A new technique based on the PDF (Population Density Function) was suggested to investigate the behavior of non-metallic inclusions after deoxidization. In comparison with the traditional analysis using the size histogram of inclusions, the application of PDF can make it possible to attain more useful information to understand the evolution of inclusions such as the period of formation and mechanism for growth. In this study, the PDF of alumina inclusions was investigated for the ultra low carbon grade steel of 20 ppm C. The lollypop samples were taken at three stages after deoxidization using aluminum; at the end of RH degassing process, at tundish during casting operations, and in cast slabs after solidification. For all the samples except for the contaminated ones, the PDF shows a fractal distribution. The exponent in fractal distribution was –3.54 near the end of RH process at 7–13 minutes after deoxidization, which is similar with the previously reported value. In contrast, the exponent was changed to –2.76 in tundish and –2.38 in cast slab, respectively. Different expressions of the fractal distribution can be attributed to the changes in fluid condition of molten steel. The application of PDF also provides the quantitative evaluation for abnormal reoxidization of molten steel. The deviation of PDF from the reference distribution is in accordance with other evidences of reoxidization of molten steel such as the increase of nitrogen pick-up and the decrease of soluble aluminum.
To guide the application of a new automated steel-teeming system which in continuous casting is controlled by electromagnetic induction technology, the parameters of the induction coil and system reliability need to be analyzed. The teeming time of an industrial ladle (1.5 t) with the new system was investigated using experimental and numerical methods. The calculated results were consistent with experimental data. The dependence of teeming efficiency on coil parameters for a larger ladle (300 t) was investigated; the influence of the electromagnetic induction system on the temperature and equivalent stress distribution in the ladle system was also analyzed. The results provided optimum coil parameters for a larger ladle normally used in continuous casting processing. An installed coil with surrounding insulating material had little influence on temperature distribution, thermal stability, and structural safety of the ladle. The ladle lining and insulation met safety requirements established for the system. The coil and the steel shell performed reliably during induction heating of steel while teeming. Therefore, the electromagnetic induction-controlled automated steel-teeming system can be safely used in steel production.
A thermodynamic database for the oxyfluoride system CaO–MgO–Al2O3–SiO2–Na2O–K2O–Li2O–MnO–FeO–F has been developed based on the critical evaluation and optimization of all available experimental thermodynamic and phase diagram data. The developed database can be used for phase diagram and equilibrium solidification calculations for multicomponent systems. Such accurate database with high predictability capability assists in understanding the crystallization behavior of mold fluxes. In addition, a kinetic model was developed to simulate the interactions between the mold flux and molten steel using effective equilibrium reaction volumes combined with the thermodynamic database. The kinetic model successfully reproduced the significant Al2O3 accumulation observed when casting high Al steel with CaO–SiO2 based mold flux. Equilibrium solidification calculation performed on the Al2O3-rich mold slag revealed detrimental changes in the solidification temperature, the primary phase and the evolution of the liquid fraction with temperature.
Within an investigation focused on effect of casting conditions on steel quality in an industrial beam blanks mould, different nozzle geometries were tested with Computational Fluid Dynamics modelling. The innovative nature of the work consisted in feeding with only one nozzle, whereas two nozzles in the flange-tip zone are commonly used. This configuration has the advantage of a simplified mono-slide gate casting layout, but single nozzle feeding can bring about risks of too high steel velocity in the mould, harmful for shell integrity and meniscus stability. Having in mind the mentioned constraints, different geometry solutions were checked and, to assess the solutions found, suitable indices were defined, related to flow conditions able to prevent slag entrapment at the meniscus, and hot-spotting at walls, harmful for the solid shell integrity. The modelling work gave general indications on undesired flow features and guidelines to improve reference conditions, involving number of holes and holes angle, size and shape. For the caster mould and the operating conditions under concern, a solution was found satisfying the indices, and expected to fulfil the quality requests. It consisted of a nozzle with a 50 mm diameter throat, a 50 mm× 60 mm elliptical lateral port inclined 25° downwards and a 20 mm-diameter bottom hole. A water model check with such a nozzle prototype validated the model supporting the solution identified to be used on plant.
Based on the principle of solidification shrinkage compensation, a soft reduction amount calculation method was derived for bloom continuous casting process, and the bearing steel GCr15 was chosen as specific research steel to describe calculation process in detail. A two-dimensional heat transfer model was built to predict the solidification process of bloom, and the material properties of GCr15 were derived by weighted averaging of the phase fractions. The predicted temperature and shell thickness were verified by a thermal infrared camera and nail shooting results, respectively. The soft reduction amount of typical high carbon alloy steel blooms were calculated and discussed. The plant results showed that after the application of soft reduction to the bloom, centerline segregation and “V” type segregation were improved significantly. The carbon and sulfur ratios of the bloom centerline were reduced from 1.39 to 1.09 and 2.14 to 1.29, respectively.
In this investigation, porosities in fatigue specimens obtained from practical ADC12 high pressure die castings were detected and reconstructed with high resolution X-ray computed tomography technology. Three dimensional (3D) characterizations of the porosities were analyzed. The high cycle fatigue tests were carried out at five stress amplitudes on seven groups of the specimens with different porosity contents. The Weibull analysis suggested less scatter of the fatigue life at larger stress condition. With the SEM observation on the fatigue fractured surfaces, the porosities initializing the fatigue cracks were identified. A pore-fatigue life prediction equation was deduced with the pore characteristics from the fracture surface and 3D X-ray tomography inspection. With 3D reconstruction of tomography data and FEA method, the simulation of the stress distribution around the actual 3D pores were carried out and analyzed further.
The recent contributions on changes induced by high magnetic fields in transport phenomena, such as convection, solute diffusion, solute or phase migration in the liquid, are reviewed and analyzed. Selectivity provided by the Lorentz, thermoelectromagnetic (a special kind of Lorentz force), and magnetic forces or combinations enables the control of transport phenomena in liquids. This possibility, together with the capability of the transport phenomena to affect solidification in alloys, allows a level of control over solidification microstructures. As a result, recent relevant work can be found dealing with the effects of high magnetic fields on transport phenomena and the corresponding solidification microstructure evolution of alloys, based on the Lorentz, thermoelectromagnetic, and magnetic forces or combinations thereof.
Dendritic microstructures are most dominant patterns in solidified alloys. The microstructural features of these structures control the segregation profiles of solute elements in the interdendritic regions, thus determining the mechanical properties of cast structures. In this study, a 2D model of solid/liquid interface instability in a low carbon steel was introduced, using the multi-phase-field software code MICRESS® combined with an in-situ study of solidification in a laser-scanning confocal microscope. The use of a moving-frame boundary condition and a linear temperature gradient within the simulation allows further optimization of the solidification studies in the laser-scanning confocal microscope. By analysing the shape of the delta-ferrite grain boundary at the solid/liquid interface, in-situ and at temperature, it was possible to experimentally determine the Gibbs-Thomson coefficient and the solid/liquid interfacial energy of the alloy. The interface mobility of the solid/liquid interface was calibrated in the model so as to reproduce the experimentally measured interface velocity at the onset of interface instability. The proposed model was used to describe the morphological transitions from planar to cellular to dendritic modes during solidification and solute segregation under a variety of processing conditions such as cooling rate and temperature gradient. The importance of this approach is that the verified model has been used to extend the prediction of microstructural development to cooling rates well beyond what can be achieved experimentally and into the regime pertinent to high-speed continuous casting. Significant microstructural differences that arise as a result of varying processing conditions are discussed.
We present further developments and enhancements of the concentric solidification technique for high-temperature laser-scanning confocal microscopy. These recent enhancements include an automated in-situ determination of phase fractions during solidification using purposely developed image processing software, more accurate temperature calibration, reproducibility tests as well as close coupling of the experimental results with computational simulations. In the present study, the newly developed capabilities of the concentric solidification technique have been applied to a study of the peritectic phase transition in the Fe–C system.
The effect of Mg and Ca treatment on the behavior and the particle size of inclusions in bearing steels were studied by industrial experiments and thermodynamic calculations. The results showed that the excess addition of Mg wires is not conducive to control the total oxygen content in bearing steel because of the secondary oxidation. The irregular and clustered Al2O3 inclusions are the dominant in the aluminium killed bearing steels. The different quantity Mg wires were added, which can change the irregular and clustered Al2O3 inclusions into the spherical MgO or MgO·Al2O3 inclusions. When the Ca addition is insufficient, the Al2O3 and MgO·Al2O3 inclusions could not completely change into the spherical CaO–MgO–Al2O3 system inclusions. By the three-dimensional morphologies analyze, Al2O3 inclusions are easy to gather and the size of clustered Al2O3 inclusions is large. By the Mg or Ca treatment, the size of Al2O3 inclusions can be reduced, but the large size CaO inclusions are brought into steel after the Ca treatment.
Hydrothermal treatment has various possibilities for adding value to blast furnace (BF) slag by forming hydroxide or hydrate crystals and introducing pores into the reaction product. To optimize the hydrothermal reaction process, understanding of the reaction behavior of BF slag during hydrothermal treatment is indispensable. In the present work, the mechanism of the hydrothermal reaction of BF slag was investigated by focusing on the reaction at the slag surface. The surface reaction behavior was reproduced using slag plate samples, which adjusted the effective amount of hot water participating in the reaction. The changes in the surface morphology of BF slag and synthesized CaO–SiO2–Al2O3(–MgO) slags during hydrothermal treatment at 250°C were examined. The reaction mechanism of BF slag as well as the effect of MgO on the reaction were discussed from the observed phenomena.
Al2O3–C sensor based on the blackbody cavity theory achieved a continuous measurement of molten steel temperature. Its mechanical properties were affected by the firing temperature. Firing temperature has great influences on the weight changing, decalescence/heat release reaction and structure evolution of the resin binder used for Al2O3–C sensor. Results showed that the porosity increased and the strength declined below 750°C, main exothermic reaction and weight loss of the binder occurred. As the firing temperature increased to 800°C, a great enhancement of endothermic reaction and a drastic increase of crystallite size were observed, relating to the rapid shrinkage of the binder. The porosity decreased from 10.3% to 8.8% and the strength improved remarkably from 6.5 to 8.2 MPa in this temperature range. Strengths and porosities of the sensors fired under 800–950°C were similar (8.2–8.5 MPa and 8.8%–8.4% respectively). Moreover, the temperature response and lifetime of the sensor fired at 800°C were almost equal to the sensor fired at 950°C according to industrial tests, which were about 165 s and 24 h.
A significant quantity of chromite ore is available in form of fines and is friable in nature. Agglomeration is necessary for utilizing these fines. Briquetting gives green agglomerates with inferior high temperature properties. Pelletization requires further grinding of the naturally available ore fines and the subsequent firing of the green pellets for strength development which make it energy-intensive and complex process. In contrast, sintering can be done directly on the as-received friable chromite ore in the presence of coke breeze (as in case of iron ore sintering), which is likely to be free from the above limitations. In the current work, an optimum combination of temperature, flux (added to increase the relative quantity of molten phase required for sintering) and coke (added as fuel to attain the sintering temperature in a sinter pot) was computed using the thermochemical software, FactSage 6.1 and enthalpy balance calculation. Sintering of a mixture of chromite ore fines and flux with the optimum composition at 1600°C was carried out in; (i) resistance furnace (100-g scale), without using carbon and (ii) a pot sintering set-up (10-kg scale), using the computed quantity of carbon. A good correlation between experimental result and predicted equilibrium phases has been observed. The characterization of the sinters prepared in pot sintering set-up was done by conducting shatter, tumbler, and abrasion tests, and their phase identifications by XRD and EPMA/EDS. The developed sinter was found to possess adequate handling strength that would be well acceptable to produce ferrochrome in the SAF.
In order to make clear the mechanism how the non-metallic inclusions were removed by bubble wake flow in the molten steel, water model experiments were conducted by high speed video and image processing software. The bubble wake flow zone was partitioned and the characteristics of removing inclusions through bubble wake flow were analyzed, and the effects of various factors including bubble size, inclusion size and concentration on the removal behavior of inclusions were also investigated. The results show that the bubble wake flow is useful for the floatation of inclusions. The bubble wake flow involves the boundary zone and the rising zone, and the process of inclusion removal by the bubble wake flow can be decomposed into three sub-processes: firstly approaching and passing into the boundary zone, secondly passing into the rising zone and finally going on floating up or escaping from the rising zone. The increasing of the bubble diameter Db and the particle concentration Cp is in favor of inclusion removal by bubble wake flow. If the particle diameter Dp is smaller, the inclusions are easier to be removed by wake flow.
Iron ore’s assimilation characteristic reflecting the beginning formation temperature of liquid phase in sintering process plays very important role on the fluidity of liquid phase and bonding strength of sinter body. Experimental study of assimilation characteristics of 12 kinds of iron ores were conducted using micro-sinter equipment, and pure reagent simulating tests of assimilation characteristic were also carried out for the purpose of achieving the influence of chemical composition on the assimilation characteristic. In addition, effects of assimilation characteristic of iron ore on the fluidity and bonding capacity of bonding phase were also researched. This study showed that SiO2 and LOI promoted the assimilation of iron ore, low Al2O3 (<1.5 mass%) was good to the assimilation, but high Al2O3 (≥1.5 mass%) was bad, MgO was adverse to assimilation of magnetite concentrate. In addition, lower assimilation temperature of iron ore led to higher superheat degree of liquid phase at a certain sintering temperature, then higher liquid fluidity and bonding strength.
Carbon was deposited on the surface of an iron powder to study the influence of carbon content and microstructure on defluidization prevention at 823–1173 K. It was found that at each temperature there existed a minimal carbon content (Cmin), below which defluidization occurred and Cmin increases with increasing operation temperature. Microstructure of the deposited carbon, tailored by adjusting deposition conditions, showed significant influence on defluidization. Less carbon would be needed to prevent defluidization under a lower rate of carbon deposition since a more uniformly coating of carbon can be obtainable under such conditions. When the fluidizing gas is nitrogen, defluidization will eventually occur after extended time of fluidization even if the initial carbon content is greater than Cmin, due to attrition that causes the decrease of carbon content with increasing time of fluidization. However, when the fluidizing gas is 70% CO-30% H2, defluidization will not occur if the initial carbon content is greater than Cmin since the carbon content will increase with increasing time of fluidization due to the further deposition of carbon under the CO–H2 atmosphere. Furthermore, a fluidizing phase diagram was established for the carbon-coated iron powder and the mechanism of defluidization prevention was explained using a cohesive force based model.
The role of ferrous raw materials and iron ore agglomeration in energy consumption of integrated steelmaking has been evaluated using a system-wide model. Four steelplant cases were defined: typical European steelplant with sinterplant; Nordic steelplant with sinterplant; European steelplant with sinter:pellet ratio of 50%, and Nordic steelplant charging pellets and a small amount of briquettes. Energy consumption in the mining system were estimated from published statistics at 150 MJ/t for lump ore and sinter fines, 650 MJ/t for pellets made from magnetite and 1050 MJ/t for pellets made from hematite. An integrated steelplant model including all major unit operations was used to calculate overall system energy consumption from iron ore mining to hot rolled coil. Adjustments were made accounting for energy benefit of ground granulated blast furnace slag in cement production, energy required for cement production required for briquetting, and excess BF and BOF gas producing electricity in a 32% efficient power plant. The system-wide net adjusted energy in the first three steeplant cases showed marginal improvement with use of high grade sinter fines and decrease of pellet/sinter ratio to 50% compared to typical European case. Nordic steelplant charging pellets and briquettes had a reduction in system-wide energy of 5% to 8% for charging pellets from hematite or magnetite respectively compared to the typical European steelplant charging sinter and pellets made from hematite ore. Replacement of sinter with pellets was mainly responsible for the improvement with smaller contributions from magnetite ore in pelletizing.
To explore the possibility of successfully processing iron ore pellets with a high content of hematite, thermogravimetric tests were performed to study the induration process of pellets composed of a mixture of iron ore concentrates (magnetite and 35% wt of hematite). Thermogravimetric tests were performed nonisothermally from 25°C to 1400°C using two heating rates, 5 and 50°C/min. To identify the reactions involved and to follow the microstructural evolution throughout the induration process, selected tests were arrested at predetermined temperatures, and samples were rapidly cooled to room temperature for later characterization using X-ray diffraction (XRD) and scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS). It was found that the formation of phases such as calcium ferrite (CF), magnesium ferrite (MF), silico-ferrites of calcium (SCF) and silico-ferrites of calcium and aluminum (SCFA) are influenced by the heating rate. The microstructure of the fired pellet processed at 50°C/min showed compact small grains of the sintered phase of the secondary hematite (SH), partially surrounded by a slag phase. In contrast, the fired pellet processed at 5°C/min exhibited a microstructure consisting of the SH phase with a faceted morphology surrounded by a relatively large amount of the slag phase. The results suggest that the pellet processed at 50°C/min had a more satisfactory response to the induration process.
In-depth investigations were carried out on the thermal degradation and structural evolution of bakelite by heat treatment at different temperatures; the structural transformation to graphitic carbon at 1450°C was confirmed through X-ray diffraction. High amounts of residual carbon were obtained after the high temperature charring of bakelite. The reduction behavior of iron oxide/bakelite composite pellets was studied at 1450°C to investigate waste bakelite as a carbon resource in ironmaking towards a partial replacement of traditional carbon sources. These studies were carried out for raw bakelite as well as for bakelite char. The reduction of iron oxide by raw bakelite resulted in the non-separation of metal, slag and in the formation of direct reduced iron pellets. On the other hand, bakelite char pellet showed clear separation of iron nuggets from slag. This study has established bakelite as an alternative carbonaceous resource for reduction reactions in new ironmaking processes.
Microfines of iron ore are generally utilized in Blast furnace in form of indurated pellets because sinter bed has limitation of accepting fines. Charging of acid pellets with basic sinter is the normal practice in blast furnace. However induration of pellets is very cost intensive. Further more, due to low angle of repose pellets distribution during charging with other materials in blast furnace creates inhomogeneous distribution. In order to alleviate the above problem, a composite mass of acid pellet and basic sinter has been developed, wherein; green pellets made-up of microfines were mixed with basic sinter mix and sintered the combined mass in a sinter bed of 10–12 kg scale. A composite mass of indurated pellet and sinter named as ‘Pellet-Sinter Composite Agglomerate’ was obtained. Linz Donawitz converter sludge and mill scale were used in pellet mix to provide in-situ heat in pellets that enhances incipient fusion to form bond in pellets. The developed sinter shows good shatter index (92%), tumbler index (67.5%) abrasion index (7.5%) and reducibility index (70%) and low reduction degradation index (27%), which are comparable with the conventional iron ore sinter made in the same set-up keeping other condition identical. This innovative technique help improving 30% microfines utilization in sinter bed, reduce coke breeze/energy consumption, reduce overall basicity of sinter and decrease flux composition.
The properties of metallurgical coke are critical to the performance of the blast furnace for iron making. While extensive work has gone into understanding the relationship between the properties of coke and its behaviour in the blast furnace, the heterogeneous nature of coke makes understanding these relationships difficult. Herein we report the use of a laboratory produced coke analogue to examine the effects of minerals on the reactivity behaviour of coke in a pseudo-CRI test. The effects of a range of minerals on the reactivity of the coke analogue are demonstrated and the effects of binary combinations of silicon and iron bearing minerals are examined.
The problem of the refractory nature of gold bearing arsenide ores is described. The basic principle, characteristics and application of pretreatment technique of arsenic-bearing gold ores are presented in this paper. Several different classes of process options for pretreating refractory ores are considered. These options include: roasting oxidation; wet chemical treatment; bacterial peroxidation; and other pretreatments such as: eliminating arsenic in vacuum, volatile smelting, segregation of roasting, electrochemical oxidation. Its development tendency in the future is also looked ahead.
We consider a multi-tank train stowage planning problem of coil (TSPP) where the given coils are assigned into the tanks of the train. Different from stowage problems in previous studies, this problem has its characteristics such as the multi-tank transportation mode, the minimum load restriction of each tank and the rigorous balance constraints. We formulate the problem as a novel mixed integer linear programming model which objectives are to maximize the total weight of loaded coils and to minimize the differences of stack positions of the coils in each tank. The NP-hardness of the problem and intractableness of optimally solving the model motivate us to develop an improved tabu search algorithm to solve it approximately. The algorithm is initiated by a two-stage heuristic where a multi-exchange neighborhood is designed to further improve the initial solutions. And then K-cycle move is used regarded as a diversification strategy in tabu search. Computational results using real data from a specialty steel manufacturer show that for small problems, which can be solved optimally by the model, the proposed algorithm can generate close-to-optimal solutions. For large practical problems the algorithm can obtain good solutions within a shorter time compared with the upper bound.
For the basis of understanding hydrogen embrittlement, hydrogen thermal desorption curves are subjected to the analysis for making clear the kinds and amounts of traps in normalized carbon steels that are composed of ferrite and pearlite. While the theoretical desorption curves should be analyzed basically by non-symmetrical curves such as obtained by Kissinger equation, the measured curves are also deformed and approach to symmetrical form. Actually they are successfully fitted by combination of two symmetrical Gaussians; one is desorption from dislocation trap and the other is from grain boundary trap. Applying this method to different heats of JIS S45C steel, grain boundary trap of high phosphorus content shifts to higher temperature side, suggesting that hydrogen trap is enhanced by phosphorus segregation along grain boundary. An increase in cathodic current density causes more hydrogen partition to grain boundary. Analysis with the use of Gaussian is practical and reasonable to understand the properties of hydrogen traps.
The dynamical recrystallization of Micro-alloyed forging steel was investigated at deformation temperatures of 850-1150°C and strain rates of 0.01–5 s–1 on a Gleeble-1500 dynamic thermo-mechanical simulator. The stress-strain curves at lower strain rates are typical of the occurrence of DRX and exhibit a peak in the flow stress before reaching steady state. The critical strain for the initiation of DRX has been estimated through the analysis of stress-strain curves and the result showed that the critical strain was correlated to the peak strain by εc = 0.68εp. Utilizing the peak stresses σp measured from the stress-strain curves, constitutive equation governing the dynamic recrystallization has been analyzed and activation energy was determined to be Q = 379 kJ/mole, which was significantly, larger than that of same composition of V-micro alloyed steel. The grain size was refined from 140 μm to 8–60 μm by DRX. The dynamically recrystallized grain size has been measured and the result showed that logarithm of grain size appeared to be linearly decreasing with the increase in the logarithm of Zener-Holloman parameter Z = ε ′ exp(Q/RT). However, when the logarithm of grain size was plotted in terms of the inverse of deformation temperature, i.e. 1/T, the plot showed a significant deviation from the linearity expected from the above linear relationship.
The high temperature viscosity of the TiO2-MnO-Al2O3-8.64ZrO2-2.77Na2O welding flux system was measured by the rotating spindle method to identify the relationship between the viscosity and melt structure at various compositions of TiO2, MnO, and Al2O3 contents. At temperatures of 1773 K to 1748 K and fixed TiO2/MnO ratio, the effect of Al2O3 on the viscosity was not significant, but slightly increased with higher Al2O3. At temperatures below 1748 K, the effect of Al2O3 was more pronounced with increments of Al2O3 significantly increasing the viscosity of the molten flux. Increased extended basicity ((TiO2/+1.13MnO)/SiO2) depolymerized the network structure, where TiO2 and MnO works to depolymerize the present melt. Raman analysis of as-quenched oxide melts from 1773 K showed the symmetric [AlO4]-tetrahedral stretching vibrations to increase and the asymmetric [AlO6]-octahedral stretching vibrations to decrease with higher concentration of Al2O3 at various fixed TiO2/MnO ratios suggesting polymerization of the structure with Al2O3 additions. The opposite trend could be observed with increasing extended basicity. XPS (x-ray photoelectron spectroscopy) results showed the bridged oxygen (Oo) to increase and the non-bridged oxygen (O–) to decrease with Al2O3 additions and lower extended basicity also suggesting polymerization of the network structure in the present melt system.
In the process of hot dip galvanizing high tensile strength sheet steels containing Si and Mn, selective surface oxidation of Si and Mn causes coating defects. One promising method for overcoming this problem is an oxidation-reduction process. When the steel surface is exposed to an oxidizing atmosphere, it will react primarily by forming an Fe oxide, which can be reduced by hydrogen in a reduction process that follows. It has been explained that good wettability can be obtained due to the formation of pure iron. However, the mechanism of suppression of selective surface oxidation has not been clearly understood in detail yet. In order to reveal this mechanism, the present study focused on both Mn and Fe oxidation behavior during the oxidation-reduction process for a cold-rolled sheet steel containing 0.25mass%Si-1.8mass%Mn. Surface and cross-sectional analyses were performed by using secondary electron microscopy and transmission electron microscopy. Selective surface oxidation behavior was investigated by glow discharge optical emission spectroscopy. The main results obtained are as follows. First, selective surface oxidation of Mn was suppressed even if soaking was continued after completion of the reduction of the Fe oxide. Second, as the reduction process proceeded, Mn was trapped as an internal oxide under the Fe oxide layer. Moreover, depletion of solute Mn was observed in the matrix. From these results, depletion of solute Mn is supposed to suppress the outer diffusion of Mn during soaking. Therefore, selective surface oxidation of Mn is suppressed even after Fe oxide reduction is completed.
The effect of Cu–Sn coating on steel towards improving the adhesion between steel and typical styrene butadiene rubber (SBR) based tyre bead composition has been investigated in this work. Steel coupons were coated with varying compositions of Cu–Sn via immersion coating, where the electrolyte bath composition was varied. Chemical analysis of the coatings using ICP-OES confirmed increase in Sn content with increasing SnSO4 concentration in the coating baths, keeping other parameters constant. No change in the surface roughness and coating weight was observed with change in Sn concentration in the coatings. The coated steel plates were vulcanized with SBR based rubber and peel strength was measured. The results confirmed an optimum Sn concentration of 3–4 wt% in the coatings up to which an increase (~ 25%) in adhesion strength was exhibited compared to only Cu coatings. Stereo-microscopic analysis of the peel tested samples validated mixed mode i.e. both adhesive and cohesive modes of failure.
The present study investigates the role of aluminium nitride (AlN) on grain boundary pinning during reheating in presence of niobium carbonitrides (Nb(C,N)) and subsequent evolution of grain size distribution. Three as continuously cast slabs of high strength low alloy steels containing different levels of Nb (between 0.045 – 0.019 wt%) and Al (between 0.057 – 0.02 wt%) have been characterized in terms of phase balance, ferrite grain size distribution and particle size distribution. Precipitate distributions have also been determined following simulated reheating schedules. The prior austenite grain size distributions after reheating have been correlated with precipitate distribution. Quantification of precipitate and prior austenite grain size distributions after reheating unveils the governing mechanisms for precipitate dissolution/coarsening. It is observed that grain boundary pinning is controlled by AlN at temperatures below 1125°C, but by Nb(C,N) at higher temperatures.
The effect of boron on the nucleation and growth of ferrite at austenite grain boundaries is examined theoretically under the assumption that the junction of 4-austenite grain boundaries (i.e., the 4-grain junctions) are the dominant nucleation sites of ferrite. Boron segregates to the austenite grain boundaries and reduces the grain-boundary energy; it thereby retards ferrite nucleation at the grain boundary. The retardation is expressed as a decrease in nucleation density due to an increase in the critical activation energy for nucleation, and the calculated value of the fraction of active nucleation sites is in satisfactory agreement with the experimental results. The reduction of the austenite grain-boundary energy, which we obtained by applying the Gibbs isotherm for adsorption to the boron segregation, is of the same order of magnitude as the reduction is deduced from the results of calculations for a decrease in the nucleation density based on experimental results. The growth of ferrite was calculated using DICTRA, which yielded both the volume fraction and the grain size of transformed ferrite as functions of time; the results agreed with the experimental results. This agreement suggests that the influence of boron on the growth rate is negligible. However, the increase in the size of the diffusion cell due to the addition of boron is considered to be the main reason for the slightly larger grain size of ferrite compared with that in boron-free steel; this result is also in good agreement with experimental observations.
The corrosion protection performance of epoxy coated High Tensile Strength (HT) steel was evaluated by using Electrochemical Impedance Spectroscopy (EIS) and Scanning Electrochemical Microscope (SECM) analysis. EIS was performed on coated HT steel with a scratch in a 0.1 M NaCl solution after a wet/dry cyclic corrosion test. The charge transfer resistance (Rct) and film resistance (Rf) of coated HT steel displayed a higher value than coated carbon steel. SECM was conducted to estimate the corrosion performance of the epoxy coated HT steel immersed in a 0.1 M NaCl solution. It was measured that dissolution of Fe2+ was suppressed at the scratch on the coated HT steel due to the higher resistance for anodic dissolution of the substrate. SEM/EDX analysis showed that Cr and Mo were enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layers containing Cr, Ni and Mo in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.
In the present work the application of the variable magnetic field to investigate the composition of phases present in the alloys is presented. In order to make a study in the variable magnetic field a prototype apparatus was performed. The magnetic leakage of the alloy (ks) was measured in the reversible range of magnetic field. Experimental tests were conducted on samples of Fe–Cu alloys have contained the different volume fraction of phases components. Comparison of volume fraction of the solid solution αFe determined by weight and magnetic methods was performed. The linear dependence between the magnetic coupling and the volume fraction of phases components was observed. This observation can be used to estimate the quantitative phase composition in a biphase alloys. It has been shown that in the reversible range of the magnetic field, the magnetic leakage of the alloy is equal to the sum of products of volumetric proportions of individual phase components and their magnetic leakage. In the present work a new method for quantitatively assessing the phase composition using a variable magnetic field is presented which is universal for two-phase alloys if the two phases have different magnetic leakage. This can be particularly useful for assessing the proportion of austenite and retained austenite in heat-treated alloys of iron and carbon.
The solidification conditions to reduce the porosity of air-cooled blast furnace slag were investigated. From cross-sectinal observation of solidified slag, growth of gas bubble generated in molten slag was estimated to be cause of high porosity. With low thermal conductivity slag, increasing the cooling rate by thin slag casting was effective for reducing the porosity of air-cooled blast furnace slag. As a method of reducing the porosity of air-cooled blast furnace slag, a process was developed in which the slag is solidified to a plate thickness of 20–30 mm in about 2 minutes by pouring the molten slag in a cast steel mold. When porosity reduced, the abrasion resistance of the slag improved. The possibility of using low porosity slag as aggregate for drainage pavement was confirmed in an experiment with test pavement.