough chloride additives were added, the differences of Zn removal rate among ZnS, ZnO and ZnFe2O4 would disappear. In addition, the presence of Al2O3, SiO2, CaO and MgO decreases the Zn removal rate from ZnFe2O4, and the presence of Al2O3 and MgO decreases the Zn removal rate from ZnO while the presence of SiO2 and CaO improves the Zn removal rate from ZnO. Fe3O4 influences the Zn removal rate from ZnO and ZnFe2O4 positively.
Traditional techniques of inclusion size determination are time consuming and cannot be implemented for on-line quality control. With the development of pulse discrimination analysis – optical emission spectroscopy (PDA-OES), the on-line determination of inclusions has become possible. However, PDA-OES measures only the number of inclusions present in the steel irrespective of size. In the present paper, the potential of PDA to determine the inclusion size is evaluated by employing two methodologies: (i) obtaining the average inclusion size by dividing the difference of total and soluble aluminium concentration by the number of Al based inclusions for 200 industrial ULC heats and (ii) measuring the Al concentration for individual peak intensity for specific heats, giving the inclusion size distribution. The methodologies of inclusion size measurement by PDA-OES as well as the possible causes of the discrepancies obtained after comparison with the inclusion extraction technique are explained in detail.
The hydrogen solubility in the CaF2–CaO–SiO2 slag system has been studied to identify and compare the hydrogen dissolution behavior according to basicity and CaF2 content at high temperature of 1823 K. The hydrogen solubility typically increases with higher CaF2 content across the entire compositional range, but its effect is more pronounced at higher basicity. At low basicity, CaF2 seems to slightly polymerize the slag network increasing the available incorporation sites, where hydrogen can attach and increase hydrogen content in slag. At high basicity, the slag structure is already highly depolymerized and CaF2 addition does not affect the silicate structure, but likely affects the slag hydrogen solubility by lowering the hydroxyl activity. CaO additions lowered the hydrogen content in slag at low basicity and increased the hydrogen content in slag at high basicity. From the temperature dependence of the hydrogen solubility, the dissolution energy of hydrogen in slag was found to be 42.3 kcal/mol.
Any improvement in Blast Furnace productivity under a given set of operating conditions is fundamentally related to better flow distribution of gas through layered burden structure in Blast Furnace. Flow distribution and hence pressure drop of gas in granular zone of blast furnace is dependent on number and thickness of alternating layers of coke and metallic burden. A significant part of this total pressure drop in granular zone can be attributed to interfacial resistance between two successive layers. Whereas, pressure drop in porous layers of materials can be described by well known Ergun's equation in terms of all physical parameters, interface resistance needs specific treatment. Systematic study to investigate the effect of interfacial resistance on gas flow between two successive layers of different material has been attempted in this work. Laboratory scale experiments in scale down model of blast furnace were conducted to establish and quantify interface resistance for different layer configurations.
Coke strength is mainly determined by pores and cracks that cause fracture of coke. In this study, connected pores that were considered to cause fracture of coke were investigated. In order to evaluate connected pores quantitatively, low roundness pores (whose roundness were below 0.2) were measured by image analysis technique of microscopic photographs of cokes. The relationship between the amount of low roundness pores and coke strength (DI1506) showed a good correlation. It is thought that the amount of low roundness pores is one of the factors determining coke strength.
The relationship between compressive stress and loading cycles in MgO–C bricks with various carbon contents was investigated at room temperature and high temperature. The relationship between fatigue failure and thermal spalling was investigated by estimating a characteristic material constant, which represents the degree of sensitivity of crack growth, in terms of fracture mechanics. The relationship between the ratio of compressive stress for compressive strength and loading cycles in MgO–C bricks is not affected by the temperature of the atmosphere. At the same acting stress ratio, fatigue fracture life decreased as the carbon content in the MgO–C bricks decreased. In the thermal spalling test, the number of heating cycles at which small cracks and large cracks were generated decreased as the carbon content decreased. In the fatigue failure test, the ratio of the dynamic elastic modulus to the initial elastic modulus decreased gradually. This ratio also showed a gradual decrease in the thermal spalling test as the number of heating cycles increased. A characteristic material constant was obtained and compared based on the results of a fracture mechanics discussion. The characteristic material constant obtained from the fatigue failure test was substantially the same as that obtained from the thermal spalling test. From this, a relationship in which crack growth behavior leading to fatigue failure is equivalent to that of thermal spalling in MgO–C brick was recognized.
Cu-11 mass% Fe alloy samples were solidified with and without a high magnetic field. The influence of a high magnetic field and cooling rate on the morphology, alignment and distribution of primarily precipitated Fe-rich phase has been investigated. We found that the primary phase of Fe-rich was equiaxed dendrites or columnar dendrites under the combinations effect of magnetic field and initial cooling rate. And Fe-rich primary phase with random alignment was mainly observed in the upper region of the sample solidified without the magnetic field. In the case of the sample solidified with the magnetic field of 7.5 T, however, Fe-rich phase was uniformly distributed and the Fe-rich phase at some areas was aligned parallel to the direction of the magnetic field. Furthermore, slower cooling rate was beneficial to the alignment but was not to the uniform distribution. These phenomena were well discussed from the viewpoint of magnetic shape anisotropy and convection under the high magnetic field.
For the clarification of falling behavior of an electrically insulating spherical second phase in the vicinity of a wall under the imposition of a horizontal static magnetic field, distance between the wall and a falling Polytetrafluoroethylene spherical ball in a saturated sodium chloride aqueous solution was observed under the imposition of the horizontal magnetic field where magnetic field intensity and its direction, and electrical conductivity of the wall were chosen as experimental parameters. The obtained distances were statistically analyzed. As the results, the distance when the horizontal magnetic field direction was parallel to the wall, and the distance when the wall was electrically insulating, were the same with the distance when the magnetic field was not imposed. On the other hand, the distance was smaller than the distance when the magnetic field direction was perpendicular to the electrically conductive wall.
Effects of Nb addition on as-cast γ-austenite grain structure in 0.2 mass% carbon steel are investigated by means of furnace cooling and permanent mold casting experiments. In the furnace-cooled samples with Nb addition, Nb(C,N) particles crystallize from the last-solidifying liquid in non-equilibrium solidification condition and they act as pinning particles for γ grain growth just after the solidification completion. The Nb addition produces a strong pinning effect on the as-cast γ grain structure. In the permanent mold casting experiment, Coarse Columnar Grains (CCG) structure develops from the mold wall in the sample without Nb. The increase in Nb concentration gradually decreases the fraction of CCG region and increases the fraction of Fine Columnar Grains (FCG), thus leading to the grain refinement. This refinement could be ascribed to the pinning effect of Nb(C,N) particles.
An investigation was carried out to study the radiative heat transfer behavior of two typical mold fluxes for casting low (Flux1) and medium (Flux2) carbon steels. By using an infrared radiation emitter, a radiative heat flux was applied to a copper mold covered with solid mold flux disk to simulate the heat transfer phenomena in continuous casting. The effective thermal conductivities were determined by measuring the temperature gradient in the copper mold system. It was found that the solid crystalline mold Flux2 for casting medium carbon steel has a better capability to transfer heat than that of solid crystalline Flux1, while their glassy fluxes behave similar capability. The DHTT (Double Hot Thermocouple Technique) was employed in this paper to study the heat transfer capability of the crystalline mold fluxes. DHTT measurements suggested that the thermal diffusivity of crystalline sample of Flux2 is higher than that of Flux1. The XRD and SEM results were indicated that the precipitated crystalline phase for Flux1 is only granular cuspidine, Ca4Si2O7F2, while those for Flux2 are consisted of dendritic cuspidine, Ca4Si2O7F2 and gehlenite, Ca2Al2SiO7.
This article proposes an arc stability index for Electrical Arc Furnaces (EAF) based on the real-time processing of the line to ground three-phase voltage measurements typically available at the secondary side of the EAF's power transformer. This methodology uses the definition of a virtual neutral for the open delta connection to calculate the neutral to ground voltage waveform and its Root Mean Square value that can be considered in a simple formula as stability indicator of the arc itself and for the power delivery to the arc. This proposed stability indicator may be used for process monitoring and power control.
The microstructures and chemical composition of nano-precipitates in vanadium (V) steels were investigated by the alloy contrast variation method (ACV) using small-angle X-ray scattering (SAXS) coupled with small-angle neutron scattering (SANS) at holding temperatures ranging between 600 and 700°C. Both the SAXS and SANS profiles exhibited clear scattering, depending on the holding temperature, due to the presence of nano-precipitates. The scattering profiles of the precipitates are characteristic of spherical or disc-like particles. The average diameters of these precipitates increased from 0.5 nm at 600°C to 23 nm at 700°C, whereas the number density of the precipitates decreases with increased holding temperature. Therefore, the increasing holding temperature results in an increase in the growth rate of the precipitates. ACV analysis revealed that the chemical composition of the precipitates corresponds to NaCl-type vanadium carbide (VC) at 675 and 700°C, and as VC0.9 at 625 and 650°C. The formation of a different heterogeneity, non-NaCl type, was found in the sample at a holding temperature of 600°C. This probably corresponds to a precursor of the NaCl phase in the initial process of precipitation.
Microstructures of a nickel/austenitic-steel (AISI304) interface, which has been bonded through in-situ cold-rolling of clean surfaces (pre-sputtered by argon ion) within a vacuum apparatus (~10–3 Pa), then followed by an annealing at 500°C, are investigated by transmission electron microscopy. We frequently find significant traces of thin oxide layers of 5–10 nm in thickness, which commonly reveal complex microstructures composed of bi-layers of different types of oxides. Origin of such interface oxides is presumably due to a slight oxygen contamination of the sputtered-surface in the present moderate vacuum condition, and the oxide precipitation at the bonded-interface has been promoted during annealing. Concerning that the strength of the present Ni/steel cold-rolled interface remarkably increases during an early stage of the annealing at 500°C, it is concluded that their strong interface bonding is supported both by nanometeric oxide-layers as well as direct metal/metal contacts.
The steel plate cooling process in hot rolling work has a variety of parameters influencing the cooling aspect of the process and the mechanical properties of products; i.e. the cooling water flow rate, the plate running speed, the cooling water temperature, the injection method of cooling water and so on. The present study deals with the cooling water flow rate and the plate running speed as vital parameters in the cooling process. The process is simulated by a fully numerical approach for a cooling type of impinging water jet on the moving plate. The previous achievement by Park1) of numerical analysis for the cooling process including the free surface capturing, the numerical modeling of boiling heat transfer, and the treatment of the moving plate is successfully adopted in the present study. The residual water height, the impinging pressure, the residual water shape, and the cooling history including the average heat flux are suggested for various cooling water flow rates and plate running speeds. The thickness distributions of the vapor film layer on the running plate are graphically presented too.
Dissimilar materials of H220 Zn-coated high strength steel and 6008 aluminum alloy were welded by median frequency resistance spot welding. Interfacial characteristics and kinetics of growth of intermetallic compound layer at steel/aluminum interface in the welded joint were investigated. The intermetallic compound layer was mainly made up of η-Fe2Al5 and θ-FeAl3 phases, and its morphology and thickness varied with positions along the interface. The growth behavior of the intermetallic compound layer was dominated by η-Fe2Al5, which exhibited parabolic characteristic. The growth coefficient of η-Fe2Al5 could be expressed as k = k0 exp(–Q/RT) with k0 of 132 m2/s and Q of 239 kJ/mol. The kinetics of growth of the intermetallic compound layer indicated that its formation and growth were mainly driven by reactive diffusion between Fe and Al atoms, and hence the thickness and morphology of the layer were dependant on interaction time between liquid aluminum alloy and solid steel, and also interfacial temperature history during welding. The brittle intermetallic compound layer at the steel/aluminum interface was the weak zone where cracks inclined to derive and propagate during tensile shear testing. The fracture surfaces of the welded joint displayed mixed fracture morphology with both brittle and ductile features.
This paper presents a comparative study on the atmospheric corrosion of steel, at two sites, in Iran. Corrosion rate values, time of wetness and the level of pollutants, namely of SO2 and chlorides, in both atmospheres, were determined for the first year of exposure in order to establish the aggressiveness of the atmospheres. The results obeyed well with the empirical kinetics equation of the form C=Ktn.
Galvanic corrosion of a model Zn/steel couple was investigated in aqueous NaCl solutions by measuring open circuit potentials (OCPs), potential and current distributions, and galvanic currents. The OCP transient of the Zn/steel couple was divided into two stages. The first stage consisted of sacrificial dissolution of zinc. At low concentrations of NaCl (0.01 mol/dm3), the cathodic reaction on the couple surface was an oxygen reduction reaction (ORR). With increasing concentrations of NaCl, the cathodic reaction at the steel surface changed from an ORR to the combination of an ORR and hydrogen evolution reaction (HER). In addition, the precipitation morphology of zinc corrosion products differed as a function of NaCl concentration, suggesting that the pH distribution on the couple surface depended on the relationship between the cathodic reactions and the hydrolysis of Zn2+. Furthermore, the findings demonstrated that both the ORR and HER were inhibited at the steel underlying precipitated zinc corrosion products. The second stage consisted of steel corrosion. The location of the onset of steel corrosion was related to the pH distribution just prior to the extinction of the galvanic action of zinc.
A several-micrometer-thick oxide layer on steel plate samples was removed by high energy density cathode spots appearing on the cathode surface in vacuum arc discharge. The samples' surface conditions before the oxide layer removal are altered by application of various concentrations of KOH aqueous solution. Such surface condition changes affect cathode spot behavior and improve the energy efficiency of the oxide layer removal.
The influence of Si addition to the coating bath on the growth of the Al–Fe alloy layer formed in the interface between the coating and steel substrate was studied utilizing a Zn–Al–Mg coating bath with 10–11 mass% Al content. While the Al–Fe intermetallic compound rapidly grew in the interface between the coating and steel substrate when dipped into a coating bath of Zn–10mass%Al–3mass%Mg at 550°C, the growth was remarkably suppressed by the addition of 0.2mass%Si to the coating bath. TEM observation revealed that, in the interface between the coating and the substrate, Si addition resulted in the uniform formation of very fine grains of 20–30 nm in diameter in the Fe2Al5 phase with dissolved Si and Zn in a solid solution. The mechanism of Si addition was postulated to be as follows: the large amount of Fe in the substrate could be dissolved easily into the liquid phase in the case of a ternary Fe–Al–Zn system, whereas in the case of a quaternary Fe–Al–Zn–Si system, the dissolution of Fe into the liquid phase was significantly suppressed by the presence of very fine, thin Fe2Al5 containing Si in the interface between the coating and the steel substrate. Thus, the growth rate of Fe2Al5 was greatly reduced.
The diffusion of carbon in austenite is important to the design and implementation of many steel heat-treating processes. The present study proposes a simple and computationally efficient equation for the diffusion of carbon in austenite for iron-carbon alloys, as well as for steels alloyed with a variety of elements. The proposed empirical model provides a pragmatic engineering approach to this important diffusion process. The model is shown to better match the carbon diffusion profiles of several carburized steel alloys, as compared to other equations that have been reported in the literature. These other equations were primarily obtained from experiments on iron-carbon alloys, and it is not surprising that they are less accurate when compared to the proposed equation that takes the full range of alloy compositions into account.
The effect of heat treatment on the microstructure and the mechanical properties of a 10%Cr steel with 0.008% boron was examined. The microstructure and the mechanical properties of this steel subjected to the normalizing were studied after tempering under different conditions. The layers of retained austenite are located along the lath boundaries. The formation of M23(B·C)6 phase having film-like shape takes place on interface boundaries of retained austenite/martensite during tempering at 525°C. As a result, the steel exhibits brittle fracture with a low value of Charpy V-notch impact toughness of 6 J/cm2. Particles of the M23(B·C)6 phase are highly resistant against the spheroidizing. The tempering at 770°C only leads to the coagulation of these particles; when the fraction of M23(B·C)6 phase significantly decreases while the fraction of M23C6 carbides increases. The tempered at 770°C steel exhibits a high value of Charpy V-notch impact toughness of 260 J/cm2. The effect of boron additives on the phase composition and the brittleness of high-chromium steels is discussed.
Supply of Fe ions is considered to be effective for the growth of kelp (a kind of seaweed). In the present research, a demonstration experiment in which seaweed beds/shoals were formed using a mixture of steelmaking slag and dredged soil was carried out in a marine area of Kawasaki City, Japan. The average strength of the mound for seaweed beds, which was made of a mixture of dredged soil and steelmaking slag, was 109.7 kN/m2. The shape of the mound was stable during the experiment period. The Fe content of the water above the mound made of the mixture was around 5 ppb higher than that above mounds made of natural sand. The average dry weight of the soft seaweed (Undariapinnatifida:wakame in Japanese) and brown seaweed (Sargassumhorneri) taken from mounds of the mixture including steelmaking slag were respectively 1.1 times and 2.1 times as much as that from mounds of natural sand. These results indicate that Fe ions, which dissolved from the steelmaking slag, have a positive effect on the growth of brown seaweed.
Indian iron mines dumps huge quantity of ultra fines containing high gangue minerals resulting in loss of iron values and environmental issues. The major gangue minerals containing alumina, silica and phosphorous are the cause for contamination of Indian iron ore. It has, therefore, become an urgent need to utilize these off-grade ultra fines after making it suitable for blast furnace charging. Due to the fine nature of these ultra fines, selective dispersion studies have been thought of. Two types of dispersants (i) inorganic, sodium hexametaphosphate and (ii) organic, sodium salt of poly acrylic acid have been tried. The performance of these two types of dispersions has been evaluated in separation process. Sodium salts of poly acrylic acid shows better separation of alumino silicate minerals in the ultra fines whereas, sodium hexametaphosphate efficiently separates out silica from the iron bearing minerals.
This study proposes a method of combining a waste input–output material flow analysis (WIO-MFA) model with trade statistical data to identify the flows of substances embedded in trade commodities. We focused on the case of Japan as a typical processing and trading country, and we estimated each mass of iron and aluminum embedded in the imports and exports of 300 product items categorized in the WIO-MFA. We found that iron ore imported from Australia, Brazil, and India as a raw material is processed and exported to South Korea, China, and other Asian countries as steel materials and to the United States as steel materials and automobiles. Primary aluminum imported from Russia, Australia, and Brazil as a raw material is processed and exported to Asia as rolled materials and to the United States as rolled materials and automobiles.