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Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
Abstract: The nano-indentation method is employed to investigate the mechanical stability of individual retained austenite grains in a Fe-5wt%Mn-0.2wt%C transformation-induced plasticity (TRIP) steel, which is a potential 3rd generation Advanced High Strength Steel (AHSS) for automotive applications. It is noted that this TRIP steel is different from the classical TRIP steels as it only contains ferrite and retained austenite. The transformed martensite under the indent was investigated by transmission electron microscopy (TEM). The TEM sample was prepared by focus ion beam (FIB) milling at the cross-section of the indented region. It is found that the orientation relationship between martensite and retained austenite obeys the Kurdjumov-Sachs (K-S) relation. By fitting the load-displacement curve to the Hertzian elastic solution, it is found that the first pop-in on the load-displacement curves of austenitic phase represents the nucleation of dislocations. The second pop-in on the load-displacement curve of austenitic phase represents the initiation of martensitic transformation. The other pop-ins may be induced by martensitic transformation or dislocation transmission across the low angle grain boundaries. Combining with the energy-dispersive X-ray (EDX) results on the Mn distribution in different austenite grains, it is found that the critical load for the martensitic transformation increases with Mn content, which implies that a higher Mn content leads to a more mechanically stable austenite.
Short-Bio of the author
Dr. Huang obtained his BSc in Engineering Mechanics and MSc in Solid Mechanics from Shanghai Jiao Tong University (SJTU), China, in 2002 and 2004, respectively. Then he moved to The Netherlands and earned his PhD from TU Delft in 2008 under the supervision of Prof. S. van der Zwaag and Dr. Pedro Rivera. After the PhD study, he was employed as a researcher at the global research centre of ArcelorMittal in Maizieres-les-Metz, France. In 2010, he joined The University of Hong Kong as an assistant professor. His current research interest includes mechanical properties-microstructure relation of TWIP, medium Mn TRIP and Q&P steels and nanostructured alloys.