Massive transformation in Fe-Mn-Al alloys

• Main Authors: Chih-Kang Lai, 來致剛
• Other Authors: Wei-Chun Cheng
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/pepqma

碩士 === 國立臺灣科技大學 === 機械工程系 === 94 === Two alloys with wt% compositions of Fe-25.3Mn-4.4Al and Fe-25Mn-7Al- 0.08C were studied in several heat treatments. Some slabs were heated at 1350℃ and quenched into cold brine. Irregular massive austenite grains were observed spread through the specimens. For those with the same heat treatment but air-cooled, large parent ferrite grains with high density of product austenite Widmanstätten precipitates were discovered. Full austenite grains were observed for the slabs heated at 1100 and furnace ℃ -cooled. It was concluded that the equilibrium phase at 1300 was a single ferrite phase and the stable phase at ℃ low temperatures was a single austenite phase. The phase transformation was a massive transformation for fast converting the high-temperature ferrite phase to the low-temperature austenite phase. The irregular shapes of the austenite grains were one of the characteristics of the massive transformation for the alloy having been experienced the high-temperature quenching. The massive austenite grains contained many mechanical twins in various sizes. For alloys heated at 1350℃ and quenched to room temperature water, small amounts of the Widmanstätten precipitates appeared at the grain boundaries of the parent ferrite phase, and all the other space was occupied by the irregular massive austenite grains. For the two alloys being heated at 1350 and cooled on ℃ the ground, the alloys contained an almost equal amount of austenite Widmanstätten side-plates and massive austenite grains in the parent ferrite grains. Thus, for the formation of massive austenite grains and the formation of Widmanstätten side-plates in the parent ferrite grains, the cooling rate played an important role. The massive austenite phase dominated in the fast cooling rate, while the austenite Widmanstätten precipitates preferred the slower cooling rate. The massive transformation, from ferrite to austenite, was observed throughout the Fe-Mn-Al alloy and not confined to the specific locations, during the high-temperature quenching. For the first time, the massive transformation was discovered in the ferrous alloys for fast converting ferrite to austenite during the high-temperature quenching.