A series of tests on the nature of self-fluxing sinter was carried out using a small sintering pan. In one case limestone was added to Larap ore (rich in magnetite) to make a basisity, CaO/SiO2 having a planned value at a constant coke ratio (ordinary basisity: 0·5, 0·9, 1·3; high basisity: 2, 3, 4). In another case coke rates in raw mixture were changed from 1·2 to 8·7 per cent by different limestone additions. Subsidiary tests, dealing with small firedcompacts of the same materials, were performed successfully to explain some of the effects of sintering temperature and atmosphere. The addition of limestone had a good effect on permeability in sintering, and decreased the time required considerably. A brief survey of the expected degree of remaining freelime, which was involved in hydration, was given. A considerable increase was found in the microstrength of sinter by the addition of limestone. The reducibility of sinter was decreased gradually as the lime was increased. The principal factor involved was an increase in the quantity of slag. Evidence was obtained which indicated some of the conditions necessary for sulphur evolution to occur in sintering. The results suggested that it should be possible to increase the desulphurization ratio to some extent. Also the microscopic study of sinter structure was widely carried out.
Following the foundamental exgeriment, which was reported previously, on a test method using a radioisotope for measuring wear of the blast furnace brickwork during its operation, 22 specimens containing Co60 were buried in the brickwork of Kamaishi No. 1 B. F. which was reconstructed from Aug. to Nov. 1958. The buried positions were 11 in 4 levels and two specimens which trisected the brickwork were buried on each position. Measurements were done once a week on the mantle of these positions with a portable scintillation counter. As the average radioactivity of Co60 buried was about 0·5mc., there was no problem about safety. The wearing state had been measured since Nov. 18, 1958, when the No. 1 B.F. was blown in, and on the bosh level the two buried specimens were dropped within only 4 weeks.
In order to study the behaviour of titanium-oxide in molten slags and to obtain some informations concerning the electric-smelting of titaniferous iron sand, the electrical conductivity of the CaO-SiO2-TiO2 system was measured in the temperature range 1470-1200°C. The one electrode and the crucible, which itself functioned as theother electrode, were made of platinum. The measured ranges of compositions were CaO/SiO2 0·67-1·22 at TiO2 19·5mol%, CaO/SiO2 0·70-1·28 at TiO2 30mol% and TiO2 24·6-46·0mol% at CaO/SiO2=1. The specific electrical conductivity was of the order of 0·1-1Ω-1cm-1, while the activation energy of conduction was 25-30kcal/g-mol. It was presumed that the conduction mechanism was ionic and the mobile ion was Ca2+. At a constant TiO2 concentration the specific electrical conductivity was increased with CaO/SiO2, but the conductivity (μ) equivalent to one grammole of CaO had a maximum at near CaO/Sio2 =1·1. At CaO/SiO2=1 the conductivity was increased with the increase of TiO2 content. This could be ascribed to the fact that Ti ion strogly weakend Si-O network owing to the coordination number of six and the comparatively strong Ti-O bond. It was in this respect that TiO2 had a behaviour different from that of Al203 or SiO2 whose coordination number was four and which was able to form network. Furthermore, it was presumed that if any small quantities of FeO and Ti203 were contained in the CaO-SiO2-TiO2 slag as in the practice of the titaniferous iron sand smelting, the electrical conductivity would be increased more sharply with the increase of the titaniumoxide content owing to the semi-conductive behaviour of titanium-Oxide. This fact had great significances in the practical operation of an electric smelting furnace.
The study of the load-change of a low-carbon killed steel containing 0·17%C under-the impact bending load was carried out in the transition temperature range from ductile to brittle fracture. At the test, a miniature Charpy impact testing machine, being of 2kg-m capacity, was used and the load acting on the specimen was measured by the use of piezoelectricity of quartz crystals and a cathode-ray oscillograph. In this apparatus there was no electric disturbance between the quartz and the oscillograph, and then the precise load-time curve was recorded on the film inside the oscillograph. The states of the specimens were: (i) cold-drawn state and the state normalized at 950°C. (ii) the states annealed at 700°, 800°, 920° and 1000°C respectively after cold drawing. (iii) the states quenched in water from 700°, 800° and 920°C respectively after normalizing at 950°C and (iv) the states aged atroom temperature (about 25°C), 50°C and 100°C for various durations after the quench from 700°C of normalized specimens. The results in this investigation were summarized as follows: (1) The load-time curves in the range from ductile to brittle fracture were classified into five types. (2) The definition of transition temperature, the temperature at which the crack appeared at first, was reasonable not only theoretically but also in practice. And it was concluded that this transition temperature was very sensitive to the heat-treated states of specimens. (3) A characteristic load-time curve was recorded in the test of cold-drawn specimen. This curve showed that the crack was propagated intermittently and then the specimen was fractured. (4) Specimen annealed at 700°C had a low transition temperature (-70°C), while that annealed at 800°C had much higher one (10°C). The transition temperature thereafter rose slightly with the annealing temperature. (5) Specimens quenched from higher temperatures (800° and 920°C) than the transformation point had not definite transition temperatures and showed much greater work-hardening than that of other specimens. (6) Among three kinds of quench-age-hardened specimens, the specimen aged at room temperature showed the most remarkable change in transition temperature. This change was parallel to the marked change in Vicker's hardness number. (7) In all tests, the rapid increase of maximum load with decrease of testing temperature was observed in transition temperature range, and then the load became smaller rapidly owing to the initiation and propagation of severe cracks.
The normal tensile specimen and V-notched tensile specimen (so-called Tipper specimen) were cut out from the steel plate and mechnical properties were measured by statical tensile tests at various temperatures. The results obtained were as follows: 1) The tensile strength of Tipper specimen at low temperature showed the same directionality with rolling direction as V-notched Charpy absorption energy did. It seems to the author that this tendency is one of the characters of brittle fracture. 2) While the elongation of each test piece showed the remarkable directionality in ally with rolling direction, the reduction of area of normal tensile specimens did not. That was, in normal tensile specimen, the plastic deformation which made the steel to be fractured in ductile manner seemed to be constant. 3) Directionality of elongation in Tipper specimen was the same as that of reduction of area. In other words, the plastic deformation that was necessary for brittle fracture of test pieces was mainly due to uniform elongation, not to local elongation. 4) The change of manner of fracture was explained by the modified Orowan-Ludwik curve and strain-hardening factor. 5) The energy of crack propergation was absorbed at the grain boundaries and the fine grain steel (air-cooled specimen) was more ductile than the coarse grain steel (furnace-cooled specimen). But at such high temperature as the cracked initiation resistance was high, directionality of grain size was not effective on the directionality of this resistance.
Creep-rupture tests up to about 10, 000h., were carried out with the type 321 stainless steel in the two solution-treated conditions (1050°C W. Q. and 1200°C W. Q.) at 600, 650 and 700 . Stresses and rupture times showed good straight-line relationship up to about 1000h., but beyond that point the line inclined downward. This tendency was more pronominent for 1050°C W. Q. specimens. Solution-treatment at 1200°C gave higher rupture strengths for the whole testing conditions. The difference of rupture strength between these two heat treatments was increased with higher temperature and longer time. The shapes of creep curves showed marked difference too. 1200°C W. Q. specimens were fractured suddenly without any large creep. On the contrary, 1050°C W. Q. specimens revealed relatively large creep from the early stage and fractured after large elongation. Microstructure of 1050°C W. Q. specimens fractured at about 2500h. or longer showed the prominent precipitation of σ-phase at grain boundries.
This paper deals with the influence of nitrogen content of 20% Cr-Fe alloys containing 0·04%N, 0·11%N, 0·23%N, 0·33%N, or 0·24%N plus 0·13%C on the austenite formation due to the nitrogen absorption of these alloys in one-atmospheric pure nitrogen. The austenite formation due to the nitrogen absorption and the thermal behavior of the formed austenite were clarified. The results obtained were as follows: (1) The depth of the single austenite zone formed at the surface of 20% Cr-Fe alloys by the nitrogen absorption during the heating for 4 hours in the pure nitrogen at 1250°C was 0·4-0·6mm, and the nitrogen content at the surface zone was 0·5-0·6%. The weight increase due to the nitrogen absorption was decreased gradually as the nitrogen content of the alloys was increased from 0·04% to 0·33%. When 0·13%C was added to 20% Cr-Fe alloy containing 0·24%N, the nitrogen absorption was promoted. (2) The single austenite zone at the surface was richer in carbon than the cabon conent in the inner zone consisting of a mixture of both austenite and ferrite, which was presumed to be caused by the diffusion of cabon from the inner zone into the outer surface consisting of single austenite phase during the nitrogen absorption. As regards to the carbon content in the single austenite zone, it was found in the alloy containing 0·24%N plus 0·13%C that the surface zone was likely to have fairly lower carbon level than that in the inner zone. (3) The austenite which was formed in the nitrogen bearing alloys by the nitrogen absorption at 1250°C was found to decompose in to ferrite and Cr2N during the furnace cooling. The change from ferrite to austenite on heating was found to occur at about 900°C-1050°C. (4) It was found that the austenite retained by quenching the single austenite zone formed by the nitrogen absorption was sensible to the subzero treatment considerably, and the stabilization of the retained austenite during the holding at room temperature after the quenching was not pronounced. (5) On the tempering at 600°C, such retained austenite became unstable, and decomposed rather rapidly by the tempering at 700°C or thereabouts.