To clarify the effect of aluminum upon the austenite grain size of plain carbon steel, the behaviors of its nitride, oxide and sulfide were investigated as follows:
(1) Under the special conditions, such as in vacuum, or in nitrogen and oxidizing atmospheres, various amounts of aluminum or sulfur were added to a high carbon steel melted with a 35KVA induction furnace.
(2) To high and low carbon steel, melted with a 250kg test furnace, various amounts of aluminum were added in the ladle. Silicon was added in the furnace or in the ladle; or not at all. To some low-carbon heats various amounts of sulfur were added in the ladle.
(3) Amounts of aluminum were varied to some extent when they were added in the ladle to many heats of low-carbon fine-grain steel, melted with a 60ton basic open hearth and high carbon coarse grain steel, melted with a 100ton basic open hearth furnace.
Austenite grain size of these steels was determined by the carburizing method. The relation between austenite grain size and various components of these steels, including nonmetallic inclusions, was studied.
The main results were as follows:
(1) AlN was the most dominant factor in retarding the growth of austenite grains by addition of aluminum.
(2) Al₂O₃ reduced the effect of AlN in fine-grain steel.
(3) In a coarse grain steel containing a little aluminum, oxides, such as Al₂O₃, or sulfides also retarded the growth of austenite grain to some extent.
(4) Duplex grain was necessarily formed at the transition state of grain growth while it was also caused by segregation of Al₂O₃.
(5) Furnace deoxidation (blocking) in the basic open hearth furnace would be valuable to attain to the stability of grain size control.

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Among the several theories on the cause of flaking in steel, the hydrogen theory is most plausible. The theory is acknowledged to be more conclusive if co-working stresses of various kinds are taken into account, but the relation between both factors has been left rather unnoticed.
The authors found, as formerly reported in this Journal, (Tetsu-to-Hagane, No. 5, 1953 p. 524-531) that the evolution of hydrogen from steel specimen was accelerated by stress.
This report was the first step of the fundamental studies on this finding, the outline of method and results of which were stated as folllows:
1. Experimental method:
From a 0.4% C basic steel forging with 180mm dia., at sufficient distance from ends, two adjacent disks of thickness 21mm were removed; then machined and lightly polished to 20mm along the adjoining surfaces of both slices. Next a sheet of cellophane was attached to each finished surface by means of small quantity of oil.
While the specimen thus arranged was left in room temperature, the evolving hydrogen was captured between the cellophane and surface in the form of dispersed bubbles, the total area of which showed the rate of evolution. Under the action of stress the area increased, thus indicating the accelerated evolution of hydrogen in a qualitative way.
The effect of stress was known by comparison between the two specimens, one of which was a given stress.
2. Results:
When the specimens were subjected to stresses under 12kg/mm², tensile or compressive, the promoted evolution of hydrogen by stress was the more marked, if
1) The sharper was the concentration gradient of hydrogen near specimen surface.
2) And the larger was the magnitude of stress.

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In order to harden, without quenching cracks, the small but complex shaped forgings of high carbon-chromium steels containing about 1% C and 0.1-0.4% Cr, the authors studied on the fundamental conditions about the martempering treatment.
The results obtained were as follows:
1) As for the cooling abilities of quenching media, the so-called "severity of quench" H was determined. H of the Pb-Cd-Sn metal bath and the NaNO₃-KNO₃-NaNO₂ salt bath were 0.95 and 0.5-0.7 respectively. But H of the latter was apt to decrease during the use.
2) At the martempering treatment of the steel bars of 1″ diameter which had the larger hardenability than that of 0.4% Cr steel, the state of hardening was not influenced by the heating temperature between 830 and 880°C.
3) Under the above conditions, the state of hardening of martempering treatment was the same as that of quenching in water, so far as the holding time above the Ms point was shorter than the transformation-beginning period.
4) The authors measured the residual stress at the various heat treatment. The result of the air-cooling after martempering was the best, the oil-quenching the next and watercooling after martempering and the water-quenching the nearly same.
The residual stress became maximum when the isothermal treatment was held till the transformation began.

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The precipitation phenomena of Timken 16-25-6, heat resisting alloy for gas turbine materials, were already reported in author's paper (Tetsu-to-Hagane, August 1954 p. 785).
In this report, micro-hardness at a point in the middle of the grain, near the boundary and on the boundary, were determined for the purpose of studying the precipitation phenomena. Samples used in this report were the same as those used in the report (V) in this issue. There were three different chemical compositions among the samples. They were solution-treated at 1150°C (2100°F) for 1 hour, and aged at 700°C (1290°F), 800°C (1470°F), and 900°C (1650°F). The aged sample at each temperature for each time was tested by micro-Vickers hardness and observed through microstructure.
Results were as follows:
(1) In the case of micro-hardness testing, it is usually said that the micro-hardness at the middle of the grain is observed to be lower than the hardness at a point near the grain boundary, because of the metal flow which is caused by the diamond cone. However. according to the author's tests, this must be more complex, in accordance with crystallography. Because, the samples which were aged and precipitated excessively showed that the micro-hardness at points near the grain boundary, on the grain boundary, and in the middle of the grain had similar hardness, although there were different hardness at points in the middle of the grain, on the grain boundary, and near grain boundary at the stage immediately after solution treatment.
(2) Besides, the difference of micro-hardness between points in the middle of the grain and points near the grain boundary was found very often during precipitation process. So, the statistical significance tests were made between them, and most of them showed that the bypothesis was true at level of significance 1%.
(3) Sometimes, the different micro-hardness was recognized in one sample, when a different micro-structure, especially a different degree of precipitation, was also found.
(4) The relation between the micro-hardness and microstructure was considered. At early stage of the percipitation process, in general, the hardening at points on the middle of the grain was larger than the hardening at points near the grain boundary. At the next stage, when an intertmediate maximum of usual hardness was observed, the micro-hardness at points in the middle of the grain continued to harden in its own place, but the micro-hardness at points near the grain boundary showed an intermediate maximum hardness parallel to the usual hardness. According to this point of view, the phenomena of the intermediate maximum hardness are related with that which depends, on the micro-hardness at points near the grain boundary.
In this report, as described above, the information of precipitation phenomena of Timken 16-25-6 alloy made one step forward.

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Automatic control has increased its importance for rationalization of the iron and steel industry. This paper aims to give an approach to automatic control for engineers concerned in the industry.
The principal contents are as follows:
1) Basic concepts of automatic control,
2) Types of automatic controller action,
3) Fundamentals about how to synthesize automatic control systems,
4) Applications of automatic control to the iron and steel industry.
As for applications, open hearth furnaces and soaking pits are taken as examples, and the practice of temperature, pressure and fuel flow control is described.

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