A self-recording apparatus of expansion-time curve during quenching of steel was constructed. With this apparatus, the expansion-time curve was obtained for 4 carbon steels and 32 steels containing less than 2% of Mn, Ni, Co, V, Cr, Si, W or Mo with nearly eutectoid carbon content. The quenching temperature varied from 850°C to 1, 100°C, the quenching medium being oil.
The velocity of expansion due to martensitization was calculated by the following formula, dx/dt=K(a-x'), in which x shows the amount of martensite formed at time, t, a amount of martensite after cooled to room temperature, and K a constant Then, the velocity of martensitization is shown by dx/dt=1/2·Ka, when x is 1/2·a
By the value 1/2·Ka the effects of special elements and quenching temperature on the velocity of expansion were studied. The Values 1/2·Ka and a change with the rise of quenching temperature, the maximum value being the case quenched from 900-1, 000°C The be inning temperature of martensitization generally falls, as the quenching temperature rises,
In the plain carbon steel of nearly eutectoid composition the martensite is formed by oil-quenching, while in those of the hyper-and hypo-eutectoid composition the troostite is formed by the same operation. In alloy steels tested in the present work, the martensitization takes place on quenching in oil, except in 1.94% cobalt steel. The velocity and amount of expansion of vanadium steels are small and those of tungsten steels. are large. Among the steels containing 0.5 and 1% of special element added, manganese steel has the largest, velocity of expansion, while among those with 1.5% or 2% of special element, tungsten steel is the largest.

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When white cast iron is annealed with iron oxide in the same vessel, there occures the decarburisation in the casting as explained in the first report; and in the second report, the mechanism on the decarburisation of white cast iron at high temperature is principally explained.
The change of distribution of carbon in the white cast iron during decarburisation is very complicated commparing in the case of carbon steel, because there are many sources of carbon as temper carbon or free cementite in the matrix of austenite. However, if the properties of these sources of carbon were studied, the migration of carbon in the cast iron could be treated by the diffusion theory of carbon as in the case of carbon steel. And the mechanism of the decarburisation was presumed after many experimental observations and mathematical treatments on the distribution of carbon in the decarburized sample.
The effect of graphitization and the chemical composition of white cast iron on the decarburisation was also investigated.

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