Abstract
The main purposes of the present studies are to investigate the phase transformations of the Fe-8Al-15Mn-1Si-0.4C alloy by using optical microscopy (OM) and transmission electron microscopy (TEM). The microstructure of the alloy after being solution heat-treated at 1100℃ for 30 min and then quenched. It reveals a (γ+α) phase microstructure. The austenite matrix was single-phase and the ferrite matrix were (α+B2+DO3) phases microstructure, where the (α+B2+DO3) were formed by a continuous ordering transition during quenching. When the as-quenched specimen aged at the temperature from the 200℃~650℃ for longer times, no evidence of the (Fe,Mn)3AlCx carbides formed on the austenite matrix could be detected. Moreover, the needle-like precipitates has L12-type structure occurred as well as the DO3 precipitates grew along directions on the ferrite matrix on the α matrix. When the aging temperature was increased to 750℃ for shorter times, a needle-like L12-type precipitates occurred on the twin boundary of austenite matrix. With increasing the aging temperatures from 200℃ to 750℃, the phase transformation sequence occurring within the α matrix is found to be (α+DO3+B2+needle-like L12-phase)→(α+ spherical DO3+ needle-like L12- phase)→(α+ quadrate DO3+ needle-like L12-phase) →(α+ B2). Furthermore, during aging, the ferrite grains grew along directions to the austenite matrix on the γ/α grain boundary.
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