High aluminum containing steels react vigorously with silica-based mold fluxes to form alumina. The change in alumina content increases the viscosity and thus silica-based mold fluxes are compensated with significant amounts of Na2O, CaF2, and Li2O to ensure both lubrication and heat transfer control. Detailed viscosity studies using the rotating spindle method showed that additions of CaF2 up to 8 wt% in the CaO–SiO2–12wt%Na2O system at a constant CaO/SiO2 ratio of 0.8 decreases the viscosity by breaking the network structure of molten fluxes, but is negligible above 8 wt%. A similar modification of the network was observed for Li2O up to 2 wt%. The viscosity data was correlated with the XPS analysis and verified CaF2 and Li2O as effective in modifying complex silicate structures into simpler silicate structures depending on the availability of complex silicates and thus was limited to below certain concentrations.
Plastic wastes have a potential to play a significant role in the reduction of iron oxides by supplying reducing gases, e.g., H2 and CO, through pyrolysis. However, they are difficult to use as reducing agents because the thermal degradation temperatures of plastics are significantly lower than the reduction temperatures of iron oxides. In this study, the reduction mechanism of iron oxides by carbon and hydrogen obtained from polyethylene in the composite at lower temperature was studied in order to attain a high utilization ratio of polyethylene to the reduction. The reduction experiments were carried out under an Ar–5%N2 gas flow with a heating rate of 0.33 K/s, and the gases formed during reduction were continuously analyzed. The reduction degree of hematite was calculated using the concentration of these gases. The peak temperatures of gas generation rate for the polyethylene–graphite–hematite composite were obtained at 770, 1070, and 1370 K. The peaks at 770 and 1070 K originated from the reaction of polyethylene, and the peak at 1370 K originated from that of graphite. Larger specific surface area of the iron ore leads to fast reduction rate of the ore by polyethylene. Therefore, high utilization rate of carbon derived from polyethylene was obtained when using iron ore with a large specific surface area, such as goethite ore.
In JSW steel limited Pellets form the major part of the iron bearing feed to Corex and Blast Furnace. These two iron making units demand high strength, lower reduction degradation index pellets to maintain good permeability of the bed to achieve high productivity and lower fuel rate. To produce good quality of pellets certain additives are important. JSWSL produces basic pellets with basicity (CaO/SiO2) 0.40 to 0.50. The quality of the pellet is affected by the type of the raw materials, gangue content, and flux proportion and their subsequent treatment to produce pellets. The limestone addition, i.e. basicity–CaO/SiO2 of pellet decides the mode, temperature and the amount of melt formed. The properties of the pellets are, therefore, largely governed by the form and degree of bonding achieved between ore particles and also by the stability of these bonding phases during the reduction of iron oxides. Hence in production of acid, basic and fluxed pellets, characterization of the bonding and crystalline phases is of prime importance in understanding the basis for the production of pellets of desired quality. To understand the influence of limestone addition (basicity) on iron ore pellets microstructural, physical and metallurgical properties basket trials have been carried out with different level of basicity from 0.08 to 1.15. From the test result it was clear that pellet properties were influenced by the bonding phases present in the pellet. The tumbler index increased from 93.15 to 95.38% and cold crushing strength increased from 176 to 264 kg/p with increase in pellet basicity from 0.08 to 1.15. This effects result from microstructural differences appeared from the flux addition. RDI of the pellet decreased initially from 16.3 to 10.9% in the pellet basicty range from 0.08 to 0.33 and again increased from 10.9 to 13.6 with increase in pellet basicty from 0.33 to 1.15. This effect is due to the change in structural properties of the pellet during reduction. Pellet with basicity 0.33 showed good physical as well metallurgical properties due to bonding phases present in the pellets.
A two-stage multichannel was designed to increase the efficiency of separating non-metallic particles from liquid metal flowing through an alternating magnetic field. Numerical method was developed to calculate the particle concentration and separation efficiency of a zinc melt containing dross particles and verified by the experimental results. The distribution of particle concentration and axial fluid velocity changed significantly due to the added walls in the sub-channel, resulting in an abrupt increase in the residence time of the inner bulk melt with high particle concentrations and a remarkable increase in particle separation efficiency when flowing through the single-channel to sub-channels. A multistage and multichannel arrangement is hence recommended for further increase in the separation efficiency of an electromagnetic separator.
The initial stage of deoxidation and the influence of the oxygen level on the inclusion features were examined. Liquid Fe with various dissolved oxygen content (O) was brought into contact with Al in a quartz tube for a short time, i.e. 1, 5, 30 and 60 s. Microscopic investigations of the quenched samples revealed the formation of Al2O3 inclusions in the Fe–Al reaction zone, resulting from the motion of the diffusion front with time. Specific attention is given to inclusion size, location and morphology as a function of interaction time and O content. The latter was found to influence the inclusion characteristics. The inclusion number increased drastically with O content, which is related to the degree of supersaturation of the melt, one of the most important factors influencing the formation of inclusions. The inclusion morphology evolved from angular to spherical with increasing O content.
Ferronickel alloys as a nickel source for high alloy steels such as stainless steels are produced from garnierite ores by means of a rotary kiln. That is basically modification of Krupp–Renn process by which clinkers, that are mixtures of ferronickel alloy particles and partially melted slag, can be extracted. It is necessary to have exact knowledge of how the ore is softening with increasing temperature because controlling this behavior is considered to be a key to stable operation. A study has been carried out to understand the melting behavior of pelletized siliceous nickel ore samples blended with limestone and anthracite heating up to 1300°C. Microscopic observation revealed that mineralogical phases in equilibrium were 2(Mg, Fe)O·SiO2 olivine and (Mg, Fe)O·SiO2 enstatite. It was further found that clear formation of liquid phase composed of CaO–SiO2–FeO–Al2O3–MgO system as a result of assimilation with CaO in the case of ore containing higher Al2O3 and CaO contents with lower MgO/SiO2 ratio. Besides, this type of ore had ability to be molten by itself to generate primary liquid inside the ore. The primary liquid formation could promote assimilation with CaO particles to spread liquid phase causing melting of the ore. Mineralogical phases at 1300°C calculated by thermodynamic software were in good agreement with the experimental results. In contrast, ore with lower Al2O3 and CaO contents with higher MgO/SiO2 ratio could not generate liquid phase even though limestone was blended. A number of remained CaO particles were observed without assimilating with the ore. It was therefore considered that higher assimilation ability of CaO with ore enhanced liquid formation and that this property was determined mainly by Al2O3 and CaO contents and MgO/SiO2 ratio of the ore.
Low reducing agent operation of the blast furnace is an essential method for mitigating CO2 emissions in ironmaking. Because the coke rate is reduced in low reducing agent operation, gas permeability tends to deteriorate. Recently, blast furnaces with inner volume larger than 5000 m3 have become usual not only in Japan, but also in other Asian nations. Under these conditions, detailed information on in-furnace phenomena is required to attain stable operation. In the present study, a combination model using the discrete element method and computational fluid dynamics (DEM-CFD) was introduced to understand the fully three-dimensional in-furnace phenomena in the whole blast furnace. Due to the limitations of computational resources, the number of DEM particles must be reduced when applying DEM to the whole blast furnace. On the other hand, small cells must be used in the continuum model in order to calculate the gas flow in detail. Thus, mutual conversion between the location of particles in DEM and the property of the cells in the continuum model is needed. In this study, a method of converting information on the locations of cluster-approximated particles treated in DEM to continuum cells was proposed. Furthermore, optimization in which cells could be obtained without conversion parameters was performed to avoid losing local information obtained by DEM calculations. Simulations of solid movement and gas flow were successfully carried out with this coupled DEM-CFD model. As a result, it became possible to understand the three-dimensional stress field among particles under gas flow, transient gas flow and pressure distribution caused by charging of the burden materials, as well as solid motion.
In order to mitigate CO2 emissions from steel industry, decreasing coke rate by shaft gas injection such as top gas recycling is a favorable way. The conception based on oxygen blast furnace is able to bring several profits for intensifying gas reduction and decreasing coke rate by massive coal injection. In these processes, gas injection from auxiliary tuyere plays an important role to inject reducing gas or make up heat balance in the upper part. Therefore, the effect of shaft gas injection is considered to be so important factor to realize the above processes. In the present study, dynamic behaviors of gas and solid flow, and stress distribution between particles in the blast furnace with gas injection at different shaft levels were three-dimensionally examined by DEM-CFD. Since the permeability resistance of burden in blast furnace is dominant for gas flow, gas injection from auxiliary tuyere is restricted to specified areas due to the insufficient horizontal inertial gas force compared with upwards gas. Although these results are slightly influenced by the number of auxiliary tuyeres and gas velocity, the overall behaviors do not change. It was estimated that shaft gas did not diffuse uniformly. The penetration of shaft gas into center of the blast furnace is limited to peripheral zone. Thus, penetration area of shaft gas in horizontal section is almost proportional to ratio of shaft gas and gas from the conventional tuyere. Then, the change of stress distribution between particles was calculated and gas penetration effect was quantitatively clarified.
An agglomeration process is developed to utilize FeMn fines of <3 mm in LD steel making process. Different types of binders (sodium silicate, bentonite, acrylic resin and phenolic resin) were tried and found that phenolic resin is most suitable binder. Mixture of binder and fines was compacted in a cylindrical die and cured at 150°C for 1 h. Briquettes of 30 mm diameter and 20 mm length were prepared and physical properties of the briquettes were tested. Tumbler index and shatter index of the briquettes were ~95% and >98%, respectively. Compressive strength was 55 MPa and density was 5200 kg/m3. Usability of FeMn briquettes along with the FeMn lumps was evaluated in lab as well as in the plant. The results of lab test revealed tha FeMn briquettes dissolved faster than lumps. Improvement in Mn recovery was also observed in case of FeMn briquettes. Preliminary cost analysis indicated significant saving in alloying cost in steel making by use of briquettes made of low cost fines.
An electrochemical reaction cell using a solid electrolyte was developed to study the thermodynamic and kinetic behavior of interfacial oxides. Al2O3 and TiO2 existing between the Fe alloy melt and the magnesia stabilized zirconia solid electrolyte could be controlled using an electrochemical method of an external direct current at 1823 K. This novel approach could control the electron density near the interface of the oxides and subsequently the interfacial oxygen. In this study, a direct current of 0.1 ampere resulted in the decomposition of the interfacial oxides and an interfacial oxygen concentration below 3 ppm. Furthermore, morphological observations using EPMA confirmed the interfacial oxide control corresponding to the external electrical potential.
In the BOS process liquid slag together with dispersed metal droplets, solid particles and process gases form an expanding foam. Certain process conditions may lead to excessive foam growth, forcing foam out through the vessel mouth, an event commonly known as ‘slopping’. Slopping results in loss of valuable metal, equipment damage and lost production time. In the early 1980s a system for foam level and slopping control was installed at SSAB's steel plant in Luleå, a system based on the correlation between BOS vessel vibration in a narrow low frequency band and foam development. The technique, in this case with an accelerometer mounted on the trunnion bearing housing, soon showed its usefulness, for example when adapting existing lance patterns to a change in oxygen lance design from a 3-hole to a 4-hole nozzle. Estimating the actual foam height in the BOS vessel was of great importance in the recently completed RFCS funded research project “IMPHOS” (Improving Phosphorus Refining). Based on the earlier positive experiences, it was decided to further develop the vessel vibration measurement technique. Trials on an industrial size BOS vessel type LD/LBE have been carried out, this time with a tri-axial accelerometer mounted on the vessel trunnion. FFT spectrum analysis has been used in order to find the frequency band with best correlation to the foam level development. The results show that there is a correlation between vessel vibration and foam height that can be used for dynamic foam level and slopping control.
The present paper deals with the investigation of evaporation of B2O3 and Na2O from F-free mold slags in the temperature range of 1573 to 1673 K by Thermogravimetric Analysis (TGA) method. The study was aimed at elucidating the evaporation mechanism during continuous casting and identifying the resulting effect on the flux composition. The basicity was found to slightly enhance the evaporation rate of mold slags, suggesting that the mass transport in the liquid phase plays a role in controlling the evaporation. TiO2 addition resulted in an increasing evaporation rate due to the decrease of viscosity of the slag. The diffusional flux resulting from gas phase mass transfer from the gas/slag interface to the bulk gas was theoretically estimated and the results suggest that this process is not the controlling step. The evaporation rate was found to increase with increasing ZrO2 addition possibly due to the fact that the solid particles existing in the slag act as nucleation sites of bubbles formation. The evaporation rate was also found to increase with increasing experimental temperatures.
A new sensing tool called the smart stress memory patch, which is made of a pure Cu cracked specimen with thin thickness, has been proposed in our previous study to estimate fatigue damage such as maximum fatigue stress, number of cycles and stress amplitude for structural health monitoring. In this study, the acoustic emission (AE) activity of pure Cu specimens heat treated under several conditions was investigated because the maximum fatigue stress can be estimated on the basis of the AE onset stress in the Kaiser effect. The obtained AE onset stress was proportional to the yield stress, and the notch sensitivity of the AE onset stress was not observed. The Kaiser effect in Cu specimens with various grain sizes was examined during reloading. The AE onset stress of the Cu specimen with a large grain size during reloading was lower than the previous maximum stress, while the AE onset stress of that with a small grain size was almost equal to the maximum stress in the first loading. The applied maximum stress in fatigue loading was compared with the AE onset stress and the result shows that a suitable stress range for a smart stress memory patch can be obtained using the heat-treated and notch-introduced electrodeposited Cu specimen.
Micro-beam X-ray fluorescence (XRF) and X-ray absorption fine structure (XAFS) techniques have been applied, for the first time, to the cross sections of a rust layer on a weathering steel exposed for 38 years to the atmospheric environment. Elemental mapping and Fe–K edge XAFS spectra were measured with a spatial resolution of about 3 μm by an X-ray micro beam formed by a K–B mirror with the synchrotron radiation. Cr distribution, including layered patterns in the rust layer, was clearly observed by the micro-beam XRF imaging. The combination of micro-XRF and extended X-ray absorption fine structure (EXAFS) analysis on identical analytical points has demonstrated that the crystallinity of α-FeOOH is strongly related to the Cr concentration. The XRF and XAFS results are presented and discussed in terms of the analytical techniques and the relationship between the crystal structure of the rust and the Cr concentration.
The heat affected zones (HAZ) of two Dual Phase steels spot welds, DP450 and DP980, were investigated experimentally with a Gleeble 3500 thermomechanical simulator. The thermal cycles experienced locally were identified by finite element analysis of the resistance spot welding process and their evolution with an increasing sheet thickness was highlighted within a usual range of [1.0–3.0] mm. The cooling rates are significantly lower in the case of thick sheets and this promotes the occurrence of diffusional phase transformations. HAZ microstructures and constitutive behaviours could be characterized with the Gleeble specimens. Experimental simulations were run in the subcritical and the coarse grain temperature ranges (700°C and 1200°C respectively) in order to address the main transformations for both steels. DP450 shows little sensitivity to the subcritical thermal cycles while DP980 exhibits significant softening. This is in accordance with their respective base metal martensite content and the occurrence of martensite tempering. On the contrary, DP450 microstructures and mechanical properties are strongly sensitive to the investigated range of coarse grained HAZ thermal cycles while the evolution is less pronounced in the case of DP980, which is related to their respective hardenability.
Thiol self-assembly super-thin films have attracted considerable attention for molecular-level surface design as in chemical sensors, molecule-based devices and corrosion resistant films. Meanwhile, chromate coatings on zinc coated steel sheets are widely used as an economical method of preventing corrosion. In response to recent environmental regulations, such as the RoHS Directive, chromate-free coatings have been developed and applied to electrical appliances. However, a thinner coating is required to obtain better electroconductivity, which influences the electromagnetic shielding performance of digital electrical appliances. In this study, we investigated the corrosion resistance and film structure of alkanethiol and triazinethiol self-assembly super thin layers on zinc coated steel sheets. The corrosion inhibition mechanism of the thiol layers was discussed in order to develop a new design concept for thinner chromate-free coatings with high corrosion resistance. The alkanethiol layers showed high water repellency and poor corrosion resistance, and the triazinethiol layers with three thiol groups per molecule showed relatively poor water repellency and excellent corrosion resistance despite the very small thickness (several monolayers), as a result of suppressed oxygen reduction reaction determined by electrochemical measurement. XPS analysis revealed that alkanethiol molecules adhered to the zinc and formed layers with no decomposition, and triazinethiol molecules adhered to the zinc and then partially decomposed and reorganized to form a new network structure.
One of the surface defects on the steel strip surface after the gas-jet wiping employing an air-knife system in the continuous hot-dip galvanizing process is called sag lines or snaky coating. The sag line defect is the oblique patterns such as “W”, “V” or “X” on the coated surface. The present paper presents an analysis of the sag line formation and a numerical simulation of sag lines by using the numerical data produced by Large Eddy Simulation (LES) of the three-dimensional compressible turbulent flow field around the air-knife system. In order to simulate the sag line formation, a novel perturbation model has been developed to predict the variation of coating thickness along the transverse direction. The thickness obtained by the proposed model yields very similar results with those obtained by the conventional equation. It is observed that the coating thickness along the transverse direction is affected more by the pressure gradient than the surface shear stress in the stagnation region, while in the far field the shear stress becomes the major factor to determine the thickness. Finally, the three-dimensional coating surface was obtained by the present perturbation model. It was found that the sag line formation is determined by the combination of the instantaneous coating thickness distribution along the transverse direction near the stagnation line and the feed speed of the steel strip. The computed mean distance between the crests and the shape of the simulated sag show relatively good resemblance with the real sag lines on the strip surface.
The effect of temperature on the static tensile properties of the metastable austenitic steel JIS-SUS304 was investigated to clarify the conditions of stress-induced martensitic transformation behavior for maximum uniform elongation. Results of the static tensile tests showed that the tensile strength increased with decreasing temperature and that uniform elongation reached a maximum value at 308 K. The inverse temperature dependence of 0.2% proof stress was observed below 243 K. The volume fraction of martensite increased with decreasing deformation temperature. The conditions under which the stress-induced transformation resulted in the maximum uniform elongation due to the transformation-induced plasticity (TRIP) effect in SUS304 steel were summarized in terms of the martensite volume fraction and rate of transformation. The martensite volume fraction at true strain, which indicates the maximum transformation rate, was found to be approximately 35% independent of the deformation temperature. In stress–strain relationships for which the maximum uniform elongation was obtained, both the evolution rate of the dislocation density and the work-hardening continued to increase until near-uniform elongation was observed, and the maximum calculated value of work-hardening was almost 20 MPa/%.
EBSD mapping was used for phase analysis of multi-phase steels. Some products of austenite decomposition could be discriminated using a range of grain-average functions and properties derived from the map data. In DP steels, martensite could be extracted from the ferrite matrix using the average band contrast or a set of geographic information. Bainite in TRIP steel was identified with the local variations of band contrast and orientation inside a grain. As the proposed method reproduced a phase map, a visual confirmation of the result and additional analyses were possible.
CMnSi steel grades with carbon contents ranging from 0.2 to 0.3 wt% and manganese contents of 3 and 5 wt% were Quenched and Partitioned (Q&P). Tensile properties were assessed and retained austenite fractions measured. Intercritically annealed and fully austenitized conditions were studied. The best combinations of tensile strength and total elongation obtained in the 0.2C–3Mn–1.6Si grade after intercritical annealing were associated with strength levels in the 1000–1200 MPa range and total elongations ranging from 14 to 20%. Optimum properties were obtained in the 0.3C–3Mn–1.6Si steel after full austenitization with tensile strength levels ranging from 1450 to 1700 MPa and total elongations ranging from 11 to 18%. The 0.2C–3Mn–1.6Si fully austenitized samples also exhibited remarkable strength/ductility combinations albeit at lower strength levels of 1200–1450 MPa UTS with 9–15% total elongation indicating the effectiveness of the manganese addition to develop novel property combinations.
Tensile behavior of a nano-TRIP steel with 0.4 μm grain size showing tensile strength of 1326 MPa and total elongation of 23% was studied under in situ neutron diffraction. In spite of ultrafine grained structure, this steel realized a high work-hardening leading to a sufficient amount of uniform elongation. In the beginning of tensile deformation, Lüders band appeared similarly to many ultrafine grained materials. The stress induced martensitic transformation was found to occur during the Lüders deformation. A double-peak fitting was applied to the overlapped neutron diffraction profile for martensite and ferrite and then the stress partitioning behavior among ferrite, retained austenite and martensite were tracked during tensile deformation, revealing that the work-hardening after Lüders deformation was caused by higher load sharing of deformation induced martensite.
The demand for iron and steel materials has been increasing mainly because of the rapid economic growth of the BRIC countries. The annual worldwide production of crude steel is approximately 2 billion tons. There has been a corresponding increase in the production of crude steel in Japan. As a result, the significance of Japan as a source of iron and steel scraps has also increased.1) Scrap recycling, however, is subject to some problems, such as unstable supply conditions and contamination by impurities.2) A significant part of these problems can be attributed to the increasing use of electric devices, such as circuit boards, motors, and wiring harnesses, in high-tech products. These electric devices/equipments contain many kinds of metals, such as copper, lead, and zinc, which can become a source of contamination of steel scrap recovered from end-of-life vehicles (ELVs) or home appliances. Here the contamination of tramp elements was analyzed using a Waste Input Output model, considering the following points: (1) the amount of ferrous scrap usage in iron and steel production process, (2) copper elimination from ELV scraps, and (3) contamination of copper in iron and steel products. The results of scenario analysis indicated that copper contamination in crude steel production associated with the use of scrap from ELVs could be reduced by 2% by the use of a more recycle-oriented ELV treatment. The effects of copper elimination on CO2 emission were more significant for ordinary steel production than special steel production.
The alkali hydrothermal synthesis of zeolite A using oxide by-products such as blast furnace (BF) slag and aluminum dross was investigated. Na–P1 (Na6Al6Si6O32·12H2O) was synthesized directly in NaOH aqueous solution for 86.4 ks at 373 K using BF slag, Al2O3, and SiO2. On the other hand, zeolite A was successfully synthesized by a two-step method including an elution treatment of Al2O3. Under optimal conditions, the formation ratio of zeolite A in various compounds contained in the product was 56%. The utilization of dross residue squeezed out from the aluminum dross as a raw material to synthesis of zeolite A let this ratio increase to 60%. The heat of water adsorption of the product synthesized by the two-step method using BF slag, SiO2, and aluminum dross residue was measured, and it was 184 J/g, being higher than that of commercial zeolite A.