In nickel or nickel-chromium steels, the Ac1 transformation occurs under a certain tamperature range, beginning at a temperature consideradly lower than that usually designated as Ac1 point. In nickel steels, the beginning point of the Ac1 change is lowered by 20° for each 1 per cent of nickel up to 5 per cent.
The addition of 0·75 and 1·50 per cent of chromium to nickel steels raises the beginning point by 20° and 40° respectively. Tungsten and molybdenum have no effect on the beginning point of the Ac1 change of nickel-chromium steels.

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In the case of hot pressing of thick or medium plates, such as end plates of boilers or disc plates for automobiles, numerous surface cracks may occur at the outer side of bends. In order to affirm the causes of such cracks, the actual working conditions and mechanism of the cracks produced were investigated, and the properties of steel plate, particularly under hot conditions, as well as the state of the variation of the properties due to oxidation when the material was heated in various gases were experimented. Further, specimens containing different percentages of copper, sulphur, oxygen, etc. were prepared, and the properties of such specimens under hot conditions and the effects of these elements upon the production of surface cracks were experimentally investigated. The results show that the principal cause for the surface cracks is the overheated working of the steel plate and is particularly the surface oxidation. Oxygen augments considerably the surface cracks and red-beat brittleness, whilst copper and sulphur increase red-beat brittleness in the existence of oxygen and also facilitate the surface cracks accompained with the surface oxidation. Although copper and sulphur exist in certain amounts as impurities, the surface cracks do not occur when the oxidation is prevented.

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In order to select the most suitable treatment for carbon steel and siliconmanganese steel among various heat treatments which are now prevailing for flat spring plates for carriages, a special repeated bend testing machine has been manufacture, which is convenient for the comparison of the durability for repeated bending of test pieces similar to the actual materials variedly heat-treated. One of the special features of the machine is that the test piece is freely supported at its ends and the load is hung at two positions near the middle of the span so as to enable bending very similar to the actual operating condition of the flat spring; whilst another special feature is that two test pieces may simultaneously be subjected to the repeated bend test at a rate of 500 times per minutes and the deflection of the test piece may suitably be adjusted to the thickness and deformation of the test piece so as to produce always a bending stress of 70kg. per sq. mm at the instant of the maximum bending until the test piece breaks down.
With this testing machine, 820 test pieces of carbon steel and silicon-manganese steel spring plates subjected to two kinds of single quenching (tempered by waste heat of quenching) and the same number of test pieces subject to two kinds of double quenching (independently tempered and heated) as well as 100 test pieces subjected to emulsified oil quenching (a sort of single quenching) were tested. The results indicate that the double quenching after independent heating for shaping and quenching is the most suitable as the heat treatment, and that carbon steel (SP 75, about 0·8%C) appears to be suitable as a spring material. Further, the test pieces which were ground to the extent of removing the decarburized, surface layer were experienced to be highly durable, and this fact may be considered to endorse the effect of grinding dealt with in Mr. R.G. Batson's paper which was read before the World Engineering Congress, 1929. (Paper No. 226). It was also observed that the durability of silicon-manganese steel is unexpectedly small in comparison with its elastic limit. This may be considered to be the bad effect of grain disposition of silicates separated in the structure or the effect of decarburized layer or uneven hardeness (silicon-manganese steel being deeply decarburized in comparison with carbon steel and liable to the occurrence of uneven hardness in the central part), so that further investigation is necessary and the author retains the problem until the future occasion.

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The problem of the wear between two metallic materials had been studied by many investigators. However, the wear between metallic and non-metallic materials, which refer to the field of industrial productive machines, is also an important problem, nevertheless the researches of this problem are few in our country. Several years ago, the present author made the comparative test of the chilled cast iron and martensitic Mn-steel and discussed the industrial value of the latter. Thereafter, the author carried on the wear tests of many kinds of metallic material, in various conditions. The present paper is referred to the nineteen kinds of metallic material of low and high grade, and the investigation was performed with a tube mill type testing machine by using clinker and sand as the abrasive. The conditions of these tests are as follows: in the dry condition wear test, at the room temperature, 600°C and 1, 000°C; in the wet condition wear test, supplying water or 5% sulphuric acid solution to the sand-abrasive.
In the case of clinker-abrasive which hardness is lower than sand, cast iron should decidedly a great amount of wear and the low grade materials showed somewhat larger amount of wear than the high grade. In the case of sand-abrasive, harder than clinker, cast iron showed again the lowest wear-resistance, as the former case, but, in this case, the low grade materials generally showed less amount of wear than high grade materials. In the case of clinker-abrasive at the high temperature, 600°C, the wear-resistance of the low grade materials, except cast iron and chilled cast iron, was much inferior to the high grade materials. In this case, the wear resistance of metallic materials depends chiefly upon their chemical composition and the resistance to oxidation. In the case of clinker-abrasive at the higher temperature, 1, 000°C, the amount of wear of low grade materials increased notably, but, on the contrary, high grade materials, except 13% Cr-steel, showed very small amount of wear. On the test of wet condition, with no load, using sand-abrasive, the low grade materials showed larger amount of wear than high grade materials in spite of the water quantity, and, especially, the wear of cast iron was most notable. In the test of wet and loaded condition, all materials generally showed over 21/2 times of amount of wear of the no-loaded condition test. But in this case, the tendency of the comparative wear was similar to the former case, and when the water supply is little the low grade materials showed larger amount of wear than the case of much supply of water, but the high grade materials showed the contrary phenomenon. In the wet condition wear test with 5% sulphric acid solution, the wear was greatly influenced by the chemical composition of these materials, and consequently had little relation to the hardness which is a serious factor to the wear, and showed the complicated results.

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