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This work was supported by the National Science Foundation under Grant No. DMR 9024255. Thanks are extended to Professors Enrique Lavernia and James Earthman for useful discussions. REFERENCES 1. P.K. Chaudhury, K.T. Park, and F.A. Mohamed: Metall. Mater. Trans. A, 1994, vol. 25A, pp. 2391-401. 2. N.Y. Tang: MetaU. Mater. Trans. A, 1995, vol. 26A, pp. 1600-01. 3. S.T. Yang and F.A. Mohamed: Metall. Mater. Trans. A, 1995, vol. 26A, pp. 493-96. 4. P.K. Chaudhury and F.A. Mohamed: Acta Metall., 1988, vol. 36, pp. 1099-1110. 5. F.A. Mohamed: J. Mater. Sci., 1983, vol. 18, pp. 582-92. 6. B. Burton: Diffusional Creep o f Polycrstalline Materials, Trans Technical Publications, Bay Village, OH, 1977, ch. 4. 7. E. Arzt and J. Rosier: Acta Metall., 1988, vol. 36, pp. 1053-60. 8. J. Rosier and E. Arzt: Acta Metall. Mater., 1990, vol. 38, pp. 671-83. 9. X.-G. Jiang, S.T. Yang, J.C. Earthman, and F.A. Mohamed: Metall. Mater. Trans. A, in press.

The Effect of Phosphorus in Base Steel on the Forming Characteristics of Galvannealed Sheet Steels: New Average Iron Content Range of Galvannealed IFP Steel C.S. LIN and M. MESHII Zinc-coated steel sheets have been extensively used in the automobile industry because of their excellent cotC.S. LIN, Graduate Student, and M. MESHII, John Evans Professor, are with the Steel Resource Center and Department of Materials Science and Engineering, Northwestern University, Evanston, IL. Manuscript submitted August 29, 1994. 1602--VOLUME 26A, JUNE 1995

rosion resistance. Among them, Fe-Zn-alloy-coated steel sheet has received ever-increasing attention because of its superior corrosion resistance, Lj,2]better weldability, TM and paintability 14] in comparison with the pure Zn coating. The production of Fe-Zn alloy coating is generally achieved by either electrodeposition or galvannealing processes. The galvanneal technology offers a more promising future than electrodeposition technology because of its high energy and material efficiency. However, powdering, the loss of the coating by various forms of microcracking during forming operations, still occasionally plagues galvanneal products and causes problems in manufacturing. The properties of Fe-Zn coating on steel sheet strongly influence most steps of the manufacturing system, such as forming, spot welding, phosphating, and painting. TM It has been thought that the extent of the galvanneal reaction is the primary factor determining these properties. The extent of the galvanneal reaction can be determined by the average Fe content of a coating. Therefore, the practice used in the industry is to specify galvanneal products by the average Fe content, often 10 to 12 wt pct, which was determined to be optimum for the coating on interstitial-free (IF) steel for the North American automobile companies. Recently, there has been a surge of interest in processing galvanneal coating on highstrength sheet steels, such as P-Nb-Ti, C-Mn-Al-killed, and Si-Nb-Ti steels, in search of stronger panel materials. The standard of the Fe content established for the coa