The study of lamellar structures from the cellular reaction in an Fe-C-Mn-Al alloy
| Autor: | Ting-Jing Hu, 胡廷菁 |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 Three kinds of phase transformations of an Fe-17.9 Mn-8.38 Al-0.85 C (wt%) alloy at low temperatures have been studied. The steel underwent solution heat treatment at 1100℃ and isothermal holding at low temperatures. Decomposition of austenite took place after the steel was heat treated at 1100℃ and followed by air-cooling. Coherent ultra-fine particles of g’ phase precipitated homogeneously in the austenite matrix during cooling. These ultra-fine particles could only be detected in TEM dark-field images. The supersaturated austenite (go) decomposed into g’ phase and another austenite (g”) through precipitation transformation. The overall transformation is as follows:go->g'+g”. A pro-eutectoid reaction happened after isothermal holding of the alloy at temperatures below 875℃-carbide precipitate in the austenite matrix (g) to reduce the solute content of the supersaturated austenite?|k-carbide (k) and ferrite (a) appear as grain boundary precipitates and cellular precipitates. The cellular precipitates are composed of lamellae of either (g+k),(a+k+g) or (a+k).Various lamellae may co-exist in the austenite. The proeutectoid transformation is go->a+k+g. The third form of phase transformation is the eutectoid reaction for the decomposition of retained supersaturated austenite into ferrite,?nk-carbide and M23C6 carbide after the precipitation of the proeutectoid k-carbide and ferrite. However, this reaction could only be observed in the steel at 600℃. The eutectoid reaction is in the form of?貪->a+k+M23C6。 |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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