1. 1)“Clean Steel” Iron and Steel Inst. Special Rept. 77, London (1963)
2. 2) Intl. Conf. on the production and application of cleen steels. Hungary (1970)
3. 3) R. K. HOPKINS: U.S. Patents 2 191479/80
4. 4) A. G. WILLIAMS:“Clean Steel” p.79
5. 10) C. J. B. KARSTEN: Arch. f. Bergan u. Huttenw., 8 (1824), p.3