The Iron and steel magazine . ed by the massof austenite. Very interesting is the observation that the austen-ite, which appears in high carbon steel only when quenched froma very high temperature, is found in cast iron at considerably * The author here evidently reverses the generally accepted mean-ings of austenite and martensite, by which the latter is considered as adisintegration product of the former. — Editor. Iron ( arbon . I lloys 205 Lower temperatures; and also the simultaneous appearandaustenite beside troostite. Quite similar conditions arc found in gray cast iron. [fwe examine th
The Iron and steel magazine . ed by the massof austenite. Very interesting is the observation that the austen-ite, which appears in high carbon steel only when quenched froma very high temperature, is found in cast iron at considerably * The author here evidently reverses the generally accepted mean-ings of austenite and martensite, by which the latter is considered as adisintegration product of the former. — Editor. Iron ( arbon . I lloys 205 Lower temperatures; and also the simultaneous appearandaustenite beside troostite. Quite similar conditions arc found in gray cast iron. [fwe examine the iron in photograph 14, we sec beside the pearliteonly a few narrow streaks of cementite; the remainder is finely divided cementite will naturally dissolve more easilythan the great masses of the cementite in the white iron (pho-tographs 12 and 13). Consequently the formation of troostitewill not occur as abundantly as in the white iron; photograph20 shows us a gray iron quenched at 9000 C. Here the effort of. Fig. 22. Magnified 500 diameters the dark martensite needles to cut into the mass of austenitein triangles is specially plainly seen. In the iron chilled at 1 ioo°C, seen in photograph 21, the effort to disintegrate is still moreplainly marked. At the same time one notices that the needlesare colored light and the ground mass dark, a phenomenon towhich Le Chatelier * has already called attention. In the last examples we have observed only reversibleprocesses. At the temperature of 7000 C, cementite dissolvesin ferrite to form martensite; if, instead of quenching in icewater, we had permitted the cooling to proceed slowly, as we * Le Chatelier: Laustenite, Revue de Metallurgie, 1504. 2o6 The Iron and Steel Magazine have seen, before the martensite would have become pearlite —cementite and ferrite. But if one heats iron, which above 7000 free cementite, a considerable time at a high tempera-ture (about 10000 C), a non-reversible process occurs
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