The melting and solidifying behaviors of CaO–SiO2–FeOx slag with changing oxygen partial pressure are important phenomena to understand the mechanisms and determine the optimum conditions for iron ore sintering process. In the present study, the liquidus for the CaO–SiO2–FeOx system at 1523 K with the oxygen partial pressure of 1.8×10−3 Pa (1.8×10−8 atm) was firstly determined by using chemical equilibration technique. The liquid area was separated into two parts, such as high and low SiO2 content regions. The fraction of liquid phase in the solid-liquid two phase region at high FeOx content area was calculated with various CaO/SiO2 ratios based on the determined phase diagram. Secondly, the melting and solidifying behaviors of CaO–SiO2–FeOx slag with changing oxygen partial pressure were directly observed at 1573 K by using a confocal scanning laser microscope. The observed melting and solidifying behaviors were compared with the previously measured phase diagrams with various oxygen partial pressures.
All available thermodynamic and phase diagram data have been critically evaluated and optimized for the liquid slag phase and for all solid phases at 1 bar pressure from 298 K to above the liquidus temperatures for the systems Al2O3–TiO2, Al2O3–Ti2O3, and Al2O3–Ti2O3–TiO2, and a database of model parameters has been prepared. The Modified Quasichemical Model was employed for the molten oxide phase. The thermodynamic modeling predicts the existence of a liquid oxide Al2O3–Ti2O3–TiO2 phase at secondary steelmaking conditions. The database was used to calculate the inclusion diagram for Al–Ti deoxidation at 1600°C.
In order to clarify the reaction behavior of phosphorus in the multi phase flux, the solid 2CaO·SiO2 piece was reacted with the CaO–SiO2–FeOx–P2O5 slag for 1 to 180 s at 1573 or 1673 K. The interfaces between the original solid and liquid phases were observed and compositions of both phases were analyzed by SEM/EDS. The result shows that P2O5 is condensed at the rim layer of 2CaO·SiO2 piece very fast in less than 1 s. The P2O5 condensed phases are identified as the mixture of 2CaO·SiO2–3CaO·P2O5 solid solution and the surrounding liquid slag. After reaction for longer time, the reaction behavior of P2O5 depends on the reaction temperature and initial slag composition. Reaction temperature and mole ratio of CaO/SiO2 in the initial slag influence the stability of P2O5 condensed phases. Higher temperature induces the dissolution of P2O5 condensed phases while larger mole ratio of CaO/SiO2 has the opposite effect.
Lining erosion is one of the key factors affecting the campaign life of the blast furnace. With the computer developments and CFD improvements, numerical simulation has already been the main way to study the refractory erosion of blast furnace. Here the most recent research results of numerical simulation and controlling on blast furnace lining corrosion were reviewed since 1960s, and some important problems of present were discussed, and some proposes for future development were given, Which will be helpful for the future theory and experiment research.
Analysis of solid motion in the vicinity of raceway of the blast furnace has been carried out by discrete element method (DEM). The physical properties of particle for DEM calculation are important factors to simulate precisely the solid motion in the blast furnace. In order to represent the feature of burden such as coke in the lower part of the blast furnace, the rolling friction was cautiously determined. Through the simulation results, it was found in the result of simulation that the contact friction and the rolling friction have a great influence on the solid motion especially in the lower part of blast furnace. In the present study, the contact friction of actual coke used for blast furnace was experimentally measured. The optimum combinations of contact and rolling friction coefficients were derived from the angle of repose obtained from the DEM. On the basis of the physical parameters optimized for blast furnace, the solid motion around the raceway where the ununiformity was remarkable in blast furnace was analyzed. The influence of variation of raceway is examined to clarify the motion of coke in the lower part of blast furnace. According to the results, it was found that the height of deadman varied with changing the depth of raceway. The interval of tuyeres seriously influences on the ununiformity of solid motion in the direction of circumference. Owing to DEM based on the optimized physical parameters, three dimensional analysis of solid motion containing the ununiform region became possible.
The potential of using biomass in ironmaking is investigated by simulation. Biomass is used to partially replace fossil reductants in the blast furnace process, which is described mathematically by a thermodynamic model. The model is cast in linear form to facilitate an efficient economic optimization of the production of raw steel, considering costs of raw materials, energy and CO2 emissions of the unit processes up to the basic oxygen furnace. The high oxygen content and low heating value of biomass makes it necessary to study a possible external pyrolysis of it prior to injection into the furnace. The economy of biomass injection and its dependence on the price structure of raw materials and emissions are investigated. The results throws light on how the prices of biomass and emission rights, compared to the price of coal and coke, affect the optimal biomass pre-processing (pyrolysis) and injection rate.
Presently, use of lump lime in BOF is often associated with operational problem due to its high melting point (~2700°C), poor dissolution property, fines generation, hygroscopic nature. Lime in combination with iron oxide is expected to quickly dissolve into steel making bath to produce low melting point oxidizing slag and to make the refining process faster. In current study, the suitability of a fluxed pellet containing 20–40% lime and waste iron oxides, developed through a novel binderless palletizing process where the strength was developed by CO2 treatment at room temperature has been tested for use in BOF. The pellets were characterized at low temperature as well as high temperature. The softening point of pellet was determined by TG-DTA and fusion study was carried out in muffle furnace. The results indicate early melting in BOF operating temperature. The pellet exhibited reasonable thermal shock resistance property, considered essential for the intended use in BOF. Deterioration of (Cold Crushing Strength) CCS on high temperature treatment is not likely to restrict its use in steel making furnace.
In most cases, the slag used in hot metal dephosphorization is saturated with dicalcium silicate in the solid phase and the partition ratio of phosphorus between dicalcium silicate and the liquid slag is high. This indicates the important role of dicalcium silicate in dephosphorization. To understand the reaction kinetics and identify optimum treatment conditions, it is very important to know the influence of the solid phases in the slag. In this study, a new reaction model for hot metal dephosphorization that considers the effects of dicalcium silicate and the dissolution rate of lime is applied to simulate laboratory-scale experiments. The calculated results are in good agreement with the experimental results for various slag compositions and methods of flux and oxidizer addition. The influence of various factors on the reaction efficiency is discussed using this simulation model. The optimum basicity and combination of stirring energy and oxidizer supply rate are found. The importance of the precipitation behavior of the solid phase in slag is clarified.
Strip in TWIP steel with the composition of Fe–23Mn–3Si–3Al fabricated by twin-roll strip casting was investigated. Large edge cracks, which were prone to occur in hot rolled TWIP steels, were avoided by using twin-roll strip casting. The cold rolled and annealed strip exhibited a reasonably good combination of strength and ductility after annealing at 1373 K for 20 min, with the tensile strength and elongation being 655 MPa and 57.4%, respectively, with the elongation of cast strip being 80% that of the conventional processed counterpart. Fine grain structure formed in cast strip increased the critical resolved shear stress (CRSS) of twinning and suppressed the generation of deformation twins during plastic deformation to make less contribution to the total elongation.
This study aims at developing a fundamental understanding of the factors controlling strip casting. Heat transfer behavior of molten iron and nickel during the first 0.2 s of solidification has been clarified experimentally. The transient phenomena during solidification were successfully observed using a photo-sensor to measure cast surface temperatures and one wire thermocouple technique to measure the copper plate temperatures. T-type thermocouples were employed as one wire thermocouple method. The following results were obtained by this study. The molten metal ejected from a silica tube was kept as liquid state during the first 0.02 s along with undercooling after which recallescence took place. In addition, fluctuations in temperatures of the cast surface and inside the copper plate, that were co-related each other, were observed during recallescence. The copper plate temperature could catch up with the cast surface temperatures at the plate side thanks to one wire thermocouple technique where one constantan wire was set inside the copper plate. The peak values of heat fluxes were found to be higher with higher superheat of the molten metal. Almost constant values of 10000 (kW/m2) were obtained over 55°C while 3500 (kW/m2) at 40°C in superheat. According to the results comparing the temperatures of the cast surface and the copper plate, the peak point of the heat flux physically implies how long molten metal state is kept as for solidification of metal.
A three-dimensional finite-element heat-transfer model was established to predict temperature of hot copper plates in a slab continuous casting mold with high casting speed and the temperature distribution and effect of casting speed on thermal behavior were simulated in detail. The results show that the calculated temperature agree well with the measured ones and the temperature of hot copper surface is influenced by the flash welded chrome (Cr) layer to a certain extent. The temperature profile of hot copper surface is determined by heat flux, material properties, solidifying shell shrinkage and mold taper and presents a certain shape. Temperature distributions in different transverse sections along effective casting height of mold are all similar and depend on mold structure and contact state between mold wall and slab. The centre temperature of hot copper surface at casting speed 1.8 m·min−1 and 2.0 m·min−1 are higher than that of 1.6 m·min−1 casting speed 4.7–5.2°C and 11.2–12.2°C respectively and temperature is not increased linearly with casting speed. Temperature difference adjacent to meniscus between mold wall and shell surface is influenced obviously by casting speed and increased 4.0–6.0°C with increment of casting speed 0.2 m·min−1. Fluctuation of temperature difference in meniscus should be a main reason to deteriorate casting effectiveness as increasing casting speed.
Effects of Ti addition on as-cast austenite structure of S45C steel have been investigated by means of furnace cooling experiment at a cooling rate of 0.03°C/s, focusing on the Ti addition ranging from 0 to 0.5 mol%. The Ti addition reduces average austenite grain diameter down to a size comparable to secondary dendrite arm spacing. In samples with the Ti addition, the austenite grain boundary is located at inter-dendritic position where Ti(C,N) particles exist and the refinement of austenite grain structure is ascribable to pinning effect of the Ti(C,N) particle formed in L+γ-Fe+Ti(C,N) phase field. The increment of Ti addition does not substantially change the size of Ti(C,N) particle but increases the number of the Ti(C,N) particles, leading to further refinement of the austenite grains.
Effects of titanium and boron addition on columnar austenite grain structure of S45C steel have been investigated in casting experiments with different cooling rates of 4.50 and 16.67°C/s. Without addition of these elements, the columnar austenite grains develop over the whole sample under the present casting conditions. The addition of titanium and boron induces formation of equiaxed austenite grains and, importantly, fully equiaxed austenite structure was observed in the sample with 0.2 mol% Ti and 0.4 mol% B. The microstructural observations indicated that this behavior of austenite structure stems from the columnar-to-equiaxed transition of ferrite dendrite structure. The addition of these elements, furthermore, leads to refinement of the columnar austenite grains, which is ascribable to pinning effect of boron nitride and titanium carbonitride.
An in-situ TiC-reinforced Hadfield manganese austenitic steel matrix composite has been synthesized by conventional melting and casting route. The microstructure has been characterized using an optical microscope, a scanning electron microscope coupled with an energy dispersive spectrometer and X-ray diffraction. Hardness and abrasion resistance have also been measured. The microstructure of the as-cast composite consists of austenite, α-ferrite and (Fe, Mn)3C together with TiC particles. The microstructure of the solution-annealed (1273 K for 36 ks) composite contains TiC particles in γ matrix. It has been observed that the abrasive wear resistance of the solution-annealed composite is significantly better than that of the solution-annealed austenitic manganese steel.
In recent years the precision ultra-high strength quenching steel plates (PUHSQS) have been widely used in the automobile production to reduce weight and improve passive safety. This paper investigates the spot welding performance of PUHSQS EN 1029TL4225, a kind of advanced high strength steel, whose tension strength can attain 1500 MPa after being quenched. Using the intermediate frequency (IF) spot welding process, two kinds of welded joints are made: the joint of two PUHSQS plates and the joint between PUHSQS EN 10292TL4225 and the micro-alloy steel H340 LAD. The mechanical performances of welded joints, such as the tension strength, the hardness distribution, are tested. Besides, the macrostructure and microstructure are also analyzed. From the results, we can see that both of two kinds of welded joints have perfect properties and internal quality, and also the mechanical performances meet the actual production requirement completely. So we conclude that the steel EN 10 292 TL4225 has good spot welding performance.
Varying nugget sizes are obtained in different coated and bare automotive steel grades applying identical spot welding parameters. The strength of sheet surface asperities and surface topography together seem to influence contact conditions under applied pressure and welding temperature. The low fractal roughness and easily deformable asperities of soft steels decreases both static and dynamic contact resistance. Contrarily, high fractal roughness and stronger asperities of higher strength steels resist successive yielding of the asperities. This, in turn, produces more heat for melting and therefore larger nuggets. The heat efficiency of welding increases with yield strength as favorable contact resistance conditions are set in. Significantly, the iron–zinc intermetallic phases in the steel coating consume part of the latent heat of fusion and decrease the energy efficiency. Continuous modification of the surface with progressive melting of the intermetallic layers also contributes to this effect. For longer weld times in coated steels, the drop in contact resistance at the early stages of welding is compensated later, which improves overall heat efficiency.
The purpose of this paper is to find out quantitatively the relationship between the surface shape and the mechanical properties of corroded reinforcement. Three-dimensional measurements were carried out on the surface shape of variously corroded reinforcements and parameters expressing the characteristics of the shape, which included the maximum decrement of sectional area of reinforcement, its distribution along the axis and the power spectral density by the Fourier Transformation. It was investigated that which parameters could correspond to the mechanical properties of corroded reinforcement and it was confirmed that the maximum decrement of sectional area of reinforcement could express the mechanical properties most appropriately. Finally, this paper proposes a constitutive model of corroded reinforcement for analyzing the structural behavior of reinforced concrete structures considering the localized corrosion of reinforcement by finite element method.
An in situ TiSi (Ti5Si3, TiSi)/TiC local reinforced steel matrix composite was successfully fabricated via combustion synthesis of Cu–Ti–Si system. XRD results show that the reinforced region of the composites is composed of Fe, Cu, TiSi and Ti5Si3 as well as TiC phases. SEM observation shows that the morphologies of the Ti5Si3 particles are coarse acicular/irregular particles and short fibrous/coarse elliptic shape in transition and reinforced region, respectively. TiC particles lie in transition region near the interface and their morphologies are polygon/quadrangle, with sizes of ~74 μm DTA analyses show that, without addition of Cu, slight TiSi (TiSi2 and Ti5Si3) compounds form via solid diffusion process. After addition of Cu, Cu and Ti reaction occurs firstly, forming a serious of Cu–Ti compounds, at the same time, the reaction heat ignites the subsequent reaction of CuTi and Si and according forms TiSi (Ti5Si3) compounds.
The microstructure evolution at interfaces of a layer-integrated steel sheet artificially constructed by ductile austenitic stainless (SUS304) and high-strength martensitic (SCM415) steel layers, which were bonded through a cold-rolling and a subsequent annealing at 1000°C, has been investigated using scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS). We find that a significant microstructural reconstruction around the SUS304/SCM415 interface has been accomplished during a short-time annealing followed by water-quenching; the resultant microstructures are found to consist of recrystallized austenite and lath martensite grains for the SUS304 and SCM415 layers, respectively. Interestingly, the original SUS304/SCM415 interface appears to migrate and extend into the SUS304 side, an occurrence of which can be reasonably explained by the martensitic transformation across the composition-gradient interface during quenching. These microstructural evolutions fairly account for a microscopic mechanism on how hetero-interface bonding can be achieved via simple cold-rolling/annealing procedures.
This paper deals with the Hydrogen Induced Cracking (HIC) of wires in a cable of a suspension bridge. The main objective is to compare the safety of a bridge system locally and globally. In a deterministic analysis stage, HIC in cable wires is calculated in order to evaluate the local safety of the main cable of suspension bridge. In the local analysis, a decoupling technique has been developed for the evaluation of crack propagations in a wire section driven by the hydrogen diffusion to a wire section, in terms of two 2-dimensional finite element models. One is for the fracture analysis in a longitudinal section, and the other is for a hydrogen diffusion model in a horizontal section. In a stochastic analysis stage, an ultimate limit state function for the cracking in cable wires is considered for the local safety of main cable. Using the ultimate limit state, the reliability of time-dependent and crack depth-dependent HIC of a cable wire has been calculated in component and parallel system reliability analysis. Globally, a serviceability limit state based on the global responses of a stiffening girder is also evaluated. Based on the observed difference of safeties between the global and local behaviors of the suspension bridge system, the proposed solutions are discussed.
The hot ductility of low manganese mild steels was investigated at a high strain rate of 22 s−1 to simulate a roughing mill in the hot rolling process for various contents of manganese and sulfur. With all steels, ductility loss occurred in a low temperature range in the austenite region after reheating at 1573 K. A decrease in the manganese content and an increase in the sulfur content deteriorated hot ductility. A low reheating temperature and a long holding time before tensile deformation improved hot ductility. Tensile strength decreased at reduction-in-area below 40% at a constant temperature, and had no relationship with chemical composition. The brittle fracture surfaces were intergranular fractured ones and were observed at reduction-in-area below 40%. (Fe,Mn)S precipitates existed in small dimples on the brittle fracture surfaces. The quantities of the precipitated sulfides were calculated by Thermo-Calc, and increased with increasing manganese and sulfur contents. An increase in the manganese content promoted coarse (Fe,Mn)S at the same temperature. The sizes of the sulfides were also correlated with thermal diffusion at various temperatures and holding times. Hot ductility was understood by the quantity and size of the precipitated sulfides at high reheating temperatures. Embrittlement was accelerated by an increase in the quantity of precipitated sulfides and a decrease in the precipitate size. At low reheating temperatures, improvement of hot ductility was recognized as a result of a decrease in solved sulfur in the reheating process.
Complete set of elastic constants Cij of α-Fe single crystal have been investigated from ambient temperature up to 893 K by electromagnetic acoustic resonance. Longitudinal component of elastic constants C11 showed linear temperature behavior and the magnitude of elastic softening was approximately 13%. The remainning two shear moduli, C44 and C′, however showed highly nonlinear behaviors with significant softenings of 50%. On a Blackman diagram, elastic constant ratios at high temperatures move to a limit, C12/C11=1 and C44/C11=0, where Born's two lattice instability criteria have been satisfied simultaneously. Violation of Cauchy relation is also significant upon heating.
A newly developed noncontact modulated laser calorimetry method was attempted to measure the isobaric specific heat capacity and thermal conductivity of liquid austenitic stainless steel (SUS 304: Japanese Industrial Standards). A stainless steel droplet was electromagnetically levitated in a radio frequency coil. A dc magnetic field of 4–5 T was superimposed to the droplet to suppress the convection in the droplet by the Lorenz force. The specific heat capacity of the liquid SUS 304 was successfully measured at temperatures ranging from 1750 to 1970 K. No clear temperature dependence was observed. The mean value over the whole temperature range is 794±76 J·kg−1·K−1. The lower thermal conductivity of the liquid SUS 304 was obtained at higher dc magnetic field, which indicates that convection in the droplet was reduced by dc magnetic field. The thermal conductivity was measured as 60±9 W·m−1·K−1 at 5 T in the same temperature range. For the thermal conductivity measurement, it is necessary to verify the effect of suppression of the convection by conducting the calorimetry at higher dc magnetic field.
The real and imaginary parts of relative complex permittivity (ε′ and ε″) and relative complex permeability (μ′ and μ″) were measured for powder and bulk SiO2 and Fe3O4 in the frequency range of 200 MHz–13.5 GHz. The ε′ and ε″ values of SiO2 powder samples are in good agreement with the previous data. The ε′ values of powder SiO2 and Fe3O4 samples with the relative density below 1 are smaller than the values estimated using the linear relation between ε′ and the relative density, and larger than those estimated using the Lichtenecker's logarithm mixed law. The μ″ values of powder Fe3O4 samples show the peaks in the frequency range of 706 MHz to 3.21 GHz. The frequency at the peak of the μ″ vs. frequency curve decreases with an increase in the particle size of Fe3O4 sample. All the powder samples with an identical relative density have almost the same μ″ values around 2 to 3 GHz irrespective of the particle size. Above ca. 3 GHz, the μ″ values of all samples become smaller as the measurement frequencies become higher. These results suggest that 2.45 GHz, the frequency of the most commercially prevailing microwave generators, may be the most suitable one for microwave heating of iron ores.