Many experiments of bench scale previously reported that hematite in sinter plays a vital role for the degradation of sinter during reduction at low temperatures. In order to elucidate this phenomenon in actual blast furnace, flue dust from blast furnace and sinter charged were compared, using the samples taken from Nagoya No 1 blast furnace which is operated with high sinter ratio of 85% in burden. The coke in the flue dust is removed with heavy media separation before undergoing to tests. The results of chemical analyses and mineral composition determination with X-Ray diffraction method showed that the hematite tends to concentrate into flue dust. The flue dust particles are classified into 6 categories according to the crystal structure of hematite, with the point counting method under microscope. The results showed that the flue dust contains a lot of paticles bearing the hematite, i. e., particles bearing rhombohedral crystals of the hematite, and the magnetite crystals with the hematite lamellae. From the above test results, it is considered that the degradation of self-fluxing sinter in the blast furnace would be influenced by the hematite, especially rhombohedral and lamellae hematites, in sinter.
The longitudinal distributions of the temperature and composition of gas in the blast furnace stack have been investigated by the use of vertical probes. The chemical reactions in the stack under 1200°C are divided into three main reactions (1) solution loss reaction (2) lime stone decomposition (3) indirect reduction of ores. Each reaction was characterized and defined by its temperature and gas composition variation for unit height as follow. R (reaction rate) =ΔX%(gas composition)/Z (height) The rate constant of these reaction was obtained as follows. k (rate constant) =R/(X%-X*%) X*%: gas composition at equilibrium condition of same temperature The three main reactions in the stack could be separated by obtaining these rate constants. The temperature of thermal reserve zone was about 700°∼800° and depended upon operational conditions. The pressure drop of gas in the stack was also measured.
Eleven kinds of the contacting methods between slag and metal to eliminate the impurity were theoretically analysed from a standpoint of kinetics. Theoretical solutions with regards to the impurity concentration in metallic phase with each operations were derived and impurity-elimination performances were compared with each others. For the multi-staged contacting, optimum policies on the duration of the operation, flow rate to the reactor and/or hold-up in the reactor of slags and metals were given by application of Lagrange's multiplier method and of Pontryagin's maximum principle.
The thermal stresses in the ingot moulds were determined based on thermo-elasticity with a aid of digital computor. The unsteady temperature distribution was first established on the nodal points of mesh screens representing the cross section of the moulds. The the rmal stresses, strains and displacements were then calculated by the finite element method, where the imaginary division of the mould as an elastic continuum into a finite number of elements is a common procedure and each of them satisfies the compatibility and eyquilibrium conditions. Because of various factors affecting the mould life, one should refrain from making a quick decision on the basis of stress analysis only, but this method of calculation is useful and promising though concrete results is incomplete without the direct measurements of stresses at present stage. The magnitude of stresses Were found to be big enough for crazing and initial cracking of mould. Comparisons of stresses were made with respect to varying wall thickness and their size.
Strengthening mechanism of ausforming were investigated for some alloy steels. Thin foils taken from ausformed alloy steels showed that special carbides could be directly formed at subboundaries in the deformed austenite. Carbon extraction replica also showed that carbides distributed along cell boundaries in ausformed martensite after tempering, while in directly transformed one carbides were extracted along lath boundaries. Furthermore, by means of direct observation, both austenite and - martensite subjected to ausforming were revealed to have a cell structures. From the above results, it was suggested that the structure having a number of cells which had been developed in austenite during ausforming was introduced to martensite through the transformation. In such an inheritance, carbide precipitates on the dislocation network should have an important role. It will be discussed that the cellular structure is responsible to the strengthening by ausforming.
The effect of Ti addition on the hardenability and strength of Mo steel was studied. The results are as follows; (1)Mo-Ti steel shows nearly the same hardenability as the Mo steel of the sarn Mo content, but the tempered hardness of Mo-Ti steel is higher than that of Mo steel. This means that Ti addition is effective in delaying softening of Mo steel. (2)Mo steel shows nearly constant tempered strength independent of the quenching temperature, but the tempered strength of Mo-Ti steel incresses with increasing quenching temperature. (3)The increase of the strength of Mo-Ti steel owing to the increase of quenching temperature from 900°C to 1250°C depends on the Ti content, whereas the increase of the strength between 900°C and 1000°C is independent on Ti content. From these results, it can be clarified that about 50% of total Ticontent is effective in increasing strength. (4)The strength of Mo-Ti steel shows, as mentioned above, a strong dependence on quenching temperature and has a particular correspondence to the residue analysis. These facts suggest that the delayed softening of Mo-Ti steel can be ascribed to the small amount of Ti soluble at temperatures lower than 1000°C.
The 13% Mn steel are widely used for abrasion resisting materials. The effects of various alloying elements have ben examined with regard to increusing the mass and the operating life of the material. In the present investigation four types of commercial steels were chosen and the effects of C, Mn and Cr in 13% Mn, of Mo in 13% Mn-%Cr, of C, V and Ti in 12%Mn-2%Mo, and of Mn and Mo in 7%Mn-2%Cr on the isothermal transformation characteristics and thein influence on impact properties were examined. The results are summarized as follows: 1) The increase of C accelerates the formation of carbide and other transformation products, and in the excess of 1.2%C acicular carbide forms. Impact values are much reduced by this acicular carbide and pearlitic constituent, but less reduced by grain boundary carbide. 2) Decreasing Mn content below 10% promotes the formation of perlitic constituent, which causes the loss of impact values, but in the range of 10-15% Mn hardly affects the properties. 3) The addition of 2% Cr accelerates the precipitation of grain boundary carbide, but decelerates the precipitation of grain boundary carbide, but decelerates the formation of pearlitic constituent. Thus Cr is effective in minimizing the loss of impact values due to grain boundary carbide. 4) Within 1%, Mo decelerates the formation of pearlitic constituent. Therefore Mo. when added together with Cr, is effective in improving the toughness of heavy section parts. 5) The addition of 0.1%V and 0.2%Ti slightly decelerates the formations of carbide and pearlitic constituent.
A study was made of the effect of alloying elements, carbon, nitrogen, copper, molybdenum and niobium on the properties of precipitation hardenable stainless steels. The results obtained were as follows. 1. The carbon content, the austenite forming element, is required to be lowered. In the case of high carbon content, carbide stabilizing element niobium is necessary to be added a least about five times as much as the carbon content, because carbon stabilizes austenite and lowers Ms temperature to near room temperature. 2. The nitrogen content is also required to be lowered, because this elements has the same behavior as that of carbon. 3. The higher content of copper is desirable, because the element has the remarkable effect on secondary hardening by precipitating e phase. Above 3% of copper, however, lower the Ms temperature remarkably and give harmful influence on the forgeability. 4. Ferrite forming element molybdenum lowers Ms temperature and a large amount of molybdenum added decreases tensile strength of the steel. The higher content of molybdenum is desirable to improve the corrosion resistance, but the efficient value is found to be about 1%, because the improvement effect by molydenum addition becomes gradual above this content. 5. Nb is required as the carbide stabilizer. In the case of niobium-free steel, austenite becomes so stable that it does not transform to martensite by single aging treatment only. In addition, the corrosion resistance of this steel is lowered owing to the precipitation of chromium carbide. Nb is necessary to be contained about five times as much as carbon content. 6. Aluminium addition with molybdenum and copper is beneficial to the improvement of the corrosion resistance of the steel.
Determination of hydrogen in steel by vacuum-fusion method is mostly desirable, because it becomes possible to determine simultaneously the gases in steel, but the results obtained by above technique tend to introduce lower values than those by conventional vacuum-heat method. To investigate the sources of this difference this study was preformed in connection with physical and chemical properties of cabon-saturated melt contributed to hydrogen behavior and the following results were obtained. 1. Graphite precipitated from the melt affects the determined value in the sense that the greater the flaky form precipitate of graphite grows the greater the amount of hydrogen absorption is. 2. The loss of extracted hydrogen occurs slightly with the use of large size of graphite crucible. 3. Hydrogen absorption introduced by evaporated metal film is recognized for high alloying samples, but it does not result in a main cause of analytical error.It is, therefore, summarized that hydrogen determination by vacuum-fusion method is to be carried out by empty graphite crucible having small space with simultaneous additicn of spheroidal graphiteforming element.
Fundamental study on isolation and determination of oxide inclusions in steels was carried out by means of nitric acid, iodine-alcohol, bromine-ester and chlorination methods. The results are as follows. 1. In the halogen-organic solution method, the oxide inclusions are isolated and determined by decomposing the plate-like specimen with iodine-alcohol or bromine-ester solution at their boiling points without considering the existence of sulphides and M3C type carbides. This method is applicable to semi-killed and killed carbon steels. In bromine-ester method, decomposition of specimen is easier and faster than in the iodine-alcohol method, and sulphides in steel are decomposed perfectly. 2. In the chlorination method, the stable oxide inclusions are isolated and determined by such procedure that the plate-like specimen is decomposed directly with chlorine at 500°C and the vaporizable chlorides are separated from the residue by heating at about 900°C in vacuo. By use of the apparatus dsiegned for this experiment, five specimens are able to chlorinate at the same time, and so the efficiency of operation is very improved. This method is applicable to semi-killed, killed carbon steels and low alloy steel, and it's precision is comparatively high because of complete decomposition of sulphides, carbides and nitrides. On the other side, there is a fault that the oxide inclusions consisting of lower valency cation tend to decompose disproportionally in the isolation process. 3. Nitric acid method is the most simple and convenient, and can be applied to killed carbon steel and low alloy steel containing aluminum. Further, the behavior of non-metallic inclusions in various isolation processes are examined by opticalmicrography, electromicrography, X-ray and electron diffractions.