The
reason for using stainless steel is that it differs from carbon steel
by the amount of chromium present and reduces the spalling.
Unprotected carbon steel rusts readily when exposed to air and
moisture. This iron oxide film (the rust) is active and accelerates
corrosion by forming more iron oxide, and due to the greater volume
of the iron oxide this tends to flake and fall away (spall).
Stainless
steels contain sufficient chromium to form a passive film of chromium
oxide, which prevents further surface corrosion by blocking oxygen
diffusion to the steel surface and blocks corrosion from spreading
into the metal's internal structure, and due to the similar size of
the steel and oxide ions they bond very strongly and remain attached
to the surface.
There
are a number of grades of stainless steel. Some of the ones that
perform better in hot conditions are:
300
Series—austenitic chromium-nickel alloys. Austenitic steels have a
cubic crystal structure. Austenite steels make up over 70% of total
stainless steel production. They contain a maximum of 0.15% carbon, a
minimum of 16% chromium and sufficient nickel and/or manganese to
retain an austenitic structure at all temperatures from the extremely
cold to the melting point of the alloy.
Type
304—the most common grade; the classic 18/8 (18% chromium, 8%
nickel) stainless steel. Outside of the US it is commonly known as
"A2 stainless steel", in accordance with ISO 3506 (not to
be confused with A2 tool steel).
Type
304L—same as the 304 grade but lower carbon content to increase
weldability. Is slightly weaker than 304.
Type
304LN—same as 304L, but also nitrogen is added to obtain a much
higher yield and tensile strength than 304L.
Type
309—better temperature resistance than 304, also sometimes used as
filler metal when welding dissimilar steels, along with inconel.
Type
316—the second most common grade (after 304); for food and surgical
uses; alloy addition of molybdenum prevents specific forms of
corrosion. It is also known as marine grade stainless steel due to
its increased resistance to chloride corrosion compared to type 304.
Type
316L—is an extra low carbon grade of 316, generally used in
stainless steel watches and marine applications, as well exclusively
in the fabrication of reactor pressure vessels for boiling water
reactors, due to its high resistance to corrosion. Also referred to
as "A4" in accordance with ISO 3506.
Type
316Ti—variant of type 316 that includes titanium for heat
resistance. It is used in flexible chimney liners.
Type
321—similar to 304 but lower risk of weld decay due to addition of
titanium.
400
Series—ferritic and martensitic chromium alloys
Type
439—ferritic grade, used for catalytic converter exhaust sections.
Increased chromium for improved high temperature corrosion/oxidation
resistance.
Type
446—For elevated temperature service
500
Series—heat-resisting chromium alloys
Based
on Wikipedia
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