STAINLESS STEEL
General Information
The many unique values provided by stainless steel make it a powerful candidate in materials selection. Engineers, specifiers and designers often underestimate or overlook these values because of what is viewed as the higher initial cost of stainless steel. However, over the total life of a project, stainless is often the best value option.

What is Stainless Steel?
Stainless steel is essentially a low carbon steel which contains chromium at 10% or more by weight. It is this addition of chromium that gives the steel its unique stainless, corrosion resisting properties.

The chromium content of the steel allows the formation of a rough, adherent, invisible, corrosion-resisting chromium oxide film on the steel surface. If damaged mechanically or chemically, this film is self-healing, providing that oxygen, even in very small amounts, is present. The corrosion resistance and other useful properties of the steel are enhanced by increased chromium content and the addition of other elements such as molybdenum, nickel and nitrogen.

There are more than 60 grades of stainless steel. However, the entire group can be divided into five classes. Each is identified by the alloying elements which affect their microstructure and for which each is named.

Benefits of Stainless Steel
Corrosion resistance
Lower alloyed grades resist corrosion in atmospheric and pure water environments, while high-alloyed grades can resist corrosion in most acids, alkaline solutions, and chlorine bearing environments, properties which are utilized in process plants.

Fire and heat resistance
Special high chromium and nickel-alloyed grades resist scaling and retain strength at high temperatures.

Hygiene
The easy cleaning ability of stainless makes it the first choice for strict hygiene conditions, such as hospitals, kitchens, abattoirs and other food processing plants.

Aesthetic appearance
The bright, easily maintained surface of stainless steel provides a modern and attractive appearance.

Strength-to-weight advantage
The work-hardening property of austenitic grades, that results in a significant strengthening of the material from cold-working alone, and the high strength duplex grades, allow reduced material thickness over conventional grades, therefore cost savings.

Ease of fabrication
Modern steel-making techniques mean that stainless can be cut, welded, formed, machined, and fabricated as readily as traditional steels.

Impact resistance
The austenitic microstructure of the 300 series provides high toughness, from elevated temperatures to far below freezing, making these steels particularly suited to cryogenic applications.

Long term value
When the total life cycle costs are considered, stainless is often the least expensive material option.

Cycle of Stainless Steel
To ensure a high quality of life, the materials that we use as consumers and manufacturers should meet not only technical performance standards, but have a Long Service Life, be Usable in a Great Number of Applications, and be Environmentally Friendly. Once their service is complete, they should be 100% Recyclable, thereby completing the life cycle to be used once again. Stainless Steel is such a material.

The longevity of stainless is the result of the alloying composition and, therefore, it has a natural corrosion resistance. Nothing is applied to the surface that could add additional material to the environment. It does not need additional systems to protect the base metal, the metal itself will last.

Stainless steel needs less maintenance and its hygienic qualities means that we do not have to use harsh cleaners to get a clean surface. There is little or nothing to dump into the drain that could have an environmental impact.

Stainless steel products complete their service life. There is less concern about disposal since this material is 100% recyclable. In fact, over 50% of new stainless steel comes from old remelted stainless steel scrap, thereby completing the full life cycle.

STAINLESS STEEL - CLASSIFICATIONS
400 Series Martensitic - Typical grade: 410
Straight chromium (12-18%), magnetic and can be hardened by heat treatment. Typical use: Fasteners, pump shafts

400 Series Ferritic - Typical grade: 430
Straight chromium (12-18%), "low" carbon, magnetic, but not heat treatable. Typical use: Appliance trim, cooking utensils

200/300 Series Austenitic - Typical grade: 304
Chromium (17-25%)/Nickel (8-25%), non-magnetic, not heat treatable. Can develop high strength by cold work. Additions of molybdenum (up to 7%) can increase the corrosion resistance. Typical use: Food equipment, chemical equipment, architectural applications

Precipitation Hardening - Typical grade: 17-4
Chromium (12-28%)/Nickel (3-9%), martensitic or austenitic. Develop strength by precipitation hardening reaction during heat treatment. Typical use: Valves, gears, petro-chemical equipment

Duplex - Typical grade: 2205
Chromium (18-25%)/Nickel (4-7%) and up to 4% molybdenum. More resistant to stress corrosion cracking than austenitic, yet tougher than fully ferritic alloys. Typical use: Pipelines, pressure vessels, shafting

STAINLESS STEEL - MARKETS
In the Home

Applications range from cookware, cutlery and sinks to appliance trim and fireplace liners.

In Industry

From food preparation and chemical process equipment, and building roofs and entrance ways, to medical instruments and implants, and computer diskettes.

STAINLESS STEEL - HISTORY
Background

The "discovery" of stainless steel occurred in the 1900 to 1915 time period. However, as with many discoveries, it was the accumulated efforts of several individuals that actually began in 1821. That year a Frenchman named Berthier found that iron when alloyed with chromium was resistant to some acids. Others studied the effects of chromium in an iron matrix, but using a low percentage of chromium. To be stainless steel, the chromium content needs to be at least 10.5%. In 1872, Messrs. Woods and Clark applied for a British patent for what they identified as an acid and weather resistant alloy containing 30 to 35% chromium and 1.5 to 2% tungsten. Then, in 1875, another Frenchman named Brustlein recognized the importance of carbon levels in addition to chromium. Stainless steels need to have a very low level of carbon at 0.15%. While many others investigated the chromium/iron composition, the difficulty in obtaining the low carbon levels persisted for many years until low carbon ferrochrome became commercially available.

Discovery

In 1904, Leon Guillet published research on alloys with composition that today would be known as 410, 420, 442, 446 and 440-C. In 1906, he also published a detailed study of an iron-nickel-chromium alloy that is the basic metallurgical structure for the 300 series of stainless steel. In 1909, Giesen published in England a lengthy account on the chromium-nickel (austenitic 300 series) stainless steels. Also in England and France, Portevin published studies on an alloy that today would be 430 stainless steel. In Germany, in 1908, Monnartz & Borchers found evidence of the relationship between a minimum level of chromium (10.5%) on corrosion resistance as well as the importance of low carbon content and the role of molybdenum in increasing corrosion resistance to chlorides.

Industrial Development

Harry Brearley, chief of the research lab run jointly by John Brown & Co. and Thomas Firth & Sons, is generally accredited as the initiator of the industrial era of stainless steel. Most of his work was on 430 (the chemical analysis was patented in 1919). The first product was table cutlery and it is still used today.

Note: There were many more investigators and researchers who played important roles in the development of stainless steel; too numerous to mention here. A very good historical account is given in the book "Stainless Steels" by Carl A. Zapffe.

INTRODUCTION
What is a Standard Finish?
“Standard” finishes are produced on an on-going basis. They are generally available off the shelf or can be obtained with a short lead-time. They are the finishes that are used for most stainless steel applications. Standard finishes are categorized as either “Mill” or “Polished”.

“Mill” finishes are the least expensive finish option. There are both hot- and cold-rolled mill finishes, and, as this description implies, their appearance is produced at least in part by passing the stainless steel through special rolls or dies. The reflectivity of these finishes varies from dull to mirror-like. These finishes become less uniform in appearance with increasing product thickness or diameter.

“Polished” finishes are produced by mechanically abrading the surface with a series of gradually finer abrasives or a special rolling procedure that simulates the appearance of mechanical abrasion. The smoothest polished finishes are buffed after mechanical polishing to produce a mirror-like appearance.

“Special” Finishes include finishes that are generally used when aesthetic appearance is important and for specialized industrial applications. This category includes non-directional scratch patterns, swirls, ground circles, embossed and coined textures, and various coloring and coating methods.

GLOSSARY
A

Age Hardening
Martensitic stainless steels are hardened by heating above their critical temperature, holding them at heat to insure uniform temperature, and cooling them rapidly by quenching in air or oil.

Alloying Element
The adding of any metallic element in stainless steel production in order to increase hardness, strength, or corrosion resistance. Molybdenum, nickel, and chromium are common alloying elements in stainless steel.

Alloy Surcharge
The producer’s selling price plus a surcharge added to offset the increasing costs of raw materials caused by increasing alloy prices.

Annealing (Solution Annealing)
A process of heating cold stainless steel to obtain maximum softness and ductility by heat treatment which also produces a homogeneous structure (in austenitic grades) or a 50/50 mixture of austenite and ferrite (in duplex grades). It relieves stresses that have built up during cold working and insures maximum corrosion resistance. Annealing can produce scale on the surface that must be removed by pickling.

Anodic Protection
Polarization to a more oxidizing potential to achieve a reduced corrosion rate by the promotion of passivity.

Argon-Oxygen Decarburisation (AOD)
A process of further reducing the carbon content of stainless steel during refinement. AOD is closely related to Electric Arc Furnaces (EAF), but has a shorter operating time and requires lower temperatures.

Austenitic Stainless Steel
Non-magnetic stainless steels that contain nickel and chromium sufficient to develop and retain the austenitic phase at room temperature. Austenitic stainless steels are the most widely used category of stainless steel.

Automatic Gauge Control
A hydraulic roll force system where stainless steel makers can monitor a stainless steel sheet’s thickness while it moves through the mill. The computer's gap sensor adjusts and monitors the thickness 50 to 60 times per second.

B
Bars
Stainless steel formed into long shapes from billets. They can be rounds, squares, hexagons, octagons or flats, either hot or cold finished.

Beam
Long pieces of squared-off metal, normally stainless steel, which are used in building construction.

Bend Tests
Tests used to assess the ductility and malleability of stainless steel subjected to bending.

Billet
A semi-finished form of stainless steel that is used for long products such as bars and forgings. Billets are normally two to seven inches square.

Blank
A section of sheet stainless steel that has the outer dimensions of a specific part but has not yet been stamped by the end user. This lowers stainless steel processor's labor and transportation costs.

Bloom
A semi-finished form of stainless steel that will be further processed into mill products. Generally having a cross section greater than 36 sq. inches.

Blooming Mill
A hot rolling mill that takes continuously cast slabs or ingots and processes them into blooms.

Brazing
Brazing and soldering are techniques for joining metals in the solid state by means of a fusible filler metal with a melting point well below that of the base metal.

Bright Annealing
The same as annealing but carried out in an atmosphere that prevents tarnishing
or scaling and therefore preserves the bright surface.

Brittle Fracture
A fracture that has little or no plastic deformation.

Burr
A subtle ridge on the edge of strip stainless steel resulting from cutting operations such as slitting, trimming, shearing, or blanking. For example, as a stainless steel processor trims the sides of the sheet stainless steel parallel or cuts a sheet of stainless steel into strips, its edges will bend with the direction of the cut.

C

Casting
To shape molten metal by pouring into a mold to produce an ingot or a continuously cast slab.

Case Hardening
Hardening a ferrous alloy to make the outside (case) much harder than the inside (core). This can be done carburizing, cyaniding, nitriding, carbonitriding, induction hardening, and flame hardening. Their application to stainless steel is limited wherever they decrease corrosion resistance.

Cathodic Corrosion
Corrosion caused by a reaction of an amphoteric metal with the alkaline products of electrolysis.

Cathodic Inhibitor
A chemical substance that prevents or slows a cathodic or reduction reaction.

Cathodic Protection
Reducing the corrosion of a metal by making the particular surface a cathode of an electrochemical cell.

Cavitation
The rapid formation and depletion of air bubbles that can damage the material at the solid/liquid interface under conditions of severe turbulent flow.

Centerless Grinding
An operation whereby the surface of a bar is ground without using a lathe.

Chemical Analysis
A report of the chemical composition of the elements, and their percentage that form a stainless steel product.

Charge
The material that is loaded into an electric furnace that will melt into a composition that will produce a stainless molten product. Normally recycled scrap, iron, and alloying elements.

Chloride Stress Corrosion Cracking
Cracking due to the combination of tensile stress and corrosion in the presence of water and chlorides.

Chromium (Cr)
An alloying element that is used in stainless steel to deter corrosion.

Cladding
Application of a stainless steel coating to a lower-alloy steel by means of pouring, welding, or coating to increase corrosion resistance at a lower cost than using steel exclusively.

Coils
A sheet of stainless steel that has been rolled into a coil to facilitate transportation and storage.

Cold Finished Bars
Hot rolled stainless steel bars that are annealed and cold worked to produce a higher surface quality and higher strength.

Cold Forming (Cold Working)
Any mechanical operation that creates permanent deformation, such as bending, rolling, drawing, etc. performed at room temperature that increases the hardness and strength of the stainless steel.

Cold Reduction
Process of rolling cold coils of pickled hot-rolled sheet through a cold reduction mill to make the stainless steel stronger, thinner, and smoother by applying pressure.

Cold-Rolled Strip (Sheet)
Stainless steel that has been run through a cold reduction mill. Sheet is under 3/16th of an inch and 24" wide and over. Strip is under 3/16 of an inch and under 24" wide.

Consumption
The physical use of stainless steel by end users. Consumption predicts changes in inventories, unlike demand figures.

Continuous Casting
Processes of pouring stainless steel into a billet, bloom, or slab directly from the furnace. This process avoids the need for large, expensive mills and also saves time because the slabs solidify in minutes rather than the several hours it takes it for an ingot to form.

Converter/Processor
Stainless steel customers demanding stainless steel in a more finished state such as tubing, pipe, and cold-rolled strip from rerollers and tube makers.

Corrosion
The attack upon metals by chemical agents converting them to nonmetallic products. Stainless steel has a passive film created by the presence of chromium (and often other alloying elements, nickel, molybdenum) that resists this process.

Corrosion Fatigue
Cracking due to repeating and fluctuating stresses in a corrosive environment.

Corrosion Potential
The potential of a corroding surface in an electrolyte relative to a reference electrode under open-circuit conditions.

Corrosion Rate
The rate at which an object corrodes.

Corrosion Resistance
A metal's ability to resist corrosion in a particular environment.

CRAP
A abbreviation for "cold rolled annealed and pickled."

Creep
Strain caused by the stress that occurs over time.

Crevice Corrosion
Corrosion of stainless steel on the surface that is fully shielded from air such that the passive film cannot be created to resist the corrosion.

Critical Pitting Potential
The lowest value of oxidizing potential at which pits can form and grow. The value depends on the test method used.

Cut-to-Length
Cutting flat-rolled stainless steel into desired length and then normally shipped flat-stacked.

D

Deburring
Removing the subtle ridge from the edge of strip metal that results from cutting operation such as slitting, trimming, shearing, or blanking.

Descaling
A process that removes the oxide scale from the surface of the stainless steel that developes from hot operations.

Drawing (Drawn)
A forming process that presses metal into or through a die (as in cold drawn wire).

Drawn-Over-Mandrel
To produce specialty tubing, this procedure uses a drawbench to pull tubing through a die and over a mandrel, allowing excellent control of the inside diameter and wall thickness.

Ductility
A measurement of the malleability of stainless steel in terms of the amount of deformation it will withstand before failure.

Duplex
Stainless steel comprised of austenitic and ferretic stainless steels that contain high amounts of chromium and nickel. This combination is stronger than both of the individual stainless steels. Duplex stainless steels are highly resistant to corrosion and cracking.

E

Edge Rolling (Edge Conditioning)
To facilitate customer manipulation, strips of stainless steel are rolled to smooth the edges and remove any burrs.

Elastic Springback
When stainless steel is bent, the metal towards the outside of the bend is in tension and the metal towards the inside is in compression. If the applied bending force is not sufficient to cause permanent plastic flow at either the inner or outer surfaces, the metal will return elastically to its original shape. Stainless steel has a greater elastic springback than mild steel.

Electric Arc Furnace (EAF)
A stainless steel producing furnace where scrap generally makes up a high percentage of the charge. Heat is supplied from electricity that arcs from the electrodes to the metal bath. These furnaces may operate on AC or DC.

Electric Resistance Welded (ERW) Pipe
Pipe made from strips of hot-rolled stainless steel, which are passed through forming rolls and welded.

Elongation
A measurement of ductility expressed in terms of the stretch having occurred over a given length on a standard tensile specimen at time of fracture, usually based upon an original length of 2 inches.

Embrittlement
A material's loss of malleability due to chemical treatment or physical change.

Erosion
The continuous depletion of a material due to mechanical interaction with a liquid, a mulitcomponent fluid, or solid particles carried with the fluid.

Erosion-Corrosion
An accelerated loss of material concerning corrosion and erosion that results from corrosive material interacting with the material.

Extrusion
A shaped piece of stainless steel produced by forcing the bloom, bar, or rod through a die of the appropriate shape.

F
Fabricator
An intermediate product producer that purchases materials and processes them specifically for a particular project.

Fatigue
A condition leading to the eventual fracture of a material due to constant or repeated stresses that exert less pressure than the tensile strength of the material.

Ferrite
The body-centred cubic crystalline phase of iron-based alloys.

Ferritic
Magnetic stainless steels that have a low carbon content and contain chromium as the main alloying element, usually between 13% and 17%. It is the second most widely used stainless steel. Ferretic stainless steels are generally used in automotive trim and exhaust systems, hot water tanks, and interior architectural trim.

Ferroalloy
Metal products such as ferrochrome, ferromanganese, and ferrosilicon that are commonly used as raw materials to aid various stages in stainless steel making.

Ferrochrome
A common raw material in stainless steel production. This alloy consists of iron and up to 72% chromium.

Ferrous
Any metal that is primarily composed of iron.

Finish
The final condition of the surface after the last phase of production.

Finishing Facilities
These facilities process semi-finished stainless steel into ready-made forms that can be used by others. Some facilities are rolling mills, pickle lines, tandem mills, annealing facilities, and temper mills.

Flat-Rolled Stainless Steel (Flat Product)
Category of stainless steel that includes shapes such as sheet, strip, and plate.

Flux
An iron cleaning agent that consists of limestone and lime. These products react with impurities in the metallic pool and float to the top of the liquid iron.

Foil
Metal with a maximum width of .005 inches.

Forging
Forming a hot or cold metal into a fixed shape by hammering, upsetting, or pressing.

Forming
A process that brings about a change in the shape of stainless steel by the application of force (i.e. cold forming, hot forming, wire forming).

Fouling
An accumulation of marine organism deposits on a submerged metal surface. Fouling also refers to the accumulation of normally inorganic deposits on heat exchanger tubing.

Free-Machining
A stainless steel to which a small amount of some relatively insoluble element (such as sulfur, selenium) is added to create a minute and widely distributed soft phase that acts as chip breakers during machining.

Fretting Corrosion
Deterioration at the interface of two contacting surfaces under load which is accelerated by their relative motion.

G

Galvanic Corrosion
Accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte.

Gauer Bar
(see edge rolling)

Gauge
The thickness of a certain stainless steel.

General Corrosion
"General corrosion" is the term used describe the attack that proceeds in a relatively uniform manner over the entire surface of a metal. Typically stainless steels do not exhibit general corrosion.

Grain (Grain Boundary)
The individual crystal units comprising the aggregate structure where the crystalline orientation does not change. The grain boundary is where these individual crystal units meet.

Grinding
A term that implies metal removal similar to fast milling where the surface is removed by abrasion.

H

HARP
An abbreviation for "hot rolled annealed and pickled."

Hardness Test
Hardness testing consists of pressing an indenter into a flat surface under a perfectly controlled load, then measuring the dimension of the resulting indentation. The three methods most commonly used for stainless steel are the Rockwell B, Rockwell C and Vickers tests. The higher the number, the harder the material.

Heat
Term referring to batch of refined stainless steel; a charged oxygen or electric furnace full of stainless steel. A heat of stainless steel can be used to cast several slabs, billets, or blooms.

Heat-Affected Zone (HAZ)
The part of a metal that is not melted during cutting, brazing, or welding, but whose microstructure and physical properties are altered by these processes.

Heat Treatment
Altering the properties of stainless steel by subjecting it to a series of temperature changes. To increase the hardness, strength, or ductility of stainless steel so that it is suitable for additional applications.

Hot Band (Hot-Rolled Stainless Steel)
Stainless steel that has been rolled on a hot-strip mill. It can be sold directly to customers or further processed into other finished products.

Hot Forming
Hot forming operations are used widely in the fabrication of stainless steel to take advantage of their lower resistance to shape change. High temperature reduces their yield strengths, and this results in a marked lowering of the force that is required to bring about plastic movement or flow from one shape to another. (hot rolling, hot stretching, etc.)

Hydrogen Embrittlement
The absorption of hydrogen by a metal resulting in a loss of ductility.

Hydrogen-Induced Cracking
Stepwise internal cracks that connect adjacent hydrogen blisters on different planes in the metal, or to the metal surface.

Hydrogen Stress Cracking
Cracking of a metal resulting from the combination of hydrogen and tensile stress.

I

Impact Test
Impact testing is used to measure the toughness of a material, corresponding to the energy necessary to cause fracture under shock loading. Low toughness is generally associated with brittle shear fracture and high toughness with ductile plastic tearing.

Ingot
Semi-finished stainless steel that has been poured into molds and then solidified. The molds are then removed and the stainless steel is ready for rolling or forging.

Integrated Mills
Facilities that combine all the stainless steel making facilities from melt shop through hot rolling and cold finishing, to produce mill products.

Intergranular Corrosion
Preferential corrosion cracking at or along the grain boundaries of a metal.

Intergranular Stress Corrosion Cracking
Stress corrosion cracking in which the cracking occurs along grain boundaries.

Iron Ore
A mineral that contains enough iron to be a factor in stainless steel production.

Iron-Based Superalloys
These alloys are at the highest end of the range of temperature and strength. Additives such as chrome, nickel, titanium, manganese, molybdenum, vanadium, silicon, and carbon may be used. These superalloys are also referred to as “super chrome stainless steels.”

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L

Levelling Line
A machine that smoothes any physical deficiencies in the sheet before it is shipped to the customer.

Life Cycle Costing
An accounting method of costing where expenses are allocated over the life of the product. Life cycle costs are often lower for stainless steel than for alternatives despite a higher initial outlay, because stainless products generally last longer and require little maintenance.

Light-Gauge Stainless Steel
A very thin sheet of stainless steel that has either been temper rolled or passed through a cold reduction mill.

Line Pipe
A pipe extending over long distances that transports oil, natural gas, and other fluids.

Long Products
Category of stainless steel that includes rods, bars, and structural products that are described as long rather than flat.

Low-Carbon Stainless Steel
Stainless steel containing less than 0.03% carbon.

M

Martensite
A hard supersaturated solid solution of iron characterized by an acicular (needle-like) microstructure.

Martensitic
A small category of magnetic stainless steels typically containing 12% chromium, a moderate level of carbon, and a very low level of nickel.

Mechanical Properties (Physical Properties)
Properties determined by mechanical testing, such as yield strength, ductility, ultimate tensile strength, hardness, bendability, impact strength, etc.

Mill Products
Generally mill forms of sheet, strip, plate, bar rod and semi-finished forms.

Molybdenum (Mo)
An alloying element that enhances corrosion resistance along with chromium in stainless steels.

N

Nickel (Ni)
An alloying element used in stainless steels to enhance ductility and corrosion resistance.

Nickel-Based Superalloys
Alloy metal produced for high-performance, high-temperature applications such as nickel-iron-chrome alloys and nickel-chrome-iron alloys.

Non-Ferrous Metal
Metal or alloy that contains no iron.

O

Oil Country Tubular Goods (OCTG)
Category of pipe products used by petroleum exploration customers. Labels bearing OCTG are applied to casting, drill pipes, oil well tubing, etc.

Ore
An iron-containing material used primarily in the melting furnace.

Oscillating
A method of winding a narrow strip of stainless steel over a much wider roll. This allows for more stainless steel per roll and allows the customer to have longer processing runs.

Oxidation
Rust or corrosion due to exposure to oxygen.

P

Passivation
When exposed in air, stainless steels passivate naturally (due to the presence of chromium). But the time required can vary. In order to ensure that the passive layer reforms rapidly after pickling, a passivation treatment is performed using a solution of nitric acid and water.

Passive
A characteristic condition of stainless steels which impedes normal corrosion tendencies to the point where the metal remains virtually un-attacked — hence passive to its environment.

Pickling
A process that removes surface scale and oxidation products by immersion in a chemically active solution, such as sulfuric or hydrochloric acid.

Pickling Paste
A commercially available product that performs the pickling function when used on the surface of stainless steel.

Pipe
Term that originally defined a tube used to transport fluids or gases. Often now, pipe and tube are used interchangeably.

Pitting
Localized corrosion (in the form of pits) of a metal surface that is confined to a small area.

Plate
Stainless steel measuring more than ten inches wide with a thickness ranging from 3/16 of an inch and over.

Postweld Heat Treatment
Heating and cooling a weldment in such a way as to obtain desired properties.

Powder Metals
Fabricating technique where fine metallic powder is compacted and heated under high pressure to solidify the material.

Precipitation Hardening (PH)
A small category of stainless steels resembling martenistic stainless steels that have great strength and hardness due to heat treatment.

Protective Coating
A temporary adhesive protective film attached to the surface that protects the surface during forming and handling operations that is stripped before final use.

R

Reinforcing Bar (Rebar)
A commodity-grade stainless steel used to reinforce concrete in highway and building structures.

Residuals
The impurities remaining in mini-mill stainless steels resulting from the wide variety of metals entering the process.

Reversing Mill
A stand of rolls that passes stainless steel back and forth between the rolls in order to reduce the stainless steel sheet or plate. The distance between the rolls is reduced after each pass.

Rod
Semi-finished stainless steel that is rolled from a billet and is commonly used for wire products, bolts, and nails.

S

Scale (Scale Removal)
The oxide that forms on the surface of stainless steel, after exposure to high temperature.

Scrap
Iron-containing stainless steel material that is normally remelted and recasted into new stainless steel. Home scrap is left over stainless steel generated from edge trimming and rejects within the mill. Also, industrial scrap that is trimmed by stampers and auctioned to buyers.

Seamless Pipe
Pipe produced from a solid billet that is heated and rotated under pressure. This rotating pressure creates a hole in the middle of the billet, which is then formed into a pipe by a mandrel.

Secondary Stainless Steel
Stainless steel that has been rejected by an original customer because of a defect in the chemistry, gauge, or surface quality. Mills then search for another customer that will accept the stainless steel at a discount.

Semi-Finished Stainless Steel
Stainless steel products such as blooms, billets, or slabs that are then rolled and processed into beams, bars, sheets, etc.

Sensitization
The phenomenon in austenitic stainless steels that causes a change to occur in the grain boundaries when heated in the general range of 850 to 1475 degree F. This change destroys the passivity in these locations.

Service Center
An operation that buys metal, stores it, (often processing it in some way) and then sells it in a slightly different form than it was purchased from the producing mills.

Shape Correcting
Levelers, edge trimmers, and temper mills reshape processed stainless steel to meet customers’ specifications. Reshaping is needed from processes that cause deformities in the stainless steel.

Shearing
Trimming of the edges of sheet strip to make them parallel. This done at either the stainless steel mill or at the stainless steel processor.

Sheet
A stainless steel flat rolled product that is under 3/16 inches in thickness and 24 inches and over in width.

Shot Blasting
Blast cleaning using stainless steel shot as the abrasive. Not recommended for stainless steel. Glass beads should be used.

Sigma Phase
An extremely brittle Fe-Cr phase that can form at elevated temperatures in austenitic and ferritic stainless steels.

Slab
A very common type of semi-finished stainless steel usually measuring 6-10 inches thick by 30-85 inches wide and average 20 feet long. After casting, slabs are sent to a strip mill where it is rolled and coiled into sheet and plate products.

Slag
The impurities in a molten pool of iron. Flux may be added to congregate the impurities into a slag. Slag is lighter than iron and will float allowing it to be skimmed.

Slitting
Cutting a sheet of stainless steel into a smaller strip to meet customers demands.

Solution Heat Treatment
Heating a metal to a high temperature and maintaining it long enough for one or more constituents to enter the solid solution. The solution is then cooled rapidly to retain the constitutes within.

Solvent Cleaning
The removal of contaminants such as oil, grease, dirt, salts, etc. by cleaning with a solvent, steam, vapor, alkali, or emulsion.

Specialty Alloys
Metals with distinct chemical and physical properties. These alloys are produced for very specific applications; considered to be on the low end of superalloys.

Specialty Steel
Category of steel that includes electric, alloy, stainless, and tool steels.

Specialty Tube
A wide variety of high quality, specialized tubular products. It is usually found in the automotive and agricultural industries, construction equipment, hydraulic cylinders, etc.

Stainless Steel
Group of corrosion resistant steels containing at least 10.5% chromium and may contain other alloying elements. These steels resist corrosion and maintain its strength at high temperatures.

Steckel Mill
A reversing stainless steel sheet reduction mill with heated coil boxes at each end. Stainless steel sheet or plate is sent through the rolls of the reversing mill and coiled at the end of the mill, reheated in the coil box, and sent back through the Steckel stands and recoiled. By reheating the stainless steel prior to each pass, the rolls can squeeze the stainless steel thinner per pass and impart a better surface finish.

Strain
The amount of elongation, force, or compression that occurs in a metal at a given level of stress. Generally in terms of inches elongation per inch of material.

Strength
The ability of stainless steel to oppose applied forces when considering resistance to stretching, forming, compressing, etc.

Stress Corrosion Cracking (SCC)
Slowly developing cracks that form in stainless steel due to mechanical stress and exposure to a corrosive environment.

Strip
A stainless steel flat rolled product that is under 3/16 inches and is under 24 inches in width.

Structurals
An architectural stainless steel product group that includes I-beams, H-beams, wide-flange beams and sheet piling. These products are used in multi-story buildings, bridges, vertical highway supports, etc.

Superalloys
Lightweight metal alloys designed specifically to withstand extreme conditions. Conventional alloys are iron-based, cobalt-based, nickel-based, and titanium-based.

T

Tailored Blanks
A section of sheet stainless steel that is cut to the manufacturer’s desire. Excess stainless steel is trimmed away to save transportation costs and is ready for the stamper to shape with a die press.

Tandem Mill
A cold-rolling mill that gives greater strength, a more uniform and smoother surface, and a reduced thickness to the stainless steel sheet. This mill rolls stainless steel through a series of rolls, to achieve a desired thickness and surface quality.

Tantalum (Ta)
A by-product of tin processing, this refractory metal is used as a barrier to corrosion of chemical processing and carbide cutting tools, and still-growing use as electronic capacitors and filaments. Melts at 2415 degrees Fahrenheit.

Tempered (Temper)
A term applied to cold worked material such as strip, sheet, wire, expressing the range of mechanical properties as produced by the cold work (as is quarter hard,
half hard, etc.).

Titanium (Ti)
A very ductile and malleable white metal that is used in aviation, aerospace, etc. because of its high strength and light weight.

Titanium-Based Superalloys
Lightweight, corrosive-resistant alloys suitable for high temperatures. These alloys are very practical for airplane parts. Titanium alloys can blended with aluminium, iron, vanadium, silicon, cobalt, tantalum, zirconium, and manganese.

Tool Stainless Steels
Hardened stainless steels that are used in the manufacturing of tools and dies.

Ton
Unit of measure for stainless steel scrap and iron ore.
Gross Ton: 2,240 pounds.
Long (net) Ton: 2,240 pounds.
Short (net) Ton: 2,000 pounds. Normal unit of statistical raw material input and stainless steel output in the United States.
Metric ton: 1,000 kilograms. (2,204.6 pounds or 1.102 short tons).

Tubing
When referring to OCTG, tubing is a separate pipe used within the casing to conduct the oil or gas to the surface. Depending on conditions and well life, tubing may have to be replaced during the operational life of a well.

Tungsten (W)
Gray metal with high tensile strength. It is ductile, malleable, and resistant to atmospheric elements and all acids except strong alkalies.

V

Vacuum Oxygen Decarburisation (VOD)
A refinement of stainless steel that reduces carbon content. Molten, unrefined stainless steel is heated and stirred by an electrical current while oxygen enters from the top. Many undesirable gases escape from the the stainless steel and are evacuated by a vacuum pump. Alloys and other additives are then mixed in to refine the molten stainless steel further.

Vanadium (V)
A grey metal that is normally used as an alloying agent for iron and stainless steel. It is also used as a strengthener of titanium-based alloys.

W

Width
The lateral dimensions of rolled stainless steel, as opposed to the length or the gauge. If width of the stainless steel strip is not controlled during rolling, the edges must be trimmed.

Wire
A cold finished stainless steel product (normally in coils) that is round, square, octagon, hexagon and flats under 3/16 inches.

Y

Yield Strength
The stress beyond which stainless steel undergoes important permanent flow — commonly specified as that stress producing a 0.2% offset from the linear portion of the stress-strain curve.

Z

Zirconium (Zr)
A strong, ductile metal obtained by the chemical processing of zircon-bearing sands. It has good corrosion resistance at high temperatures and is used as a structural material in nuclear reactors and cladding material for uranium.

FREQUENTLY ASKED QUESTIONS
 
1. What makes stainless steel stainless?

Answer: Stainless steel must contain at least 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. 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.

2. What is the difference between 18/8 and 18/10 stainless steel?

Answer: 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.

3. Can stainless steel rust? Why? (I thought stainless did not rust!)

Answer: Stainless does not "rust" as you think of regular steel rusting with a red oxide on the surface that flakes off. If you see red rust it is probably due to some iron particles that have contaminated the surface of the stainless steel and it is these iron particles that are rusting. Look at the source of the rusting and see if you can remove it from the surface. If the iron is embedded in the surface, you can try a solution of 10% nitric and 2% hydrofluoric acid at room temperature or slightly heated. Wash area well with lots and lots of water after use. Commercially available "pickling paste" can also be used.
 
4. What is the difference between 304 and 316 stainless steel?

Answer: 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)

5. Is stainless steel magnetic?

Answer: 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.

6. What is "passivation"?

Answer: When the amount of chromium (in an iron matrix) exceeds 10 ½%, a complex chrome oxide forms instantaneously that prevents the further diffusion of oxygen into the surface and results in the "passive" nature of stainless steel and its resistance to oxidation (or corrosion). A chemical "dip" into 10% nitric acid plus 2% hydrofluoric acid bath will enhance the development of this "passive" oxide.

7. Can stainless steel be "welded"?

Answer: 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.

8. Can Stainless steel be "hardened"?

Answer: YES. The 300 series stainless steel can be "hardened" BUT only by "work hardening." That is by cold working the material, either by cold rolling down to lighter and lighter gauges, or by "drawing" through a die or other size altering operation. "Annealing" stainless steel will REMOVE the work hardening effect. YES and NO. The 400 series have two different stainless steel structures. One is called "ferritic" (409, 430, 434. 439) which cannot be hardened by heat treatment. The other is called "martensitic" (403, 410, 416, 420, & 440 A,B,C) which CAN be hardened by heat treatment.

9. What does the "L" designation mean?

Answer: The use of the letter L after the grade number, i.e., 304L, means that the carbon content is restricted to a MAXIMUM of 0.03% (normal levels are 0.08% max. and in some grades can be as high as 0.15% max.). This lower level of carbon is usually used where "welding" will be performed. The lower level of carbon helps to prevent the chromium from being depleted (by forming chrome carbides at the weld site) and therefore allow it to remain over 10 ½% so it can form the "passive" oxide layer that gives stainless its corrosion resistance.

10. What is the recycle content of stainless steel?

Answer: Stainless steel can be recycled 100%. That is all stainless steel can be re-melted to made a new stainless steel. The typical amount of recycled stainless steel "scrap" that is used to make new stainless steel is between 65 & 80%.

11. The stainless steel on my refrigerator door, dishwasher, and/or countertop is scratched. How can I remove the scratches?

Answer: Scratches are difficult to remove. Most kitchen appliances, sinks, and counters have a polished finish with short directional polishing lines. Restoring a polished finish to its original appearance requires a professional such as a company that specializes in fabricating or polishing stainless steel. If the refrigerator or dishwasher door panel is replaceable, purchasing a new panel is normally more cost effective than professional refinishing. The homeowner may want to consider obtaining replacement panels with angel hair, distressed, swirl, or embossed finish. These finishes help to hide light scratching and can be obtained from companies that specialize in stainless steel finishes. Counters and appliance doors that are not easily removable must be refinished in place. When the counter is refinished, it may have long rather than short polishing lines. If a slightly different finish is acceptable and cost is a consideration, a homeowner can refinish the counter or appliance using a non-metallic abrasive pad such as a Scotch Brite® pad. This can be done by rubbing the surface with the pad using long uniform strokes in the same direction as the current polishing lines. This will not eliminate deep scratches. A professional may offer this finish as a less expensive option. The resulting finish is normally referred to as a hairline or long grain finish. Some appliance companies are starting to offer this finish.

12. What is the "annealed" condition?

Answer: Stainless steel is usually sold in the "annealed" condition. It just means that the material is in the "soft" or annealed condition. The 300 series of stainless steels can not be hardened by heat treatment (like carbon steels) but can be hardened by cold working. This cold work can be eliminated by a heating treatment (annealing) that will restore the original soft condition.

13. What does the term "CRES" mean?

Answer: CRES is something used to designate stainless steel. It stands for Corrosion RESistant steel. It does not necessarily mean that the steel is in fact stainless steel as there are other materials that are corrosion resistant but not stainless steel.

14. Can stainless steel be used at very low and very high temperatures?

Answer: Yes. Stainless steel has excellent properties at both extremes of the temperature scale. Stainless steel can be used down to liquid nitrogen temperatures and up to about 1800° F.

15. What are AISI Specifications for stainless steel?

Answer: The AISI (American Iron and Steel Institute) was the originator of the 300 and 400 series numbering system (i.e., Type 304 stainless steel). They also published a Stainless Steel products manual that listed these designations and the chemical analysis as well as most mechanical and physical properties of each individual grade. They are NOT specifications as such, just definitions of the individual grades. Most specifications that are used with stainless steel are from the ASTM (American Society for Testing Material). See "Specifications for Stainless Steel" for more information. The Iron & Steel Society took over from the AISI in publishing the Stainless Steel Products Manual a number of years ago.

16. Can stainless steel be machined?

Answer: Yes. However the standard grades of stainless steel are usually "gummy" and will not produce a clean chip when machined or turned. To solve this problem, many companies produce "free-machining" grades of stainless where they add a "chip-breaker" to the matrix. Grade 303 is the free-machining equivalent to grade 304.

Types of Stainless Steel

In addition to chromium, nickel, molybdenum, titanium, niobium and other elements may also be added to stainless steels in varying quantities to produce a range of stainless steel grades, each with different properties.

There are a number of grades to choose from, but all stainless steels can be divided into five basic categories:

austenitic
ferritic
duplex
martensitic
precipitation hardening
These are named according to the microstructure inherent in each steel group (a function of the primary alloying elements). Austenitic and ferritic grades account for approximately 95% of stainless steel applications.

Austenitic

When nickel is added to stainless steel in sufficient amounts the crystal structure changes to "austenite". The basic composition of austenitic stainless steels is 18% chromium and 8% nickel. Austenitic grades are the most commonly used stainless steels accounting for more than 70% of production (type 304 is the most commonly specified grade by far).

Basic properties

excellent corrosion resistance
excellent weldability (all processes)
excellent formability, fabricability and ductility
excellent cleanability, and hygiene characteristics
good high and excellent low temperature properties
non magnetic (if annealed)
hardenable by cold work only

Common uses

computer floppy disk shutters (304)
computer keyboard key springs (301)
kitchen sinks (304D)
food processing equipment
architectural applications
chemical plant and equipment

Common austenitic stainless steel grades and their applications

Duplex

These are stainless steels containing relatively high chromium (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). The nickel content is insufficient to generate a fully austenitic structure and the resulting combination of ferritic and austenitic structures is called duplex. Most duplex steels contain molybdenum in a range of 2.5 - 4%.

Basic properties

high resistance to stress corrosion cracking
increased resistance to chloride ion attack
higher tensile and yield strength than austenitic or ferritic steels
good weldability and formability

Common uses

marine applications, particularly at slightly elevated temperatures
desalination plant
heat exchangers
petrochemical plant

Ferritic

These are plain chromium stainless steels with varying chromium content between 12 and 18%, but with low carbon content.

Basic properties

moderate to good corrosion resistance increasing with chromium content
not hardenable by heat treatment and always used in the annealed condition magnetic
weldability is poor
formability not as good as the austenitics

Common uses

computer floppy disk hubs (430)
automotive trim (430)
automotive exhausts (409)
colliery equipment (3CR12)
hot water tanks (444)

Martensitic

Martensitic stainless steels were the first stainless steels commercially developed (as cutlery) and have relatively high carbon content (0.1 - 1.2%) compared to other stainless steels. They are plain chromium steels containing between 12 and 18% chromium.

Basic properties

moderate corrosion resistance
can be hardened by heat treatment and therefore high strength and hardness levels can be achieved
poor weldability
magnetic

Common uses

knife blades
surgical instruments
shafts
spindles
pins
 
Precipitation Hardening

Precipitation hardening stainless steels have been formulated so that they can be supplied in a solution treated condition, (in which they are machineable) and can be hardened, after fabrication, in a single low temperature "ageing" process.

Basic properties

moderate to good corrosion resistance
very high strength
good weldability
magnetic

Common uses

Shafts for pumps and valves

Environmental Credentials

In response to the growing awareness that our quality of life depends upon protection of our environment, consumers and regulators are directing their resources towards products less harmful to the environment. The challenge to specifiers is clear: understand the "cradle to grave" characteristics of materials and make ever more satisfying products from ever more benign materials.

In use stainless steel is durable and requires a minimum of maintenance, outlasting many competing products and eliminating requirements for additional potentially hazardous materials such as paint, fire protective coatings, cleaners and solvents.

Stainless steel is a valuable scrap material. It is 100% recyclable and a preferred raw material input by steel makers. Stainless steel production incorporates high levels of scrap use (as high as 80% of charged materials will be scrap stainless steel). New stainless steel comprises at least 50% recycled stainless steel product and more than half the stainless steel produced today has already been another useful stainless steel product in the past. Even beer kegs wear out eventually. Power is expensive and modern stainless mills operate close to the theoretical minimum.

Despite the very high recycling of old stainless steel products, some stainless steel will find its way to landfills or other disposal sites. In these circumstances no detrimental effect to soil or ground water is expected.

Stainless Steel Property Database

Stainless steels are produced in five alloy groups: austenitic, ferritic, duplex (ferritic-austenitic), martensitic and precipitation hardened. These groups have different microstructures, which are determined by the selected chemical compositions and the production steps involved.

Atmospheric Corrosion Resistance

Alloy Finish % Stained Area % Rusted Pit Density (A-537)
201   CR    15  1  7
301   CR    20  3  8
302   CR    5   3  8
304