Effect of pulsating flow on mass transfer in packed bed is studied by taking Fe3+-iron particle system as an example of liquid-solid system, because of the industrial requirement of iron plating. Spherical and cubic particles are used as packing materials having very different shapes. Pulsation is generated by a rotary cock or a piston. Mass transfer coefficient kL for cube-packed bed under steady flow is larger than that for sphere one. Comparison of kL under steady and pulsating flow without reverse flow (by rotary cock) shows no effect of pulsating flow on mass transfer for both sphere- and cube-packed bed. In comparison with kL under steady and pulsating flow with reverse flow (by piston), however, remarkable difference reveals. That is, mass transfer for sphere-packed bed is accelerated under quasi-steady state and that for cube-packed bed is promoted much more than in quasi-steady state, where mass transfer is assumed to proceed depending on the absolute value of velocity. Velocity fluctuations just after the bed are measured by a hot film probe and the difference between the flow fields for sphere- and cube-packed bed is discussed in connection with the difference of the mass transfer under steady and pulsating flow.
The operation of prereduction fluidized bed combined with an in-bath smelting reduction furnace was performed in NKK Fukuyama Works. Iron ore fines, such as sinter feed are directly charged into the fluidized bed. This fluidized bed was so designed as to form a dense bed and equip the circulating device. The reduction characteristics of iron ore fines were clarified through the operation in the integrated test plant. According to the above results and the simulation model based on the elutriation behavior, the appropriate residence time of coarse became 30-60 min to reduce the iron ore to 20-25% reduction degree in 800°C bed temperature. The effect of circulation of fines was not quantitatively clear in the test, but the favorable circulation ratio was estimated with a mathematical model. Moreover, it was found that the collection efficiency of cyclone was closely related to the yields of prereduced ore and the circulation ratio influenced on the losses of products. Therefore, the circulation ratio was considered to be determined from the view-points of the effect on the reduction degree of fines and the losses of products.
The integrated test plant, consisting of a prereduction fluidized bed and in-bath smelting reduction furnace characterized by high post combustion, was installed at NKK Fukuyama Works, and the operation was started in 1988. The prereduction fluidized bed used iron ore fines as feed, and the fluidizing conditions and pressure fluctuation characteristics to keep the stable fluidization were clarified by the operation of the integrated test plant. The classification behavior of fines was analyzed by the measurement of elutriation rate constant. Then, the degradation phenomena of iron ore fines were observed during the preheating and prereduction of iron ore fines in the fluidized bed, and it was quantitatively analyzed by the application of Rittinger's law for size reduction. The model including classification and degradation behavior was constructed so as to estimate the operating condition. These results were considered to be useful in the scale-up of the prereduction fluidized bed.
The dynamics of steel melt flowing in the tundish is studied in a water model for a wide range of tundish design and operating parameters. Wider tundishes are found to produce short circuiting in comparison to the narrower tundishes. Empirical correlations are proposed to determine the residence times relevent to the tundish fluid flow system and their justification are discussed by using the momentum transfer mechanism in the turbulent flow. The utility of the correlations is discussed for the tundish design modifications.
Recently, high grade quality has been demanded for strips and surface-treated steel plates. Since non-metallic inclusions are the main cause of steel plate defects, the reduction of inclusion quantity is a very important problem for steelmaking. In particular, the cleanliness of molten steel in a tundish plays a crucial part in improving the quality of steel plate as well as in preventing immersion nozzle clogging. The tundish includes the functions of flotation and removal of inclusions, though, some contamination to the molten steel also occurs in the tundish. Therefore, it is necessary to make clear the cause of each pollutant and its level in order to produce super clean steels. In this study, the contamination causes of molten steel in the tundish and their influences were analyzed by continual metal sampling during operation with respect to the size, number and composition of the inclusions. The results are as follows: (1) Air oxidation of molten steel is the biggest factor of contamination. (2) The influence of air oxidation decreases and the pollutions of slag increases during continuous operations.
In this paper the possibility is demonstrated of producing microalloyed steels with Ti, V and Nb using electrodes composed of finished steels freely available on the open market. The addition of ferroalloys to the slag pool was carried out at intervals of 1 min and it was confirmed that this interval was sufficient to obtain an acceptable microalloying distribution in the metal pool. Deoxidation was carried out with Ca-Si at rates of between 1-1.5 kg/t and it was confirmed that metal/slag reactions in the production of microalloyed steels with V and Nb are easily controllable, a uniform composition being obtained from the bottom to the top of the ingot with these metals. However, in the case of steels with Ti it was necessary to prevent the Si/Ti exchange reactions which were produced when the slag did not contain SiO2 and when the rate at which Fe-Ti was added was low. In the case of microalloyed steels with Nb and with V a thermodynamic equilibrium between the Al, Ca and O was obtained. However, in the case of steels with Ti the equilibrium was produced between the Al, Ti and O.
Inductively coupled plasma mass spectrometry was employed for the determination of trace amounts of Li, B, Mg, Cr, Mn, Ni, Co, Cu and Zr in high-purity quartz. The effects of mannitol, dulcitol and sorbitol on the suppression of B volatilization during sample decomposition with hydrofluoric acid and evaporation to dryness were examined. The volatilization of B was found to be completely suppressed by the addition of more than 1.5 mg of dulcitol or more than 3.0 mg of mannitol, while even 3.5 mg of sorbitol was insufficient for the complete suppression. Thus, the addition of 2.0 mg of dulcitol, which was most effective for the complete suppression of B volatilization, was selected. Signal loss and spectral interference on the introduction of the solutions containing the organic compounds into the inductively coupled plasma mass spectrometer were examined. Continuous operations were possible for 3 h without signal loss due to carbon deposition on the sampling cone orifice when the solution containing 2.0 mg of dulcitol was introduced. Spectral interference from 40Ar12C on 52Cr occurred in the presence of 2.0 mg of dulcitol. Therefore, the measurements were performed by dividing the elements into two groups: one group for Li, B and Mg determination, and the another for Cr, Mn, Ni, Co, Cu and Zr determination. Dulcitol was not added in the latter case. The detection limits (3σ) obtained with the present method were 0.0005-0.01 ppm.
A method is developed which makes it possible to determine with precision the static recrystallization critical temperature (SRCT) of austenite in microalloyed steels, in other words the temperature at which recrystallization starts to be inhibited. Using torsional tests and applying the back extrapolation method the recrystallized fraction of the austenite has been determined at two strains (0.20 and 0.35) and several tempratures in three with Nb, V and Ti respectively. The graphic representation of the activation energy vs. the inverse of the temperature makes it possible to determine the SRCT of each steel as a function of the strain and the austenite grain size. The comparison of the SRCT with the solubility temperature calculated for nitrides and carbides indicates the nature of the precipitates. With the results obtained a model had been constructed for the recrystallized fraction both at temperatures above and below SRCT, and this, together with other equations already published, calculates the residual strain and the austenite grain size which the steel will have at the end of rolling and before the γ→α transformation. The graphs of the recrystallized fraction vs. time show the kinetics of the induced precipitation and the PTT diagrams (precipitation-time-temperature) have been determined for the three steels.
The paper pertains to the effects of longitudinal vibration, frequency and amplitude on hardness of the weldments prepared by metal arc welding under dynamic conditions. The frequency range was 0 to 400 Hz and amplitude range was 0 to 40 μm respectively. Investigations show that the hardness of the weldments have increased when compared with the stationary welded test specimens. 0 to 400 Hz frequency range and 5 to 20 μm amplitude range produce good results.
Characteristics of hot ductility of various kinds of titanium alloys were examined and compared with that of carbon steels. Although carbon steels have three typical embrittling zones above 900 K, titanium alloys do not show any embrittlement in the temperature range between β transus and 1 500 K, which is considered to be best region for hot rolling. The embrittlement occurs just below the β transus in the coarse grain titanium alloys. The ductility is poor in the coarse grain materials, but independent of the strain rate. The mechanism of the embrittlement is considered to be due to the accumulation of strain in the β phase attached to the grain boundary α in α and α+β alloys.
Cold-working is known to be detrimental to sulfide stress cracking (SSC) resistance. However, whether the increase in strength due to cold-working or cold-working itself deteriorates SSC resistance is not clear. In this paper, the effect of cold-working on SSC resistance was investigated using a constant load SSC test for low alloy martensitic steels cold-worked by tensile deformation. Threshold stress for SSC (σth) slightly decreases with an increasing cold-working rate. However, the decrease in σth caused by an increase in yield strength resulting from an increasing cold-working rate is much smaller than that caused by lowering the tempering temperature. Fractographic observation reveals that the fracture mode is not affected by cold-working. No intergranular crack appears even at the yield strength where intergranular fracture occurs for as-tempered steels. Because there is a good correlation between σth and the percentage of intergranular fractures, the same fracture mode may give a constant value of σth. It was also clarified that fractographic morphology does not change after cold-working in case of low temperature brittle fracture. From these observations, deterioration in SSC due to cold-working is considered to be caused by an increase in yield strength due to cold-working.