| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 98 === This eassy is dedicated in the phase transformation of a Fe-29.3Mn- 4.0Al-0.92C(wt%) steel. At temperatures range from 1100 to 775℃, a single austenite phase presents in the steel; from 750 to 600℃, M3C, M23C6 and κ’ type carbides precipitate in the austenitic grains; and from 600 to 500℃, pearlites consisting of both M3C and M23C6 carbide layers with ferritic layers, independently, coexist in the austenitic grains. The eutectoid temperatures of the pearlites are between 625 and 600℃. Moreover, the nose of the TTT curves for the isothermal transformations of pearlites is near 550℃.
Comparing the solute concentrations in the constituent phases, we found the sequence of the Mn concentration from high to low is as follows: M3C, M23C6, κ’ type carbride, austenite and ferrite. The sequence of aluminum concentration is: ferrite, κ’ type carbride, austenite, M23C6 and M3C carbide. M3C carbide is almost free of aluminum. It seems to be a characteristic feature of M3C carbide. The ferritic grains in both different pearlites contain high Al, low C and Mn.
We found several orientation relationships between carbides and their neighboring grains. [101]C//[ ]γ, ( )C//(220)γ and [001]C//[ ]γ, (210)C//( )γ are orientation relationships between M3C carbide and austenite. [001]C//[113]α, ( )C//( )α and [113]C//[111]α, ( )C//( )α are between M3C carbide and ferrite. Finally, [ ]C6//[ ]α, (111)C6// (110)α and [ ]C6//[ ]α, ( )C6//( )α are orientation relationships between M23C6 carbide and ferrite.
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