Refining by partial solidification
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1. V. F. Zackay, E. R. Parker, R. D. Goolsby, and W. E. Wood: Nature Phys. ScL, 1972, vol. 236, pp. 108-09. 2. G. Clark, R. O. Ritchie, and J. F. Knott: Nature Phys. SeL, 1972, vol. 239, pp. 104-06. 3. V. F. Zackay, E. R. Parker, and W. E. Wood: Proc. 3rd. Int. Conf., "Strength of Metals and Alloys," vol. 1, pp. 175-79, Institute of Metals, Cambridge, 1973. 4. J. A. McMahon and G. Thomas: ibid., vol. 1, pp. 180-84. 5. G. D. Joy and J. Nutting: Proc. ISI/B1SRA Conf., "Effects of Second Phase Particles on Mechanical Properties of Steel," pp. 95-100, The Iron and Steel Institute, Scarborough, 1971. 6. B. J. Schulz and C. J. McMahon, Jr.: Met. Trans., 1973, voL 4, pp. 2485-89. 7. R. O. Ritchie and J. F. Knott: ActaMet., 1973, vol. 21, pp. 639-48. 8. C. E. Richards and T. C. Lindley: Eng. Fract. Mech., 1972, vol. 4, pp. 951-78. 9. R. O. Ritchie and J. F. Knott: Proc. 3rdlnt. Congress on Fracture, paper no. V-434A, Munich, 1973; extended version, Proc. BSC Conf., "Mechanics and Mechanisms of Crack Growth," British Steel Corporation, Cambridge, 1973. 10. R. O. Ritchie and J. F. Knott: Mater. Sci. Eng., 1974, vol. 14, pp. 7-14.
Refining by Partial Solidification R. MEHRABIAN, D. R. GEIGER, AND M. C. FLEMINGS
Fig. 3-Continued.
1400~ because the high sulfur level lowers the toughness by increasing the ease of t r a n s g r a n u l a r fibrous separation: consequently, the relative weakening at the grain boundaries is Insufficient to cause failure there preferentially. ~ Thus, if high austentttzing t e m p e r a t u r e s are to be used to increase the toughness of untempered and lightly tempered low alloy steels, it is essential that, unless fast quenching rates can be guaranteed throughout the section, the "overheating" temperature must not be exceeded. Since the results of Zackay et al 1 show that the Increase in toughness occurs suddenly and dramatically at around 1100~ we would suggest that an ideal austenltlzlng temperature should not be above 1150 to 1200~ so that the solution of sulfides, and thus "overheating," eannot occur. The authors would like to thank P r o f e s s o r C. J. McMahon for helpful discussions, P r o f e s s o r R. W. K. METALLURGICAL TRANSACTIONS
A major technical difficulty in refining processes which employ partial solidification when solidification is dendritic, is that the segregated liquid is interspersed on such a fine scale in interdendritic spaces that it is difficult to remove from the dendritic solid. In this note we describe two refining p r o c e s s e s which employ the basic finding that metal alloys behave as a highly fluid s l u r r y when they are as much as half solid, provided they are vigorously agitated during solidification. 1 The solid particles that form during solidification are, or approach, small spheroids. The fine dendritic structure is absent and the segregated liquid can be easily and efficiently separated from the solid. The technical and patent literature describes v a r i ous p r o c e s s e s for refining metal alloys which employ partial solidification follow
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