The aim is exploring a new MgO heterogeneous deposition coating method to increase the coating amount, and investigating its sticking prevention effect on the fluidized bed reduction of iron ore. The pure Fe2O3 or iron ore particles were coated with Mg(OH)2 using the heterogeneous deposition coating method. In order to restrain the homogeneous nucleation and promote the heterogeneous nucleation during precipitation, the NH4Cl–NH3·H2O pH buffer solution was employed to adjust the OH− concentration. The actual MgO coating amount on the particle surface has been improved to 3.8 wt%, and the sticking problem of Hualian iron ore during fluidized reduction can be avoided with the MgO coating amount of 0.91 wt%. This coating method achieved a satisfactory uniformity of the coating film, and there was nearly no uncoated part on the coated particle surface. The combination strength between the coating layer and particles’ surface with different coating methods was investigated via a blowing system, and it was concluded that the solution and heterogeneous deposition coating methods could achieve a higher coating strength than the dry or slurry coating methods.
The carbothermic reduction of ilmenite concentrate with graphite powder was investigated by isothermal experiments under nitrogen atmosphere. The reaction temperatures of the reduction-nitridation process were over a range of 1473 K to 1773 K. After various reaction time, the reduction-nitridation products obtained at various temperatures were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Mass loss was also measured and used to judge the mechanism. The reaction rate and extent of the reduction-nitridation process increased with increasing the reaction temperature. The reaction sequence of the ilmenite concentrate from 1473 K to 1773 K in nitrogen was found: FeTiO3 → Fe + Ti3O5, and Ti3O5 → TiC1-xOx → TiC1-xNx. The lowest temperature for the generation of TiC1-xOx and TiC1-xNx was 1573 K. The incorporation of the nitrogen was found to occur after the formation of TiC1-xOx. Ti2O3 did not appear as an intermediate phase due to its instability in nitrogen atmosphere.
The present study aimed to provide a deep insight of short-range and medium-range structural order for CaO–SiO2–TiO2–B2O3 glasses. From various prospects, four techniques, FTIR, Raman, XPS and NMR, were simultaneously employed and only the direct evidences indicated from the spectra were used for structural analysis. The FTIR and Raman spectra proved that the main silicon-related units were Q0(Si), Q1(Si), Q2(Si) and Q3(Si) and the results of Raman fittings revealed that a B2O3 addition resulted in an increase of Q1(Si) and Q3(Si) at the cost of Q0(Si) and Q2(Si), thus inducing an increasing Degree of Polymerization (DOP). An enhanced DOP generally implied a lower abundance of non-bridging oxygen in the networks, which was further demonstrated by the O1s XPS fittings. Additionally, the 11B NMR spectra indicated that the dominant boron-related groups were BO3 trigonal comprising ring and non-ring BO3 as well as BO4 tetrahedral comprising BO4(1B,3Si) and BO4(0B,4Si). Furthermore, it was clarified that an increase of B2O3 content promoted the ratios of BO4(1B,3Si) to BO4(0B,4Si) and BO4 tetrahedral to BO3 trigonal, which undoubtedly identified the occurrence of an equilibrium reaction between NBO, BO4 tetrahedral and BO3 trigonal in the glass.
In this study, the investigation on the isothermal enrichment of P-concentrating phase from CaO–SiO2–FeO–MgO–P2O5 melt with super gravity was carried out. The results show that there was an obvious stratification appearing in the sample after centrifugal enrichment. The upper part of the sample is loose and porous, while the lower part is smooth and compact. With the help of metallographic microscopy and X-ray diffraction, it is found that the P-concentrating phase gathered in the upper part, while it is hard to find any P-concentrating phase in the lower part of the sample. In addition, the volume fraction and equivalent diameter of P-concentrating phase present gradient distribution along the direction of super gravity. After centrifugal enrichment, the mass fraction of P2O5 in the concentrate is up to 4.92%, while that in the tailing is just 1.08%. The recovery ratio of P2O5 in the concentrate is up to 72.62% with the gravity coefficient G=600, time t=20 minutes and temperature T=1623 K.
The wetting behavior of TiO2 by liquid iron was investigated by using the sessile drop method. A partial melting behavior was found to appear at the temperature below the melting point of the pure iron. Also a solid solution TiOx–FeO phase was observed between the pure iron and TiO2 substrate. The formation of this reaction layer is due to the reaction among the pure iron, TiO2 substrate and the oxygen gas. The main source of the oxygen gas for reaction is from the TiO2 substrate decomposition and a low partial pressure of oxygen near the sample.
To achieve a high rate injection of pulverized coal into a blast furnace, it is so important to increase a combustion efficiency of pulverized coal. Enhancement of particle dispersion is one of the measures to increase combustion efficiency by accelerating oxygen-coal particle mixture in blowpipe to tuyere region. To realize this, it is found that convergent – divergent injection lance designed on the basis of fluid dynamics has superior characteristics. Divergence angle of the lance is optimized as the maximum angle free from the flow separation phenomenon in the boundary layer and convergence angle of the lance is optimized considering the inertia of coal particle in the gas-solid two phase flow. Optimum divergence angle and convergence angle is found to be 7 and 5 degrees respectively. Direct observation results by offline apparatus, hot model experiments and even in the actual blast furnace proves that dispersion of pulverized coal particles is enhanced considerably. It is confirmed that permeability is improved at an actual blast furnace when the developed lances are installed. This result suggests that high combustion efficiency had been achieved by the enhancement of particle dispersibility. It is thought that the convergent – divergent lance can be one of the practical solutions for the stable operation with high rate injection of pulverized coal because the lance can be installed almost all blast furnaces easily by its simple configuration without a large amount of investment.
With advantages of high Fe grade, less harmful impurities and relatively low price, specularite is one of ideal raw materials for improving sinter grade and reducing raw material cost. However its physicochemical characteristics lead to poor granulating performance and low degree of assimilation and melt generation at high temperature, consequently affect the productivity and quality of sinter. Unfortunately the existing methods of improving sintering performance for concentrates are not applicable to specularite concentrates. In this paper, a pre-briquetting process was developed to improve the sintering performance of specularite concentrates. Experimental results of ore blends containing 24%–36% specularite concentrate showed that pre-briqutting process made specularite into larger particles alone instead of distributing in sintering layer, consequently improved the green bed permeability by 10.28%–25.91%, the vertical sintering speed and the sintering productivity by 5.40%–18.63% and 7.09%–25.81%, respectively. Furthermore, the sinter of pre-briquetting process obtained a better tumble strength which was achieved at a lower fuel rate. By pre-briquetting process, the sinter tumble strength is improved by 1.52% while the fuel consumption is decreased by 2.00 kg/t under condition that 36% specularite was contained. Meanwhile, the reducibility (RI) and low temperature reduction disintegration (RDI+3.15) of sinter could be improved by pre-briquetting process especially when the ratio of specularite was more than 30%. Microscopic observation showed that more calcium ferrite phase and less magnetite appeared in the sinter of pre-briquetting than that of traditional sintering process, means the mineral composition and structure got ameliorated by pre-briquetting process.
Three metallurgical cokes made from coking coals over a significant range in rank were subjected to treatment with blast furnace-like gas composition-temperature profile to 1673 K, annealing under N2 to 2273 K and gasification with subsequent annealing at 1873 and 2273 K. The degradation of cokes after reaction and annealing was characterised using I-drum tumbling, tensile testing, ultra-micro indentation and X-ray diffraction. Both gasification and annealing decreased the mechanical strength of coke. Compared with annealing at 1673 K, gasification at same temperature caused larger degradation for all three cokes, and the effect was more significant on more reactive coke. In the annealing process, degradation of the cokes occurred through the entire coke lump and resulted in both tensile strength and I-drum tumbling strength decreasing simultaneously. In the process of gasification under the blast furnace-like conditions, degradation took place through the whole piece of coke with high reactivity; however, the degradation of coke with low reactivity was more severe at the periphery than in the core and therefore gasification had a minimal effect on the core of the coke and its tensile strength, but had a much stronger effect on I*600. Microstrength of coke decreased significantly with increasing annealing temperature. The change of microstrength of coke upon gasification, which occurred at relatively low temperatures, was marginal. The cokes after gasification with subsequent annealing had similar microstrength and graphitisation degree compared to those subjected only to annealing at the same temperature.
A variable-velocity stirring method is proposed to improve the desulfurization efficiency of high-sulfur hot metal for KR desulphurization process. The mixing behavior of desulfurizer and high-sulfur hot metal under the variable-velocity stirring method is investigated using the Euler-granular model. The particle volume fraction, mixing time and power consumption are discussed to illustrate the entrainment and dispersion of desulfurizer. The results show that the flow field of hot metal and the entrainment and dispersion of desulfurizer are improved obviously under the variable-velocity stirring method. The particle volume fraction distribution is uniform and the mixing time is short under the stirring mode of 90–50 rpm for 8 s switch with the moderate power consumption and torque. The stirring mode of 90–50 rpm for 8 s switch is recommended to adopted within the present system, which can optimize the entrainment and dispersion of desulfurizer in the bath.
The thermal resistances of the slag films and the air gap between the slab and the mold are important factors in heat transfer and lubrication control inside a continuous casting mold. The formation, evolution, composition and distribution of the slag film and air gap have significant influences on the initial solidification of the strand shell and slab quality. In this paper, based on experimentally measured thermocouple data and casting conditions, an inverse problem model of mold heat transfer is developed, with the purpose of accurately predicting the mold heat transfer states and slab solidification processes of actual casting conditions. Furthermore, a numerical model of the heat transfer between the air gap and the liquid/solid slag films is developed, based on analysis of the formation mechanism, distribution and heat transfer characteristics of the air gap and slag films. The non-uniform distribution of the thermal resistance of the air gap and the liquid/solid slag films, and the heat conduction and heat radiation inside them are simulated, which provide a theoretical foundation for exploring the complicated heat transfer behavior and surface crack prediction during the continuous casting process.
A novel method for the structural reconstruction of solidification kinetics in cast iron with spherical graphite (SGI) is described in this paper. The method includes an automated SEM/EDX analysis of different micro-features in SGI structure, separation of graphite nodule statistics from non-metallic inclusions, and conversion to a three dimensional Population Density Function (PDFexp). A structure integrator was developed to simulate the PDFsim for the arbitrary nucleation and growth rate functions. Structural reconstruction of the solidification kinetics in the industrial castings was done by inverse optimization and matching both PDF functions at unique parameters of graphite nodule nucleation and growth. It was shown that SGI solidification kinetics in industrial castings significantly differ from those predicted by basic nucleation models. The cooling rate and inoculation have large effects on the kinetics of graphite nodule nuclei formation during solidification. It was proved that the observed bi-modal PDF function in inoculated SGI is related to the second nucleation wave. The suggested method provides insight into the nucleation process in SGI casting and can be used as a tool for process control. Reconstructed solidification kinetics can help in the design of effective inoculants and melt treatment methods. Knowledge about nucleation parameters can be also used for improving simulations of casting solidification.
Steel industry is the irreplaceable foundation in heavy industries, which have been developed and improved. The advanced monitoring methods including detection and control technology contribute to its development of iron and steel manufacturing processes. With the development of the measurement techniques, laser-induced breakdown spectroscopy (LIBS) has been developed and applied for many industrial fields of elemental monitoring due to the non-contact, fast response, high sensitivity, real-time and multi-dimensional features. The elemental measurement methods in steel industry were summarized and compared in this paper. LIBS measurements of raw material, smelting processes, products, slag, etc. have been reviewed in detail. Challenges for the future of LIBS application in iron and steel making processes have also been discussed. LIBS has a high potential to improve the detection ability of elemental analyses and to promote the on-line monitoring characteristics in iron and steel making plants.
Technical flow chart for the typical iron and steel making processes. (Online version in color.)Fullsize Image
Recently, optimization technologies are commonly applied in logistics scheduling owing to significantly advanced computing technologies. In this paper, a new application for scheduling of crane handling in a slab yard is presented for efficient logistics in steel works. The proposed method consists of two phases: scheduling optimization and logistics simulation. The first phase in this approach utilizes a genetic algorithm that is employed to solve a relaxed scheduling problem of rearranging steel slabs in an approximate manner. Next the partial solution is iterated upon by a rule-based algorithm to obtain a feasible solution. Computational experiments are conducted with operation data of JFE Steel, allowing a comparison to be made between actual and theoretical crane handling operations. The resulted data show that this paper’s proposal can reduce the number of handlings by 30%. The effective transportation of slabs contributes to achieving the delivery time and then to the increase of the customer satisfaction.
The structure of FeO–SiO2–V2O3 slags with compositions of (1-x)(1.5FeO·SiO2)·xV2O3 (x=0–20% mole fraction) was investigated in the molten and quenched states by using molecular dynamics (MD) simulations and Fourier transform infrared (FT-IR) spectroscopy. An empirical potential for the multi-component system has been developed in this work for performing MD simulations. The local atomic structures and the micro-heterogeneity in the molten slag have been systematically investigated using MD simulations. The bond length of V–O varies from 1.92 to 1.96 Å and the averaged coordination number of V (CNV–O) increases from 4.50 to 4.96 with the addition of V2O3. The simulation results revealed that the average Si–O–Si bond angle and the degree of polymerization both decrease with increasing amount of V2O3, implying that V2O3 may behave as a network-modifying basic oxide in the FeO–SiO2–V2O3 system. This was further confirmed by the FT-IR spectrum analysis, which shows that the silicate network dissociates with the presence of V2O3.
The relationship between residual stress and fatigue strength has been researched for electron beam welded joints made of sheet metals with a thickness of approx. 10 mm. Residual stresses were analyzed by the Finite Element Method, and fatigue strength was obtained by the three-point bending fatigue test. From the results of examining the effect of heat input, a particular relationship was observed between fatigue strength and residual stress, but the effect of stress concentration on fatigue strength was not significant within the tested range of stress concentration factors with varied bead shapes. As a result of testing the effect of steel type, the correlation between fatigue strength and residual stress was confirmed with exception of S50C steel that resulted in lower fatigue strength deviating from the correlation, the deviation of which can presumably be attributed to localized hardening and narrowed area where compressive residual stress was induced.
Arc force impulse and mean arc linear energy, and the own ratios of them in the scanning course to those at the staying phase, were proposed to analyze swing arc dynamic and welding energy features for narrow gap vertical GMA process. Actual effect and influencing mechanism of swing parameters on solid and flux-cored wire arc weld formations were then investigated. Experimental results show that sidewall penetration, bottom twin peaks and transitional fillet weld grow with increasing swing frequency and staying time and decreasing arc-sidewall distance, and flux-cored wire arc weld metal surface is generally concave while solid wire one likely goes convex. Furthermore, long arc-sidewall distance, and the too great and excessively low values of swing frequency and staying time, readily cause weld pool to sag. It is also demonstrated that arc force impulse ratio and arc linear energy into groove middle jointly dominate weld pool sagging, while arc linear energy ratio determines bottom bead formation.
Principle of swing arc narrow gap vertical welding. (a) Molten pool forces; (b) Welding system.Fullsize Image
This paper concerns the function of retained austenite to resist local plastic indentation deformation in bearing steel. Three austenitizing temperatures were used to adjust the morphology, volume fraction and carbon content of retained austenite in samples. The volume fraction of retained austenite was measured by magnetic method. The higher austenitizing temperature result in higher fraction of retained austenite and higher carbon content in it, and changes the morphology of retained austenite from film-like to blocky. Resistance to plastic indentation of retained austenite was measured by nanoindentation on samples with different heat treatments. Strain induced martensite transformation was observed by pop-in phenomena on indentation curves. Results showed that indentation resistance depends mostly on the local stability of retained austenite rather than the fraction and morphology. Furthermore, the local stability of retained austenite under indentation deformation is mainly attributed to the carbon content.
In order to clarify an influence of hydrogen on the fatigue crack propagation in ultra-low frequency region, we investigated the crack propagation rates of S10C at different frequencies in hydrogen and nitrogen atmospheres. In the low-pressure hydrogen gas atmosphere, the crack propagation rate decreased with decreasing in frequency within the present experimental range. In particular, the crack propagation rate at the ultra-low frequency (10−3 Hz) became the same as that in nitrogen atmosphere. To explain the disappearance of the hydrogen effect in the ultra-low frequency, we proposed that carbon diffusion causing strain-age hardening also contributes to the decrease in crack propagation rate in the ultra-low frequency under the hydrogen atmosphere.
In this study, two kinds of micro-laminated dual phase steels with different strength were produced by simple hot rolling and air cooling processes. High carbon and aluminum contents contribute to the high strength in this kind of steel, which has close relationship with the phase ratio and micro-hardness of the ferrite and martensite phases. They were hot rolled at two temperatures (950°C and 1100°C) with different reductions (30% and 70%). The mechanical property results reveal that the effects of hot-rolling temperature and reduction on tensile properties are small. The fractography of the samples was examined to explore the relationship between the micro-laminated microstructure and the mechanical properties. It is worth noting that the impact toughness of the rolling plane is enhanced obviously at low hot-rolling temperature with large reduction. The increase of phase interface density along the thickness direction contributes to the ultrahigh impact toughness of rolling plane.
The notch-bend strength (σb,max) was investigated for High Si Solid Solution Strengthened Ferritic Ductile Cast Iron (EN-GJS-500-14) with varying the strain rate at room temperature. The notch-bend strength was also compared with the conventional ferrite-pearlite type ductile cast iron JIS-FCD500 and JIS-FCD700. Then, the application of the high Si ductile cast iron to wide industrial fields was discussed. Dynamic three-point bending tests were conducted on Charpy V-notch specimens in the range of stroke speed, 10−3~102 mm/s, at −20~22°C. The load-displacement curve for ductile fractured specimens shows that the load (P) steeply increases to the peak value (Pmax; about 10 kN) and then decreases, similar to that in the case of instrumented Charpy impact test. Even though the absorbed energy of fracture process was in the lower shelf region, the notch-bend strength did not decrease with increasing the strain rate as far as the fracture origin is ductile. It was found that the notch-bend strength is insensitive to the strain rate. The notch-bend strength (σb,max) of high Si ductile cast iron at −20°C was still equal to that at 22°C, indicating σb,max is insensitive to the temperature as well as the strain rate. High Si ductile cast iron EN-GJS-500-14 and the conventional ductile cast irons JIS-FCD500 and JIS-FCD700 show nearly the same lowest σb,max in the range of strain rate, 1.5×10−4~2.0×100s−1 at −20°C. Therefore, we think that the high Si ductile cast iron has wide industrial application potentiality.
Fracture toughness behaviors of 316LN stainless steel (SS) base metal and weld were investigated using Acoustic emission (AE) technique. Four point direct current potential drop (DCPD) method has been used to measure the crack initiation and extension, aiming at generating evidence for determination of the point of crack initiation by AE methods. Fracture toughness δQ values were estimated using AE characteristics with simultaneous ASTM standard E1820. The results in this investigation showed that 316LN SS weld exhibited lower fracture toughness than that of base metal. The points of crack initiation in 316LN SS base metal and weld could be characterized by the first peak of cumulative energy rate, the sudden increase of AE cumulative energy, counts or amplitude coupled with peak amplitude signals. The fracture toughness values of 316LN SS base metal and weld estimated using AE technique were lower than those obtained by ASTM procedure.
Single-distance phase retrieval technique was applied to contrast-enhanced phase-sensitive imaging of dual-phase microstructures in ferrite/austenite dual-phase stainless steel. Contrast between the two phases was evaluated, together with noise and spatial resolution, under varying experimental and phase retrieval conditions. Serial sectioning technique was also employed, to validate the shape accuracy of related three-dimensional images. Although the density difference between the two phases was relatively small, the two phases were successfully segmented in the three-dimensional images. The imaging technique was also applied to observe microvoid nucleation and growth behaviour during tensile loading. The loading steps at which microvoids were nucleated were identified by tracking all the microvoids observed at the final loading step, in reverse chronological order, toward the initial unloaded state. Each absorption-contrast image was then registered with a corresponding phase-contrast image, in order to classify all the targeted microvoids according to their nucleation site: ferrite, austenite or phase boundary. Premature damage initiation was observed at a relatively early stage at all the nucleation sites; however, subsequent growth was relatively moderate. On the other hand, microvoids initiated later, at fine particles located along the phase boundaries, exhibited enormous growth, thereby inducing the final rupture. It was concluded that the substantial driving force for the growth of microvoids located along morphologically characteristic austenitic particles was the predominant factor in the ductile fracture.
Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. As-drawn pearlitic steel wire is well known to have superior resistance to hydrogen embrittlement. The resistance to hydrogen embrittlement is clarified as being further improved by aging treatment at 100-°C and 300-°C for 10-min. of as-drawn 0.8 mass% C pearlitic steel wire with φ5.0 mm (ε=1.9). The higher the aging temperature is, the better the resistance to hydrogen embrittlement becomes. Simultaneously, the strength even increased slightly by aging treatment. The mechanism is investigated by exploiting thermal desorption analysis (TDA) and the newly developed TEM precession analysis. Aging at 100-°C led to a decrease in the hydrogen content at peak I around 100-°C in the TDA curve, which is inferred to be caused by C segregation to dislocations resulting in improvement of hydrogen embrittlement. Aging at 300-°C further improved the resistance to hydrogen embrittlement, which is presumably brought about by the local recovery of the heterogeneously deformed lamellar ferrite area together with the C segregation to dislocations. Here, the strength increased slightly by aging due to the softening factor of recovery and the hardening factor of strain aging.
Seaweed depletions in coastal areas of barren grounds are serious problems in Japan and other parts of the world. The lack of dissolved iron is one of the possible reasons for barren grounds. We have developed a method for restoration of seaweed beds using the mixture of steelmaking slag and composts including humic substances. The influences of seawater temperature and organic matter on the iron elution from the mixture were investigated by iron elution test in seawater in this study. It was found that the iron elution rate from the mixture accelerated as temperature increased. Meanwhile, the powdered bamboo and powdered bamboo coal char were mixed with steelmaking slag and composts used for iron elution test. The amount and the rate of iron elution in seawater became larger by mixing bamboo and its coal char with the slag-compost sample. It was also confirmed that the addition of organic matter could promote iron elution from steelmaking slag.
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