Abstract:

As-quenched martensite in carbon steels needs to be tempered to restore its ductility and toughness for practical applications. During tempering, a series of reactions relevant to carbon diffusion occur sequentially in various stages, starting from carbon segregation/clustering, metastable iron carbide precipitation, retained austenite decomposition, to cementite precipitation, which cause changes both in microstructure and physical properties of tempered martensite. In this study, multi-aspect characterization using various advanced characterization techniques, such as in-situ neutron diffraction, transmission electron microscopy (TEM), three-dimensional atom probe (3DAP), was performed, with an aim to clarify the low-temperature tempering behaviors of high-carbon martensitic steels. Furthermore, alloying effects on low-temperature tempering kinetics and microstructural evolutions were also studied. All the new findings will be introduced in detail in the lecture.

Bio:

Dr. Yongjie Zhang is an assistant professor of Microstructure Design of Structural Metallic Materials Laboratory, the Institute for Materials Research (IMR), Tohoku University, Japan. He received Bachelor degree at Shanghai Jiao Tong University, and Master and Ph. D degrees at Tohoku University, Japan. During his Ph. D course, he was recruited as the Research Fellowship for Young Scientists (DC1) by the Japan Society for the Promotion of Science (JSPS).

His research interests cover various fundamental aspects of microstructural control in steels, including nano-precipitation and strengthening, alloying effects on transformation kinetics, solute segregation at grain boundary, etc. He has authored/co-authored around 40 refereed papers, and received multiple academic awards such as the Young Researcher Award by the Japan Institute of Metals and Materials (JIM) and the Iron and Steel Institute of Japan (ISIJ), respectively.