The study of the martensitic transformation in the austenite phase of the Fe-Mn-Al alloys via orientation imaging microscopy (OIM and ASTAR).

• Main Authors: Yu-shan Lin, 林郁珊
• Other Authors: Wei-chun Cheng
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/98384416329185233665

碩士 === 國立臺灣科技大學 === 機械工程系 === 102 === Fe-Mn-Al alloys which are lower desity and lower cost of the material than the traditional Ni-Cr steel system belong to austenite steels system. Thus Fe-Mn-Al alloys have gained much attention as cheap substitutes for some of the conventional Fe-Ni-Cr stainless steels to become commercial stainless steels with the low density. However, to make it become commercial stainless steel requires building the data base such as phase transformation of steel alloys data. Due to this facts, we mainly discuss phase transformation of three different components of Fe-Mn-Al alloys after quenching process from 1195℃ to 1100℃ in this study. We use orientation imaging microscopy (OIM) and transmission electron microscope (TEM) equipped with ASTAR software to identify the phases and phase transformations between these three alloys. According to the former reaserch, the alloy A which is content with Fe-16.7Mn-3.42Al (wt %) is the single austenite phase at 1100℃. After quenching, the austenite phase will transform into BCC martensite and the rest will become retained austenite. We comfirm the results by TEM-ASTAR rapidly analyzing. In addition, the former reaserch group considered alloy B which are content with Fe-15.9Mn-4.2Al (wt %) are ferrite and austenite phase on 1100℃. After quenching, they found out there were BCC twins in the dual phases. But the result of annealing twins consisting in the ferrite was not correct. In this study, we use TEM-ASTAR to analysis alloy B and we conclude that alloy B are ferrite and austenite phases from 1195℃ to 1100℃. Furthermore, we find out there are BCC martensite and retained austenite existing in alloy B after quenching. So we conclude that the former research group think the BCC annealing twins within the alloy B is wrong. Actually, there are BCC martensite and retained austenite in the alloy B rather than BCC annealing twin. The alloy C which is content with Fe-27.6Mn-5.3Al-0.11C (wt %) is composed of ferrite and austenite phase from 1195℃ to 1100℃ by the OIM analysis. We conclude that there are ferrite and austenite phases within alloy C. However, there are no ausrenite grain transformed into BCC martensite in quenched alloy C to be found. So the pahse transformation is diffrerent from the carbon steels.