Almost 300 kinds of binary alloys have been electroplated so far modify surface properties of substrates. Electrodeposition of iron-group metal alloys has been studied most intensively for last 16 years. This trend was caused not only by the excellent properties of the coatings that were useful for many industrial applications but also by the fact that their electrodeposition behavior was interesting from an academic point of view. This review correlates the mechanism proposed so far to explain the abnormal electrodeposition behavior of iron-group metal alloys.
In-situ deformation experiments are reviewed on the subjects of martensitic transformation and shear deformation. Particular interest is directed to our recent studies dealing with γ→α and γ→ε martensitic transformations, dislocation reactions in proton irradiated Mo and steels, and dislocation motion in a high temperature strengthening alloy of ordered Ni3Al.
In the present investigation an attempt has been made to determine the effect of reduction rate on the swelling behaviour of iron ore pellets. For this purpose two Indian iron ore fines from Bailadila and Noamundi deposits and chemically pure iron oxide were used. The effects of parameters like, temperature, time, reducing gas partial pressure and flow rate have been studied. From the results obtained, it has been observed that swelling of iron ore pellet is controlled by the rate of reduction of iron oxide. The growth of iron whiskers is also controlled by reduction rate.
Titanium containing compounds are valuable materials for addition to the blast furnace to extend operational compaigns. However, the addition of these materials via the sinter plant has been known to create problems. This study investigates the effect of adding a titanomagnetite to two sintering ore blends, containing 10 and 20% pisolitic limonite respectively. The addition of up to 2% titanomagnetite did not affect the sintering parameters or sinter quality. Increasing the titanomagnetite levels to greater than 3% also had no significant influence on sintering but a signficant deterioration in sinter RDI was recorded. Results also showed that the deterioration in RDI was greater for the blend containing more pisolitic limonite. SEM studies carried out on the product sinters found most of the titanium in the glass phase. The mechanical properties of the glass was characterised using indentation fracture mechanics. Although some difficult was experienced, due to the small and disperse nature of the glass, addition studies using artifically manufactured glass indicated that the fracture toughness of the glass decreased with increasing titanium levels. It is postulated that because glass in the weakest phase in sinter and is widely dispersed any reduction in its fracture toughness will increase the vulnerability of the sinter to crack propagation, thereby increasing sinter RDI. It is also postulated that increasing the pisolitic level increased melt formation and the dispersion of the glass phase, resulting in a further deterioration in sinter RDI.
Thermal conductivities of dense pure hematite, magnetite and wustite measured using the laser flash method as reference value have been summarized in the form of an empirical equation k=1/(AT+B). Wustite shows an almost constant and the relatively low thermal conductivity due to the lattice imperfection. Thermal resistivities, 1/k, of three iron oxides appear to change linearly as a function of temperature up to the Tammann temperature. Effective thermal conductivities of fired, nonfired pellets and sinter, reduced into magnetite, wustite and metallic iron by CO-CO2 or H2 gas, have also been systematically measured in the temperature range from room temperature to 1273 K. The porosity of samples was found to change from 20 to 62% by the reduction from hematite to metallic iron. Measured effective thermal conductivity values of these iron ore agglomerates are remarkably smaller than those of dense materials due to the existence of pore. Effective thermal conductivities of metallic iron and hematite strongly depend on temperature. There is no significant difference in the effective thermal conductivities of reduced samples at the same reduction degree. The measured effective thermal conductivity values have been well-explained by the modified unit cell model originally proposed by Luikov when considering the structure composed of core part and connecting part in the solid phase. This model also clearly identify the distinction of solid structure in samples originated from the difference in preparation and reduction degree.
A new oxygen blast furnace process, which is characterized by the injection of preheating gas into the shaft, was developed. For the development of the process, operation tests using an experimental blast furnace were carried out, and proved this process to be applicable as an ironmaking process. Mathematical model simulations were also carried out and the process characteristics were clarified on a commercial scale, in comparison with those of a conventional hot blast furnace process. Through the analysis of the experimental blast furnace operation and the mathematical model simulations, this process was found to have the following characteristics; (1) Heating-up and reduction of burden assured throughout the furnace by means of the preheating gas injection. (2) Appropriate preheating gas, in which the low fuel rate is realized, is the range of preheating gas flow rates corresponding to thermal flow ratio in the upper part of 0.74-0.90 and the range of temperatures 600-1200°C. (3) The preheating gas composition has little influence on the reduction in the lower part. (4) The position of preheating gas injection is adequate in the upper shaft as long as the heat transfer is secured. (5) Operational fuel rate range is wide; 500 kg/t (with preheating gas)-1200 kg/t (without preheating gas).
A mathematical model has been developed to calculate the three dimensional and instationary temperature field in the strand during continuous casting. The numerical algorithm and the computer program were tested by application to the Neumann problem for which an analytical solution is available. It was found that this analytical solution is reproduced quite closely even if relatively coarse finite difference meshes are used. An algorithm based on the solution of the inverse heat conduction problem is applied to adjust the heat transfer coefficients for the computer model using the results of surface temperature measurements. Another algorithm was developed to calculate the material data from the steel composition. This algorithm is applicable to steel grades with low contents of alloying elements. The model fulfills the requirements concerning computing time consumption and accuracy for an on-line application. Results obtained with the model which is installed at several casters are presented.
The effective viscosity νe and the effective diffusivity of bubbles De in a vertical bubbling jet in a cylindrical bath were determined from the governing equations based on the boundary layer approximation and the Boussinesq approximation. These approximations were satisfied in the buoyancy region in the vertical bubbling jet. Gas holdup and mean bubble rising velocity needed in calculations of νe and De were measured with a two-element electro-resistivity probe, and the mean velocity of water with a laser Doppler velocimeter. The values of νe and De were almost the same on the jet axis in the buoyancy region and increased with an increase in the injected gas flow rate. The radial profile of νe was parabolic and that of De was almost uniform across the bubbling jet. The profile of νe was different from the profile of νe in a single-phase turbulent free jet.
In the steelmaking and refining processes, bottom gas blowing is a widely-used method. In these systems, the gas is blown into liquid from the bottom of the vessel at a temperature lower than liquid temperature. The mechanism of heat transfer between bubbles and liquid and the effect of heat transfer on the formation of bubbles and the rising characteristics of the bubbles were investigated, using air and helium in a water model. The injection temperature of the gases was about –110°C. Heat transfer between bubbles and liquid was almost fully completed near the nozzle. Bubble expansion due to the heat transfer resulted in the increase of gas holdup in the radial direction. In the region far from the nozzle, the bubble characteristics accompanying cold gas injection were the same as those initiated by an ambient temperature gas injection at the same mass flow rate.
The critical hot rolling condition which prevents abnormally large grains from forming in the microstructure was investigated in Interstitial Free (IF) steel, using thermomechanical simulation equipment. Abnormal grain structure was produced at finishing temperatures (FT) below 900°C, accompanied by coiling temperature (CT) above 700°C. The said critical FT and CT represent the dynamic transformation temperature (DTT) and the secondary recrystallization temperature (SRT), respectively. The unusually large size grain of >150 μm in diameter is attributed to the high driving force due to the extremely fine grains around itself. These grains are produced through the transformation from unrecrystallized austenite. The austenite recrystallization rate was drastically reduced through the drag effect of dissolved Ti atoms. Unlike typical low carbon steel, a strong retardation of ferrite grain growth due to TiC precipitates resulted in the elimination of the abnormal grain below SRT coiling. Precipitation hardening due to TiC as well as hot deformation hardening was recognized in IF steel. Excessively high hardness might be encountered, if the FT is <DTT and the CT is <SRT.