1. A. Pacz, U.S. Patent No. 1387900 (1920).
2. J.D. Edwards, F.C. Frary, and H.V. Churchill, U.S. patent 1410461 (1920).
3. D.A. Granger and R. Elliott, ASM Handbook, 15 (Materials Park, OH: ASM, 1992), p. 159.
4. E.L. Rooy, ASM Handbook, 15 (Materials Park, OH: ASM, 1992), p. 743.
5. H. Morrogh and W.J. Williams, J. Iron Steel Inst. London, 155 (1947), p. 321.