1. K. Yoshida, Reports, Inst, of Physical and Chemical Research, 44 (1968), 169.
2. T. Kobayashi, H. Iida and S. Sato, Proc. Int. Conf. Sci. Tech. Iron and Steel, Tokyo, (1971), 837.
3. S. P. Keeler, Sheet Met. Ind., 42 (1965), 683.
4. G. M. Goodwin, SAE Paper No. 680093, (1968).
5. K. Nakazima, T. Kikuma and K. Renko, Preprint of 19th Joint Meeting for Plastic Working, (1968), 277.