As typical reaction models used in the analysis of gaseous reduction of porous iron-oxide pellet, the unreacted-core model, intermediate model, parallel model, and homogeneous-reaction model are noticed. The intermediate model in which the distribution of reduction degree in the reaction zone is neglected is useful to know the effect of gas penetration into the unreacted-core, since the model gives an analytical solution. The parallel model which allows the parallel proceeding of the chemical reaction and gaseous diffusion in the reaction zone is the most adequate one for actual conditions, though analytical solution could not be obtained. However, if Thiele's modulus φ defined as r0 [3kc (1+1/K)(1-ε0)/(reDe, 0)] 1/2 is more than 20, the same type of equation to the unreacted-core model could be applied approximately. In the case of very large intraparticle diffusivity, the homogeneous-reaction model is to be realized, but it is to be considered that the applicability of the model is very scarce as far as the shell and core structure exist.
A mathematical model for the isothermal fixed bed and one of the numerical calculating method are presented. The reaction rate used in this model is determined on the basis of the rate measured for single iron oxide pellet. In order to clarify the availability of the mathematical model for analyzing the metallurgical reactors, change in the average fractional reduction over the whole bed with the lapse of time was observed during the reduction of iron oxide pellets with CO and H2 in the experimental fixed bed. The observed data were in good agreement with the calculated values except in the case where the pellets cracked badly during the reduction. It is, therefore, found that the distributions of process variables in isothermal fixed bed are estimated with the considerable accuracy by the model mentioned above and that the reaction rates of pellets with CO and H2 used in this paper are expected to be available for the process analysis of metallurgical reactors.
To analyze some primary factors that determine the driving rate of the blast furnace, the characteristics of pressure drop in the countercurrent moving bed were studied. The following results were obtained: 1. The flow of particles seemed to be the piston flow up to channeling state. 2. The Ergun's equation could be applied to the pressure drop of room temperature blast up to channeling state. 3. The differences of the characteristics between fixed bed and moving bed were observed to be in, (1) the packing state in the upper parts of packed column, (2) the process of the development of channeling state. 4. The observed pressure drop of the hot blast was a little higher for lower air velocity, but a little lower for higher air velocity than that of cold blast at the same velocity. The Ergun's equation could also be applied to the pressure drop of hot blast up to channeling state.
A kinetic study of decarburization has been done by blowing CO-CO2 gas mixtures onto the inductively stirred Fe-C melts under various conditions. At high carbon contents, the apparent rate of decarburization is independent of carbon concentration and markedly influenced by the flow rate of CO-CO2 gas mixture. Temperature dependence of the rate is relatively small. A reaction model involving the counter diffusion of CO and CO2 in gas phase and the adsorption of CO2 on the liquid iron surface has been developed. It is concluded that at high carbon contents the rate of decarburization is controlled predominantly by the diffusion rate in gaseous phase. It is also presumed that the rate constant of adsorption of CO2 on the liquid iron surface is higher than 0.001mol/cm2·Esec·Eatm, which is consistent with the extrapolated value of the reection constant for solid Fe-C alloy.
The solidification and macroscopic segregation of steel cast in chilled and sand moulds were investigated. The growth of solidifying steel shell with the lapse of time was calculated under simplified postulations, when steel was cast in moulds with the shape of infinite wide plate or long cylinder and sphere. The longitudinal solidification rate of ingots and castings were measured by bar test method, and compared with the calculated values. Further, discussion was made on the relation between the rate of vertical or horizontal solidification and the formation of macroscopic segregation, under consideration of inter-dendritic solidification. The results obtained are as follows; (1) The calculated results agree well with the measured results by bar test method. (2) There exists close correlation of macroscopic segregation with condition of solidification and thickness of solid-liquid coexisting zone in dendrite. In other words the macroscopic segregation is induced by the upwards floating of light liquid metal enriched with solute in solidifying dendrite arms. The easiness of floatation depends upon the direction of macroscopic solidification and also the width of solid-liquid coexisting zone. On the other hand the width of solid-liquid coexisting zone is influenced by the temperature gradient of solidification front and the temperature range of solidus and liquidus of steel. The mutual relations of these factors are made clear.
An investigation was done on the entrapped scums and pinholes in continuously-cast plain carbon steel billets of 80 to 160 square and 260 by 370mm section. The results obtained are summarized as follows: 1) The number of entrapped scums in the billets cast with open nozzles and oil was increased with decreasing manganese-to-silicon ratio and carbon content in the steels, excess addition of aluminum wire in a mold, addition of titanium to a low manganese steel, air oxidation of teeming stream in a mold, and increasing billet size. 2) Utilizing submerged nozzles and fluxing powders remarkably removed such scums. 3) These observations are discussed in terms of the melting point, fluidity, interfacial tension, and the amount of scums formed. 4) The number of pinholes in the billets cast with open nozzles and oil was decreased with decreasing carbon content of the steels, by using strong deoxidizers such as aluminum, calcium-silicide, or titanium, protecting air oxidation, drying ferroalloys, and with decreasing billet size. The use of water-free fluxing powders perfectly prevented the formation of pinholes.
The effects of silicon content on the fatigue life and other properties have been investigated by using 0.5% carbon steels and SUJ 2 bearing steels (JIS) containing various amounts of silicon. The results may be summarized as follows: (1) The fatigue life of 0.5% carbon steel without undissolved carbide is increased by existence of about 1.5% silicon, that is, the fatigue life is much influenced by silicon in martensite. But the mechanical properties as hardness and compressive breaking strength are not influenced. (2) The fatigue life of bearing steel with undissolved carbide in martensite is also much improved by existence of about 1.5% silicon. (3) The toughness of bearing steel as quenched and tempered is increased by silicon, but the element is, not very much expected for the improvement of machinability and cold formability in annealed state. (4) The fatigue life becomes longer as the silicon content in steel increases. The reason is considered to be due to the increase of resistance to the softening by tempering.
Fatigue limits under rotating bending of transverse manual arc butt-welds in high tensile steels are examined by varying welding heat input in a wide range. A fatigue crack initiates almost at the softened zone of heat-affected zone (HAZ), but those fatigue limits are not lower than those of base metals. Influence of hardness change in welds or fatigue was also examined by using high tensile steels heat treated by a synthetic apparatus for weld thermal cycle, or steels heat treated by TIG arc process. The fatigue limit of the specimen having hardness change of Hv 100 shows just a little lower value than that of the specimen having no hardness change. Notched fatigue strengths in HAZ of welds of various microstructures in high tensile steels are investigated in detail. Those fatigue limits are almost equal to those of base metals, the notch sensitivities of HAZ's are not high compared with those of base metals. It is discussed that there are essentially little metallurgical factors affecting fatigue strengths of welds and a low fatigue strength of welds in high tensile steel may be due to a stress concentration of about 4 near a toe of reinforcement of welded joint.
When high sulfur steels were analysed by the constant volume pressure measuring type vacuun fusion method, the sulfur gave positive errors on the determination of oxygen. The CS and CS2 gases were generated by the reaction of sulfur and graphite crucible and then extracted together with CO from the crucible. These CS and CS2 were oxidized by the oxidizing reagent in the system and CO2 and SO2 were generated, the volume becoming two or three times. Of the sulfide generation the lower limit of sulfur content was about 0.1% in ordinary samples. To prevent these errors, a circulating system containing a Liq. O2 trap was newly set in the apparatus and with it the sulfides in extracted gases were separated. Thereby a good analytical precision (standard deviations were 3.7ppm and 14ppm for samples of 34ppm and 135.5ppm respectively.) was obtained on the determination of oxygen. The components of the evaporated-condensed film on the inner wall of reaction tube and the residual metals in the crucible were analysed and the reaction mechanisms of evaporation, deposition, adsorption, and reduction of extracted gases and metals were discussed.
On 20 elements-Na, K, Mg, Ca, Ti, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn, Cd, Al, Si, Sn, Pb, and Bi-which were determinable by atomic absorption analysis in steel-making, the interference mechanism by Al and Sr in air-C2H2 flame and N2O-C2H2 flame was discussed. Of those elements, 6 elements-Mg, Ca, Ti, V, Cr, and Mo-were appreciably interfered with by Al and Sr in some flames. The interferences in Mg, Ca, and Cr could be explained by chemical interferences in air-C2H2 flame. It was suggested that Ti, V and Mo were also interfered with chemically in N2O-C2H2 flame, but their interference mechanisms might be complicated and influenced by the presence of anions.