Special silica bricks containing Cr2O3 8% have the property of higher resistance to iron oxide absorption than common silica bricks, retaining, however, the characteristics of silica bricks which have high-softening temperature, strong compressive strength, and high thermal expansion. The characteristics of these bricks are as follows; (1) Absorption of Fe2O3 in these bricks are nearly stoPPed only at the surface layer. (2) Decrease of refractoriness by the absorption of Fe2O3 in these bricks are smaller than comrnon silica bricks. The results of the practical test of these bricks are as follows; (1) Corrosion of these bricks is decreased 36-64% than high-Al2O3 chamotte bricks, when on lower part of the side walls of the up-take is used. (2) Corrosion of these bricks is decreased 59-70% than common silica bricks, when they are used on the walls of the slag-chamber, (3) Corrosion of these bricks is decreased 50% than common silica bricks, when they are used on the slag-chamber arch.
From the previous research (Tetsu-to-HaganHagané, vol. 44, No. 2, 1958, p 122) it was learned that nozzles tappered at the entrance and with a short parallel straight part at the outlet had good flowing characteristics when they were fully opened. In this research the characteristics of these specially designed nozzles at the small opening by a stopper and some other flowing properties of nozzles were studieb. The results obtained were as follows. (1) A nozzle tappered at the entrance and a short parallel linear part at the outlet had almost the same flow characteristics as a normal long nozzle, when the nozzle was a little opened by a stopper. (2) Violent turbulent flow caused by erosion or deformation of nozzles were seen in two cases, when the nozzle-diameter had been increased at the outlet by erosion, and when the nozzle-diameter had been decreasd at the entrance by deformation which was thought to occur sometimes from the shock of closing the stopper. (3) When the jet from the nozzle hit the liquid in the mold, the depth to which the jet penetrated the liquid was mainly affected by the nozzle diameter and slightly influenced by the head from the fluid surface to the inlet of the nozzle and by the distance from the outlet of the uozzle to the liquid surface in the mold. (4) Refractory-nozzles whose surface-friction was higher were thought to have slightly worse flowing propertis than glass-nozzles. The influence of the length of a refractory-nozzle upon the speed of the jet was smaller than that of a glass-nozzle, when the head from the inlet of a nozzle to the liquid-surface was the same.
The carbides isolated electrolytically from two kinds of high speed steels-18-4-1 and 11-4-2-were studied by chemical analysis and X-ray examination. The results obtained are as follows. (1) The carbides in the annealed structure of these high speed steels are composed of M6C, M23C6 and a little amount of MC, as reported by many investigators. (2) By austenitizing treatment, M23C6 completely dissolves into matrix, but most part of M6C remains as undissolved carbides. By the same treatment, MC in 18-4-1 steel is dissolved completely, but in the case of 11-4-2 steel, a part of it remaias. (3) The chemical composition of the matrix of these steels quenched from 1250°C are very similar as follows: (4) On tempering above 400°C, cementite appears first, and then W2C, MC and M7C3 transitionally precipitate, and finaly M6C and M23C6 are formed. (5) The tungsten concentration in precipitated carbides increases gradually with the rise of tempering temperature. But the vanadium concentration in precipitated carbides reaches to a maximum percentage, and then dicreases with the rise of tempering temperature: This may result from the fact that the rate of carbide formation of tungsten is slower than that of vanadium, and so the previously formed vanadium carbides are diluted by the later formed tungsten carbides.
The behavior of pure iron under impact tensile loading was studied with two kinds of pure irons and a commercial low carbon steel. One half of specimens were annealed in vacuum at 600, 700, 800, 850, 920 and 1000°C for 1 hour and the others were quenched in oil after keeping them at these temperatures for 1 hour in vacuum. At the impact tensile test, in which the specimen was loaded by the hammex, falling by gravity and weighing 25kg, the load acting on the specimen was measured by the use of piezoelectricity of quartz crystals and the cathode ray oscillograph. X-direciion of the oscillograph was fed by piezoelectricity, Y-axis corresponded to time axis There was no electronic circuit between quartz and a deflection plate of the oscillograph and the load-time curve was directly recorded on the film inside the oscillograph. The strain rates at the impact tests were approximately 20-1201/sec The results obtained in this investigation were as follows. (1) The peak appeared in the load-time curve under impact test seemed to be upper yield point. (2) Yield stress and tensile strength were larger and total elongation was smaller than those under static test. (3) Increasing the strain rate, both yield stress and tensile strength increased and total elongation decreased slightly. The rate of increase of yield stress was greater than that of teasile streagth. (4) The test specimens annealed at comparatively lower temperatures sucb as 600°C-700°C fractured in brittle manner even after the completion of recrystallization but this phenomenon was not observed under the statical test. It was supposed that thin phenomenon was due to the manner of distribution af cementite. Quenched specimens shawed mare ductile fracture.
Effect of N, Ni and C content on aging characteristics of the low Ni Timken 16 Cr-15 Ni-6 Mo (-7.5Mn) type alloys was studied by measurements of differential dilatation, hardness, and microstructure. The results were summerized as follows: (1) Maximum amount of N addition was limited at about 0.3%, above which sound specimens of the alloys couldaot be produced by melting and casting in air. (2) Two stages of contraction in differential dilatation due to the precipitation were observed at 500-600°C and above 800°C during tempering of the solntion-treated alloys irrespective of both the composition and the hot-cold working. It seems that the later contraction was due to the precipitation of nitrides and carbides, especially a large contraction being observed at above 750°C in the carbon containing alloys. (3) In all of the solution-treated (1200°C 1h, water-quenched) alloys, hot-cold worked ones, and subsequently aged ones at 700°C, the hardness, increased with increasing amount of nitrogen addition. Effect of Ni ranging from 13 to 17% on the aging characteristics was not significant, and addition of carbon up to 0.15% promoted the age-hardening but resulted in rapid softening in prolonged heating. (4) X-ray analysis of precipitants in very slowly cooled alloys showed only the formation of the sigma phase, no evidence of other precipitants being found out. Considering both the dilatometric behavior and the microscopic appearance, the rapid hardening in early period of the aging may be attributed to the precipitation of carbides, and the comparatively slow hardening may be due to both the precipitation of the sigma phase and nitrides.
Effects of Ti, Al and gas content on stress-rupture characteristics at 750°C and 26.8kg/mm2 were investigated. Stress-rupture life increased with an increase of Ti+Al atm% containing below 2.9% Tiand 1.44% Al. Elongation after stress-rupture was small and the effect of Ti and Al content on it was not clear. Stress-rupture life depends not only on the amount of Ti and Al but also on the amount of nitrogen and oxygen or hydrogen, which arises from the melting procedure and content of raw materials. As in the case of an iacrease of the amount of gas content causes the decrease of stress-rupture life remark ably, so the material vacuum-melted or the mterial which is air-melted after vacuum-melting have more stress-rupture life than the material air-melted from fresh raw material. As the fact that the increase of gas content causes much precipitate around grain boundary, and tends to soften the material during stress-rupture testing by overaging, so stress-rupture life decreases. Effect of micrtructure on stress-rupture life is presumably the same phenomena as heat treatments such as A and B to the effect of gas content.