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Stainless Steel
DATE:2013-04-05   Views:37  Back

 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.

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.)

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.


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.

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.

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.

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.

The gradual degradation or alteration of steel caused by atmosphere, moisture, or other agents.

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).

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.

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.

The thickness of sheet steel. Better-quality steel has a consistent gauge to prevent weak spots or deformation.

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.

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."

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.
Fermentation is the conversion of a carbohydrate such as sugar into an acid or an alcohol. More specifically, fermentation can refer to the use of yeast to change sugar into alcohol or the use of bacteria to create lactic acid in certain foods. Fermentation occurs naturally in many different foods given the right conditions, and humans have intentionally made use of it for many thousands of years.
The earliest uses of fermentation were most likely to create alcoholic beverages such as mead, wine, and beer. These beverages may have been created as far back as 7,000 BCE in parts of the Middle East. The fermentation of foods such as milk and various vegetables probably happened sometime a few thousand years later, in both the Middle East and China. While the general principle of fermentation is the same across all of these drinks and foods, the precise methods of achieving it, and the end results, differ.
Beer is made by taking a grain, such as barley, wheat, or rye, germinating and drying it, and pulping it into a mash. This mash is then mixed with hot water, and some fermentation begins. After being further treated, the liquid is transferred to a fermentation vessel, where yeast is added to the mixture. This yeast “eats” the sugar present in the mash and converts it into carbon dioxide and alcohol. After a few weeks of fermentation and a further period of conditioning, the beer is ready to be filtered and consumed.
Wine is created using a similar method that also involves fermentation. Grapes are crushed to release the sugar-rich juices, which are then either transferred quickly away from the skins or left to rest for a time to absorb some of the flavor, tannins, and color of the skins. Yeast is then added, and the grape juice is allowed to ferment for a number of weeks, at which point it is moved to different containers and fermented at a slower rate, and eventually aged or bottled.
Pickling foods, such as cucumbers, may be accomplished by submerging the vegetable one wants to pickle in a salty water solution with vinegar added. Over time, bacteria create the lactic acid that gives the food its distinctive flavor and helps to preserve it. Other foods can be pickled simply by packing them in dry salt and allowing a natural fermentation process to occur.
Milk can also be cultured, and people have been using fermentation with dairy products for nearly 5,000 years. It is speculated that early fermented dairy, such as yogurt, was the result of a natural process of fermentation that occurred when the milk was cultured by bacteria that dwelt in skin sacks used to store dairy. Yogurt these days is made by adding a number of special bacteria, such as L. acidophilus and L. bulgaricus to milk and keeping it at the proper temperature. The bacteria begin converting the sugar in the dairy to lactic acid, eventually creating what we know as yogurt.

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