STUDY OF ALUMINUM NITRIDE PRECIPITATION IN PURE FE-AL-N ALLOY BY THERMOELECTRIC-POWER MEASUREMENTS

Aluminium nitride (AlN) precipitation in an Fe-Al-N alloy was investig ated using thermoelectric power (TEP). The TEP variations due to annea ling at high temperature are connected with the solubility of AlN. Ana lysis of AlN precipitation during annealing in alpha-phase enables us to distinguish one range of temperature (500-575 degrees C) correspond ing to an activation energy of 60 kcal/mole and another range (575-700 degrees C) corresponding to an activation energy of 50 kcal/mole. Fro m TEM observations, the difference was related to the temperature effe ct on the nucleation: the first range corresponds to a homogeneous pre cipitation, while in the second range the nucleation occurs on the dis locations. In steel which also contains carbon and manganese a second stage for long isothermal annealings was observed and was attributed t o manganese enrichment of iron carbides. The precipitation at low temp erature, and the influence of an initial cold-rolling before annealing on TEP variations were also examined. (C) 1997 Acta Metallurgica Inc.