Note the severe intergranular corrosion
that occurred in just three weeks of
service in nitric acid.
test reports say so,
or have you confirmed the test
reports are accurate
and represent the
actual casting that
will be used?
treatments may provide guidance for
resistance or certain
mechanical properties, but they do not
guarantee the highest quality. For
solution annealing of
cast austenitic stain-
less steel requires
the correct chemistry holding at suffi-
cient temperature and time followed by a
rapid quench. If done properly, the result-
ing microstructure would appear as
shown in Figure 1, contrasting with Fig-
ures 2 and 3, which do not exhibit the
How often do you verify the quality
of your cast austenitic stainless steel?
Figure 4 shows a CF8M valve body that
was not quenched at an acceptable rate.
Repair welding: competence and
It is impractical to expect 100% perfect
castings every time; defects are
inevitable. Repair of defects at foundries
is commonplace, but it is often overlooked. I strongly recommend that you
visit the weld repair room whenever visiting a foundry. Are the welders routinely
qualified to any standard? Do they have
weld procedures to control their processes? Do they follow those procedures? Is
the equipment in good shape and appropriate for the types of repair being done?
Are the filler metals the correct ones and
are they stored properly? Are defects
fully excavated before welding? This
plenitude of questions, when left unan-swered, puts you at high risk for low
quality. See Figure 5.
There are many ways for free iron to
embed into the surface of stainless steel.
In sand castings, reuse of sand previously used for carbon steel, cleaning of
stainless castings with carbon steel shot
or carbon steel wire brushes are examples. If no steps are taken to check for
and remove the free iron, your stainless
steel casting can rust on the exterior.
Passivation is one way to remove this
free iron. See Figure 6.
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