In this paper the author describes some of the effects of the operation for rivet-making and riveting on the mechanical properties and microstructures of high tensile steel rivets. The effects on mechanical properties was studied by means of tensile, hardness, and impact tests.
The resuets of the investigation indicate that (1) the overheating accentuates the blue-brittleness, secondary-brittleness and transformation-brittleness of high tensile steel rivet bar, (2) the high tensile rivets always decrease in tensile strength and elongation with the clenching operation within the blue-btittleness and secondary-brittleness range, and (3) the best temperatures of heating will be as follows:-
For rivet-making, 900°C
For pneumatic riveting,
1, 050°C-(10-30sec) when heated by an electric furnace,
1, 100°C-(1-3sec) when heated by a coke firing furnace.

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In view of a wrong representation of the cementation equilibrium by formula 3Fe+2CO=Fe₃C+CO₂, the author has discussed that the cementation velocity can never exceed the saturation point of solid solution Agr and the cementation phenomena never occur below A1 point. for which some opposite opinions have been evoked. The adversary states that a converse experiment is possible; for instance, the cementation may be carried out in CO-gas current even beyond Agr point and free crystale of Fe3C can be produced. Such a contrary opinion is, however, insignificant. So far as the equilibrium such as 2CO C+CO₂ exists from the theory of cementation equilibrium, it is absolutely impossible to produce Fe3C, but under the circumstances such as pure CO which does not contain any CO₂ or as 2CO→C+CO₂ in the way of dissociation, CO might act with Fe and Fe3C might be produced. Consequently, there being possibility of the occurence of Fe3C in pure CO-gas current, the incidental occurrence of Fe₃C in an experiment is not contrary to the theory of equilibrium.
Infact, Fe₃C can never actually be produced in CO-gas current. The reason is that Fe is the most conspicuous catalyser which augments the dissociation of CO and at the moment of contact with Fe the equilibrium of 2CO C+CO₂ is attained with the instantaneous dissociation of CO; hence the actual action of pure CO and Fe is impossible even in CO-gas current. Fe₃C might, however, occur at a temperature below 500°C, as the dissociation velocity becomes small at a comparatively low temperature. The property of Fe which considerably augments the dissociation of CO plays an interesting role in the cementation reaction.
Generally the action of cementation in CO-gas current becomes weak when the current velocity becomes small. This is due to the diffusionayer made on the surface of specimen by CO₂ which is generated by the cementation reaction, i.e., for augmenting cementation some large current velocity is necessary so as to remove incessantly CO₂ generated whether or not the cementation is conspicuously made in gas current may be detected by the soot attached to the surface of specimoen; i.e., if the soot attached, the surface is proved to be at the saturation of cementation, and if not, it indicates the cementation is not saturated.

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The author studied the vacuum extraction method for the estimation of hydrogen in iron and steel. Utilizing this method, he investigated the variation of the quantity of hydrogen in the course of steel-making operations and the method for the reduction of hydrogen, which are outlined below:-
(1) It is demonstrated that the vacuum extraction at 800°C is the most suitable for the estimation of hydrogen, and further the sampling method of specimens for the accurate analysis is dealt with in detail.
(2) The variation of hydrogen and other elements in various stages of steel-melting operations, and the means for the reduction of hydrogen are explained.
(3) The relation of the hydrogen in steel in the course of melting with that in slag is investigated, and the mechanism of intrusion of the hydrogen is studied.
(4) Analysing the hydrogen contents in ingots and forged materials, the reduction of hydrogen due to the heat treatment is explained.

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