The South African Wessels and Australian Groote Eylandt manganese ores were characterized using XRD, optical, SEM and EPMA analyses. Two grades of Groote Eylandt ore were examined, one of them contained a high concentration of silica, 34.4 mass%. Wessels ore had high iron oxide and calcia content, and low concentration of silica. Major manganese-containing phases were bixbyite, braunite, manganite and hausmannite in Wessels ore, and pyrolusite in Groote Eylandt ore; both grades of Groote Eylandt ore contained silica inclusions. In the process of sintering in air and argon at 1000°C, MnO2 was reduced to Mn2O3 and Mn3O4, while in sintering in hydrogen manganese oxides were reduced to MnO and iron oxides to metallic iron. In the process of sintering of high-silica Groote Eylandt ore at 1200°C in inert atmosphere, tephroite was formed which was partially decomposed to rhodonite and MnO with increasing sintering time to 30 min. In the ore sintered at 1200°C in hydrogen for 1 h, major phases identified by XRD analysis were MnO, silica and tephroite.
Non-isothermal and isothermal carbothermal reduction of Australian Groote Eylandt and South African Wessels manganese ores was studied in hydrogen, helium, argon and hydrogen–carbon monoxide atmospheres. Reduction experiments were conducted in a fixed bed reactor in a vertical tube furnace, with on-line monitoring of gas composition by CO–CO2 infrared sensor. The extent of reduction was calculated using the off-gas composition and oxygen content in the reduced samples measured by LECO. The reduced samples were analyzed by XRD and EPMA. Reduction of manganese ores was strongly affected by temperature and ore chemistry. In all gas atmospheres, the reaction rate increased with increasing temperature. The reduction rate of manganese ore in hydrogen was higher than in helium, and in helium higher than in argon. Rate and extent of reduction of Wessels ore were higher in comparison with Groote Eylandt ores.
The paper considers phase development in the process of solid state carbothermal reduction of Wessels (South Africa) and Groote Eylandt (Australia) manganese ores in inert gases and hydrogen. Reduction starts with reduction of higher manganese oxides to MnO and iron oxides to metallic iron. When the graphite content in the graphite/ore mixture was in excess relative to the stoichiometric ratio, the final reduction product was (Fe, Mn)7C3 carbide. In the process of reduction of Groote Eylandt ore, silica also was reduced. In the reduction of high silica-ore, manganese oxide was predominantly reduced from tephroite and rhodonite. Silicon in the alloy was present in the form of ferro-manganese-silicon carbide and silicide (Fe, Mn)5Si3.
Remarkable deviation of metal fraction in the liquid drained out of blast furnace tap hole has been occasionally observed between the operated tap holes and/or tapping time stages. Introducing the concept of low permeability zone whose wall, due to the difference in two liquid phases' viscosity and/or wettabilitiy to coke particle, allows for metal to permeate freely but for slag not to permeate, the liquid drainage behaviors are examined by furnace hearth mathematical model simulations. The deviation of metal fraction between two operated tap holes is materialized under the hypothesis that furnace heath is divided into two sections by planar vertical low permeability wall (VLPW). While, the variation of time series change in liquid metal fraction during tapping operation is reproduced by hypothesizing the formation of cylindrical low permeability wall (CLPW) which concentrically parts the furnace hearth into center and peripheral area. Since the results of calculation for VLPW or CLPW formation indicate the notable raise of liquid level in furnace which could influence on abrupt increase of blowing pressure, the effectiveness of several operational optimization is assessed, resulting in suggestive conclusion that increasing the initial tap hole diameter is the most effective.
The process of Al deoxidation and Ti alloying during RH degassing treatment was studied under an Ar atmosphere at secondary steelmaking temperature (1600—1650°C) in an induction furnace equipped with an oxygen probe and a steel sampler. The formation of inclusions during partial Al deoxidation and Ti addition, and the reduction of Ti–Al–O inclusions by second Al addition are discussed using thermodynamic calculations. Specific attention is given to inclusion size and the compositional relation between the inclusions and the steel. The combination of experimental and calculated results shows that, in order to prevent Ti oxidation in liquid steel, it is essential to control [Al] in liquid steel to a level of approximately 200 ppm prior to Ti addition to achieve around 500 ppm [Ti] with minimal Ti loss during the alloying process.
Steels with low concentrations of nitrogen, hydrogen and carbon have in large demand lately. The RH process is a secondary refining process that can simultaneously attain significant levels of removal of these interstitial elements from liquid steel. In the RH process, the melt circulation rate plays a very important role in determining productivity of the equipment, since it affects the decarburization rate. In the present work, a physical model of a RH degasser in a 1 : 5 scale of an industrial reactor from USIMINAS (Minas Gerais, Brazil). This model has been built and used in the study of the circulation rate and of the kinetics of decarburization. The effects of the gas flow rate and of the configurations of the nozzles used in the injection of the gas have been analyzed. The effect of gas injection in the vacuum chamber was also investigated. The decarburization reaction of liquid steel was simulated using a reaction involving CO2 and caustic solutions. The concentration of CO2 in the solution was evaluated using pH measurements. The experimental results indicated that the kinetic of decarburization is controlled by mass transfer in the liquid phase. It was also observed that, in certain configurations, the injection of gas in the vacuum chamber can increase the decarburization rate.
An electromagnetic vibration (EMV) was generated by simultaneously imposing a strong static magnetic field and an alternative electric current to the metal. Its effects of refining solidification structure of aluminum have been investigated systematically. It is found that the macrostructure can not be refined by solely imposing strong magnetic field or alternative electric current while it is refined under the electromagnetic vibration. The refining period of the structure was examined by changing the imposing period of the electromagnetic vibration. From these experimental results, the refinement behavior in this process is that crystal nuclei dissociated from surface due to surface oscillation and disturbance in the initial stage of the solidification. And owing to the fall of refined grains during electromagnetic vibration, the refined structure was normally gained only at the bottom region of the sample. Finally, a method was proposed to restrain crystal shower by using an upward magnetic force, and a uniform refined structure can be obtained by using this method.
Some computational results on dendritic growth in binary alloy are obtained by using a phase–field model coupled the solute gradient term. The effect of crystalline anisotropy on the morphological formation, tip steady state and the solute partition is investigated for different dendrites. The interface formation and tip steady state are affected evidently with increase in anisotropy for ‹100› dendrite growth, but the solute partition coefficient is not significantly influenced. For ‹110› preferred growth directions, when the anisotropy strength is lower than the critical value, the tip velocity of  direction is lower than  and  directions. As the anisotropy strength crosses the critical value, the tip velocity of  direction increases suddenly, larger than the tip velocity of  and  directions, showing strong solute trapping.
Mold powder plays an important role in the continuous casting process for high quality steel production. Qualitatively, it is well known that mold powder entrapment causes surface defects in steel sheets, and high viscosity of the mold powder prevents the entrapment of the mold powder into the molten steel in ultra-low carbon steel. This paper deals quantitatively with the entrapment of mold powder caused by suction by Karman's vortex in a laboratory experiment. First, in a water model experiment using oil as a substitute for mold powder, the effects of the viscosity of the oil and the interfacial tension between the water and oil were investigated. Following this, hot model experiments were carried out with mold powder and molten steel. The amount of mold powder entrapment was affected by the viscosity of the molten mold powder and the interfacial tension between the molten steel and mold powder. As the result, the following equation for mold powder entrapment was obtained.
where m: weight of entrapped mold powder (g/100 g-steel), η: viscosity of mold powder at 1573 K (Pa·s), and γm–s: interfacial tension between molten steel and mold powder (mN/m). The amount of mold powder entrapment decreased when the viscosity and interfacial tension increased. However, the effect of viscosity on mold powder entrapment was larger than that of interfacial tension in the case of an industrial mold powder when viscosity was under 0.5 Pa·s and interfacial tension was from 1200 to 1300 mN/m.
Rollers are used widely in the transfer of the steel plate in steel mills. This method causes very loud impact noise because of the deflection of the steel plate and causes noise pollution in the labor environment. In this paper, the relationship between the impact noise and the impact force was examined. Also, a method for reducing the impact force was implemented in order to reduce the impact noise. The noise index was introduced to quantify the relation between impact noise and impact force. Dynamic and impact analyses were carried out using the finite element method. Experiments on impact were also carried out in order to validate the results.
In this paper, we propose a molten steel level controller for a continuous caster that is based on an adaptive fuzzy estimator. The main objective of the proposed controller is to reject the bulging disturbance that occurs in the continuous casting process. If we know the bulging frequencies and phases, and the system time delay, then we can efficiently reject the bulging disturbance by using an adaptive fuzzy estimator. It generates the estimated bulging compensation signal taking the system nonlinearities and delay into account and this signal is added with the PID output to reject the real bulging disturbance efficiently. Computer simulations and experiments were executed with one-to-four-scale H/W simulator.
The most sensitive emission lines for determination of cobalt, nickel, and vanadium in steel samples were investigated when krypton was employed as an alternative plasma gas in glow discharge optical emission spectrometry. A thorough survey in the emission spectra indicated that more sensitive ionic lines of nickel as well as cobalt, which were free from spectral interference from iron, could be found when using krypton gas instead of argon gas; therefore, the krypton plasma was recommended in the determination of nickel and cobalt in iron-matrix alloy samples. However, the argon plasma yielded more intense ionic lines of vanadium suitable for the vanadium determination in iron-matrix alloy samples. These phenomena could be explained by resonance energy-transfer collisions with the plasma gases which selectively populate different excited levels of these ions between the krypton and the argon plasmas.
This study is concerned with effects of oxides on Charpy impact properties of heat affected zone (HAZ) of API X70 linepipe steels. Various oxides were formed by adding alloying elements of Ti, Al, and Mg to the API X70 steels, and effects of these oxides on HAZ microstructures and Charpy impact properties were investigated. Oxides present in the steels were sized about 2 μm, and had characteristics of complex oxides composed of various elements. The steel containing more Al, Ti, and Mg showed higher volume fraction of oxides than the conventional steel. After the HAZ simulation test, the oxide-containing steel HAZs were composed mainly of acicular ferrite, together with small amount of bainite, whereas the conventional steel HAZ were composed mainly of bainite with a small amount of acicular ferrite. This formation of acicular ferrite in the oxide-containing steel HAZs was associated with the active nucleation of acicular ferrite at oxides, thereby leading to the great (five times or more) improvement of Charpy impact properties of the HAZs over the conventional steel HAZs.
Nanostructured surface layer was synthesized on the end face of Ti–4Al–2V alloy and 0Cr18Ni9Ti austenite stainless steel rods by means of Surface self-nanocrystallization(SSNC). Making treated end surfaces as bonding interfaces, transition joint of Ti–4Al–2V alloy and 0Cr18Ni9Ti stainless steel bars was prepared by pluse pressuring diffusion bonding (PPDB) on Gleeble-1500D tester at 850°C for 80 s, the maximum and minimum pluse pressuring were 8 MPa and 50 MPa respectively, and cycle (N) and frequency (f) of pulse load were 40 times and 0.5 Hz respectively. Bonded joints were tensed on CMT5105 style instron. Microstructure of transition joint was investigated by scanning electron microscope (SEM) and X-ray energy dispersive spectroscope (EDS). The reaction products on the fracture were detected using X-ray diffraction (XRD). Research results showed that the maximum tensile strength reached 384.0 MPa, cleavage fracture took place while tension test of joints. Brittle intermetallic compounds such as Fe2Ti, FeTi and σ phase presented on the fracture, and on the titanium alloy side, α-Ti transformed into β-Ti in the vicinity of interface while diffusion bonding.
Chloride-laden and carbonated environments were selected for the investigation of corrosion acceleration due to galvanic corrosion of normal rebars in contact with corrosion-resistant Cr-bearing rebars embedded in concrete. Concrete specimens simulating these environments were fabricated using normal steel (SD345) rebars in contact with Cr-bearing rebars and subjected to corrosion-accelerating curing with high temperature/high humidity and low temperature/low humidity cycles. The half-cell potential, corrosion area, and corrosion loss of the normal steel rebars were measured at the specified test ages. No corrosion acceleration due to galvanic corrosion was observed on SD345 rebars in contact with Cr-bearing rebars in chloride-laden and carbonated concretes, suggesting the possibility of the selective use of Cr-bearing rebars for newly built structures only where necessary and their use as a repair material for patching.
Phase equilibria between the α (A2), α′ (B2) and γ (A1) phases in the Fe–Rh binary system were investigated using electron probe micro-analysis (EPMA) and differential scanning calorimetry (DSC) techniques. The A2/B2 order-disorder transformation temperature was also examined by a transmission electron microscope (TEM) observations and high-temperature X-ray diffraction (HTXRD). It was confirmed that while the transition temperature from the α (A2) phase to the γ (A1) phase decreases with increasing Rh content up to about 20 at% Rh, the b.c.c. region is stabilized by further Rh addition in the composition range between about 20 and 50 at% Rh, and then again the stability of b.c.c. phase decreases in the composition region over 50 at% Rh. It was also shown by TEM observation and HTXRD examination that the compositions of the phase boundary of the A2/B2 ordering at 500°C and 600°C were determined to be 16.5 and 19.1 at% Rh, respectively. On the basis of those experimental results, a thermodynamic analysis was carried out. The results of the thermodynamic calculation suggest that the anomalous behavior of the stability of the b.c.c. phase is caused by the A2/B2 ordering.
The in-situ X-ray diffraction observations of the bainitic transformation of high silicon cast steel were performed using the high temperature X-ray diffraction technique. The volume fraction and carbon content of austenite depend on the transformation temperature. The experimental result has shown that the volume fraction of austenite ceases to a constant value which indicate that the transformation is almost finished after holding for about 1000 s. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation due to a heterogeneous distribution of carbon in different regions of austenite and thus exists two types of austenite: low-carbon austenite (γLC) and the high-carbon austenite (γHC). The volume fraction of bulk austenite with low carbon decreases greatly at the early stage of transformation and then tends towards zero. The lattice parameter of both low-carbon and high-carbon austenite increases with the holding time due to the carbon partition from the supersaturated ferrite to the austenite. The experimental results supports that the bainite growth is by a diffusionless mechanism when austempering temperature is in the lower bainite transformation temperature range.
Tensile tests were performed for two kinds of model alloys containing soft Cu particles or hard VC particles. Work hardening rate was obviously smaller in the Cu particle dispersion steel than in the VC particle dispersion steel. TEM observation for the cold-rolled specimens revealed the different dislocation arrangement; high density dislocations are introduced around the carbide particles in the VC steel, while dislocations are less accumulated in the Cu steel because dislocations can pass through Cu particles during plastic deformation.
The fractal dimension of the grain-boundary fracture, Df, (2<Df<3), which represents the fracture surface pattern with grain-boundary microcracks in three-dimensional space, is proposed for characterization of high-temperature fracture in materials. The value of Df as well as its two dimensional value, Dfp (the fractal dimension of the grain-boundary fracture surface profile, 1<Dfp<2), was estimated in the length scale range more than about one grain-boundary length using the height data of fracture surfaces of heat-resistant alloys obtained by the stereo matching method. The value of Df increased with increasing fractal dimension of the grain-boundary surface profile (DGB, 1<DGB<2) in the specimens of the HS-21 alloy ruptured at 1089 K. Both rupture life and creep ductility increased with increasing value of Df in these specimens. Similar results were obtained by the two-dimensional fractal analysis on other specimens of cobalt-base, nickel-base and iron-base heat-resistant alloys. Creep fracture process including the growth of the main creep crack was examined by the fractal analysis using the fractal dimension map (FDM, a color-coded map) on the surface notched specimens. The result of the fractal analysis was compared with that of the FRASTA (fracture surface topography analysis) in the Inconel X-750 alloy. The fractal analysis used in this study is more convenient and more advantageous than the FRASTA, and is widely applicable to the investigation of high-temperature fracture in materials.
The use of CADI, a variant of Austempered Ductile Iron (ADI) containing free carbides, is on the increase thanks to its excellent combination of high abrasion resistance and good impact toughness, when compared to other materials with similar wear resistance. The present work focuses on the study of two CADI variants in which carbides were obtained by a combination of alloying elements and the effect of a cooper chill located in the mould. A detailed microstructural characterization of the material was made; and the content and composition of the carbides as well as their stability during the heat treatment were particularly studied. The abrasion wear resistance was evaluated by testing under the ASTM G 65 standard, and comparing the relative wear resistance of samples taken just beside the cooper chill up to locations where the chill did not affect the solidification rate. The relative wear resistance, determined by using ADI as a reference material, ranged from E≈3 to E≈2 for samples taken from the different locations, close and far to the chill, respectively. For samples taken from the same locations, the impact toughness ranged from 6.5 to 10 J, respectively. The results allow establishing a relationship between the solidification rate, the microstructure and the mechanical properties, thereby enabling to predict their effect on current applications.
Nickel-free austenitic stainless steel (Fe–25Cr–1N) was produced by solution nitriding, and then the grain size was variously controlled by the two-step phase transformation method. Mechanical property of the steel with different grain size was investigated by means of tensile testing to clarify the effect of grain size on the strength, elongation and fracture surface. The as-solution-nitrided material with a coarse grain size caused brittle intergranular fracture on the way of uniform deformation before the onset of local necking deformation. As a result of grain refinement, intergranular fracture was markedly suppressed, and this leads to the enlargement of elongation as well as increase in yield strength and tensile strength. The suppression mechanism of intergranular fracture was discussed on the basis of dislocation pile-up model together with the experimental results of TEM observation for dislocation substructure in tensile-deformed materials. It was then concluded that the stress concentration at grain boundary is reduced by grain refinement, and this contributed to the suppression of intergranular fracture and enlargement of elongation in the grain-refined material.
The study of the initiation fracture toughness (JIC) and J–R curve of low carbon SA333 Gr. 6 steel by compact tension (CT) indicates that for thicker specimens, JIC decreases with the increasing ratio of crack depth (a) to specimen width (W), a/W, both for deep and shallow cracks. However, for thinner specimen, JIC decreases with a/W ratio for shallow cracks but for deep cracks, JIC is insensitive to a/W ratio. Initiation fracture toughness increases with decreasing thickness but at relatively lower thicknesses beyond plane strain condition, initiation fracture toughness increases significantly with increasing specimen thickness for different a/W ratio investigated.
The effect of microwave irradiation on the hydrothermal treatment of blast furnace (BF) slag was investigated using a 2.45 GHz microwave irradiation system. The comparison of the features of a microwave-hydrothermal (M-H) reaction with those of a conventional hydrothermal (C-H) reaction showed that in both these reactions, tobermorite (Ca5Si6O16(OH)2·4H2O) was formed as the major phase in the treated samples. When the BF slag was hydrothermally treated by the C-H reaction, tobermorite was formed in the vapor state as the major phase at 200°C after a holding time of 48 h; in the M-H reaction, tobermorite was rapidly formed within 3 h at the same temperature. It was elucidated that microwave irradiation promoted the hydrothermal reaction to a significant extent. Furthermore, effects of microwave irradiation on BF slag subjected to hydrothermal hot-pressing were investigated. After microwave irradiation, the compressive strength of the slag compact and rate of porosity in the compact after treatment increased and decreased, respectively, in comparison with those before treatment. Moreover, microwave irradiation was advantageous over conventional heating at the same temperature in that it enhanced the compressive strength of the BF slag.
In this paper, a dynamic substance flow model of zinc in Japan was conducted. Currently, approximately 60% of zinc in Japan is used for galvanized steel (galvanized sheet and other galvanized products), followed by brass. In other words, zinc has many linkages to other substances. A dynamic model was used to look at these linkages of zinc to other substances in the production stage through other stages. In addition, dissipated zinc used in galvanized sheets and other galvanized products during the use stage was taken into account, using the results of previous atmospheric-exposure tests. Most discarded zinc is recovered as steel scrap or copper-alloy scrap. When used steel is remelted in an electric arc furnace (EAF), zinc is vaporized and collected as EAF dust. Therefore, this steel-associated zinc reenters the zinc cycle. By comparison, when zinc is used in copper alloys, zinc is not recycled and ends its life in the copper cycle. The mass balance of zinc as derived by our substance flow analysis was verified by comparing estimated values of the model with statistics and other estimates on zinc recovery. Using this model, zinc stocks in Japan was estimated to total approximately 3300 kt at 2005 (26 kg/cap), or enough for around seven years. The amount of unrecovered zinc in 2005 was estimated at around 182 kt. Of this zinc loss, 73% went unrecovered in the steel cycle, e.g. it dissipated into the environment as sacrificial materials, or was in steel that was not collected for recycling.