鐵鋼の材質に及ぼす酸素の影響 (III)
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概要
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In the first and the second reports, it was cleared that oxygen is one of the greatest factors which influence upon grain size and hardenability of iron and steel. (Tetsu-to-Hagane, vol.36, 1950, 108∿113 ; vol.37, 1951, 283∿290.) However, it was not yet made clear what type of oxygen in iron or steel was so significant. In the practical steel making process, most of steels are deoxidized by deoxidizers at the finishing period of the process, so steel is used to contain oxides in the form of non-metallic-inclusion. Moreover, even in the steel deoxidized by addition of much amount of deoxidizers, it has been recognized that the difference of oxygen content in the molten steel bath before addition of deoxidizers influences upon mechanical properties of these steels. Therefore, from the above mentiond viewpoint, in order to know whether these effects were owing to the presence of oxides in steel or not, the auther prepared aluminium steel samples which contain constant amount of carbon and various amount of alumina in a laboratory furnace, and then, by using these samples, investigated their cleanliness, grain-size and hardenability. Results obtained are as follows. 1) The aluminium steel containing little alumina had greater tendency to have large and uniform grain-size, but when containing much alumina, was apt to form fine grain-size and over-heated structure. 2) In the aluminium steel containing little aluminium and much alumina, the abnormal structure was apt to appear, but even if in the steel containing much alumina, when it contained more than 0.4 percent aluminium, the abnormal structure was not observed. 3) The aluminium steel containing much alumina had distinctly lower hardenability, however, even in such steel, when it contained more than 0.5 percent aluminium, they became to have the same hardenability as that containing less alumina. 4) In the aluminium steels containing the same amount of total oxygen, the effect of oxygen present in the form of alumina on their grain-size and hardenability was larger than that of present in the form of ferrous oxide. From the above mentiond, it was made clear that oxygen present in the form of oxides in steel influences on the properties of steel. Therefore it is beyond doubt that the practical steel making process have to be performed chiefly to prevent oxidation of molten steel bath, futhermore, also in the case of using deoxidizers, it is presumed that the process must be operated to float and to separate deoxidized resultants in steel.
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