Rapid Solidification Behavior of Fe-Cr-Mn-Mo-Si-C Alloys
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HIGH-SOLUTE-CONTENT Fe-base alloys subjected to rapid solidification often exhibit metastable phases very different from those obtained at slow cooling rates.[1–7] The occurrence of nonequilibrium compositions in the solid phases,[1–9] associated with values of the solid/liquid partition coefficients of the solute elements close to one,[10] have been reported in rapidly-solidified Fe-base alloys. In certain cases, such as in melt-spun Fe40Ni40P14B6 samples,[11] a transition from a crystalline to an amorphous structure has been observed. As a result of the limited partitioning of the solute elements between the solid and the liquid during solidification, large amounts of alloying elements can be supersaturated in the metastable phases obtained. In particular, large carbon contents can be retained in solid solution in alloys that would form carbide particles under equilibrium conditions.[1–7] Inoue et al.[1] observed the formation of metastable single (austenite) or duplex (austenite + lath martensite) structures in meltspun Fe-Ni-Cr-Al-C alloys (with up to 8 at. pct C, 11 at. pct Al, 20 at. pct Cr, and 8 at. pct Ni), instead of the equilibrium structure composed of ferrite, FeAl, M7C3, and M23C6 phases. Elliot et al.[8] studied the structure of melt-spun Fe-Ni-Cr-C-base alloys and reported a supersaturation of up to 8 at. pct C in an austenitic phase. High supersaturations of carbon, up to 4.8 wt pct, were reported in the metastable c, e, and w phases formed in melt-spun high-C, high-Cr, and high-Mo Fe-Cr-Mo-Si-C alloys.[2] SATHEES RANGANATHAN, Doctoral Student, ADVENIT MAKAYA, Researcher, HASSE FREDRIKSSON, Professor, and STEVEN SAVAGE, Associate Professor, are with Materials Processing, Royal Institute of Technology, SE-100 44, Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted March 15, 2006. Article published online December 1, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
The interest in supersaturating large amounts of carbon and carbide-forming elements in solid solution lies in the possibility of forming fine structures with small homogeneously distributed carbides upon reheating, instead of the coarse carbide particles obtained under equilibrium conditions. This can lead to the development of steels with high strength, hardness, and toughness values.[1,3] However, the structures listed above were obtained by melt spinning or splat-cooling processes, i.e., at very high cooling rates (>105 K/s) and for limited sample thicknesses (850 HV) could be exploited in the development of high strength steels.
ACKNOWLEDGMENT The authors thank Mr. Hans Bergquist for assistance with the TEM analyses.
VOLUME 38B, DECEMBER 2007—925
REFERENCES 1. A. Inoue, H. Tomioka, N. Yano, and T. Masumoto: Proc. 5th Int. Conf. on Rapidly Quenched Metals, Wuˆrzburg, Germany, Sept. 3–7, 1984, S. Steeb and H. Warlimont, eds., North-Holland Physics Publishing, Amsterdam, The Netherlands, 1985, pp. 1783– 86. 2. K. Kishitake, H. Era, and P. Li: Mater. Trans., JIM, 1993, vol. 34, pp. 54–61. 3. K. Kishitake,
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