Investigating the effects of cold-work on the transformation of cobalt, Wassermann and Nisiyama reported the following phenomena. Cobalt which was treated with an intense cold-work such as filling or rolling and then was heated to the temperature in certain range above the transition point, does not show complete transformation β→α, but retains a large quantity of β even at room temperature, and this β can be transformed to a with the cold-work. The phenomena, in the present investigation, were recognized not only at the case of the cold-worked cobalt but also of the electro-deposited cobalt.
Electro-deposited cobalt is composed of α and β each of which is of texture depending on the solution, and when treated with the cold-work, it transforms themselves to α, and, after heating, retains β almost completely at room temperature.
Supposing that the phenomenon of retainning β be related to magnetic properties, the effects of outer magnetic fields are surveyed. The results, however, do not show any decissive change.

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The Charpy impact test of the high speed steel of the type 18:4:1 was carried out under the following conditions; (i)Tests at room temperature, using specimens quenched from 1200, 1250 and 1300°, all tempered at 100, 250, 400, 550, 650 and 750° for twenty-minutes. (ii) Tests at the higher temperatures of 100, 200, and 300°, using specimens quenched from the same temperatures as under (i), all tempered at 400, 550 and 650° for the same time.
There are many literatures on the impact value of the high speed steel of the type 18:4:1 after quenched and tempered, but none of them has tried the impact test of these heat-treated steels at higher temperature to which the high speed tool steel might attain during the cutting operation. That was the main reason why the author came to execute these tests under the conditions (i) and (ii), attaching special importance to (ii), and gained the following results.
(1) The curve gained here between the Charpy impact value and the tempering temperature is almost similar to Grossmann's result⁽¹⁾, and the specimen quenched from the lower temperature shows the higher impact value. To obtain the toughest high speed tool steel, it is advisable to quench it from 1200° and temper at 350_??_400°. Moreover, the steel treated at these temperatures also shows, at the testing temperature of 300°, higher impact value than any one treated at other temperature does. (2) The impact tests of specimens quenched from 1200, 1250 and 1300°C, all tempered. at 550°, show that the steel quenched from 1200° has the higher impact value at the testing temperature of 300° than at 200°, while it has almost the same value at either testing temperature when quenched from 1250°. Reversely, when quenched from 1300°, the impact value is higher at the testing temperature of 200° than at 300°. So if a tool steel suffers higher cutting temperature and then is required to be tougher, it should be quenched below the temperature of about 1250°

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It is said that when high speed steel is quenchedin hot bath at 600°, that is, tempering temperature for the steel, both hardening and tempering are effected at the same time and no further tempering is necessary. The writer has experimented on No. 2, 3, and-4 high speed steels specified in the J. E. S. From the hardening temperature of 1300° they were thrown into hot bath at 100_??_600° for different durations of immersion; then they were taken out and cooled in the still air. After examining their hardnesses and structures, it wa's found that high speed steel was scarcely better hardened by hot bath quenching below 600° than by oil quenching, and that to attain the effect of temper hardening, the hot bath quenching had to be followed by a usual tempering at 600° The sames was true for a steel kept in hot bath at 600° for about five days. But when immersed at 600° for more than twenty days, it developed troostite on the boundary of austenite and had its quenched hardness reduced. In the case of the hot bath raised to 650_??_700° it also developed troostite, had its hardening effect greatly reduced and no satis factory temper hardening was secured even if tempered at 600°. In other words, hot bath quenching of high speed steel serves a prevention against quenching crack and deformation rather than temper hardening and the effective hot bath temperature is below 600°. A two-step hot bath quenching was also tried. In this method, steel was immersed from the hardening temperature into a hot bath below 600° (1 st hot bath), and, without being cooled in the'air, was immediately dipped into the tempering hot bath (2 nd hot bath). After being kept there for the adequate duration of time, it was taken out and cooled in the still air. The result showed that at 200_??_600° of the Ist hot bath, the two-step method could no more effect temper hardening than the simple hot bath quenching. In this case stell must be tempered at 600° for any tempering effect; hardness was found to be independent of hot bath temperature. At 100° of the 1 st hot bath, however, temper hardening was effected by the two-step method with the same hardness and structure obtained as by ordinary oil hardening and tempering. Therefore it can be concluded that high speed steel must be cooled down to 200° during its quenching before it can be tempered at 600° with any satisfactory effect: it must be cooled nearly to room temperature before tempering.

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By means of the bending and tensile tests together with determination and penetration of hydrogen, the author investigated the acid-brittleness of various steels dipped in HCl or H₂SO₄ solution where FeS was contained. The results are as follows : (1). The Acid-brittleness is accelerated by S'', As… P… Pb… and Hg… in acid solution. And the S'' ion is the most strong and probable accelerator in the actual pickling procedure. (2). Only in the HCl or H₂SO₄ solution, the alloy steel does not absorb hydrogen and not be embrittled, but the carbon steel absorbss hydrogen and is embrittled. (3). The acid-brittleness of steels dipped in H₂S saturated acid solution is the most typical one to investigate. (a) In the case of embrittled rimmed-steels, the tensile strength increases slightly at the beginning of dipping, but later decreases again, and inspite of the heat-treatment of the samples, granular frocculant defect appears in the fractures and the sample steel cracks along the grain boundary. But in the case of killed steels which was tempered at low temperature, the tensile strength decreases to the great extent, the yield point disappeares, and the frocculant defects, which is very similar to the flake in alloy steel, appear in the fractures. In the case of steels tempered at high temperature, the tensile strength and the yield point are not changed at all and no froccurant defects are seen in the fractures. (b) The higher the pickling temperatures are, the more the acid-brittleness decreasse. This is due to the decrease of the supersaturated hydrogen in the specimen by at high pickling temperature. (4). By standing specimens in the boiling water, the occluded hydrogen removes easily from the specimen's surfaces and the original properties are gradually. restored, but in case of frocculant defective specimens, their original properties are not restored. (5). The acid -brittleness is prevented by the addition of such substances as these which remove S'' from the H₂S acid solution by means of changing S'' into insoluble compounds or of oxidising S'' into SO₄'' in the pickling solution.
The anther found that the results of this work would solve many incoinsitant results of acid-britlleness reported by many investigators.

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Hardness is, in the industrial world, used merly to show quantitatively the solidity of an object and therefore no absoluteness lies in it. Consequently, it is the numerical value which, is shown only when all the conditions are satisfactorily completed.
It changes most especially by the load, decreasing gradually as the load becomes smaller, but-(1) By seeking the relation between the load and hardness, the singularity of hardening can be explained from the difference in “Hardness curves”, though it has hitherto shown the same value in the measurement of hardness under the fixed load. (2) By measuring hardness tinder the small load, very small changes, that have never been found out before, can be recognized in the structure after tempering.
By this phenomenon that could be recognized for the first time under the small load, we learn that by hardness also the study of structure which has not been obtained hitherto can be deepened.
This is the reason why the writer adovocates the use of the words “Hardness analysis”.

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