Having worked with and around Stainless Steel for quite some time, there
are some myths about the metal that seem to get taken as fact. I'll go over
some of the popular ones:
Big Myth #1: Stainless Steel is rustproof.
Reality: SS is rust resistant because rust is Iron Oxide. If the molecular
structure of the metal is such that the oxygen in water can't get to the
"Iron" (or ferrous) parts of the metal then it doesn't really "rust", but the
truth is that it's nearly impossble to stop this reaction from happening, all
SS mixtures do is slow the process down some to such a small point that we
could almost call it "rust proof".
Myth#2: Stainless Steel is a coating.
Reality: A coating is something that is applied to an "object" after it is
created. SS is created in the firing process of the metal when external
components such as chromium, nickel, molybdenum and austentite are added to
the metal to create SS. Certain types and grades of SS (due to the process of
manufacture) push these additives towards the surfaces of cast objects or, in
time, they migrate towards those surfaces forming a 'film'. Here's a clip
from the Austrailian Stainless Steel Developers Association regarding Marine
Grades of Stainless Steel:
"Stainless steel's corrosion resistance depends on the formation of a
"passive" chromium oxide film on the metal surface which is highly resistant
to corrosion. In grades 304 and 316, about 18% of chromium is added to
generate this film and, in 316, 2% molybdenum is added to further improve the
corrosion resistance. Grade 304 is usually only suitable for fittings which
are frequently washed with fresh water. Grade 316 is suitable for the
construction of deck fittings and critical rigging components where salt can
concentrate due to evaporation and lie in crevices - conditions which can
cause pitting of 304."
So even if you strip off this film, the metal can still resist rusting, but
not as well. Then again, only some grades are greatly bothered by the loss of
the film, duplex SS mixtures don't depend greatly upon that film for
protection.
Myth#3: Stainless Steel is Stainless Steel
Reality: As you can tell by reading the above quoted info, there are many
grades of Stainless Steel. Each one has it's uses whether its cost
effectiveness or absolute rust resistance. The problem seems to be, the more
additives you put in the steel to make it not rust, the weaker the metal
either by brittleness or softness.
Now that we've all had our SS lessons for the day (I had to look a lot of
this up), I would think that using it in a Throttle Body would be fine, even
with a lower grade of SS. I don't think Bruce and Frank need to be tossing
Medical Grade Surgical Stainless Steel in there just because the occasional
bit of moisture might accumulate on the shaft. I'm sure they both know that
and are using a nice piece of machinable SS. Some of the grades of SS are so
hard they almost can't be machined except with diamond bits (ran into some
like this).
Shaun H.
"What do ya mean you can barely scratch it? Isn't it just chrome plated
metal?"
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