. Transactions. pearlite and perhaps its con-tent of carbon depend largely on the rate at which the steelpasses through this critical temperature. Rapid cooling inair, for instance, yields very fine pearlite, while very slow cool-ing gives us the coarsely laminated variety whose pearly ap-pearance is marked to the naked eye. Fig. 9 shows a steelwith C, , and Mn, per cent., as cast. Such coarsely crystalline material is brittle, and must be an-nealed, or, more properly speaking, refined. This is done byreheating to above the upper critical point, Ac2_3; that is, justabove GOS. On passi
. Transactions. pearlite and perhaps its con-tent of carbon depend largely on the rate at which the steelpasses through this critical temperature. Rapid cooling inair, for instance, yields very fine pearlite, while very slow cool-ing gives us the coarsely laminated variety whose pearly ap-pearance is marked to the naked eye. Fig. 9 shows a steelwith C, , and Mn, per cent., as cast. Such coarsely crystalline material is brittle, and must be an-nealed, or, more properly speaking, refined. This is done byreheating to above the upper critical point, Ac2_3; that is, justabove GOS. On passing the line PSK, or Acp the pearlitechanges over into austenite, and with increase in temperaturethe solid solution austenite dissolves more and more of theferrite until, on the change being completed, we have ^ See Heyn. Report on Progress of Metallography, Proceedings of the Internn-ional Association for Testing Materials, vol. li., No. 11 (1912). I TIIR MICROSTRUCTURE OF IRON AND STEEL. 497 ; ^V^.
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