**9. Acknowledgements**

The author deeply appreciates Profs. Jae Il Lee and Se-Kyeun Kwon for their decades-long discussions and critics on this subject. A special acknowledgement is dedicated to Prof. Byeong-Joo Lee for his mentoring advises on the CALPHAD methods. Prof. H. K. D. H. Bhadeshia should receive thanks of the author for his comments from a metallurgist's view point.

This work was supported in part by POSCO Steel Innovation Program and in part by the Basic Science Research Program (Grant No. 2009-0088216) and the World Class University (WCU) Program (Project No. R32-2008-000-10147-0) through the National Research Foundation funded by the Ministry of Education, Science and Technology of Republic of Korea. This article is dedicated for the memory of Late Prof. Duk-Joo Kim.
