Austenite Reversion of Fe-15 Mn-0.03 C (wt. %) Steel
Date Issued
2016
Date
2016
Author(s)
Huang, Yu-Han
Abstract
In this work, the annealing is carried out by dilatometer. Applying the Koistinen-Marburger equation and calculated grain size, the Ms temperature was estimated and compared to which was measured from dilatometeric curve. It was found that annealing at a lower temperature leads to extremely small grains and low Ms temperature. This demonstrates that chemically unstable austenite can be preserved as a metastable phase at room temperature when a significant reduction in grain size is achieved. Besides, the annealed microstructure and mechanical properties of Fe-15 Mn-0.03 C (in wt. %) steel have been investigated by using transmission electron microscopy, X-ray analysis, electron backscattered diffraction and transmission Kikuchi diffraction in this work. It was found that annealing at a lower temperature leads to both high tensile strength and excellent elongation in spite of its extremely small grains. The best tensile properties is found annealing at 600 °C and 650 °C, which leading to both high tensile strength (~1.2GPa) and excellent elongation (~35%). The reason is that refinement of austenite grain size due to lowering annealing temperature could significantly inhibits martensite transformation during quenching to room temperature. Hence, during plastic deformation, tiny and metastable austenite transformed into ε martensite and α'' martensite, producing high strength and excellent ductility via TRIP effects.
Subjects
AHSS
ultrafined grain
austenite reversion
Type
thesis
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