1. Siemens Halske, German Patent 154,998.
2. G. Naeser and F. Zirm, Stahl u. Eisen 70:995 (1950).
3. S. R. Crooks, Iron and Steel Eng. p. 72, Feb., 1962.
4. P. E. Evans and G. C. Smith, Symposium on Powder Metallurgy, 1954, J. Iron and Steel Inst, Special Rept. 58:131 (1956).
5. P. E. Evans and G. C. Smith, Powder Met. 26(3) 1 (1959).