The author studied on the relation between the positions of the blow-holes and the thicknesses of the ingot-moulds for the incompletely "Killed" steel ingots. And consequently it was deduced that a slightly good influence recognized by increasing the thickness of the ingot-mould. From this experiment, the author also explained the mechanism of the occurrence of the blow-holes, and that the important point of smelting of this steel is "the moderate deoxidation degree and the supercooling of the molten steel on the solidification"

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The diffusion act on of Nitrogen in Iron-Plates was investigated by means of microscopic and chemical analysis.
"Armco" Iron Plates, 30×40×3mm in size were taken as specimens.
Each specimen was heated in a stream of ammonia gas, free from atmosphere, to the temperatures, 670°, 760° and 600° Centigrade, and retained at these heats for periods ranging from one hour to fifty hours, and then cooled slowly in the furnace.
The microstructures of each specimen thus treated were then carefully studied, when the micrographs showed that the microstructure of these specimens nitritied at 670°C consisted of three phases-
1. the "outer η-phase"
2. the "eutectoid"
3. the "ferrite"
These separate layers are distinct in all specimens excepting in the cases of those treated for one hour and 25 hours.
The microstructures of the specimens nitrified at 760°C differ from the above in that the three phases mentioned above cannot be distinctly traced, the "eutectoid" structure having no distinct boundary, whilst the "iron-nitride", (corresponding to the ε-phase) is distributed in a net-work state along the boundary grain of the "ferrite".
It was also observed that the specimens treated at 600°C were different in structure to both the above cases. At this temperature almost one thin layer of the "iron-nitride" (corresponding to the η-phase or ε-phase) was formed, with needle crystals of the nitride near the surface layer.
The Nitrogen contents of each layer of the specimen were estimated by the distillation method, and the amount of Nitrogen in these specimens per unit volume were thus determined by calculation.
From these results it will be seen that the Nitrogen penetrates into the iron-plate in sine periodic form, producing various iron-nitrides which alternately form and decompose, as shown in Figs 2-4. These Figures represent graphically the relationship between the iron-nitride zone and the penetration period at each temperature, 670°, 760° and 600°C.
It was found that the same phenomenon exiats between the diffused mass of the Nitrogen in unit volume of the specimens and its time at a constand temperature as shown in Figs 5-7, and also that the change in Brinnel Hardness for all specimens above treated is almost proportional to the depth of iron-nitride zone formed at that temperature.

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