A series of tests on the measurement of the gas transit time and the distribution of the gas in operation of a 1, 000 ton blast furnace were carried out using radioactive tracer at Hirohata Works of the Fuji Iron and Steel Co. As soon as the radon contained in a gold tube was detonated into the furnace by the electrical burster container fitted up one tuyere latch of the furnace, a series of gas samples were caught at 0.7 second intervals by the gas sampler installed at the top of the furnace. The gas samples were transfered first into the flasks and subsequently analyzed for their radio-active content by the pulsed-ionization chamber method.
The samples were simultaneously withdrawn through four steel tubes inserted above the stockline at a center and three different positions near the furnace wall.
Some preliminary tests in 1955 and a series of forty experiments from August to October in 1956, were performed successfully, and the furnace conditions were taken into consideration in relation to their results.
Some results obtained from these tests are as follows.
(1) By using the pulsed ionization chamber method gas radioactivity was detected much more precisely than by the Geiger-Müller counter method. The radon as much as 0.6m.C. is sufficient to analyze the gas radioactivity, and under the favorable conditions it is counted beyoud 1, 000cpm.
(2) The transit time of the gas determined from a series of thirty experiments is shown in Table 4, the average and the 95% confidence limit obtained by statical analysis as to the center of the furnace and the vertical point of the inwall above the tuyere through which the radon is projected. It is observed that the transit time of the gas is faster in the center of the furnace than near the furnace wall by these results; 3-5 seconds to reach the maximum radio-activity at the center against over 5-6 seconds at the inwall, and the transit time varies more at the center than at the inwall, and the gas flow is influenced by pig tapping or slag tapping.
(3) As shown in Fig. 5, experimental results seem to be assorted into four types on therelative curves between the gas radioactivity and the transit time. It will be recognized that these figures and the furnace conditions are substantially related, that is to say, when the furnace condition is stable the figure is often found out as A type, and under instable condition as C or D.

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In the 2nd Report, the effect of gravity on the vertical segregation proceeding in the melt of solidifying core of ingots has been indicated from a new standpoint.
To know this phenomenon more explicitly, four ingots weighing 4.9 tons with round section were cast in sand moulds (Fig. 1), and the moulds were held either vertically or inclinedly, otherwise alternately inclined and re-erected, during solidification.
Investigations on these ingots (Fig. 3-8) revealed the following facts:
1) The V-segregates are formed even in the zone of negative segregation, confirming some of the previous views.
2) The "germs" of V-segregates are already formed in the solidifying melt, which are fixed as V-segregates when the solid-liquid interface passes them. At some stage of solidifi-cation, they can move independently of the growing crystals.
3) When a solidifying ingot is inclined (22-25°C in this experiment), the germs of V-segre-gates in the melt move towards the direction of the new perpendicular. While, when the ingot is solidified inclinedly from right after the pour, the V-segregates disappear within the half of lower level of gravity.
These show that the effect of gravity on the formation of V-segregates is very conspicuous and delicate.
4) The effect of inclination is also notable for inverse V-segregates.
5) Convection in the solidifying melt seems to be negligible.

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A study on the origin of non-metallic inclusions was carried out by the use of radio-isotope tracers. The radio-isotope ⁴⁵Ca or ⁹⁵Zr was impregnated in the pouring refractories which were the fertile source of inclusions. Mild steel was melted and refined in a 150KVA. Héroult furnace, tapped into the tagged ladle, and an ingot of about 90kg was obtained. Non-metallic inclusions extracted from the ingot, ingot scum, slag and all other radio-active products were collected, weighed and counted.
Thus, the behaviors of the eroded refractory materials carried along by the pouring stream were quantitatively traced with the following results:
When nozzles, stoppers and fireclay mortar were tagged (pouring temperature: 1550°C) 70.071g of the tagged parts was eroded, 6.04% of which was once transported into the ingot case. 52.3% of the transported refractories was floated as the ingot scum, and the rest (47.7%) was retained in the ingot as non-metallic inclusions. The ratio of the non-metallic inclusions of the tagged refractory origin to the total inclusions in the ingot was 2.86%.
In the case when all the refractories of the ladle were tagged (pouring temperature: 1550 °C), inclusions of refractory origin amounted to 8.74% of the total content of inclusions.
The behaviors of the eroded refractory materials were found to depend largely on pouring conditions. For instance, when pouring temperature increased, the erosion became stronger, but a larger amount of the eroded materials was floated as ingot scum than in the case of lower pouring temperature, and a cleaner ingot was obtained.

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The origin of sand marks is caused by the ingot defects, and those defects are not changed macroscopically by the heat treatment, but will be deformed by forging or rolling.
Generally, the origin of sand marks is considered as ingot defects, such as non-metallic inclusions, blow holes, pin holes, cavities and segregations. But the sand marks of the steel rod appear more or less (mostly) in all the steel rod and its surface anywhere, therefore. the origin of sand marks must be the defects that appear very frequently in ingots.
(A) Blow holes, pin holes and cavities
(a) By experimental results, generally, those defects (blow holes, pin holes) appear rarely in ingots.
(b) Many cavities appear in the center of long and small diameter ingots, but those cavities are welded by rolling. Therefore, it is considered that, when cavities, blow holes and pin holes in ingots have not oxides in the inside, they are welded by rolling or forging and do not appear as flaws (such as the sand marks) of steel rods.
(c) If the small blow holes of H₂ are the origin of sand marks, the sand marks are to appear with more uniformity than they are.
(d) Surface blow holes, and pin holes of ingots, cut by about 4-5mm inside from the periphery, are seldom.
Therefore, the origin of sand marks is not caused by blow holes, pin holes and cavities of ingots.
(B) Segregations:
The segregation sand mark is very rare, and it has origin only in high-C steel such as bearing steel.
(C) Non-metallic inclusions
(a) Non-metallic inclusions appear very often and every where in ingots.
(b) Non-metallic inclusions are deformed and elongated by rolling or forging.
(c) In parallel to increase of the forging ratio, non-metallic inclusions are elongated,

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In order to obtain a fundamental information on an applicability of hot-bath quenching below Ms temperature to an improvement of properties of a 1.0% C-1.0% Cr-1.4% W tool steel, its isothermal transformation and structural constituents after hot bath quenching were investigated by means of microscopic observation, dilatometric and magnetic analysis, as well as hardness test.
The main results obtained are summarized as follows: In hot-bath quenching below the Ms (162°C), there take place, at earlier stage, athermal and isothermal austenite-martensite reactions, and then, at later stage, austenite-lower bainite reaction, which promotes the stabilization of austenite markedly in a similar way as an isothermal reaction in austempering at above the Ms; thus, a mixed structure of tempered martensite and lower bainite containing a lot of retained austenite is obtained by a quenching under certain conditions.

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Following the 17th. report (Tetsu to Hagane Vol. 42 (1956), No. 6 p. 37), the rapid softening method by water .and air annealing of high speed steels (SKH 8 & SKH 6) was studied by micrography and hardness test.
The results obtained were summarized as follows:
The hardness of the quenched high speed steel that had been annealed in water or air from 800°C (just below the transformation point) was nearly equal to such hardness at which was possible to be machined, although it was less softened as compared with the hardness obtained by full annealing furnace.

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In the report (1), the methods for determination of the total Fe, TiO₂ and FeO in sand iron and ilmenite were developed. In this roport, a simple spectrophotometric methods is described for the determination of SiO₂, Al₂O₃, V₂O₅ and Cr₂O₃ which are contained in sand iron and ilmenite. SiO₂ is determined by the molybdenum blue reaction. Al₂O₃ is determined by the oxinate extraction method. V₂O₅ is determined by the H₂SO₄ method. Cr₂O₃ is determined by the diphenylcarbazide method.

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