1. 1) T.Obara and K.Sakata : 39th Mechanical Working and Steel Processing Conference Proc., vol. xxxv, ISS, Pennsylvania (1998), 307.
2. 3) N.Takahashi, M.Shibata and Y.Furuno : Tetsu-to-Hagané, 66 (1980), S1127.
3. 4) T.Suda, M.Sakai, K.Tayama, K.Araki, M.Wada and H.Kajitani : Tetsu-to-Hagané, 63 (1983), S1365.
4. 5) E.Yasuhara, K.Sakata, T.Kato and O.Hashimoto : ISIJ Int., 34 (1994) 99.
5. 6) I.Tsukatani : Tetsu-to-Hagané, 75 (1989), 774.