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Page Contents:
-What is stainless steel
-What are benefits of stainless steel in the
kitchen
-What gives stainless steel its properties
-How can stainless steel affect my health
-What precautions to take when using
stainless steel
-How do I clean stainless steel cookware
-How do I clean stainless steel knives
-How are stainless steels classified
-How are different classes of stainless steel used
-Glossary of terms
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Stainless Steel
What is stainless steel?
Stainless Steel is a common name for metal alloys that consist of 10.5%
or more Chromium (Cr) and more than 50% Iron (Fe). Although it is called
"stainless", a better term for it is "highly stain resistant". A somewhat
dark metal, it looks bright because it reflects light.
What are the main
benefits of stainless steel in kitchen utensils?
♦ It is one of the most hygienic surfaces for the preparation of foods
and very easy to clean, as its unique surface has no pores or cracks to
harbor dirt, grime or bacteria.
♦ It is very attractive and requires minimal care, since it won't chip
or easily rust and it takes little seasoning.
♦ It will not affect flavor, as it does not react with acidic foods
during food preparation or cooking.
♦ With proper care, it has a useful life expectancy of over 100 years,
and it is totally recyclable.
What gives stainless
steel its properties?
The chromium content in stainless steel alloys is what generally prevents
corrosion. Pure iron, the primary element of stainless steel, is extracted
from its natural state as iron ore, it is unstable by itself, and naturally
wants to corrode (rust). The chromium helps to procrastinate nature's
attempts to combine the pure iron with oxygen and water to form rust.
The chromium works by reacting with oxygen to form a tough, adherent,
invisible, passive layer of chromium oxide film on the steel surface. If
damaged mechanically or chemically, this film is self healing as long as it
has enough oxygen.
Because oxygen is necessary for the reaction, liquids and other foodstuffs
stored for a prolonged time in stainless can prevent oxygen contact and thus
promote corrosion, as can prolonged contact with household cleaners such as
bleach.
Generally, an increase of chromium content improves the corrosion resistance
of stainless steels. The addition of nickel is used to raise the general
corrosion resistance required in more aggressive usage or conditions. The
presence of molybdenum (Mo) improves the localized corrosion resistance,
such as against pitting (scarring).
Other alloying metals are also used to improve the structure and properties
of stainless steels, such as Titanium, Vanadium and Copper. Non metal
additions typically include natural elements such as Carbon & Nitrogen, as
well as Silicon.
High-carbon stainless steel contains a minimum of 0.3% carbon. The higher
the carbon content, the less formable and the tougher the steel becomes. Its
hardness makes it suitable for things such as cutting edges, and other
high-wear applications like plow blades. Carbon thus helps makes the edge
easier to sharpen, and helps retain a sharp edge longer.
How can stainless steel
affect my health?
The principal elements in stainless that have effects on our health are
iron, chromium and nickel.
♦ Iron can be very beneficial and a required mineral in a normal diet.
♦ Chromium is also beneficial in small quantities, and you would have
to cook four complete meals in the same stainless steel pots every day to
come anywhere close to reaching any adverse affects from chromium intake.
♦ Although nickel is poisonous in large quantities, only trace amounts
go into the food - not enough to make a difference. The few who are allergic
to nickel, however, should avoid using stainless altogether.
What precautions do I
need to take when using stainless steel in my kitchen?
♦ To prevent hot spots when using stovetop cookware, it should have a
heat diffusing base, either visible or encapsulated, that is made of a
better heat-diffusing material, like copper or aluminum. These metals are
highly conductive of heat, so use moderate heat to maximize the even
spreading of heat, minimize sticking, and to get tastier, more evenly cooked
food with less stirring.
♦ Do not store food or liquids in stainless steel cookware after
cooking.
♦ To keep the surface smooth and scratch-free, do not use abrasives,
bleach or ammonia. See cleaning instructions below.
Top
How do I
clean stainless steel cookware?
♦ To remove manufacturer or price stickers from cookware...
Soak the area with warm water, then scrape off with your fingernail or with
a hard-plastic spatula. A bit of rubbing alcohol, or a citrus oil based
cleaner, will remove any remaining glue.
♦ When using a pan for the first time... Wash it well
with soapy warm water and dry thoroughly. We recommend washing by hand.
♦ Whitish or chalkish deposits inside pan... Remove
calcium deposits by boiling water with some white vinegar, allowing your pan
to cool, then washing it with warm, soapy water. Help prevent white spots
and pitting by adding salt to your cookware only after the water has reached
a boil.
♦ Burnt food is stuck in pan... Cover the stuck
foodstuffs with warm soapy water, allow to soak for some time, then boil for
10 minutes, allow it to cool, then use a soft cloth, or a nylon scourer if
stubborn, and warm, soapy water.
♦ Still not clean out of the dishwasher... You might
select a Pre-wash cycle if your pan's instructions indicate it is safe to
clean in the dishwasher.
♦ Spills or overflows... Wash or clean the exterior
before placing it again over heat.
♦ Filled pan left to cool on stove and lid won't come off...
Warm the pan, then twist the lid to remove it.
♦ Left empty on heated surface... Allow it to cool
slowly; do not immerse it in cold water.
♦ Stainless pan was left on heated surface, liquid has dried and
yellow or blue streaks appear... On polished stainless, use a metal
cleaner, such as Wenol or Red Bear, with a soft cloth. On satin stainless,
use a nylon scourer, such as Scotch-Brite.
♦ Scratches on surface after washing repeatedly...
Change your cleaning product to a gentler kind, such as Bon Ami.
♦ Cleaners not recommended for stainless surfaces...
Bleach or ammonia should not be used on stainless steel.
How do I clean stainless
steel knives?
The easiest and safest way to clean knives is to wipe them during and
immediately after use, before food gets a chance to stick and dry on the
blade. That's one of the reasons why professional cooks have a dish towel
tucked at their waist.
Be sure to use caution when cleaning knives, to prevent cuts. Always draw
the knife away from its cutting edge on the towel, starting near the handle.
(Use caution.)
Top
How are stainless steels
classified?
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. Hardenable 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, hardenable 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.
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 cookware use 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 take
a sharp edge, whereas the more ductile 304 stainless is easier to work and
therefore more suitable for objects that have to undergo numerous shaping,
buffing and grinding processes.
The best quality stainless steel knife blades have a high carbon content,
and usually have molybdenum and vanadium in their composition.
Glossary
From: www.steel.org/learning/glossary/glossary.htm
Alloy Steel
An iron-based mixture is considered to be an alloy steel when manganese is
greater than 1.65%, silicon over 0.5%, copper above 0.6%, or other minimum
quantities of alloying elements such as chromium, nickel, molybdenum, or
tungsten are present. An enormous variety of distinct properties can be
created for the steel by substituting these elements in the recipe.
Annealing
A heat or thermal treatment process by which a previously cold-rolled steel
coil is made more suitable for forming and bending. The steel sheet is
heated to a designated temperature for a sufficient amount of time and then
cooled. The bonds between the grains of the metal are stretched when a coil
is cold rolled, leaving the steel brittle and breakable. Annealing "recrystallizes"
the grain structure of steel by allowing for new bonds to be formed at the
high temperature.
Austenitic
The largest category of stainless steel, accounting for about 70% of all
production. The austenitic class offers the most resistance to corrosion in
the stainless group, owing to its substantial nickel content and higher
levels of chromium. Austenitic stainless steels are hardened and
strengthened through cold working (changing the structure and shape of steel
by applying stress at low temperature) instead of by heat treatment.
Ductility (ability to change shape without fracture) is exceptional for the
austenitic stainless steels. Excellent weldability and superior performance
in very low-temperature services are additional features of this class.
Applications include cooking utensils, food processing equipment, exterior
architecture, equipment for the chemical industry, truck trailers, and
kitchen sinks. The two most common grades are type 304 (the most widely
specified stainless steel, providing corrosion resistance in numerous
standard services) and type 316 (similar to 304 with molybdenum added, to
increase opposition to various forms of deterioration).
Carbon Steel
Steel that has properties made up mostly of the element carbon (C) and which
relies on the carbon content for structure. Most of the steel produced in
the world is carbon steel.
Chromium (Cr)
An alloying element that is the essential stainless steel raw material for
conferring corrosion resistance. A film that naturally forms on the surface
of stainless steel self-repairs in the presence of oxygen if the steel is
damaged mechanically or chemically, and thus prevents corrosion from
occurring.
Cladding
Method of applying a stainless steel coating to carbon steel or lower-alloy
steel (i.e., steel with alloying element content below 5%). This increases
corrosion resistance at lower initial cost than exclusive use of stainless
steel, and is made by (1) welding stainless steel onto carbon steel, (2)
pouring melted stainless steel around a solid carbon steel slab in a mold,
or (3) placing a slab of carbon steel between two plates of stainless steel
and bonding them by rolling at high temperature on a plate mill.
Cold Working (Rolling)
Changes in the structure and shape of steel achieved through rolling,
hammering, or stretching the steel at a low temperature (often room
temperature). This creates a permanent increase in the hardness and strength
of the steel. The application of forces to the steel causes changes in the
composition that enhance certain properties. In order for these improvements
to be sustained, the temperature must be below a certain range, because the
structural changes are eliminated by higher temperatures.
Corrosion
The gradual degradation or alteration of steel caused by atmosphere,
moisture, or other agents.
Ferritic
The second-largest class of stainless steel, constituting approximately 25%
of stainless production. Ferritic stainless steels are plain chromium steels
with no significant nickel content; the lack of nickel results in lower
corrosion resistance than the austenitics (chromium-nickel stainless
steels). Ferritics are best suited for general and high-temperature
corrosion applications rather than services requiring high strength. They
are used in automotive trim and exhaust systems, interior architectural
trim, and hot water tanks. Two of the most common grades are type 430
(general-purpose grade for many applications, including decorative ones) and
type 409 (low-cost grade well suited to withstanding high temperatures).
Ferrochrome
An alloy of iron and chromium with up to 72% chromium. Ferrochrome is
commonly used as a raw material in the making of stainless steel.
Ferrous
Metals that consist primarily of iron.
Galvanized Steel
Steel coated with zinc to provide corrosion resistance for a wide range of
products including automobiles, bridges, storage tanks, structural steel,
fasteners, duct work, light poles, pipe, sign supports, reinforcing steel
and wire.
Gauge
The thickness of sheet steel. Better-quality steel has a consistent gauge to
prevent weak spots or deformation.
Hardening
Process that increases the hardness of steel, i.e., the degree to which
steel will resist cutting, abrasion, penetration, bending, and stretching.
This increases the endurance provided by hardening and makes steel suitable
for additional applications. Hardening can be achieved through various
methods, including (1) heat treatment, where the properties of steel are
altered by subjecting the steel to a series of temperature changes; and (2)
cold working, in which changes in the structure and shape of steel are
achieved through rolling, hammering, or stretching the steel at a relatively
low temperature.
Heat Treatment
Alters the properties of steel by subjecting it to a series of temperature
changes. This increases the hardness, strength, or ductility of steel so
that it is suitable for additional applications. The steel is heated and
then cooled as necessary to provide changes in the structural form that will
impart the desired characteristics. The time spent at each temperature and
the rates of cooling have significant impact on the effect of the treatment.
High-Carbon Steel
Steel with more than 0.3% carbon. The more carbon that is dissolved in the
iron, the less formable and the tougher the steel becomes. High-carbon
steel's hardness makes it suitable for plow blades, shovels, bedsprings,
cutting edges, or other high-wear applications.
Iron Ore
Mineral containing enough iron to be a commercially viable source of the
element for use in steelmaking. Except for fragments of meteorites found on
Earth, iron is not a free element; instead, it is trapped in the earth's
crust in its oxidized form.
Low-Carbon Steel
Steel with less than 0.005% carbon is more ductile (malleable): It is
capable of being drawn out or rolled thin for use in automotive body
applications. Carbon is removed from the steel bath through vacuum
degassing.
Martensitic
Small category of stainless steel characterized by the use of heat treatment
for hardening and strengthening. Martensitic stainless steels are plain
chromium steels with no significant nickel content. They are utilized in
equipment for the chemical and oil industries and in surgical instruments.
The most popular martensitic stainless steel is type 410 (a grade
appropriate for non-severe corrosion environments requiring high strength).
Molybdenum (Mo)
An alloying element used as a raw material for some classes of stainless
steel. Molybdenum in the presence of chromium enhances the corrosion
resistance of stainless steel.
Nickel (Ni)
An alloying element used as a raw material for certain classes of stainless
steel. Nickel provides high degrees of ductility (ability to change shape
without fracture) as well as resistance to corrosion. Approximately 65% of
all nickel is used in the making of stainless steel.
Pig Iron
The name for the melted iron produced in a blast furnace, containing a large
quantity of carbon (above 1.5%). Named long ago when molten iron was poured
through a trench in the ground to flow into shallow earthen holes, the
arrangement looked like newborn pigs suckling. The central channel became
known as the "sow," and the molds were "pigs."
Sintering
A process that combines iron-bearing particles into small pellets or chunks.
(Some knives and other utensils are made of separately manufactured parts
that are sintered together to form one piece. Sintering is also used in
other industries, such as ceramics.)
Stainless Steel
The generic term for grades of steel that contain more than 10% chromium,
with or without other alloying elements. Stainless Steel may also have
varying additions of Nickel, Molybdenum, Titanium, Niobium and other
elements. Stainless steel resists corrosion, maintains its strength at high
temperatures, and is easily maintained. The chromium in the steel combines
with oxygen in the atmosphere to form a thin, invisible layer of
chrome-containing oxide. The most common grades of stainless steel are:
TYPE 304 - The most commonly specified austenitic (chromium-nickel stainless
class) stainless steel, accounting for more than half of the stainless steel
produced in the world. This grade withstands ordinary corrosion in
architecture, is durable in typical food processing environments, and
resists most chemicals. Type 304 is available in virtually all product forms
and finishes.
TYPE 316 - Austenitic (chromium-nickel stainless class) stainless steel
containing 2%-3% molybdenum (whereas 304 has none). The inclusion of
molybdenum gives 316 greater resistance to various forms of deterioration.
TYPE 409 - Ferritic (plain chromium stainless category) stainless steel
suitable for high temperatures. This grade has the lowest chromium content
of all stainless steels and thus is the least expensive.
TYPE 410 - The most widely used martensitic (plain chromium stainless class
with exceptional strength) stainless steel, featuring the high level of
strength conferred by the martensitics. It is a low-cost, heat-treatable
grade suitable for non-severe corrosion applications.
TYPE 430 - The most widely used ferritic (plain chromium stainless category)
stainless steel, offering general-purpose corrosion resistance, often in
decorative applications.
Tin/Chrome Plating
A plating process whereby the molecules from the positively charged tin or
chromium anode attach to the negatively charged sheet steel. The thickness
of the coating is readily controlled through regulation of the voltage and
speed of the sheet through the plating area. |
