Studies with two-and three-dimensional models made clear the followings concerning fundamental features of the flow and the flow in lower furnaces:- (1) The flow turning angle, corner, projection or hollow spot behaves as if it 'knows where it is going1)'. In the dead spots of the flow secondary vortices appear. (2) A main flow in the slag pocket passes curving in the upper space of it and threedimensional vortices occupy the space under the main flow. The curving flow and vortices separate dusts. (3) The fantail does not play the role of flow equalizer. It is better to decline the fantail roof toward the checker chamber in order to distribute outgoing flow uniformly to the checker and to send unbiased incoming air to the air-uptakes. (4) The flow into the checker chamber inclines to pass through the farther side of the chamber. This inclination is rectified effectively by deflectors as shown in Fig. 10 (c), (d). Double path checker chambers answer the purpose also.
(1) The relation between the cooling conditions of ingot bottom and the flow-up speed of macroscopic inclusions were researched. Here the experimentally designed 500kg ingot molds whose bottoms were lined with refractories were compared with the normal molds by investigation of experimental ingots or forged billets. Al additions in the ladle were 200-500g/t. The results obtained were as follows. (i) The streak seams were far less found in the bottoms of the ingots which were made with the special molds using refractories at their bottoms than in those with normal molds. (ii) When Al additions in the ladle were 210g/t, Fe-Mn-Al silicate-seams with high Al2O3-content were found in the sample-ingots, but the seams of Al2O3-type increased by addition of 500g/t Al. These silicate-seams presumably had been molten in the mold because of the appearance of almost perfect sphere, while Al2O3-seams (cubic crystals) had been at solid state in the molten steel. (iii) The relations between the crystal structure of ingot and the seams-distribution were not clearly recognized. (iv) A small secondary pipe was found in the ingot bottom which was made by the special mold. (2) The relations between the crystal structure of ingots and the seams-distribution in 5 ton practical ingot (top-poured) were investigated. (i) The seams almost never occurred in the columnar crystals. (ii) The seams were found at random within the end of columnar crystals at the ingotbottom. These inclinations of seams-distribution presumably were as much influenced by other causes as by crystal structure. (iii) The group seams which were very rarely found in the ring ghost were recogniged to have been influenced by segregation at the solidification of the ingot.
The work rolls for cold rolling mills are usually forged from high-carbon-chromium steel, spheroidized, machined and finally heat treated to secure favorable rolling properties. The electron microscopic structure at the surface layer of heat-treated roll consists of spheroidized carbides, martensite matrix and some amount of retained austenite. If considerable amount of austenite are retained and spherical carbides are few, the working character of the roll is insufficient. To obtain properly spheroidized structure after forging, several experiments by small specimens were pursued. The results show that the most effective annealing methods are likely to be the types in which phase transformation are applied. The cooling rate after holding at 780°C is quite important. The slower cooling rate produces the better carbide distributions. By repeated heatings and coolings between 700°C and 780°C, the carbides grow larger and pearlite lamellae develops remarkably.
Hydrogen in steel is a harmful element which causes hydrogen-embrittlement phenomena; i.e. white spots, hair-line cracks and pickling embrittlement etc. Therefore many investigations as to behaviors of hydrogen in steel were previously reported. However even at present, there are many unsolved problems. Accordingly an experiment on some hypo-eutectoid carbon steels including pure iron and eutectoid steel was made. The authors measured amounts of evolved hydrogen, changes of internal friction as a structure-sensitive quantity and mechanical properties as a measure of actual embrittlement during the evolution (at room temperature) of electrically charged hydrogen, and then investigated the relationships among them. The results obtained on these steels are summarized as follows. Microscopically speaking, diffusible hydrogen (at room temperature) was much absorbed in free ferrite than ferrite in pearlite, but macroscopically existed in uniform distribution of concentration. This hydrogen evolved with the diffusion process described with the Fick's formula, and the diffusion constant was calculated to be D=3.7×10-5 cm2/mn. (at room temperature). On the other hand decrease of the elongation and reduction of area in tensile testing, decrease of the impact value, and increase of the internal friction were caused by absorbed hydrogen, but each change took its own form of recovery by aging; i.e. though the recovery of ductility in tensile testing was parallel to hydrogen evolution, the one of internal friction was more rapid than the former and the one of impact value was far more rapid.
Special kinds of carbides like the big carbide which is the product of eutectic reaction, the net carbide which is precipitated at Acm transformation and the plate carbide which is precipitated at A1 transformation, have the tendency to make cracks easily than matrixferrite or martensite These cracks in carbides made the rupture strength of steel decreased considerably. Net or massive carbides which are precipitated at Acm transformation in 1.4% C file steel show different kinds of cracks depending on different kinds of stresses-compressive or tensile. When compressive stress was forced to the sample, unusual cracks such as "burst of carbide" were observed.
To investigate the influence of Mo and V additions on the properties of Si-Cr-W shockresisting steel containing 0.55% carbon, 1.4% chromium and 2.1% tungsten, the authors measured the transformation point, quenching and tempering hardness, hardenability, rate of deformation, mechanical properties at elevated temperature and microstructures. From the results of these experiments, the authors ascertained that through the Mo and V additions to the Si-Cr-W shock-resisting steel, its properties were improved remarkably.
(1) To establish the production technique of the large forgings of the super-high grade heatresisting steel LCN-155 and its weldings, the authors studied, experimentally on manufacturing the large composite wheel, of which rim is made of LCN-155, outer dia. 600×inner dia. 300×thickness 60mm, and of which the boss is made of Car-Mo steel. (2) After several tests with small capacity furnace, they melted LCN-155 by a 2-ton high frequency induction furnace, especially investigating raw materials and melting conditions, and casted the octagonal 350kg ingots. (3) After enough diffusion annealing of these ingots, they forged and swaged them cautiously, checking the temperature and the methods of forging, but the cracks were found at the end surface while swaging φ8"×length 540mm→φ270×length 330mm by 2, 000 ton hydraulic press. According to the results of macro-and micro-structure examinations, these cracks were considered to be caused by "inner wrinkles" due to the enomous segregations of the impurities, carbides and others. (4) Referring to the previous test, they melted LCN-155 again by 2 ton induction furnace, swaged, core-punched, ring-forged and at last succeeded to make up the rim without any cracks. (5) Before welding, they solutiontreated the rim at 1, 200°C and annealed the boss. After welding they heated the wheel at 800°C×24h followed by furnace cool, which represented both of stress-relief and aging of the rim. (6) Because they could not obtain the welding rods of AISI 309 Cb in both of domestic and abroad markets at that time (1953-4), they made trial manufacture of the coiled φ1.6mm wires for sigma welding from melting to wire-drawing. (7) For the grooves which were designed by many preliminary welding results, they performed the sigma welding semi-auto-matically; but, for the reason that the size and the quality of rod were not sufficiently uniform, welding was often stopped. In the result the deposits were unsatisfactory and ununiform. Therefore, they used AISI 310 rods of Lindé Co. for welding the opposite side. (8) It was very difficult to cut this welded wheel. The welding of the deposits was observed to be not good by the macro-structure test for the longitudinal section of the wheel. (9) For these super-high grade heat-resisting steels, it was better to be welded by the similar meta1 rods, so they prepared the rim and boss of same dimension and LCN-155 φ5mm welding rods, and welded by the argon-arc tungsten method, checking the welding procedure in detail. (10) By macro-and micro-structure tests for the longitudinal section, it was observed that the deposits were well welded. Consulting with the high temperature mechanical test results, they confirmed that the mechanical strength of the rim, which was exposed at high temperature, corresponded well to that of boss which was rather kept at lower temperature. However, without checking by the spin test, they cannot mention at present about the influences of the low elongation, contraction and impact values when the test pieces break at the deposits. (11) By these studies the authors could complete the large composite wheel as aimed at the first time, of which rim became superior in the material quality through core-punched and ring-forged, and could resist up to about 750-800°C Also they could save 1/3-1/4 quantity of the expensive heat-resisting steel in the composite wheelas compared with the solid wheel.