The present paper investigates how the mass ratio between Al2O3 and SiO2 (mAl2O3/mSiO2) in slag compositions influences the structure, viscosity and crystallization of the slag melts. The objective is to study the variations in viscosity and structure of slags with increasing mAl2O3/mSiO2 ratio. In practice the results of the study are relevant to the significant changes in slag property caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. The viscosity was found to decrease slightly with increasing mAl2O3/mSiO2 ratio up to 0.56. The degree of polymerization for [SiO4]-tetrahedra was found to decrease with increasing mAl2O3/mSiO2 ratio based on the Fourier Transformation-Infrared Spectra (FT-IR) and Raman spectra, which could explain the observed decrease in viscosity. AtmAl2O3/mSiO2 ratios above 0.56, the viscosity was found to abruptly increase which could be caused by the presence of spinel crystals. The activity coefficient was computed and it was found that the activity coefficient of alumina presents negative deviation when mAl2O3/mSiO2 ratio is less than 0.35, while it shows a positive deviation when mAl2O3/mSiO2 ratio exceeds 0.35. This phenomenon may be related to the change of the primary phase region correlating to the phase diagram to the slag composition.
The sulfide capacities of the CaO–SiO2–MnO–Al2O3–5 mass% MgO slags were measured at 1873 K over a wide composition range using a gas–slag equilibration method. The effects of basicity and the activity coefficient of sulfide on the sulfide capacity of molten slag were also investigated based on the structural view of silicate melts. In the multicomponent silicate melts containing high MnO (up to about 50 mass%), the sulfide capacity mainly increased with increasing MnO content. The capacity and modified Vee ratio, i.e. (CaO+MnO+MgO)/ (SiO2+Al2O3), showed a good linear relationship. Assuming that the basicity and the stability of sulfide ions in the slag are proportional to the activity of basic oxides and the activity coefficient of sulfides, the composition dependency of the sulfide capacity is well described by changes in the aMO to γMS (M=Ca, Mn) ratio. The substitution of silica by alumina did not affect the sulfide capacity of the slags not only because of an increase in the activity of basic oxides but also because of a decrease in the stability of sulfides as Al2O3/SiO2 ratio increased. In the high silica melts of which silica content greater than about 30 mass%, the sulfide capacity increased with increasing MnO/CaO ratio, whereas it decreased by increasing the MnO/CaO ratio in the low silica melts (< about 30 mass%). This tendency of sulfide capacity resulted in the clock-wisely rotating iso-capacity contours in the CaO–SiO2–MnO–Al2O3–MgO system at 1873 K. The dissolution mechanism of sulfur in the MnO–containing calcium silicate melts can be explained not only by the difference in the structural role of Ca2+ and Mn2+ ions but also by the changes in the content of O2– ions according to the silica content.
A comparative study on structural variations during the solidification of Fe-C and Fe-B eutectic alloys was conducted by synchrotron x-ray diffraction under containerless cooling conditions using a conical nozzle levitation technique. It was revealed that a metastable phase composed of Fe23B6 precipitated as the primary crystalline phase from the undercooled liquid Fe83B17 alloy, whereas solidification of the Fe83C17 alloy occurred via a normal phase transformation process according to the Fe-C phase diagram. In addition, decomposition of the metastable Fe23B6 phase to the equilibrium phases shows a dependence on the cooling rate of the sample. By comparing the primary crystalline phase in the Fe83C17 and Fe83B17 alloys, we suggest that the formability of the metastable Cr23C6-type structure is closely related to the glass-forming ability of Fe-metalloid binary alloys.
Blast gas discharge from the taphole in the course of the blast furnace hearth drainage was experimentally studied using a packed bed cold model. It was found that gas break-through time was strongly influenced by the furnace operating conditions and coke bed structure. Gas break-through time decreases with (a) increasing draining rate; (b) decreasing slag and iron levels in the hearth; and (c) increasing slag viscosity. It increases with an increase in the coke-free layer depth and coke-free space width. Under certain conditions, the gas-liquid interface in the region directly above the taphole becomes unstable, leading to viscous finger formation and subsequently early blast gas discharge from the taphole. The amount of blast gas entrained into the taphole due to viscous fingering, when it occurs, is sufficient to cause a splashy taphole stream.
Biomass use has been identified as one of the possibilities to mitigate fossil greenhouse gas emissions in iron and steelmaking. Biomass can be used to replace part of the fossil-based reducing agents in blast furnace without compromising the quality of the final product. The advantage of biomass compared to fossil-based fuels is that it is renewable energy source and can thus be considered carbon dioxide neutral within specified system boundaries. Few studies have been conducted where the effect of biomass introduction to blast furnace process have been evaluated with mathematical modeling or lab-scale experiments. The other body of literature concerns the life cycle based assessments. This study presents the effects of biomass use in plant site scale with energy balances and CO2 reduction potential. For the evaluation purposes integrated steel plant model based on physico-chemical relationships was developed. The model can be used for calculating gate-to-gate life cycle inventory for evaluating the environmental burden of the integrated steel plant. Effect of charcoal as tuyére injectant to blast furnace process was firstly evaluated. The results indicate that to replace 1 kg of specific heavy oil, 1.15 kg charcoal would be needed. Plant-wide effects of two distinct charcoal usage scenarios were evaluated and compared to base case scenario with fossil-based reducing agents. Plant site evaluation suggests that by introducing biomass to integrated steel plant, major changes in energy balances occur and significant fossil CO2 emission reduction can be achieved. This study indicates that 15.4 to 26.4% reduction in fossil CO2 emissions could be achieved in plant scale.
Inter-particle percolation at the interface between the burden layers in the blast furnace influences the permeability in the lumpy zone, and, in particular, in the cohesive zone, where the iron-bearing materials start softening to finally melt. This paper presents a simulation study of the effect of particle properties on inter-particle percolation of small particles (pellets) into a layer of larger particles (coke) during burden descent in the blast furnace. An expanding experimental device in small scale was applied to mimic the conditions at burden descent in a shaft with growing radius, and results from these experiments were used as a reference for the simulations and to validate the computational results. The simulations, which were based on the discrete element method, studied the effect of factors such as friction and restitution coefficients, shear modulus, as well as pellet diameter on the extent of percolating particles. It was found that coke shape, pellet diameter, static friction and inter-particle rolling friction and restitution had a marked effect on the percolation, while rate of expansion of the device, density of pellet and shear modulus proved to be of minor importance.
The phosphorus in high-phosphorus (>0.1% P) iron ores from the Pilbara area of Western Australia is mainly associated with the goethite fraction of the ore. Physical separation methods and simple leaching processes do not remove sufficient phosphorus from the ores to meet market specifications of 0.075% P. Processing to disrupt the goethite structure to make the phosphorus amenable to leaching is necessary. Phosphorus associated with the goethite in high-phosphorus iron ores can be removed to 0.075% P using a heat treatment at 300–350°C for 1 h with 10 wt% NaOH, followed by a water leach. Heating at higher temperatures, up to 500°C, with heating times of 0.5 h to 4 h, gave no improvement in phosphorus removal. Similar phosphorus removal was achieved by heating the ore at 300–350°C for more than 0.5 h and leaching with 1–5 M NaOH at the boiling point for 3 h. The concentration of sodium hydroxide required depended on the amount of phosphorus to be removed. Heating for up to 2 h or at higher temperatures up to 750°C did not improve the amount of phosphorus removed in the caustic leach. The temperature of the leach had a significant effect on the amount of phosphorus removed with less phosphorus being removed below the boiling point of the leach liquor. The heat treatment at 300–350°C is considered to dehydroxylate the goethite to form a hematite intermediate phase, ‘protohematite’, from which the phosphorus is dissolved during the leach step.
Recent Electric Arc Furnaces are equipped with ultra high power transformers to provide maximum values of electric power and minimize the melting time. The active power is increased by increasing arc length and arc voltage, however in these conditions energy losses due to radiation can also be increased with a consequent decrease in thermal efficiency. The energy radiated from the electric arcs is transferred to the walls inside the EAF promoting hot spots which represent a catastrophic operational condition. This work reports a radiation model which describes the formation of hot spots as a function of arc length and foamy slag height in an industrial EAF of 210 ton. of nominal capacity. Temperature profiles on the surface of the water cooled panels and values for the incident radiation were computed as a function of foamy slag height, used subsequently to define conditions to eliminate the formation of hot spots.
A multiphase numerical analysis focused on flow dynamics and particle trajectories during steel tapping operations was developed. The numerical results indicate that lighter additions than steel (ferrosilicon and aluminum) are independent from bath level, fall height and flow dynamics of the melt. Neutral buoyant additions (Fe–Mn) are strongly dependent on fluid dynamics of the melt and bath height. Denser additions (like Fe–Nb) yields long residence time inside the melt before first emerging to the bath surface. However, when this ferroalloy is added at high bath levels, close to the end of tapping, the particles remain in the corner formed by the bottom and the wall of the ladle during long times prolonging their melting rates.
A combined cellular automaton-finite difference (CA-FD) model has been developed to simulate solute diffusion controlled solidification in continuous steel casting. Constitutional and curvature undercooling were both solved to determine the equilibrium temperature and growth velocity of the solid/liquid interface. Simulations were firstly performed for both the free dendritic growth from an undercooled melt and the columnar dendritic growth in unidirectional solidification. Finally, competitive dendritic growth and columnar to equiaxed transition (CET) occurring in solidification of continuous casting process were reproduced by the present CA-FD model. The effect of the fragmentation of dendrites due to fluid flow induced by EMS in mould on nuclei was taken into consideration by increasing the grain density. The comparison between the simulated and experimentally observed results shows that the present model can be used to simulate solidification structure formation during the continuous casting process of steel. The influence of superheat on solidification structure was also analyzed, and it was found that increasing superheat increases the columnar dendritic growth and reduces the equiaxed ratio, as it is empirical well known.
The influence of steel grade on the oxidation rate of molten steel in tundish was studied by conducting oxidation experiments on the Ti and Ti–Al deoxidized molten steel and comparing the obtained oxidation rates with that of the Al deoxidized molten steel as measured in a previous report. In the still state, the oxidation rate of the Ti deoxidized molten steel is faster than those of the Ti–Al deoxidized molten steel and the Al deoxidized molten steel, showing dependence on the steel grade. This means that in the still state, while the oxidation rates of the Ti–Al and Al deoxidized molten steel are controlled by the mass transfer of oxygen in the oxide film, the oxidation rate of the Ti deoxidized molten steel is controlled by the mass transfer of O2 gas in the gas phase because the surface is not covered with oxide films. In addition, in the stirred state, the oxidation rates of the Ti and Ti–Al deoxidized molten steel become faster than that of the Al deoxidized molten steel in the region where the O2 gas partial pressure exceeds 10 kPa. This dependence on the steel grade can be explained by the mechanism of accelerating the mass transfer in the gas phase due to active iron evaporation in the Ti and Ti–Al deoxidized molten steel, in which the surface disturbance is larger than that in the Al deoxidized molten steel.
Sumitomo Metal Industries, Ltd. (SMI) has developed a new temperature measurement method (Fountain pyrometer) and an associated control system, for hot strip cooled by water in cooling banks. High tensile steel is seeing increasing use in lightweight cars to improve fuel economy and reduce CO2 emissions. Reliable material quality of hot strip products, including high tensile steel, requires good temperature control on the run-out table. The conventional control method is not good enough because the temperature of a hot strip cannot be accurately measured in the cooling banks, where the cooling water interferes with thermal radiation from the hot strip surface. SMI has developed the Fountain pyrometer, which uses a water purge to stabilize the passage of thermal radiation from the hot strip surface. Experiment confirms that Fountain pyrometers can reliably measure hot strip temperatures above 360 degrees Centigrade even in cooling banks with a great deal of cooling water. The response time of Fountain pyrometers is 10 or 20 ms. SMI has also developed a new control system using Fountain pyrometers, a combination that allows very precise temperature control of hot strip on the run-out table.
Oil-in-water (O/W) emulsions are widely used in tandem cold rolling mills as coolants in order to reduce frictional forces and prevent heat scratches. Although the lubricating properties of O/W emulsions are determined by various factors, two particularly important ones are the amount of plate-out oil on the strip surface and the dynamic concentration mechanics of the emulsion at the inlet of roll bite, which has been a subject of much interest since the 1970s. As many studies have focused only on a single phenomenon, it is important to simulate the interaction of the two phenomena as it occurs in actual cold rolling. In this paper, first, a new method of evaluating the relationship between plate-out oil and lubrication characteristics is proposed, which enables control of plate-out oil before rolling. It was found that rolling force decreased when a plate-out oil film was formed before rolling, but the reduction of rolling force was saturated when the amount of plate-out oil exceeded a certain level. The influence of roughness, the roll coolant, and other factors were also examined using the proposed method. In particular, in tandem cold rolling, it is necessary to consider the influence of plate-out oil carried over by the preceding stand on the lubrication characteristics of the following stand. The results of this research suggest that it is possible to clarify the mechanism of emulsion lubrication using the proposed method.
Lubrication is an important parameter in cold working of steels. Metal soap on phosphate coating is the most commonly used lubrication system in industries at present, but the technique is less productive and environmentally hazardous. The authors proposed an alternative lubrication process which makes use of porous layer formed on the surface of the workpiece by oxidization and chemical reduction in the previous paper. The technique, due to the porous layer, enables to hold more liquid lubricant on the surface and consequently to decrease the friction. This research expands the range of application of this technique. The porous layer is applied to three types of steels containing different levels of carbon and its effects are analyzed under three lubrication conditions; unlubricated, machine oil and grease, by ring-compression test. Another important condition, compression speed is investigated by using two types of equipments, a hydraulic press (low speed) or a mechanical press (high speed). This study proves that the porous layer technique is applicable to a range of types of steels reducing the friction coefficient, and at the same time provides some insights to explain the mechanics of the technique. The lubrication effects are explained by the thickness of lubricant held at the interface between the die and the surface of workpiece.
Pitting corrosion of type 430 stainless steel under a chloride solution layer was investigated to clarify the pitting corrosion behavior. The solution layers containing 2 mol/dm3 chloride ion with four different thicknesses of 1000, 500, 250, and 125 μm were placed on the stainless steel surface and dried by decreasing the relative humidity at various rates at 300 K. The corrosion potential and solution resistance were simultaneously monitored during drying in order to determine the concentration of chloride ion at the commencement of pitting corrosion. The results showed that the lowest chloride concentration for occurrence of pitting corrosion for type 430 is about 4.5 mol/dm3, and that pitting corrosion occurs at higher chloride concentration as the drying rate increases.
Tempering effects on the austenite stability and mechanical properties of 0.2C–5Mn steel were investigated in the temperature range from 100°C to 600°C with 1 hour. It was found that tempering doesn't result in a significant change of the austenite plus ferrite duplex structure, which was developed in the previous annealing through austenite reverted transformation, whereas significant decreasing of the austenite fraction and carbon concentration was found in the specimens tempered at 200°C and 500°C due to the precipitation of carbides. Correspondingly tempering slightly deteriorates the ductility when the specimens were tempered at 200°C and 500°C without effects on mechanical properties around 400°C. Based on the analysis of relationship between mechanical properties and retained austenite, it was found that the product of tensile strength to total elongation (Rm*AT) was strongly dependent on the product of the volume fraction and carbon concentration of retained austenite (fA*Cγ). Furthermore, the optimal mechanical properties with tensile strength 1000 MPa and total elongation 40% could be obtained after tempering at 400°C with 1 hour, which means that galvanization is feasible in the 0.2C–5Mn steel with ferrite and austenite duplex structure.
An ultrafine grained (UFG) ferrite/cementite steel was subjected to intercritical annealing in order to obtain an UFG ferrite/martensite dual-phase (DP) steel. The intercritical annealing parameters, namely, holding temperature and time, heating rate, and cooling rate were varied independently by applying dilatometer experiments. Microstructure characterization was performed using scanning electron microscopy (SEM) and high-resolution electron backscatter diffraction (EBSD). An EBSD data post-processing routine is proposed that allows precise distinction between the ferrite and the martensite phase. The sensitivity of the microstructure to the different annealing conditions is identified. As in conventional DP steels, the martensite fraction and the ferrite grain size increase with intercritical annealing time and temperature. Furthermore, the variations of the microstructure are explained in terms of the changes in phase transformation kinetics due to grain refinement and the manganese enrichment in cementite during warm deformation.
Cold rolled (40, 60 and 80% thickness reductions from hot-band) interstitial free (IF) steel samples were recovered at 500°C for different times (15 min to 32 h). The recovery kinetics, studied through a combination of X-ray line profile analysis and high resolution electron diffraction, were best represented by logarithmic relationship. Though the kinetics was dependent on the prior deformation, γ (ND//<111>) fibre clearly had stronger recovery than θ (ND//<100>) fibre. Recovery was observed, statistically to create grain interior strain localizations: an orientation independent phenomenon. Increase in misorientation across such strain localizations was, however, orientation dependent. This was responsible for enhanced in-grain misorientation in recovered γ-fibre grains/bands. Extended recovery of 80% pre-deformed samples also led to coarsening of γ-fibre bands: strain induced boundary migration (SIBM) or uniform movement of γ-fibre boundaries into neighbouring non γ-fibre orientations.
Hot band, fully recrystallized, interstitial free (IF) steel samples were cold rolled to 10–80% thickness reductions. After characterizing the developments in deformed microstructures, 50–80% deformed samples were fully recrystallized at 650°C. Though different annealing times were used, use of a relatively lower annealing temperature and repeated trials ascertained absence of significant post-recrystallization grain coarsening. Recrystallization brought in a steady improvement in γ-fibre (ND//<111>) and drop in θ-fibre (ND//<100>). The only exception was 80% prior deformed microstructure, where the trend was reversed: enforcing a drop in texture estimated normal anisotropy or r value. The study brought out growth inhibition of recrystallized γ-fibre grains, caused by non-γ fibre bands and by orientation pinning of recrystallized γ-γ boundaries, as the mechanism behind the observed trend reversal.
Microstructure and creep strength of two high-Cr ferritic heat resistant steels –11Cr and 9Cr - were investigated at a temperature of 650°C. 11Cr steel containing relatively higher carbon, aluminum and nickel than 9Cr steel showed a significant drop in creep strength after 1000 h, while 9Cr showed a recovery in creep strength after a slight drop. 11Cr steel contained M23(CB)6, Z phase and a relatively coarsened Laves phase as precipitates after 7000 h at a temperature of 650°C, while the 9Cr steel contained fine MX, ultrafine M6C, as well as M23(CB)6 and Laves phase. Z phase was not found and the growth of Laves phase was retarded in the 9Cr steel. Hence, it was concluded that the drop in creep strength of 11Cr steel was attributed to the coarsened Laves and Z phases, and the recovery of creep strength in the 9Cr steel to the fine MX and M6C precipitates. The experimental results on the effect of steel composition on the stability of precipitates in steels were thermodynamically consistent with the Thermo-Calc calculation results, which used an existing database. We concluded that chromium and aluminum increased the kinetics of the formation and coarsening of the precipitates.
Fatigue strength is one of the key properties in the practical use of ultrafine grained steels. Fatigue tests were conducted on notched specimens by conventional electromagnetic resonance fatigue testing machines. The electromagnetic resonance fatigue testing was carried out at 150 Hz up to 107 cycles. The investigated steels had different levels of carbon, 0.15 wt%, 0.30 wt% and 0.60 wt% with tensile strengths of 850 MPa, 950 MPa and 1105 MPa, respectively. With increasing in carbon content, the tensile strength increased and the total elongation decreased. The notched specimens never showed internal fracture and showed a clear fatigue limit. The notch fatigue limit increased with an increase in tensile strength from 850 MPa to 970 MPa, when the carbon content was 0.15 and 0.30 wt% with microstructures consisting of ultrafine ferrite grains and cementite particles. On the other hand, when the carbon content was 0.60 wt%, the notch fatigue limit decreased, though tensile strength increased to 1105 MPa. Retained pearlite grains were observed in 0.60 wt%C steel in addition to ultrafine ferrite grains and cementite particles. These retained pearlite grains which were coarse and high angle grain boundary poor regions were attributed to the lower notch fatigue limit.
The brittle-to-ductile transition (BDT) behaviour in nickel-free austenitic stainless steel with high nitrogen was investigated. Fall-weight impact tests revealed that Fe–25mass%Cr–1.1mass%N austenitic steel exhibits a sharp BDT behaviour in spite of an fcc alloy. The aspects of plastic deformation after the impact tests indicate that the BDT observed in this austenitic steel is induced by poor ductility at low temperatures as is the same as that in ferritic steels. In order to measure the activation energy for the BDT, the strain rate dependence of the BDT temperature was examined by using four-point bending tests. The weak dependence of the BDT temperature on the strain rate was observed. The Arrhenius plot of the BDT temperature against the strain rate elucidated that the activation energy for the BDT of Fe–25mass%Cr–1.1mass%N is much higher than that of low carbon ferritic steels. The origins of such distinct BDT behaviour and its large value of the activation energy in this high-nitrogen steel are discussed in terms of the reduction of dislocation mobility at low temperatures due to the interaction between glide dislocations and nitrogen solute atoms.
We produced the nano-structured graphitic materials by pyrolysis of end-of-life kitchen melamine-formaldehyde (MF) plate without externally supplied catalyst/additive at 1600°C under nitrogen flow of 2 L/min. Different types of morphologies of carbon materials were observed under the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) such as, sheet, rod and porous particle. In Raman analysis, the material shows high level of crystallinity (~70% crystalline and remaining amorphous carbons) with high purity. We have applied this material in the carbon dissolution experiment with pure iron pellets under similar condition for a wide range of contact time. The carbon dissolution shows a linear relationship with contact time, and the maximum ~5.65% is determined for 45 min. The highly ordered spherical particles are assembled in the interfacial region of iron/MF. The high magnification of the spherical particle on SEM shows different types of phases containing carbon along with visible grain boundaries. The progression of carbon diffusion is found from the interface to the beneath of the surface in the polished iron pellet. The process is a promising recycling of sustainable material, end-of-life MF products for value-added advanced products as new carbon resource in steelmaking process for energy savings.
For the efficient supply of nutrition for phytoplankton multiplication in marine environment, the dissolution behaviors and the dissolution mechanisms of Ca, Si, P and Fe elements from steelmaking slag into seawater were investigated. The shaking experiment with synthesized CaO–SiO2–P2O5–FeO slag was conducted at room temperature. The variations of shaking time, the CaO/SiO2 ratio of slag and the slag/seawater ratio were taken into consideration. The dissolution behavior of elements especially Si and P, pH of solution and the effect of slag/seawater ratio on dissolution are classified into two types by the CaO/SiO2 ratio of slag. The dissolved concentration of Ca of slag with large CaO/SiO2 ratio is much larger than that with small ratio. Mg2+ ion originally contained in seawater provides an obvious buffering action on pH increasing process which is caused by the dissolution of Ca. Moreover, the solubility diagrams are applied to elucidate the dissolution mechanisms. Additionally the dissolution of Fe is also analyzed with potential - pH diagram.