抄録
As reported previously, the authors could give the same hardness as Widia to the 18% Co super-high-speed steel, by a particular heat-treatment and, at the same time, they found a fact that by applying this heat-treatment they did not necessitate the use of widia to drill the hard special steel plate, and the cutting work was carried out fast and easily, even with ordinary machines of old type. This particular heat-treatment is composed of quenching and the repetition of such tempering as to heat for short time and to cool, and by this tempering method the hardness of that tool steel became higher than that by the ordinary continuous tempering process. In the present paper, the authors dealt with the physico-metallurgical research refering to the machanism between this heat-treatment and thereafter hardness increment, and also the investigation of elements which are necessary for such increase of hardness. From the results of their studies, the authors reached to the following conclusions: The chief cause of this increase of hardness is the fine and uniform precipitation of carbides with the transformation A→M which occurs at relatively low temperature in the course of cooling, by this heat-treatment. And this transformation is not the socalled Ar, " but the transformation A→M which follows to the precipitation: The essential elements which are absolutely necessary for such hardness increment, are W, Cr, V and Co, and Mo is the secondary element which merely promote this increase of hardness.
These researches were carried out during the period from 1933 till 1934 and published on the Spring meeting, 1936, in Tokyo.
