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Q. What is stainless steel?
Stainless steel is the generic name for a number of different
steels used primarily because of their
corrosion resistance. All stainless steels share a minimum
percentage of 10.5% chromium. It is this
element that reacts with the oxygen in the air to form a complex
chrome-oxide surface layer that is
invisible but strong enough to prevent further oxygen from
"staining" (rusting) the surface.
The film itself is extremely thin, about 130 Angstroms and one
Angstrom is one millionth of a centimeter.
This layer is described as passive (does not react or influence
other materials), tenacious (clings to the
layer of steel and is not transferred elsewhere) and
self-renewing (if damaged, more chromium from the
steel will be exposed to the air and form more chromium
oxide).
This means that over a period of years a stainless steel knife
can literally be worn away by daily use and
will still remain stainless. Higher levels of chromium and the
addition of other alloying elements such as
nickel and molybdenum enhance this surface layer and improve the
corrosion resistance of the stainless
material. Chromium is always the deciding factor, although other
elements, particularly nickel and
molybdenum, are added to improve corrosion resistance.
Furthermore, stainless steel is fully recyclable.
The three major classes of stainless steel are:
Austenitic: Chromium-nickel-iron alloys with 16-26% chromium,
6-22% nickel (Ni), and low carbon
content, with non-magnetic properties (if annealed - working it
at low temperatures, then heated and
cooled). Nickel increases corrosion resistance. Harden able by
cold-working (worked at low temperatures)
as well as tempering (heated then cooled). Type 304 (S30400) or
"18/8" (18% chromium 8% nickel), is
the most commonly used grade or composition.
Martensitic: Chromium-iron alloys with 10.5-17% chromium and
carefully controlled carbon content,
harden able by quenching (quickly cooled in water or oil) and
tempering (heated then cooled). It has
magnetic properties. Commonly used in knives. Martensitic grades
are strong and hard, but are brittle and
difficult to form and weld. Type 420 (S42000) is a typical
example.
Ferritic: Chromium-iron alloys with 17-27% chromium and low
carbon content, with magnetic properties.Cooking utensils made of
this type contain the higher chromium levels. Type 430 is the most
commonly
used ferritic. Two additional classes worth mentioning include
Duplex (with austenitic and ferritic
structures), and Precipitation Hardening stainless steel, used
in certain extreme conditions.
Q. What does chrome-nickel content mean?
Chrome-Nickel content refers to the percentage of chrome and
nickel in the stainless steel. Chrome gives
the stainless steel its luster & durability, while the
nickel is for the hardness & strength. 18/10 Stainless
Steel means it contains 18% Chromium or Chrome and 10% Nickel. A
sink with an 18/10 chrome-nickel
content is considered to be an excellent grade, due to its
corrosive resistance and greater durability.
Q. What is the difference between 18/8 and 18/10 stainless
steel?
The first number is the amount of chromium that is contained in
the stainless, i.e., 18 is 18% chromium.
The second number is the amount of nickel, i.e., 8 stands for 8%
nickel. So 18/8 means that this stainless
steel contains 18% chromium and 8% nickel. 18/10 is 18% chromium
and 10% nickel.
The higher the numbers the more corrosion resistant the
material. Both 18/8 and 18/10 contain nickel
and are part of the grade family "300 series" stainless. 18/0
means that there is 18% chromium but zero
nickel. When there is no nickel the stainless grade family is
the "400 series".
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8/22/2019 About Stainless Steel Questions
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400 series are not as corrosion resistant as the 300 series and
are magnetic, where the 300 series are
non-magnetic and is the grade mainly used for sinks, Food
processing equipment, Restaurant food
preparation areas etc.
Q. What is the difference between 304 and 316 stainless
steel?
304 contains 18% chromium and 8% nickel. 316 contains 16%
chromium, 10% nickel and 2%molybdenum. The "moly" is added to help
resist corrosion to chlorides (like sea water and de-icing
salts.
Q. Can stainless steel be "welded"?
YES. Stainless steel is easily welded, but the welding procedure
is different than that used with carbon
steel. The "filler" rod or electrode must be stainless
steel.
Q. What temperatures can stainless steel withstand?
Stainless steel has excellent properties at both extremes of the
temperature scale. Some stainless steel
can be used down to liquid nitrogen temperatures and some up to
about 1800 F.
Q. What is the recycle content of stainless steel?
Stainless steel can be recycled 100%. That is all stainless
steel can be re-melted to make new stainless
steel. The typical amount of recycled stainless steel "scrap"
that is used to make new stainless steel is
between 65 & 80%.
Q. Can stainless steel rust? Why? (I thought stainless did not
rust!)
Stainless does not "rust" as you think of regular steel rusting
with a red oxide on the surface that flakes
off. Corrosion is generally caused by contaminants settling on
the surface of the stainless steel.
Q. Is stainless steel magnetic?
There are several "types" of stainless steel. The 300 series
(which contains nickel) is NOT magnetic. The
400 series (which just contains chromium and no nickel) ARE
magnetic.
Q. How are different classes of stainless steels used?
The austenitic microstructure is most commonly used for knives
and cooking utensils. It is very tough,
hardened through a process that consists of heating, cooling and
heating. It resists scaling and retains
strength at high temperatures.
Both ferritics and austenitics are used in kitchenware and
household appliances. Austenitics are preferred
in the food industry and beverage equipment due to the superior
corrosion resistance and ease of
cleaning. Type 301, for example, is an austenitic stainless
steel, with 17% chromium, 7% nickel, and
.05% carbon, and is widely used for institutional food
preparation utensils.
You can easily make do with the lesser quality cookware for most
oven use. For stovetop cooking,
however, don't skimp on quality; buy only the better ones. Most
manufacturers of high quality cookwareuse stainless steel similar
to the Type 304 grade, with thick heat diffusing bottoms. Metals
that provide
better diffusion of heat, such as copper and aluminum, are
attached to the bottom for heat diffusion, to
prevent hot spots and uneven cooking.
Low quality cutlery is generally made out of grades like 409 and
430 (ferritic), while the finest Sheffield
cutlery uses specially produced 410 and 420 (martensitic) for
the knives, and 304 (austenitic) for the
spoons and forks. Grades like the 410/420 can be hardened and
tempered so that the knife blades will
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