The study of layer austenite twins adjacent to kappa-carbide plates in the cellular structure of an Fe-C-Mn-Al alloy

• Main Authors: Po-Yen Liu, 劉柏言
• Other Authors: Wei-chun Cheng
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/15530686745342041638

碩士 === 國立臺灣科技大學 === 機械工程系 === 100 === Three types of low-temperature phase transformations in an Fe-12.5 Mn-6.53 Al-1.28 C (wt%) alloy have been studied. The steel underwent solution heat treatment at 1100℃ and isothermal holding at low temperatures. r’ phase appears in the austenite matrix in the air-cooled steel. Coherent ultra-fine particles of r’ phase precipitated uniformly in the austenite matrix after the air-cooling process. These ultra-fine particles were very small and only could be detected by TEM through dark-field images. After short periods of isothermal holding at low temperatures these particles of r’ phase grew and could be easily detected by TEM. A pro-eutectoid reaction happened after isothermal holding at temperatures below 875℃. Proeutectoid K-carbide and ferrite appear in the austenite matrix as grain boundary precipitates and cellular precipitates. The cellular precipitates are composed of lamellar K-carbide and austenite. The lamellar K-carbide grains are always accompanied by layers of austenite twins. The presence of twin layers adhering to the K-carbide plates might be attributed to the lower activation energy for the precipitation of K-carbide plates in the austenite. The final form of phase transformation is the eutectoid reaction for the decomposition of supersaturated austenite into stable K-carbide and ferrite phases at temperatures below 700℃. The ferrite and K-carbide are in the form of pearlite lamellae.