Metallography: Principles and Practices - ASM International
Metallography: Principles and Practices - ASM International
Metallography: Principles and Practices - ASM International
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<strong>Metallography</strong>: <strong>Principles</strong> <strong>and</strong> Practice (#06785G)<br />
Author(s): George F. V<strong>and</strong>er Voort<br />
1-2.5 Classification of Macroetch Features<br />
Copyright © 1984 <strong>ASM</strong> <strong>International</strong> ®<br />
All rights reserved.<br />
www.asminternational.org<br />
MACROSTRUCTURE 11<br />
Macroetching reveals many types of detail pertinent to the manufacturing process.<br />
It is important to categorize these defects <strong>and</strong> imperfections using unambiguous,<br />
universally understood terminology. Unfortunately, mill metallurgists do not<br />
all use the same jargon when describing macroetching features, which produces<br />
some confusion. The following lists the defects <strong>and</strong> imperfections associated with<br />
specific types of products.<br />
1. Macroscopic features in castings<br />
a. Blowholes. Round or elongated, smooth-walled cavities that are due to<br />
entrapped air or gas generation from molding or core s<strong>and</strong> <strong>and</strong> inadequate<br />
venting.<br />
b. Cold shut (cold lap). An interface caused by lack of fusion between two<br />
streams of metal during die casting due to inadequate fluidity.<br />
c. Contraction crack (hot tear). A crack formed during cooling. The crack<br />
location is fixed by the casting design <strong>and</strong> contraction resistance due to the<br />
mold or cores.<br />
d. Gas holes (pinholes). Small, uniformly distributed spherical cavities with<br />
bright walls, due to gas evolution.<br />
e. Oxide <strong>and</strong> dross inclusions. Macroscopic included matter entrapped in the<br />
castings that results from the entry of slag or dross into the casting during<br />
pouring.<br />
/. S<strong>and</strong> holes. Irregularly shaped cavities containing entrapped s<strong>and</strong> from<br />
the mold.<br />
g. Shrinkage cavity. Irregularly shaped cavities within the casting that are<br />
due to inadequate feeding.<br />
h. Shrinkage porosity. Irregularly shaped pores usually observed at a change<br />
of section or at the center of heavy sections that are due to inadequate<br />
feeding.<br />
2. Macroscopic features in wrought ingot products<br />
a. Surface defects such as seams or laps. Seams are perpendicular to the bar<br />
surface <strong>and</strong> follow the hot-working axis. Laps are developed during hot<br />
working by the folding over of surface metal.<br />
b. Pipe. A remnant of the ingot-solidification cavity usually associated with<br />
segregated impurities. In so-called primary pipe, the cavity is opened to the<br />
atmosphere <strong>and</strong> the cavity surfaces are oxidized. In "secondary" pipe<br />
there is no opening to the atmosphere <strong>and</strong> the cavity surfaces are not<br />
oxidized. Secondary pipe can be healed by further hot working, while<br />
primary pipe cannot.<br />
c. Burst. An internal void or crack, generally in the center of the bar, due to<br />
improper hot-working procedures.<br />
d. Center porosity. Possibly due to a discontinuity, such as pipe, or to gas<br />
evolution.<br />
e. Nonmetallic inclusions. Generally concentrated toward the center of the
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