In the practical operations of blast furnace, ore and coke burdens charged alternately to the top of the furnace descend at a state with layer by layer and contact with the ascending gas. To clarify the operating characteristics of the furnace with the horizontal layers of burdens, a comparatively simple model has been developed by taking account of the indirect reduction of iron ores, the decomposition of limestone and the solution loss in the model building. With the aid of this model, the longitudinal distributions of process variables, such as the temperatures of gas and solid particles, the fractional conversions of iron ore, limestone and coke, the volume flow rate of gas, the composition of gas, the gas density and the bulk densities of ore and coke layers, have been cal culated numerically over the region from the top to the melting zone of the furnace. Furthermore, the characteristic features in the furnace with the horizontal layers of burdens have been discussed on the basis of the computed results.
Measurements have been done on the rates of carbon and oxygen transfer between CO-CO2 mixtures and levitated iron droplet. Supposing that the mass transfers between two phases determine the total reaction rate, the kinetics of this reaction has been considered. Results obtained here are as follows: Type of reaction at the initial period is different from that at the later period. At the initial, a simple absorption of gas takes place independently of the composition of gas mixture. The rate is controlled by the mass transfer at the melt side. At the later period, decarburization or carburization proceeds and the countercurrent flow of CO and CO2 in gas phase controls the total rate. It is concluded that whether iron is melted by the levitation technique or in usual crucibles, there is no essential differences in the mechanism of reaction, and that one or both of the mass transfers at gas and melt determines the total rate of reaction according to the experimental conditions such as the flow rate and composition of gas, mass and violency of stirring of melt. Re-examinations have been done for the previous investigations which proposed the interfacial chemical reaction mechanism as the rate determining step.
In order to develop the austenitic steel for cryogenic use, micro structure, mechanical properties especially low temperature toughness, and thermal expansion coefficient of manganese-chromium steels with much amount of manganese as an austenitizing element, have been investigated.The results obtained are as follows. It is found that 25 Mn-5Cr-1Ni steel, selected as optimum base composition, has excellent notch toughness and low thermal expansion coefficient of6.7-7.2×10-6/°C. Further the addition of niobium, vanadium and titanium to base composition result in the refinement of austenite grain size which increase the strength considerably but decrease the notch toughness a little. Especially the addition of 0.1% niobium contribute to the high tensile strength of 70 kg/mm2 and keep the low temperature toughness υE-196 more than 5 kgm. The addition of nitrogen increases only the 0.2% proof strength.
The effect of alloying element, Ni, on the reversible temper embrittlement susceptibility of Ni-Cr low alloy steels was investigated by giving embrittling (step cooling)-reannealing (recovery of embrittlement) treatment cycles with the aid of Charpy impact test and electrical resistivity measurement. The reversible change of resistivity during heat treatment cycle was observed, which amount was directly related to Ni content and reversible change of fracture appearance transition temperature, that is, the amount of reversible change of resistivity became larger as the Ni content or the ΔFATT was higher. The resistivity change during heat treatment cycles involved both irreversible and reversible portions, in which the former came out of tempering process such as dislocation anihilation, carbide precipitation and growth. Thus, reversible portion of resistivity could be separated by tempering the specimen at 600°C for long time prior to the heat treatment cycle. Fracture mode of Charpy specimens also changed reversively from transcrystalline to intercrystalline along prior-austenite grain boundaries for the first heat treatment cycle, while some smaller interface fracture than prior-austenite grain occurred after the second embrittling treatment.
Ageing behaipurs of tensile properties and correlation of the content of hydrogen in killed steels have been carried out and the results obtained are summarized as follows: 1. There was a clear recovery of ductility in terms of total elongation and reduction of area owing to ageing. 2. Change in yield stress or 0.2% proof stress was shown to be considerably large in some cases. This phenomenon seemed to be more complex in comparison with that of ductility because the change in yield stress was much dependent on preparation of tensile specimens; yield stress was lowered as the result of ageing in the test pieces with the full thickness or diameter of hot rolled products, and in the test pieces machined out from the center of the products, yield stress was increased, and the smaller the test pieces was, the more increase the yield stress was. 3. Although the ageing phenomena may not be directly related to hydrogen in the steel, the hydrogen contents of specimens were analysed on various locations in the fractured test pieces. When ageing was in progress, hydrogen was extremely enriched in the region near the fractured part of the specimen, and when hydrogen level was naturally decreased to some extent after the completion of the ageing, and the enrichment of hydrogen near the fractured edge also became very slight. 4. The loss of ductility is thought to be caused by an extreme enrichment of hydrogen to the stressed region and not primarily dependent on the whole concentration of hydrogen. The recovery of ductility due to ageing could also be explained in terms of hydrogen contents. But, because of different ageing behaviour, the change in yield stress during aging was not attributable to hydrogen behaviour.
It is known that 12% Cr heat resisting steel is one of the most economical heat resisting steels. It is, how-ever, inferior to austenitic heat resisting steels in the creep rupture strength above 600°C. So, the effects of Mo and W were investigated in order to improve the creep rupture strength of 12% Cr heat resisting steel containing V, Nb, and B. (1) The creep rupture strength of 12% Cr heat resisting steel is increased by the additions of Mo and W. Additions of Mo and W result in solid solution strengthening as well as precipitation hardening. (2) In the case of a single addition, optimum amount of Mo is about 1.5% and that of W is about 3.0%. Whereas in the case of a combined addition, optimum amounts of M and W are both about 1.0%. (3) It is observed in an electron microscope that coalescence of precipitated carbide perticle are retarded by the additions of Mo and W to the steel.
In order to improve the roll material and to prevent the breaking of the slabbing and heavy rougher mill rolls, the thermal fatigue test, rotating bending fatigue test, impact test, and tensile test were carried out for the conventional roll materials. The main results are as follows. (I) Nickel-chromium cast steel (SNI) is superior to chromium cast steel (SCR) and ductile cast iron (DC) in the properties of toughness, thermal fatigue strength and fatigue notch sensitivity. It is appropriate to use the SNI steel as a roll material to prevent the breaking of the roll. (2) The fatigue notch factors of the roll materials are smaller than 1.5
An indirect determination of F by atomic absorption spectrophotometry was studied. F was precipitated as CaF2, and Ca in CaF2 which was separated by filtering was determined by atomic absorption analysis. The results are as follows: (1) The addition of excess CaCl2 as a reagent for precipitation decreased the solubility of CaF2 in the solution. (2) The solution was boiled for formation of CaF2, and CeCl3 was added to the solution, after cooling to room temperature F-dissolved in the solution was precipitated as CeF3. (3) When absorbance of Ca2+was measured after HClO4 dryness of CaF2, and CeF3, the presence of Ce3+in CeF3 increased absorbance of Ca2+. (4) The amount of F, when 20 mg or over, recovered by both Ca2+ and Cf3+ was about 96.5% actually, and the amount of F obtained from the absorbance of Ca2+, which was increased by Ce3+, was indicated twice as much as F (about 1.5%) recovered by Ce3+, but the amount of F recovered as CaF2 was about 95%, and as CeF3 was about 1.5%. These values were nearly constant so that the effect of the increase of the absorbance was used in that condition for increase of value of F, and F could be determined as the recovery of about 98%. (5) The method was successfully applied to the determination of F in the coating of the low hydrogen type of electrode, fluorides of alkaline earth metals, and cryolite.
The stress-wave emission (SWE) in several alloy steels which are frequently used as structural materials si observed during tensile testing. As to steels SB42, A387-C, and A515, a great amount of SWE is detected in the stage of initial yielding of every specimen annealed even at comparative low temperatures. This experimental result suggests the usefulness of the SWE technique for nondestructive testing and safety monitoring of structures. On the other hand, in case of stainless steel SUS 27 that is solution-treated, little SWE is recorded compared with the alloys above mentioned.
Corrosion resistance of various ferrous materials has been examined in a geothermal power station. Tests mere conducted in the atmosphere, cooling water, hot water and, in a test loop simulating the steam well. Increase amount of chromium is beneficial in hot water and under steam well conditions, giving little corrosion and/or erosion occur above 13%Cr. Weathering and other low alloy steels give better corrosion resistance in the atmosphere, whereas their use is of little advantage in the cooling water.