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3. Iron and Steel, p. 16, Bureau of Mines, U.S. Department of the Interior, MCP-15, July 1978.
4. William T. Hogan:Iron Steel Eng., p. 28, November, 1977.
5. Peter Schmidt and Donald H. Avery.Science, 1978, vol. 201, no. 4361, pp. 1085–89.