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melting point results in a break-up and spheroidization of the iron rods together with diffusion of iron to the surface and grain boundaries of specimens. The driving force for these processes is a tendency by the system to minimize its interfacial energy. The spheroidizing of iron rods as a means of decreasing the interracial energy, is aided by the absence of preferred crystallographic orientations. The eutectic is considerably more thermally unstable than both the A1-CuA12 and A1-A13Ni eutectic possibly because of: a) its higher interfacial energy, and b) the higher heat treatment temperatures used.The stability of the eutectic structures was found to be a function of: a) time and temperature of heat treatment, b) interrod spacings, and c) oxygen content of the alloys. Point a) affects the diffusion characteristics of the system, whereas b) and c) affect the initial interracial energy of the system.

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Metallographer’s Guide: Practice and Procedures for Irons and Steels provides an overview of the important metallurgical concepts related to the microstructures of irons and steels, with detailed guidelines for the proper metallographic techniques used to reveal, capture, and understand microstructures. The book includes an explanation of the various types of steels and cast irons available in the commercial world. Examples of the microstructures that the metallographer will encounter, how they are created, and how they can be altered by heat treatment and other means is explained. The book emphasizes light (optical) metallography; detail about how a metallurgical microscope works is included. The book describes step-by-step instructions for laboratory equipment selection and use, microscopy techniques, specimen preparation, and etching. For information on the print version, ISBN 978-0-87170-748-2, follow this link.

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The effect of variations in cooling rate on the morphology and kinetics of pearlite was studied and was contrasted with the isothermal and isovelocity modes of transformation. It was found that continuous cooling suppresses the pearlite transformation to a lower reaction temperature where finer nodule diameters and interlamellar spacings are produced. Growth rates in continuous cooling were in agreement with those for the isovelocity and isothermal transformations, the rate-controlling process for growth in the temperature range studied being volume diffusion in all three cases. The relationship between interlamellar spacing and undercooling was found to be SOT = 8.02>< 10 4A K, regardless of the mode of transformation.THE morphology and kinetics of pearlite is well established in the literature and has been carefully reviewed in several papers."" Growth-rate measurements and interlamellar spacing on both pure Fe-C alloys and ternary alloys have been made for isothermally produced pearlite. 3' 4 Recently, pearlite transformed through a steep temperature gradient has produced bidirectional pearlite, i.e., pearlite colonies that are ±450 to the growth axes, 5 and a morphological study of the substructure has been reported. s Kinetic studies of this type of transformation have been conducted and have shown that the two modes of growth, i.e., isothermal and isovelocity, can be interrelated.' , ' A critical appraisal of these two modes of transformation has also been recently reported in the literature. 9 On the other hand, the effect of continuous cooling on the morphology and kinetics of the pearlite transformation, though of considerable practical importance, has received little attention in the literature. The effect of cooling rate on the partial transformation to pearlite in low-carbon steel has been studied, 1° but the kinetics of the transformation have not been investigated because of the experimental difficulties involved. Recently, a hot-stage cinephotomicrography technique has been developed that allows for the in situ study of pearlite growth during cooling.' 1 The present paper describes the results of this hot-stage technique in the study of the morphology and kinetics of pearlite transformed by continuous cooling. EXPERIMENTAL PROCEDURESamples of an Fe-0.81 C binary alloy* were austeni-*tized at 1010°C for 2 min in the hot-stage microscope and cooled at various rates up to 10,000°C/ min. Detailed discussion of the hot-stage technique was given in previous papers.' 8 ' 13 Nodule-diameter measurements were made on five separate planes of polish for each specimen, and at least thirty measurements were made for each cooling rate. Difficulties were encountered in obtaining the true nodule diameter, because pearlite nodules, as defined by Hull and Mehl, 14 vary in size for a given condition, depending on which nodule nucleated first, and a plane of pol -i s h w i l l n o t b e a b l e t o c u t a l l t h e n o d u l e s i n a p o p u l a t i o n precisely at the true diameter of the nodule (sphere). Because ...