Volume 31, Issue 3

Traditionally, steelmaking reactions have been analyzed by thermodynamics. Recently, software packages that can be used to calculate the equilibrium conditions have improved greatly. In some cases, information obtained in this software is useful for analyzing the steelmaking reaction. On the other hand, in industrial operation, steelmaking reactions, i.e., decarburization, dephosphorization, desulfurization or nitrogen removal, do not reach the equilibrium condition. Therefore, the kinetic model is very important for gaining a theoretical understanding of the steelmaking reaction. In this paper, the following recent research activities were shown; 1) mass transfer of impurities between solid oxide and liquid slag, 2) simulation model of hot metal dephosphorization by multiphase slag, 3) evaluation of reaction rate at bath surface in gas-liquid reaction system and 4) condition for forming of metal emulsion by bottom bubbling.

The interaction parameters have been calculated for 120 ferrous alloy solutions using the pseudo-potential formalism coupled with the free energy of the hard sphere model. An agreement between calculation and experimental data appears to be reasonable with the 83%reliability in predicting the correct sign. The interaction parameters of oxygen in silicon melt were also estimated for 10 minor elements. The results, obtained only from some fundamental physical constants as inputs, are found to be useful in making qualitative discussion about the solubility of the desired element in metallic solutions.

Most of reactions in the metallurgy are heterogeneous that have a complicated mechanism, for which the kinetic treatment is complex. In general, one has to find the controlling step first, and based on which to derive the corresponding kinetic formula to describe the kinetic behavior. Currently, the most popular method to determine the controlling step is so called the Sharp method, that is, deriving a series of formulae based on different assumed controlling steps in a consecutive heterogeneous reaction, then comparing the experimental data with various kinds of formulae to decide which formula can meet the experiment data well, and from which to select the most suitable controlling step. Nevertheless, because all these formulae used in estimating the controlling step involve some unknown parameters, for instance, the Jander equation, Gingstling-Brounshtein equation, parabolic equation… etc. all involve an unknown parameter “ k ”, that will prevent us from obtaining an accurate activation energy. In this article, we will give a new method based on our series of new formulae concerning the kinetics of multiphase reactions, in which all parameters contained have clear physical meanings, therefore, when they have been used to fit the experimental data, one can obtain a more accurate activation energy and the least relative errors. Some examples have been presented to show the advantages of this new method.

Softening and melting behaviour of the iron ore materials was studied towards understanding the mechanism of formation of liquid slag and metal phases in the pre-reduced sinter and pellets. Wide range of the sinter and pellets samples was investigated revealing the effect of gangue amount and composition on temperature indices corresponding to gas permeability loss in the bed ( T 1 ) and to the largest portion of liquid products dripping ( T 2 ). For both sinter and pellets, the growth of bacisity is followed by T 1 increase which is explained by raised temperature of primary liquid phase appearance during the heating-reduction treatment. Relationship of T 2 with the bacisity corresponds to the basicity effect on slag liquidus temperature. Both slag and metal phases were only partially evacuated from the crucible with essential portions of both phases captured in the coke bed. Growing divergence of the basicities of effluent slag and of slag captured in crucible was observed with the increase of sinter basicity. Increased share of the effluent metal with the sinter bacisity growth is explained by the decreased adhesion of slag to iron surface which assists carburization. Growth of melt-down temperature with the increase of gangue amount is explained by less active carburization owing to larger quantity of slag minimising direct contact of sponge with carbonaceous materials.

A mathematical model of the continuous casting process for steel has been developed. This coupled model predicts metal flow, slag infiltration, shell solidification and heat flux. The model predicts values for the thicknesses of the solid and liquid slag films and the solidified shell, powder consumption and heat fluxes, all of which are in excellent agreement with plant data. The model has been used to study the mechanisms involved in (i) slag entrapment, (ii) the effect of mould oscillation on powder consumption, heat flux and shell solidification, (iii) oscillation mark (OM) formation and (iv) high and low frequency fluctuations.

The electrical and electronic and ionic transference numbers were measured for slags in the system MnO-CaO-SiO 2 using the stepped potential chronoamperometry method. Transference numbers were measured over a range of oxygen partial pressure to evaluate the effect of MnO-CaO-SiO 2 . The data were compared with previously measured data for the FeO-CaO-SiO 2 system. Data were found to fit well, the Diffusion Assisted Hopping Model for electronic conduction previously develop in the authors' laboratory. The only adjustable parameter employed in fitting the data to this model, was, r * , the maximum spacing at which hopping can occur. A single value for this parameter was used for all manganese data. The value of r * obtained for the MnO-CaO-SiO 2 system was slightly smaller than that for the FeO-CaO-SiO 2 system which is in keeping with the relative magnitude of the third ionization energies for Fe and Mn.

Industrial metal processes, such as casting, primary production and welding are frequently simulated using physical models which require alloy properties including liquidus and solidus temperatures and fraction solid; properties associated with heat flow: enthalpy, heat capacity and thermal conductivity and properties associated with fluid flow: density, surface tension and viscosity. These properties are required both as a function of temperature and composition. In recent years, significant developments in the experimental methods for measuring these properties have occurred, but their measurement still remains difficult and expensive. These constraints have driven the development of methods for the prediction of the properties based upon the chemical composition of the alloy. The paper describes a software program to predict properties of alloys based upon their chemical composition. The properties included are enthalpy, enthalpy of fusion, heat capacity, density, volume, fraction solid during solidification, solidification range, thermal conductivity, phases formed during solidification and viscosity. Most of the underlying models are based upon thermodynamic calculations using MTDATA, a software tool for the calculation of thermodynamics and phase equilibria developed at NPL. Transport properties such as thermal conductivity and viscosity are difficult to model and for example, thermal conductivity is estimated using empirical relationships. The program has been deliberately designed for the engineer who is not expert in thermophysical properties. The predictions will be compared with measurements for selected alloys.

Low cycle fatigue (LCF) tests on 316L(N) austenitic stainless steel base and weld joints were at 823 K and 873 K at a constant strain rate of 3 × 10 -3 s -1 with strain ranges varying from {±}0.4 % to {±}1.0 % in a servo-hydraulic fatigue test system under flowing sodium environment. The cyclic stress response exhibited a similar trend as that in air comprising of an initial rapid hardening, followed by a slight softening stage before saturation. The fatigue lives are significantly improved in sodium environment when compared to identical testing conditions in air environment. The lack of oxidation in sodium environment is attributed to the delayed crack initiation, reduced crack propagation rate and consequent increase in fatigue life. Comparison of the data evaluated in sodium with RCC-MR design code, derived on the basis of data obtained from air shows that the design based on air tests is conservative.

In this study crown magnesium produced from Turkish calcined dolomite by the Pigeon Process was refined and corrosion tests were applied. By using factsage thermodynamic program metalothermic reduction behavior of magnesium oxide and silicate formation structure during this reaction were investigated. After thermodynamic studies were completed, calcination of dolomite and it's metalothermic reduction at temperatures of 1473 K, 1523 K and within a vacuum (varied from 20 to 200 Pa) and refining of crown magnesium was studied. Different flux compositions consisting of MgCl 2 , KCl, CaCl 2 , MgO, CaF 2 , NaCl, and SiO 2 with and without B 2 O 3 additions were selected for the refining process. These tests were carried out at 963 K for 15, 30 and 45 minutes setting time. Considerable amount of iron was transferred into the sludge phase and its amount decreased from 0.08% to 0.027%. This refined magnesium was suitable for the production of various magnesium alloys. As a result of decreasing iron content, minimum corrosion rate of refined magnesium was obtained 2.35 g / m 2 / day. The results are compared with previous studies.

This article presents an analysis of experimental data with reference to material properties, short-time creep and relaxation phenomena of 1.4122 steel (AISI 420RM) at high temperatures. The behaviour of the material subjected to uniaxial stress is indicated by engineering stress – strain diagrams. The data referring to tensile strength, 0.2 percent offset yield strength, the modulus of elasticity and total deformation, are shown through tables and curves presenting the dependence of these quantities on temperature. Creep and relaxation curves regarding certain level of stresses at selected temperatures are also shown. In addition, modelling of both creep and relaxation phenomena is presented.

Two new samples of reinforce polyamidemontmorillonite nanocomposites were synthesized by a convenient solution intercalation technique. Polyamide (PA) 3 as a source of polymer matrix was synthesized by the direct polycondensation reaction of pyrazine 2,3-dicarboxylic acid 1 with 4,4'-diamino diphenyl ether 2 in the presence of triphenyl phosphite (TPP), CaCl 2 , pyridine and N -methyl-2-pyrrolidone (NMP). The resulting nanocomposite films were characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results showed that organo-modified clay was dispersed homogeneously in PA matrix. TGA indicated an enhancement of thermal stability of new nanocomposites compared with the pure polymer.

In our previous paper, a slag modification process involving the mixing of stainless steelmaking and nonferrous smelting slags was proposed for preventing the disintegration of the stainless steelmaking slag. In order to use this method, the behavior of heavy metals especially PbO contained in the nonferrous slag has to be assessed. In the present study, the activity coefficient of PbO in CaO-SiO 2 -Fe t O-Al 2 O 3 -MgO and CaO-SiO 2 -Fe t O slags saturated with iron was measured at 1673 K. The results showed that the activity coefficient of PbO increased with basicity and had a maximum value when the basicity was approximately 1.0. The equilibrium PbO content in the modified slag had a minimum value that corresponded to a mixing ratio of 0.6. The trend was similar to the change in the removal ratio of PbO observed in the previous study. Therefore, the change in the oxygen potential and the change in the activity coefficient of PbO can be considered the cause of this trend.

Microstructural refinement by two steps heat treatment in Ti-47Al-2Cr-2Nb at.% alloy, with samples' dimension of ⌀ 15 mm × 80 mm, is studied in this paper. A coarse fully lamellar microstructure can be refined to a near gamma (NG) one with a grain size of ∼ 180 μm by one step heat treatment of 1150 ° C for 12 h. The instability of initial structure plays an important role in the transformation. Some samples are subsequently treated at 1280 ° C for 2 h, the NG structure is further converted to a new lamellar structure through α laths precipitated with different directions within each γ grain and room temperature tensile elongation of the alloy is reached to a value of 1.28% after two steps heat treatments.

The polarization studies have been performed on the electrochemical reduction of TiO 2 in a molten CaCl 2 bath at 950°C. The cathodic and anodic plots have been drawn by taking TiO 2 pellet as cathode and graphite rod as anode, respectively. The cathodic and anodic over-potentials at various cell voltages have been measured. Prolonged electrolysis has been carried out at a cell voltage of 3 V and the resultant products have been analyzed by X-ray Diffraction to find out the reaction pathway through which TiO 2 is reduced to titanium. The results indicate that the electrochemical reduction of TiO 2 to titanium proceeds through a multi-step reduction process.