The reductions of Panzhihua coke bearing oxidized ilmenite pellets in a microwave field at the temperature ranging from 800 to 1100°C were studied. The reduction of composite pellets by conventional heating at 900 to 1200°C was also investigated as a comparison. A higher reduction reaction rate has obtained in the microwave field. Lower temperature and shorter time were demand for the microwave reduction of ilmenite due to the hotpots in the composite pellets inside the microwave field. The microwave irradiation has some special effect on phase and morphology change. The presence of crack and holes in composite pellets inside microwave field are beneficial due to the atmosphere diffusion and subsequent procedures such as separation of Fe metal and titanium oxide.
Water model experiments are carried out to understand the mixing behavior of the steel refining processes agitated by horizontal gas injection. Mixing time in a cylindrical water bath agitated by horizontal air injection through an L-shaped top lance is measured with an electric conductivity meter. Several types of bath surface oscillations are induced by the gas injection depending on the operation parameters such as the vessel diameter and gas flow rate. Particular emphasis is placed on the condition that a swirl motion of the deep-water wave type appears in the bath. This is because the swirl motion plays a practically important role for bath mixing. The diameter of the bath, lance exit position, bath depth, and gas flow rate are varied over a wide range. An empirical equation is proposed for the mixing time in the presence of the swirl motion.
Among different ways to reduce the coke consumption in the blast furnace, not so much attention was paid for decreasing the coke losses through finding suitable application of small size coke called “nut coke”. In meantime modern blast furnaces use nut coke with different amount (10–140 kg/t hot metal) and different grain size (10–40 mm) in the sinter layer to reduce the coke losses. The objective of this paper is to clarify the influence of nut coke on the shaft permeability and sinter reducibility under blast furnace simulating conditions. The effect of various factors such as nut coke rate, gas flow rate, and layer thickness on the shaft permeability was estimated using cold model rig. The influence of nut coke on the isothermal and non-isothermal reduction of sinter was estimated under different gas compositions and temperatures using muffle reduction furnaces. The isothermal reduction of sinter with 30%CO–70%N2 exhibited reduction retardation at elevated temperatures (>1373 K). The reduction retardation increased by the presence of CO2 gas in the reducing atmosphere while decreased by participation of H2 gas. Mixing nut coke in the sinter bed improves the sinter reducibility and inhibits the reduction retardation phenomenon.
Relationship between coking pressure and displacement of oven wall during carbonization in coke oven was investigated at Hokkai No. 6 coke oven battery (preheated-coal charging system). Determination was performed at both a superannuated oven chamber after 26 years from start and a sturdy oven chamber after a year from replacement of oven top, entire walls and oven sole. Wall displacement was observed when the internal gas pressure of plastic layer at oven center became the maximum in both oven chambers. The wall displacement increased in proportion to the internal gas pressure of plastic layer at oven center, and the displacement at superannuated oven per maximum gas pressure was larger than the one at sturdy oven. The pushing force (maximum electric current of pushing machine) greatly changed according to gas pressure of plastic layer at superannuated oven compared with the one at sturdy oven. The conclusion of this study is that the wall displacement by coking pressure greatly influences the pushing force of coke cake at superannuated oven chamber.
Mathematical modeling of the combined side and top blowing AOD refining process of stainless steel has further been studied. A new model proposed is generally based on the analysis and assumptions made for the process in our previous investigation. Particularly, the heat transfer characteristics of the vessel are analyzed in terms of the two-dimensional transient heat-conduction problems of composite walls. The heat and mass balances of the system are more comprehensively and precisely performed. The model has been applied to 28 heats of 304-grade austenitic stainless steel refining in a 120 t AOD converter. The results present that the changes in the composition and temperature of the liquid steel with the time during the whole process can be accurately predicted using the model. The competitive oxidation among the elements in the steel during the oxidative refining with the relevant oxygen distribution ratios, and the competitive reduction of the oxides in the slag during the Ar agitating and reductive refining with the appropriate oxygen supply ratios can be well characterized and reasonably determined using the Gibbs free energies of the reactions. The critical carbon concentrations (after which the decarburization alters to be limited by the mass transfer of carbon in liquid steel) for the top, side and combined blowing of 304-grade steel in this work are in the ranges of 0.895 to 0.942, 0.078 to 0.224, 0.144 to 0.255 mass%, respectively. The effects of some factors on the refining result and the optimization of blowing technology have been considered from the model predictions. The model can provide a reliable basis and useful information for determining and optimizing the technology of this AOD process of stainless steel, and controlling the process in real time and on-line.
The effect of a simulated reoxidizing environment on the chemical and morphological evolution of non-metallic oxide inclusions was studied. Additions of 545 ppm and 274 ppm of soluble oxygen were introduced to an Al killed melt containing approximately 600 ppm of Ti and 600 ppm of Al. It was found that inclusion chemistry evolved from Al2O3, Al2TiO5 and eventually to Ti3O5 for the higher oxygen addition case and to Al–Ti complex oxides for the lower oxygen addition one. Morphologically, it was observed that irregular inclusions gradually were replaced by spherical ones during the reoxidation process. These changes are discussed through the coupling of thermodynamic prediction and experimental conditions, and considerations on the local variations of O and metallic element activities.
The following paper presents an approach to the mathematical modeling of 3-phase AC, electric arc furnace (EAF) processes for control-design and process-optimization purposes. The EAF can be, from the modeling point of view, considered as a combination of electrical, hydraulic, chemical, thermal and several energy-balance sub-processes or sub-models. In this paper the modeling of the electrical and hydraulic sub-models is presented in detail, since the two represent a very complex and important sub-system of the complete EAF model. The presented sub-models are obtained in accordance with different mathematical, electrical and mechanical laws. Several parameters, which are necessary to successfully identify the scrap-melting process, were fitted experimentally, using the measured operational data of an 80 MVA AC furnace during different periods of the melting process. Similar data has also been used for the validation of the developed model in typical EAF operating situations. The aim of the presented EAF modeling is to obtain an accurate, robust and realistic mathematical model of the scrap-melting process, which will later be used for control-design purposes, the optimization of the energy consumption and the development of an operator-training simulator. The main advantage of our modeling approach over the existent EAF-related models is a more macroscopic level of modeling, which accurately simulates the electrical and hydraulic processes under different conditions in the EAF.
A mathematical model of three-dimensional fluid flow, heat transfer and solidification in thin slab casting is developed based on the enthalpy-porosity approach in a single-phase framework and used to analyze and compare the fluid flow and thermal behaviors in the funnel-type molds of Compact Strip Production (CSP®) and Flexible Thin Slab Casting (FTSC®) caster. An Electromagnetic Brake (EMBR) model is also incorporated into this coupled model to see the effects of EMBR on fluid flow and solidification in a CSP caster with EMBR system. The numerical treatments specific to the complex funnel-shaped mold boundaries are discussed. The obtained numerical results are partly validated by those available in literature and theoretical analyses. The fluid flow and thermal features of thin slab in CSP mold and FTSC mold are analyzed and their comparisons between them are made. It is found that the flow pattern, level fluctuation, superheat dissipation, temperature distribution and shell growth in both molds present different features. The structure of SEN strongly affects the flow pattern of the impinging jet from SEN ports, and then the dissipation mode of the melt superheat and the uniform growth of solidification shell. A four-port SEN® with two small upper ports in FTSC mold is helpful to activate the meniscus flow and increase the meniscus temperature, but high level fluctuation may occur. The EMBR in a CSP mold can both suppress the meniscus flow and increase the meniscus temperature. A complete flow-control system including the design of SEN, EMBR and operational conditions is essential for thin slab production considering their individual flow and thermal features in the funnel-type molds of CSP and FTSC casters.
Time-resolved X-ray imaging of dendritic solidification for pure Fe and carbon steels with sufficient spatial and time resolutions has been developed for the first time by overcoming essential problems in low contrast between solid and liquid phases and in high melting temperatures. Static observation showed that the solid/liquid interface in pure Fe specimen was determined by the absorption contrast at photon energy ranging from 16 to 30 keV. In addition, the phase contrast was also observed in the vicinity of the interface. Dynamic observation showed that cellular growth in pure Fe specimen was observed at a growth velocity up to 400 μm/s. Feasibility observation was also performed for two different carbon steels (0.0025 mass% C and 0.45 mass% C). Growing dendrites were observed in-situ at a growth velocity up to 500 μm/s. This study proves that the developed imaging enabled to observe solidification phenomena in-situ for various kinds of steels.
These works was made in a compact strip plant (CSP) and represent an effort to decrease the amount of coils of steel rejected by a cosmetic defect called primary oxide, the morphology of the scale and its characterization by optic and scanning electron microscope was presented. Different trials were made in order to find the mechanism and phenomena of how the primary oxide is formed. The different theories of how the scale is removed by a descaling system are described. The benefits obtained from this research are mentioned.
It has always been of greatest importance to control the temperature distribution in the products throughout the hot strip rolling process including the final coiling operation. A computational model of the latter has been developed and validated, which is presented in this paper. Furthermore, the influences of the different parameters on the transient thermal distribution are evaluated. The formulated model as accounts for two-dimensional heat conduction is assuming axi-symmetric conditions. Temperature dependent properties are accounted for results in a nonlinear heat conduction problem that is solved by use of the Finite Element Method (FEM). The calculations have been validated by two full scale measurement campaigns and show a good agreement with measurements.
In our previous paper, the eutectic liquid that appears between the cementite (θ) foil and austenite was proposed to be most suitable for rapid transient-liquid-phase (TLP) bonding of steels. A partial substitution with Cr was required for metastable θ to be thermodynamically stable up to the solidus temperature. On the other hand, the liquid region disappeared quickly by C diffusion, leaving severe Cr segregation along the bonded interface. The present study aims to decrease the ratio of Cr substitution in θ so as to eliminate the homogenization step and allow the use of steel parts as-bonded. Compared to θ with a higher Cr substitution, the synthesized θ with 1 mass% Cr (1Cr-θ) showed an enhanced tendency to decompose on cooling from 1373 K. However, the 1Cr-θ foil was confirmed to give the eutectic liquid that dissolved V during TLP bonding of V-microalloyed steels. After holding for 180 s at 1453 K, a gradient ferrite–pearlite microstructure was obtained in the bond without any boundaries or hard layers due to Cr segregation. The bonded steel showed a tensile strength and elongation corresponding to those of the original V-steel.
This paper aims to evaluate and simulate the mechanical behavior of laser beam welded TRIP700 steel sheet under uniaxial tensile loading. In this work TRIP700 steel sheets with thickness of 1.2 mm were butt welded by CO2 laser beam welding using 4.5 kW as a laser beam power and 0 mm as a focus position. The welding speed was ranged from 2.1 to 3.9 m/min. Microhardness measurements and transverse tensile testing were carried out to characterize the welds. Numerical simulation with the finite element analysis code ABAQUS/CAE v6.9-1 was used to describe the elastoplastic behavior of the welded sheets. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal and the strengths were somewhat higher than those of base metal. The numerical results of the tensile testing had a good agreement with the experimental results.
Titania-containing organic–inorganic hybrid sol–gel film was developed to improve the corrosion resistance property of steel. Titania precursor was prepared from titanium-isopropoxide and methyl hydrogen silicone was used as a coupling agent to enhance the adhesion and hydrophobic nature of coating. The kinetics, thermal resistance and morphology of films were analyzed by, fourier transformed infrared spectroscopy, thermo-gravimetric and differential thermal analysis and scanning electron microscopy. The anticorrosion performance of the sol–gel coated sample was investigated by electrochemical impedance spectroscopy. The results demonstrated that coatings were dense, uniform and provided excellent corrosion resistance properties.
A series of laser cladding layers of Ni35 on a medium carbon steel substrate by varying powder feeding rate and laser scanning speed were obtained. An investigation of the effects of the laser scanning speed and the powder feeding rate on microstructure and hardness was presented in this paper. The phase constitution, microstructure and hardness were investigated by X-ray diffractometer, energy dispersion spectroscopy, scanning electron microscope and Vickers hardness tester. The results show that as the scanning speed increases, the ratio of the temperature gradient G to the solidification rate R decreases which results in the finer microstructure of the cladding layer, as the powder feeding rate increases, the microstructure becomes finer due to the decrease of the temperature of the substrate and specific energy per unit mass of the powder. Furthermore, as the scanning speed and the powder feeding rate increase, the hardness of the cladding layer increases. This is because that the finer microstructure of the cladding layer results in the increase of grain boundary area, which results in the increase in the ability of deformation resistance. An intuitive and facilitative method which combining the line that joining the turning points of the hardness profile to show the effect rules of the laser scanning and the powder feeding rate on the range of dilution and the region of heat affect zone (HAZ) is adopted. This method is helpful to the study of the bonding interface, the control of the dilution range, the microstructure and properties of the cladding layer.
In this work PVD-TiN coatings are deposited on ADI substrates austempered at 280 and 360°C, with nodule counts varying between 490 and 1100 nod/mm2. The deposition is performed at 300°C by the arc ion plating technique. The effects of the substrates' microstructure on the characteristics of the coatings and the possible changes in ausferritic microstructure owing to the effects of the deposition process are evaluated. The existing phases, preferred orientation, film thickness, hardness, Young's modulus, surface topography and adhesion of each coated sample are determined. A metallographic characterisation of the ausferritic matrices and determination of the retained austenite content are performed before and after deposition. The results obtained indicate that PVD-TiN coatings feature a preferred orientation of (111) planes parallel to the surface and film thicknesses of about 2 μm. Knoop hardness is influenced by the substrates characteristics, the values range from 1700 to 2100 HK0.015. Nanohardness values are close to 25 GPa, while Young's modulus shows some scattering (323 to 336 GPa). The surface topography is dependent on the microstructure of the substrates and the surface preparation method employed as well as on the deposition process used. The adhesion strength quality of the coatings, according to the Rockwell-C adhesion test, can be related to HF1–HF2 and is affected neither by the hardness differences between the different substrates nor by the nodule count variation. After the coating process, the microstructure of ADI substrates only suffers negligible changes and the amount of retained austenite decreases slightly.
Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of the addition of Cu on the suppression of hydrogen embrittlement in a solution of HCl, hydrogen permeation tests and dynamic polarization measurements were conducted on TS 1470 MPa grade, low-carbon martensite steels. To this end, steels containing 0.19% C, 0.2% Si, 1.3% Mn, Cr, Ti, Nb and B were prepared with and without 0.16% Cu. For comparison, ferrite and pearlite steels were also examined. The results of hydrogen permeation tests indicated that the steady-state hydrogen permeation current (JH) of steel containing 0.16% Cu was considerably lower than that of basic steel in 0.1 N HCl at the corrosion potential. Moreover, the JH of martensite steel was suppressed by the addition of Cu, and the cathode current, (iC) and the JH/iC were reduced. The results obtained in this study corroborated the hypothesis that the 1 or 2-μm metallic Cu particles precipitated on the surface of the steel in a solution of HCl suppressed the cathodic reaction and the introduction of hydrogen. The hydrogen diffusion constant (Deff) was obtained from hydrogen permeation tests under a potential gradient. Cu addition has only small effect on Deff regardless of microstructure. The occupancy of trap site (nX) was estimated to be greater than 99% independent of Cu content and microstructure.
The purpose of this study is to clarify the effect of dry and wet processes on the mechanisms of edge corrosion of hot dip 55 mass% Al–Zn alloy coated steel sheet. The corrosion tests employed were continuous salt-spray tests and cyclic corrosion tests using NaCl solution or artificial seawater. It was confirmed that the edge corrosion is suppressed during the salt-spray test using artificial seawater. Furthermore, the suppression was not prevented by dry and wet processes. In order to reveal the corrosion mechanisms, the galvanic current and the cathodic polarization curves at exposed steel were measured and the corrosion products were characterized. It is suggested that the artificial seawater forms anti-corrosive corrosion products and that suppress the cathodic reaction on the steel which is exposed on the shear cut edge. The corrosion products are not changed by dry and wet processes. The numerical analysis also revealed the influence of the dry and wet process on edge corrosion.
The amount of retained austenite formed during tempering process can moderately improve the structure and properties of martensitic stainless steels. In the present study, 25 heat treatment cycles were carried out on specimens cast in CA6NM in order to investigate the effect of tempering treatment on the structure and mechanical properties of this alloy. X-Ray diffraction, mechanical testing, optical and scanning electron microscopy were employed for evaluation of the specimens. SEM micrographs and X-ray diffraction patterns indicated that with enhancement of tempering temperature, the amount of retained austenite initially increased and then decreased. The changes in mechanical properties of specimens including hardness, impact toughness, elongation, yield and tensile strength were found to depend mainly on the amount of retained austenite. Such variations are discussed in terms of amount of retained austenite and its stability during tempering process of martensite.
Based on the thermo-mechanical controlled process, the effects of Si on microstructural evolution, tensile properties, impact toughness, and stretch-flangeability of ferrite and bainite dual-phase (FBDP) steels were systematically investigated. The addition of Si from 0 to 0.95% promoted the formation of fine and equiaxed ferrite grains, and high Si (0.95%) also resulted in the formation of blocky martensite islands and retained austenite. Yield and tensile strengths, and uniform and total elongations all increased with increasing Si content. Therefore, the tensile strength and ductility balance was improved by Si addition due to the increasing strain-hardening rate. The fractured morphologies after hole-expansion showed that the excellent stretch-flangeability of FBDP steels was associated with the micro-cracks propagating through in ferrite phase as well as the elongated ferrite grains along the direction perpendicular to the crack. 0.95% Si steel had a similar high combination of tensile strength and impact toughness to 0.55% Si steel, and especially 0.95% Si steel exhibited an excellent combination of tensile strength and stretch-flangeability.
Modeling non-monotonous and/or non-proportional deformation is challenging partly because of lack of constitutive equations and more so because of unavailability of sufficient experimental data. In the present work, two different experiments involving non-monotonous/non-proportional deformation have been proposed. The model based on combined isotropic-kinematic hardening with permanent softening was utilized to simulate the deformation behavior under such deformation conditions and it was found that the above model was capable of correctly predicting the deformations for both cases considered here. It was also noticed that the incorporation of permanent softening often observed during reverse loading, is important for accurately predicting the deformation when bending-unbending (or strain reversals) takes place.
The real and imaginary parts of relative permittivity (εr′ and εr″) and permeability (μr′ and μr″) of Fe3O4 powder were successfully measured over the temperature range of 25–575°C by means of the coaxial transmission line method in order to elucidate the heating behaviours of Fe3O4 powder. The measurement frequency range is from 0.2 to 13.5 GHz. With respect to the temperature dependencies of the complex permittivity, the εr′ values show a peak around 450–500°C. The εr″ values monotonically increase with increasing temperature, in particular, showing abrupt increase above ca. 400°C. As for the complex permeability, the μr′ values decrease with an increase in temperature, and reach the same level as that of vacuum (μr′=1) at 575°C, i.e., the maximum measurement temperature. The μr″ values increase with temperature until 500°C below 3.5 GHz although they monotonically decrease with an increase in temperature above 3.5 GHz.
In Australia, the use of plastics has increased tremendously over the last few decades, but less than 20% of the waste plastics are recycled. The rest is usually landfilled, which poses major environmental problems. The solution to this problem involves the development of novel environmentally-benign technologies that would utilise these waste materials. This work investigates the reduction of EAF slags (47% FeO) by blends of metallurgical coke with High-Density Polyethylene (HDPE) plastics at 1550°C. The experiments were conducted in a laboratory-scale horizontal tube furnace, and were coupled with off-gas analysis using an infrared gas analyser and a multiple gas chromatographic analyser. The results indicate that the rate of FeO reduction in slags is significantly higher when the coke/plastics blends were used compared to pure coke, with the maximum rate of reduction (Blend 4) being over twice that of coke. Moreover, the CO2 content in the off-gas was observed to decrease (by ~75%) with increase in the polymer content of the blend. Additionally, the degree of carburisation and the removal of sulphur from the metal improved considerably when the coke was blended with plastics. The observed improvements in the rates of reduction, carburisation and desulphurisation are attributed to the reactions of hydrogen evolved from the waste plastics at these high temperatures.
Elution of fluorine from landfill slag by rainwater or groundwater causes serious problems; hence, fixation of fluorine in electric arc furnace reducing slag (EAFRS) is crucial. The phase including fluorine was identified for some EAFRS specimens and confirmed is as (3CaO·2SiO2)·CaF2 in the current work. Experiments to determine the dissolution of fluorine from the EAFRS into water were conducted at pH 4, 7, and 10. It was found that fluorine tended to elute under acidic conditions. Therefore, the elution of fluorine from fluorine-containing substances into water at pH 4 was investigated in detail. It was found that 2(2CaO·SiO2)·CaF2, (3CaO·2SiO2)·CaF2, and CaF2 were unstable, while the 3(3CaO·P2O5)·CaF2 phase was stable; further, fluorine elution from 3(3CaO·P2O5)·CaF2 into water was found to be limited. On the basis of these results, it was concluded that the dissolution of fluorine into water can be suppressed by adding a sufficient amount of P2O5 to EAFRS, so that the formation of unstable fluorine-containing substances is prevented.
The bioavailability and durability of Fe released from decarburization steelmaking slag was examined for two marine diatom species. The bioavailability of Fe released from the slag was compared with that from the reagent FeCl3·6H2O in the presence or absence of the synthetic chelator ethylenediaminetetraacetic acid, which affects Fe speciation in seawater. The duration of bioavailability was determined by the recovery of the growth rate on intermittent additions of macro-nutrients other than Fe. Abiotic reduction of bioavailable Fe from the slag in seawater was also investigated for 5 or 15 d. Thus, the bioavailability of Fe released from the slag was observed to be sufficiently high to promote the maximum growth rate; this was similar to that observed with the reagent inorganic Fe. This implies that the iron released from the slag is a dissolved ferric and/or ferrous ion/hydroxide species. In the culture media, to which the slag was added at the concentration of 20 mg L−1, the slag supplied bioavailable Fe to two diatoms for 50 d. The probable duration for which the slag was available as an Fe source was approximately 10 times longer than the reported duration in in situ iron fertilization experiments. These results indicate that continuous Fe fertilization can be achieved by a single addition of the slag, and hence, we can reduce the energy and cost of ocean fertilization and also create a resource of microalgae biofuels.