| Summary: | 碩士 === 國立屏東科技大學 === 機械工程系 === 94 === The main purposes of the present studies are to investigate the phase transformation of the Fe-8.7Al-28.3Mn-1C-5.5Cr alloy by using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on the experimental results, the microstructure of the as-forged alloy was single austenite (γ) phase with stress-induced twins. Being solution heat treatment (SHT) in the range of 800~1000℃, the microstructure of the alloy was a mixture of (γ+ Cr7C3) phases. The Cr7C3 particles increased with increasing the SHT temperature. Being SHT in the range of 1050~1200℃, the microstructures of the alloy was a single γ phases. Increasing the SHT temperature to 1250 to 1400℃, some re-solidification region with γ+(α+DO3) phases was found.
During the 400℃~500℃ aging processes, some κ-phase carbides were observed within the austenite matrix and the grain boundaries. When the specimen aged at the temperature to the 550℃ and 650℃, a γ→(γ+Cr23C6)→(γ+Cr23C6+Cr7C3) phase transition was observed within the austenite matrix. Moreover, a γ→(DO3+Cr23C6)→(DO3+Cr23C6+Cr7C3) phase transition was found on the grain boundaries. Increasing the aging temperature to the 700℃~800℃, a γ→(γ+Cr7C3) phase transition was found, and a γ→(DO3+Cr7C3) phase transition found on the grain boundaries.
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