Dendrite morphology of several steady state unidirectionally solidified iron base alloys
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INTRODUCTION
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CURRENTLY, many research activities are performed with the aim of improving the properties of solid materials. Increasing attention is being directed toward the casting process and the resulting solidification structure which, in most commercial steels, is dendritic. The segregation phenomena such as microsegregation, inclusion precipitation, and macrosegregation are influenced strongly by the solidification structure and can only be understood quantitatively if the detailed data on the relationship between growth morphology and freezing parameters are available. The dendrite spacings are controlled, for a given composition, by the growth rate R and the temperature gradient, G. Most previous investigations on steels have been carried out on ingot solidified material. In ingot solidification the growth rate and the temperature field are coupled by heat flow so that they cannot be varied independently. Independent control of G and R is possible, however, in steady state crystal growth methods. However, due to the experimental difficulties involved at the high temperatures, this technique has been applied only in a few investigations. ~-4Hence, data on steel are scarce. In a previous work from this laboratory 1 the growth morphology and dendrite arm spacings were studied with the steady state technique in two low alloyed steels containing 0.59 and 1.48 pct carbon. Dendrite arm spacings were related by the empirical equation A = KRmG ", where the exponents m and n were different for primary arms, but almost identical for secondary arms. In the present work the experiments were extended to a wider range of temperature gradient and to other alloyed steels with the objective of elucidating the effect of composition and the influence of the primary phase (3-iron or y-iron) crystallizing from the melt. MOHAMED AHMED TAHA is with the Department of Mechanical Design and Production Engineering, Ain-Shams University, Cairo, Egypt; HATTO JACOBI is with Mannesmann Forschungsinstitut, 41 DuisburgHuckingen, Ehinger Str. 200, Germany; MASANA IMAGUMBAI is with Nippon Steel, Kimitsu Work, Chiba, Japan; KLAUS SCHWERDTFEGER is with Institut fiir Theoretische Metallurgie, Technische Universitat Clausthal, 3392 Clausthal-Zellerfeld, Agricolastr. 6, Germany. All the authors were with Max-Planck lnstitut for Eisenforschung, 4 Dtisseldorf 1, Max-Planck-Str. 1, Germany, at the time this investigation was carried out. Manuscript submitted January 18, 1982.
METALLURGICAL TRANSACTIONS A
EXPERIMENTAL TECHNIQUE
The chemical compositions of the investigated steels are given in Table I. Steel A was investigated in the earlier work.l Steel A-1 is identical to A with respect to carbon (0.6 pct), but it is higher in sulfur and silicon and lower in manganese. Steels C to F are highly alloyed. Steels C, D, and E have about the same contents of substitutional elements (25 to 28 pct), but C and D crystallize as austenite whereas in E the primary solid phase is ferrite. The carbon content was fixed at about 0.6 pct. Steel F is a co
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