Stainless Steel

Stainless steel alloys develop a passivation layer of chromium oxide on their outer surface, effectively coating the steel and protecting it from the harmful oxidation that occurs between exposed iron and oxygen molecules in the air, which makes stainless steel more affective and attractive then regular steel.. This protecting layer of chromium oxide easily reforms when scratched, making stainless steel an excellent, durable solution with no surface cracking or pores. Austenitic Stainless Steel has the highest ratio of chromium, and is by far the most common type. Stainless steel is produced in over a hundred different grades, which differ depending on their alloys, strengths, temperature resistances and applications. One of the most popular stainless steel grades, 316 stainless steel, is super corrosion resistant because it contains more nickel. Steel service centers manufacture stainless steel into a variety of shapes and products, including stainless steel foil, stainless steel strip, stainless steel wire, stainless steel plate, stainless steel bars, stainless steel rods, stainless steel coil and stainless steel sheets via hot rolling and forming processes. It is used to make consumer goods, including domestic kitchen supplies and tableware, sinks, laundry equipment, flatware and electronic appliances, and in the food and beverage industry to make silos, vats, kegs and large kitchen equipment.  Stainless steel is also found in the construction and engineering industries as roofing, gutters, elevator doors, public seating, and is used to build large skyscrapers. Automotive parts, bus frames, pipes, valves, pumps and industrial mixers are also often made out of stainless steel.

There are 3 main types of stainless steel which combine nickel, carbon and molybdenum in different ratios to achieve different qualities. Austenitic stainless steel combines the largest ratios of chromium, nickel and molybdenum and accounts for about 70% of fabricated stainless steel, with the most common grade being 18/10 stainless, an alloy which is very hard, durable and resistant to corrosion. Austenitic steels have a great strength-to-weight advantage over other materials; they also provide impact resistance and toughness in extreme temperatures, making them suitable for cryogenic applications. Ferritic stainless steel has very low nickel content, higher carbon content and is very corrosion resistant but less strong and durable than austenitic stainless. Martensitic stainless steel contains higher levels of carbon and often molybdenum, making it extremely strong and durable with lower corrosion resistance. Some types of stainless steel can transform from martensite to austenitic under heat treatment or with the addition of chromium. For example, maraging steel, a specialty low-carbon ultra-high strength steel alloy, is transformed into martensite when a portion of the alloy's nickel content is substituted by chromium to enhance corrosion resistance and hardness.

There are 150 grades of steel, which are classified in 4 different groups according to their varying corrosion resistance and mechanical properties. 200 series stainless steels are non magnetic, austenitic, and have the most resistance to attack. They contain 17% chromium, 4% nickel and 7% manganese. 300 level series are almost identical to 200, except they are a bit less attack-resistant and contain slightly more chromium and 8% nickel. 316 Stainless Steel is a 300 level steel, and because it contains more nickel, it has superior corrosion resistance. 400 series stainless steels are magnetic, martenistic, have a poor corrosion resistance and contain 11% chromium and 1% manganese. Finally, 600 series steels, often referred to as precipitation hardening, can be heat treated to very high strength levels and are therefore very resistant against water and chloride attack.

Manufacturing stainless steel is a 7 step process, and produces many different forms and parts. First, the raw materials are melted together in an electric furnace for 8 to 12 hours, until they reach their recrystallization temperature. The molten steel is then cast into semi-finished forms called blooms, billets, slabs, rods and tube rounds. The unfinished shapes then undergo a forming process via hot rolling, where blooms and billets become bars, wire and coil, and slabs form plates, strips, sheets and foil. They are then heat treated through annealing, where the steel is heated and then cooled through quenching or air hardening. The steel hardens or softens, depending on the amount of time it is let to cool. When it has cooled, the stainless steel is descaled, which removes any buildup by pickling or electrocleaning. It is then cut to obtain its final desired shape and size by shearing, blanking, nibbling or flame cutting. Further processing to acquire a certain finish, dull or shiny, is done through hot rolling, cold rolling, annealing, descaling, or different combinations of these processes. Before becoming parts and components in industrial and commercial products, all stainless steel must meet specific requirements, such as toughness or corrosion resistance, put fourth by the American Society for Testing and Materials (ASTM) to ensure quality and safety.

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Stainless Steel Types

• 303 stainless steel is an austenitic alloy that has sulfur and/or selenium added to create a free-machining stainless steel. 303 stainless steels take less time to machine, resulting in longer lasting machine tool bits and lower production cost.
• 304 stainless steel is an austenitic alloy that is easily formed and welded but is not a free-machining material. 304 stainless steel is commonly used for sheet metal products that are not subject to harsh environments.
• 304L stainless steel is one of the most frequently used austenitic alloys in the stainless steel family. 304L stainless steel is utilized when parts are to be welded, especially if the weld might come in contact with chlorinated water.
• 305 stainless steel is an austenitic alloy that is very corrosion resistant and has a higher nickel content. 305 stainless has a decreased tendency to work-harden during the cold heading process.
• 316 stainless steel is a non-magnetic material that contains molybdenum and a higher nickel content. 316 stainless steel, an austenitic alloy, is very corrosion resistant but is subject to attack if exposed to high levels of chlorine for a long period of time.
• 316L stainless steel is a highly corrosion resistant austenitic alloy that is second only to 304 stainless steel in importance. 316L stainless steel is commonly used in heavy gauge welded components, as it offers higher creep, stress-to-rupture and tensile strength at elevated temperatures.
• 384 stainless steel has a very high nickel content and is very corrosion resistant to chlorides. 384 stainless steel, an austenitic alloy, cold heads well.
• Austenitic stainless steel is comprised of chromium and nickel and is used in mild, harsh and corrosive environments. Austenitic stainless steel alloys account for about 70% of the stainless steel family.
• Duplex stainless steels, along with the elements iron, chromium and nickel, contain molybdenum, nitrogen, copper and very little carbon. Duplex stainless steel has double the strength of austenitic stainless steel and better corrosion resistance than martensitic stainless steel.
• Ferrite stainless steel (type 430) consists of only iron and chromium. Ferrite stainless steel is magnetic, cannot be hardened and is used mainly in decorative trim and mufflers for vehicles.
• Martensitic stainless steels (types 403, 414 and 420) have low chromium levels and high carbon content but do not contain nickel. Martensitic stainless steel is a magnetic material that has reduced corrosion resistance but can be heat-treated to provide high strength and toughness characteristics.
• Precipitation-hardened stainless steels are chromium-nickel grades that can be strengthened and hardened by adding such elements as copper and aluminum in an aging treatment at elevated temperatures.
• Stainless steel alloys offer higher corrosion resistance due to their ability to develop a passivation layer of chromium oxide on their outer surface, effectively coating the steel and protecting it from the harmful oxidation that occurs between exposed iron and oxygen molecules in the air.
• Stainless steel bars are solid pieces of various grade stainless steels that are rolled from billets. Stainless steel bars can be hot or cold finished and formed into rounds, squares, hexagons, octagons or flats.
• Stainless steel coil is a rolled product that is formed from stainless steel strip. 
• Stainless steel foil offers increased corrosion resistance, strength and electrical resistance as compared to traditional metal foils such as aluminum and copper foil.
• Stainless steel grades are categorized into six different series: 100 series, 200 series, 300 series, 400 series, 500 series and 600 series.
• Stainless steel pipes are tubes that are used to transport gases or liquids. Stainless steel pipes are much longer lasting than similar products consisting of other metals, because of the corrosion resistance of the material.
• Stainless steel plates have a width over eight inches and a thickness from one quarter of an inch to over a foot.
• Stainless steel rods are long cylinder-shaped objects made of stainless steel.
• Stainless steel sheets are large, thin slices of stainless steel. Usually rectangular or square shaped, stainless steel sheets offer the flexibility of being custom fabricated or molded.
• Stainless steel suppliers provide the rods, sheets, and plates used in the assembly of many products.
• Stainless steel strip is a flat-rolled, very thin sheet of stainless steel.
• Stainless steel tubing ranges in size from less than .01 inches to more than six inches in diameter.
• Stainless steel wires offer good strength-to-weight ratios, as well as rustproof performance. Common diameters of stainless steel wires range anywhere from .01 inches to 1-1/16 inches.

Stainless Steel Grades

*These figures are guidelines based on industry research; they should not be presumed accurate under all circumstances and are not a substitute for certified measurements. The information is not to be interpreted as absolute material properties nor does it constitute a representation or warranty for which we assume legal liability. User shall determine suitability of the material for the intended use and assumes all risk and liability whatsoever in connection therewith.

Stainless Steel Terms

Age Hardening - A heat-treating process used on martensitic stainless steels to harden them. The material is heated above its critical temperature, held at that temperature to ensure uniform temperature and then quenched in air or oil to quickly cool it.
 
Alloy - A solid solution of two or more metals. All forms of stainless steel are alloys.
 
Annealing - A process by which a cold-rolled steel coil is heated to a designated temperature and then cooled. The annealing process makes the coil easier to bend and form.
 
Argon-Oxygen Decarburization (AOD) - A process with a short operation time and low temperatures that is used to reduce the carbon content of stainless steel during the refinement process.
 
Billet - A short bar of metal.
 
Blank - A piece of sheet stainless steel that has the specified outer dimensions of a part but has not yet been stamped by the end user. Blanks decrease the cost of labor and transportation for the stainless steel processor.
 
Blast Furnace - A cylinder lined with heat resistant bricks that steel mills use to smelt iron from ore. The name originates from the blast of hot air that is forced up through the ore.
 
Bloom - A semi-finished form of stainless steel that typically has a cross-section greater than 36 sq. inches. A bloom will be further processed into mill products.
 
Burr - A ridge on the edge of strip stainless steel that is caused by cutting operations, including blanking, trimming, shearing or slitting.
 
Chromium (Cr) - An element added to stainless steel, resulting in a corrosion resistant alloy.
 
Cold Forming - Also called "cold working" it is any kind of mechanical operation performed at room temperature that causes permanent deformation. Cold forming, which includes bending, rolling and drawing, increases the hardness and strength of stainless steel.
 
Continuous Casting - A time-saving process of pouring stainless steel directly from the furnace into a billet, bloom or slab. Continuous casting eliminates the need for large, expensive mills.
 
Ductility - The ability of steel to go through permanent changes of shape without fracturing.
 
Galvanized - Coated with zinc. Galvanizing provides more corrosion resistance and is used on auto underbody parts, storage tanks, garbage cans, etc.
 
Grade - A number or symbol given to different varieties of steel. Different grade steels have varying characteristics and compositions.
 
Oscillating - Method used to wind narrow strip steel over a wider roll. The oscillating process is similar to winding fishing line over a spool.
 
Reinforcing Bar (Rebar) - A steel bar used to further strengthen concrete. Rebars are vital for highway reinforcement as well as building construction.