Two sorts of stepped quenchig are studied. The first is an austempering-ike quenching, that is before quenching in water, the sample is dipped in a 300°C salt bath for a little while. The secend is characterized by the short time heating beyond A₃ point just before queuching.
Hardness distribution curves revoal some interesting, results which conform with structural aspects. Residual strese curves show that the thermal and the transformational stress can be superposed in various ways according to the time of heating boyond A₃, or the time of dipping in a 300°C salt bath.

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The author has investigated the ferrite banding of free cutting steel, and arrived at the following results.
(1) The ferrite banding of hypo-eutectoid steel disappears by rapid cooling, whereas it appears by slow cooling. (2) As the cooling velocity changes from slow to rapid, the bandei structure changes into granurous structure, and "the cooling velocity" which is required for getting boundary structure is defined by the author as" Critical cooling velocity of ferrite banding". (3) The critical cooling velocity of ferrite banding goes downwards by the influence of heating temperature and time. (4) The existence of the banded structure of hypoeutectoid steel, does not affect its mechanical properties.

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Synopsis: -The author investigated the effects of-repeated melting, addition of fresh material and melting temperature on graphitization of pig iron The results obtained are as follows:-
(1) The defects from the use of turning scraps are chiefly due to reduction of components by oxidizing; and the reduction of Si closely related with the structure and mechanical properties.
(2) "Sand' inereases rapidly just below 1350°C,
(3) For graphitization, Si is one of the most important factors, "Sand" act as graphite nuclei, and FeO in molten iron hinders the growth of graphite.

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Synopsis; - Following the fifth report- (Tetu to Hagane, Vol. 33 (1947) April-June p. 21-23) the author studied the effect of nitragen, hydrogen on oxygen gas on the sintered tungsten carbide series tool and 18-4-1 standard high speed steel bath, and examined the effect of chromium gilding on the surface of 18-4-1 high speed steel by means of hardness test, microscopic examination and cutting test, etc.

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Some fundamental experiments related to the formingmechanism and the preventing method of the flake-like defects in steel were performed. The main results are as follows.
(1) In this experiments the very small ingot (60mm in dia., about 100mm length and 2-3 kg in weight) was used. This small ingot casted from the molten steel was forged into a billet (forging ratio about 2.5) before the casted ingot be cooled and quenched into water after the forging. This billet was annealed several days ago and broken or macroetched to research the appearance of the flake. On the fracture of this billet flakes have found frequently.
(2) This small ingot and the normal large ingot made from the same molten steel have a similar tendency to the flake formation. Then all the experiments were performed by this method.
(3). If the hydrogen content of the molten steel be increasd by any methods, that is, the blowing of H₂ gas or the addition of the calcium carbide on the molten steel, flakes appeared violently and on the contrary if the hydrogen content be decreased by some method, that is, the addition of mill scale or the blowing of the N2 gas the appearance of flakes was weakened or vanished.
(4) In the quenching testpiece flakes did not appear during the quenching, but they appeared while it is keeping in the room temperature and flakes in it became larger as the keeping time is longer.
(5) In the electric steel making the cffect of the additional materials and the tapping ladle on the flakeformation was confirmed directly by this small ingot method and was confirmed that both, egpecially the tapping ladle promote the flakeformation.

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