1. 2) H. Yada, Y. Matsumura and K. Nakajima: United State Patent No. 4,466,842, (1984).
2. 3) P. D. Hodgson, M. R. Hickson and R. K. Gibbs: United State Patent No. 6,027,587, (2000).
3. The Effect of Chemistry on the Formation of Ultrafine Ferrite in Steel.
4. 5) W.-Y. Choo, K. K. Um, J. S. Lee, D. H. Seo and J. K. Choi: Int. Symp. on Ultrafine Grained Steels, ISIJ, Tokyo, Japan, (2001), 2.