Metallography: Principles and Practices - ASM International

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Metallography: Principles and Practice (#06785G) Author(s): George F. Vander Voort 14 METALLOGRAPHY Figure 1-1 Cold etch of disc cut from small ingot (10% aqueous HNO,). W : vliM Copyright © 1984 ASM International ® All rights reserved. www.asminternational.org Figure 1-2 Macrostructure of centrifugally cast 99.8% aluminum after a minor amount of reduction (3'/4 x ; etehant, solution of 5 mL HN03, 5 mL HCl, 5 mL HF, and 95 mL H20). (Courtesy ofR. D. Buchheit, Battelle-Columbus Laboratories.)
Metallography: Principles and Practice (#06785G) Author(s): George F. Vander Voort 0 1 2 3 1 , I , I , I , I , I , I Copyright © 1984 ASM International ® All rights reserved. www.asminternational.org MACROSTRUCTURE 15 Figure 1-3 Macrostructure of directionally solidified nickel-base eutectic alloy (etchant, solution of 1 mL H202 and 99 mL HC1). (Courtesy ofW. Yankausas, TRW, Inc.) The presence of a coarse columnar grain structure can impart useful properties to a material that is to be used at high temperature. Considerable effort has been made to preferentially grow such grains in high-temperature alloys used in turbines. Figure 1-3 shows the macrostructure of a directionally solidified nickelbase eutectic alloy in several product forms. 1-3.2 Billet and Bloom Macrostructures In general, the steelmaker uses the hot-acid etch on discs cut, with respect to the ingot location, from the top and bottom or the top, middle, and bottom of billets or bloomst rolled from the first, middle, and last ingots teemed from the heat. If a disc reveals a rejectable condition, billet material is rejected until the condition is removed. Figure 1-4 shows "dirty" corners, a lap, several small seams, and freckle-type segregation in a hot-acid etched disc of bearing steel. The inclusion present in the dirty corner (lower right) is a Mn-Fe-Al silicate. Figure 1-5 shows ingot pattern and pits from inclusions in alloy steel. In Figure 1-6 the standard hot etching has revealed entrapped gas, heavy segregation, voids, and ingot pattern in a disc of AISI4140 alloy steel. Figure 1-7 shows the microstructure near the center of this disc (longitudinal plane through the disc). The center of the disc is coarse and exhibits an open pipe condition and associated segregation. t Blooms are rolled sections larger than 6 by 6 in, while billets are smaller than this.
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Metallography: Principles and Practices - ASM International

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