Metallography: Principles and Practices - ASM International

Metallography: Principles and Practice (#06785G)
Author(s): George F. Vander Voort
Copyright © 1984 ASM International ®
All rights reserved.
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MACROSTRUCTURE 51
ground surface, and any air bubbles are removed. The specimen with the paper
underneath is placed on an aluminum plate. The aluminum plate contacting the
paper is connected to the positive terminal of a dc power supply, and the specimen
is connected to the negative terminal. A potential of 3 V is applied for 10 s,
producing an image of the sulfur distribution. The print is then removed and
processed in the usual manner.
Figure 1-38 illustrates the use of sulfur prints in the study of macrostructures
and shows a sulfur print of the macroetched disc presented in Fig. 1-6. Note that
the sulfur print exhibits the same features as revealed by macroetching.
The intensity of sulfur prints can be influenced by chromium in the sulfides, a
problem that was recognized in work with stainless steels. Monypenny, in his
classic book on stainless steels, states that sulfur prints in stainless steels frequently
do not show images [39]. In some of these stainless steel alloys that print
poorly, the manganese content is about 0.20%, while chromium is 18% or
greater. However if the manganese content in the stainless is 0.60% or greater, a
print can be obtained. Garvin and Larrimore examined sulfur print response in
AISI430 stainless steel [40]. These authors made four ingots with 0.08,0.42,0.77,
and 1.56% manganese. Low-manganese heats contained chromium sulfides and
did not produce an image on the sulfur print. As the manganese content
increased, print intensity increased. Figure 1-39 shows sulfur prints of discs cut
from steels with two slightly different compositions but with the same sulfur
content. On the right is a print of normal intensity in which little chromium is
present in the sulfides, while on the left is a sulfur print which is considerably
lighter because considerable chromium is present in the sulfides.
Figure 1-39 Sulfur print intensity is influenced by the composition of the sulfide inclusions. Both of the
sulfur-printed discs shown contain 0.06% sulfur, but the print on the left is very light because most of
the sulfides contain considerable chromium and are low in manganese content. The sulfides in the disc
at the right contain very little chromium.