How stainless steel is made - material, manufacture, used, processing, parts, components, structure, steps Process The manufacture of stainless steel involves a series of processes. First, the steel is melted, To make stainless steel, the raw materials—iron ore, chromium, silicon, nickel, etc.—are melted together in an electric furnace. This step usually involves 8 to 12 hours of intense heat. Next, the mixture is cast into one of several shapes, including blooms, billets, and slabs. and then it is cast into solid form. After various forming steps, the steel is heat treated and then cleaned and polished to give it the desired finish. Next, it is packaged and sent to manufacturers, who weld and join the steel to produce the desired shapes. Melting and casting 1 The raw materials are first melted together in an electric furnace. This step usually requires 8 to 12 hours of intense heat. When the melting is finished, the molten steel is cast into semi-finished forms. These include blooms (rectangular shapes), billets (round or square shapes 1.5 inches or 3.8 centimeters in thickness), slabs, rods, and tube rounds.

Forming 2 Next, the semi-finished steel goes through forming operations, beginning with hot rolling, in which the steel is heated and passed through huge rolls. Blooms and billets are formed into bar and wire, while slabs are formed into plate, strip, and sheet. Bars are available in all grades and come in rounds, squares, octagons, or hexagons 0.25 inch (.63 centimeter) in size. Wire is usually available up to 0.5 inch (1.27 centimeters) in diameter or size. Plate is more than 0.1875 inch (.47 centimeter) thick and over 10 inches (25.4 centimeters) wide. Strip is less than 0.185 inch (.47 centimeter) thick and less than 24 inches (61 centimeters) wide. Sheet is less than 0.1875 (.47 centimeter) thick and more than 24 (61 centimeters) wide. Heat treatment 3 After the stainless steel is formed, most types must go through an annealing step.

Annealing is a heat treatment in which the steel is heated and cooled under controlled conditions to relieve internal stresses and soften the metal. Some steels are heat treated for higher strength. However, such a heat treatment—also known as age hardening —requires careful control, for even small changes from the recommended temperature, time, or cooling rate can seriously affect the properties. Lower aging temperatures produce high strength with low fracture toughness, while higher-temperature aging produces a lower strength, tougher material. Though the heating rate to reach the aging temperature (900 to 1000 degrees Fahrenheit or 482 to 537 degrees Celsius) does not effect the properties, the cooling rate does. A post-aging quenching (rapid cooling) treatment can increase the toughness without a significant loss in strength. One such process involves water quenching the material in a 35-degree Fahrenheit (1.6-degree Celsius) ice-water bath for a minimum of two hours. The type of heat treatment depends on the type of steel; in other words, whether it is austenitic, ferritic, or martensitic.

Austenitic steels are heated to above 1900 degrees Fahrenheit (1037 degrees Celsius) for a time depending on the thickness. Water quenching is used for thick sections, whereas air cooling or air blasting is used for thin sections. If cooled too slowly, carbide precipitation can occur. This buildup can be eliminated by thermal stabilization. In this method, the steel is held for several hours at 1500 to 1600 degrees Fahrenheit (815 to 871 degrees Celsius). Cleaning part surfaces of contaminants before heat treatment is sometimes also necessary to achieve proper heat treatment. Descaling 4 Annealing causes a scale or build-up to form on the steel. The scale can be removed using several processes. One of the most common methods, pickling, uses a nitric-hydrofluoric acid bath to descale the steel. In another method, electrocleaning, an electric current is applied to the surface using a cathode and phosphoric acid, and the scale is removed. The annealing and descaling steps occur at different stages depending on the type of steel being worked.

Bar and wire, for instance, go through further forming steps (more hot rolling, forging, or extruding) after the initial hot rolling before being annealed and descaled. Sheet and strip, on the other hand, go through an initial annealing and descaling step immediately after hot rolling. After cold rolling (passing through rolls at a relatively low temperature), which produces a further reduction in thickness, sheet and strip are annealed and descaled again. A final cold rolling step then prepares the steel for final processing. Cutting 5 Cutting operations are usually necessary to obtain the desired blank shape or size to trim the part to final size. Mechanical cutting is accomplished by a variety of methods, including straight shearing using guillotine knives, circle shearing using circular knives horizontally and vertically positioned, sawing using high speed steel blades, blanking, and nibbling. Blanking uses metal punches and dies to punch out the shape by shearing. Nibbling is a process of cutting by blanking out a series of overlapping holes and is ideally suited for irregular shapes. Stainless steel can also be cut using flame cutting, which involves a flame-fired torch using oxygen and propane in conjunction with iron powder. This method is clean and fast.

Another cutting method is known as plasma jet cutting, in which an ionized gas column in conjunction with an electric arc through a small orifice makes the cut. The gas produces extremely high temperatures to melt the metal. Finishing 6 Surface finish is an important specification for stainless steel products and is critical in applications where appearance is also important. Certain surface finishes also make stainless steel easier to clean, which is obviously important for sanitary applications. A smooth surface as obtained by polishing also provides better corrosion resistance. On the other hand, rough finishes are often required for lubrication applications, as well as to facilitate further manufacturing steps. Surface finishes are the result of processes used in fabricating the various forms or are the result of further processing. There are a variety of methods used for finishing. A dull finish is produced by hot rolling, annealing, and descaling. A bright finish is obtained by first hot rolling and then cold rolling on polished rolls. A highly reflective finish is produced by cold rolling in combination with annealing in a controlled atmosphere furnace, by grinding with abrasives, or by buffing a finely ground surface. A mirror finish is produced by polishing with progressively finer abrasives, followed by extensive buffing.

For grinding or polishing, grinding wheels or abrasive belts are normally used. Buffing uses cloth wheels in combination with cutting compounds containing very fine abrasive particles in bar or stick forms. Other finishing methods include tumbling, which forces The initial steel shapes—blooms, billets, slabs, etc.—are hot rolled into bar, wire, sheet, strip, and plate. Depending on the form, the steel then undergoes further rolling steps (both hot and cold rolling), heat treatment (annealing), descaling Ito remove buildup), and polishing to produce the finished stainless steel. The steel is then sent the end user. movement of a tumbling material against surfaces of parts, dry etching (sandblasting), wet etching using acid solutions, and surface dulling. The latter uses sandblasting, wire brushing, or pickling techniques. Manufacturing at the fabricator or end user 7 After the stainless steel in its various forms are packed and shipped to the fabricator or end user, a variety of other processes are needed. Further shaping is accomplished using a variety of methods, such as roll forming, press forming, forging, press drawing, and extrusion. Additional heat treating (annealing), machining, and cleaning processes are also often required.

There are a variety of methods for joining stainless steel, with welding being the most common. Fusion and resistance welding are the two basic methods generally used with many variations for both. In fusion welding, heat is provided by an electric arc struck between an electrode and the metal to be welded. In resistance welding, bonding is the result of heat and pressure. Heat is produced by the resistance to the flow of electric current through the parts to be welded, and pressure is applied by the electrodes. After parts are welded together, they must be cleaned around the joined area. Quality Control In addition to in-process control during manufacture and fabrication, stainless steels must meet specifications developed by the American Society for Testing and Materials (ASTM) with regard to mechanical properties such as toughness and corrosion resistance. Metallography can sometimes be correlated to corrosion tests to help monitor quality. The Future Use of stainless and super stainless steels is expanding in a variety of markets. To meet the requirements of the new Clean Air Act, coal-fired power plants are installing stainless steel stack liners.

Other new industrial applications include secondary heat exchangers for high-efficiency home furnaces, service-water piping in nuclear power plants, ballast tanks and fire-suppression systems for offshore drilling platforms, flexible pipe for oil and gas distribution systems, and heliostats for solar-energy plants. Environmental legislation is also forcing the petrochemical and refinery industries to recycle secondary cooling water in closed systems rather than simply discharge it. Reuse results in cooling water with elevated levels of chloride, resulting in pitting-corrosion problems. Duplex stainless steel tubing will play an increasingly important role in solving such industrial corrosion problems, since it costs less than other materials. Manufacturers are developing highly corrosion-resistant steels in respond to this demand. In the automotive industry, one steel manufacturer has estimated that stainless-steel usage per vehicle will increase from 55 to 66 pounds (25 to 30 kilograms) to more than 100 pounds (45 kilograms) by the turn of the century. New applications include metallic substrates for catalytic converters, air bag components, composite bumpers, fuel line and other fuel-system parts compatible with alternate fuels, brake lines, and long-life exhaust systems.

With improvements in process technology, superaustenitic stainless steels (with nitrogen contents up to 0.5 percent) are being developed. These steels are used in pulp-mill bleach plants, sea water and phosphoric-acid handling systems, scrubbers, offshore platforms, and other highly corrosive applications. A number of manufacturers have begun marketing such materials in sheet, plate, and other forms. Other new compositions are being developed: ferritic iron-base alloys containing 8 and 12 percent Cr for magnetic applications, and austenitic stainless with extra low sulfur content for parts used in the manufacture of semiconductors and pharmaceuticals. Research will continue to develop improved and unique materials. For instance, Japanese researchers have recently developed several. One is a corrosion-resistant stainless steel that displays the shape-memory effect. This type of material returns to its original shape upon heating after being plastically deformed. Potential applications include assembly components (pipe fittings, clips, fasteners, clamps), temperature sensing (circuit breakers and fire alarms), and springs. An improved martensitic stainless steel has also been developed for precision miniature and instrument rolling-contact bearings, which has reduced vibration levels, improved life expectancy, and better surface finish compared to conventional materials.

Where To Learn More Which metals make up stainless steel? | Reference.com Which metals make up stainless steel? A: Quick Answer Stainless steel is a special form of steel that is made of chromium added to steel. Regular steel is an alloy that is made of both iron and carbon. There are different types of stainless steel depending on how much chromium is added and if there are any other elements added in small amounts like nickel. Why Is Stainless Steel Stainless? Why Is Stainless Steel Stainless? Why Is Stainless Steel Stainless? What It Is and How It Works! Cookware is often made of stainless steel because it is durable, inexpensive, and doesn't rust. Coyau, Creative Commons Updated July 18, 2016. What Is Stainless Steel and Why Is it Stainless? In 1913, English metallurgist Harry Brearly, working on a project to improve rifle barrels, accidentally discovered that adding chromium to low carbon steel gives it stain resistance. In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel .

It is the addition of a minimum of 12% chromium to the steel that makes it resist rust, or stain 'less' than other types of steel. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the passive film. The sizes of chromium atoms and their oxides are similar, so they pack neatly together on the surface of the metal, forming a stable layer only a few atoms thick. If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and recover the exposed surface, protecting it from oxidative corrosion . continue reading below our video 10 Best Universities in the United States (Iron, on the other hand, rusts quickly because atomic iron is much smaller than its oxide, so the oxide forms a loose rather than tightly-packed layer and flakes away.) The passive film requires oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen and poor circulation environments. In seawater, chlorides from the salt will attack and destroy the passive film more quickly than it can be repaired in a low oxygen environment.

Types of Stainless Steel The three main types of stainless steels are austenitic, ferritic, and martensitic. These three types of steels are identified by their microstructure or predominant crystal phase. Austenitic: Austenitic steels have austenite as their primary phase (face centered cubic crystal). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not hardenable by heat treatment. The most familiar stainless steel is probably Type 304, sometimes called T304 or simply 304. Type 304 surgical stainless steel is an austenitic steel containing 18-20% chromium and 8-10% nickel. Ferritic: Ferritic steels have ferrite (body centered cubic crystal) as their main phase. These steels contain iron and chromium, based on the Type 430 composition of 17% chromium. Ferritic steel is less ductile than austenitic steel and is not hardenable by heat treatment .

Martensitic: The characteristic orthorhombic martensite microstructure was first observed by German microscopist Adolf Martens around 1890. Martensitic steels are low carbon steels built around the Type 410 composition of iron, 12% chromium, and 0.12% carbon. They may be tempered and hardened. Martensite gives steel great hardness, but it also reduces its toughness and makes it brittle, so few steels are fully hardened. There are also other grades of stainless steels, such as precipitation-hardened, duplex, and cast stainless steels. Stainless steel can be produced in a variety of finishes and textures and can be tinted over a broad spectrum of colors. Passivation There is some dispute over whether the corrosion resistance of stainless steel can be enhanced by the process of passivation. Essentially, passivation is the removal of free iron from the surface of the steel. This is performed by immersing the steel in an oxidant, such as nitric acid or citric acid solution . Since the top layer of iron is removed, passivation diminishes surface discoloration.

While passivation does not affect the thickness or effectiveness of the passive layer, it is useful in producing a clean surface for a further treatment, such as plating or painting. On the other hand, if the oxidant is incompletely removed from the steel, as sometimes happens in pieces with tight joints or corners, then crevice corrosion may result. Most research indicates that diminishing surface particle corrosion does not reduce susceptibility to pitting corrosion. Additional Reading Citric Acid Passivation of Stainless Steel - Lee V. Kremer's article discusses the use of citric acid passivation as an alternative to nitric acid passivation of stainless steel. Passivation of Stainless Steel - Dan Englebert's article defines passivation and describes how it is performed and verified. Phase Diagram Glossary - These are definitions of several relevant terms, including 'ferritic steel', 'microstructure', and 'plain carbon steel'. The Stainless Steel Information Center - The Specialty Steel Industry of North America sponsors this resource, which includes general information about stainless steel, industry news, publications, workshops and training, and information for students. What Are Martensites? - This site offers a description and pictures of the martensitic crystal transformation in steels. What is Stainless Steel?

(with pictures) What is Stainless Steel? Last Modified Date: 20 December 2016 Copyright Protected: Top 10 unbelievable historical concurrencies Stainless steel is the universal name for a number of different steels used primarily for their anti-corrosive element. This steel has been developed to resist a number of corrosive environments. It ensures that our workplaces are safe, that buildings last longer and that our food preparation surfaces are hygienic. It is also an earth friendly material; it can be melted down, recycled and made into something else. Stainless steel is always made using chromium . The minimum amount of chromium used is 10.5%; it is chromium that makes the steel stainless. Chromium also improves the corrosion resistance by forming a chromium oxide film on the steel. This very thin layer, when placed under the right conditions, can also be self-repairing. There are other elements used to make this steel as well, including nickel, nitrogen and molybdenum . Bringing these elements together forms different crystal structures that enable a variety of properties in machining , welding and forming. There are four major types of stainless steel. Of these, austenitic is the most widely used type.

It has a nickel content of at least 7%, which makes it very flexible. It is used in a range of houseware products, industrial piping and vessels, constructional structures and architectural facades. Ferritic stainless steel has similar properties to mild steel , but better corrosion resistance. This type of steel is commonly used in washing machines, boilers and indoor architecture. Martensitic stainless steel is a very hard, strong steel. It contains around 13% chromium and is used to make knives and turbine blades. There is also a duplex steel that is a composite of austenitic and ferritic steels. This steel is both strong and flexible. Duplex steels are most commonly used in the paper, pulp and shipbuilding industries. They are also widely used in the petrochemical industry. Stainless steel is a very versatile material. It can literally be used for years and remain stainless. Products made from it have a significantly longer lifespan than products made of other materials. The maintenance costs are lower, and stainless steel also has a very high scrap value . Ad honeybees Post 16 @StarJo: I have stainless steel cookware but it is not considered nonstick.

I use some olive oil or some other type of cooking spray to keep food from sticking. It has been years since I got rid of all of my nonstick cookware. When I read some of the studies about the chemicals they leaked out into your food, I made the change to stainless steel. Another advantage to using stainless steel cookware is this will last a lifetime if you take care of it. My mom has been using the same stainless steel set of pans for 50 years and you would never guess from looking at them they are that old. JackWhack Post 15 I think that stainless steel appliances are beautiful. They just look so modern and expensive. My neighbor has all stainless steel appliances in her kitchen. She has a huge silver refrigerator that looks so shiny and cool. I love the fact that it matches her dishwasher and stove. If I could afford all new appliances, I would get stainless steel. I will probably just buy one at a time as they need replacing. That will be a good way to build up my stainless steel collection. OeKc05 Post 14 @StarJo: No, they aren't nonstick pans. In fact, food seems to stick to them a lot.

I've noticed that when I cook meat in a stainless steel pan, even if I add cooking oil first, it sticks to the pan. This is frustrating when I'm trying to fry chicken, because it strips the batter right off of the meat. If you want a nonstick pan, don't buy a stainless steel one. Stainless steel pans are great for caramelizing food like onions, but they are awful for cooking meat. myharley Post 12 @julies-- Have you tried any of the special cleaners made specifically for stainless steel products? These cost more than a regular cleaner, but this is the only thing I have found to keep my stainless steel appliances clean and streak free. The cleaner I use sprays out like a foam and I spray this on a towel instead of directly on the appliance. I use the moist towel to wipe it down and follow up with a dry towel for a clean, shiny look. It's too bad it doesn't last a little bit longer than it does, but at least it stays clean for awhile anyway. StarJo Post 11 Do all stainless steel pans have nonstick surfaces? I've always just assumed that food would not stick to stainless steel.

Maybe the word “stainless” makes me think that nothing will be left behind on the surface. julies Post 10 I have stainless steel appliances in my kitchen. This includes a stainless steel sink, refrigerator and dishwasher. These appliances were already in the house when we moved in. Stainless steel has been very popular for kitchen appliances the last few years and I love the modern look. The only thing I don't like about the refrigerator and the dishwasher is I find the fingerprints hard to clean off. No matter what type of cleaner I have used, it seems to leave streaks. With three young kids in the house you can imagine the number of fingerprints I get on my refrigerator in a day. As far as the stainless steel sink I really love it. It is so much easier to clean and I can really get it looking clean and shiny without much effort. Perdido Post 9 My kitchen has a stainless steel sink. It looked pretty dull when we moved in, because it hadn't been polished in years, but my husband made it look brilliantly shiny. He used an electric sander with a buffer pad attached to return the sink to its original state of bright silver.

He buffed it in circles, so there was a light circular pattern left behind. I never believed that the sink could look so shiny. I'm glad that he knew this trick, because I could have scrubbed for half an hour with a brush and would still have been unable to achieve these results. LisaLou Post 8 @lamaestra-- I am also hoping they don't come out and say that stainless steel has harmful chemicals. I replaced all my plastic water bottles with stainless steel. Hopefully the stainless steel won't leak out chemicals like they say the plastic does. I can tell a difference in the taste of my water. My water really does taste a lot better when it doesn't have that hint of plastic taste to it. anon173178 what are the engineering properties of stainless steel? sschwartz Post 6 Stainless steel, like all metals, is a renewable resource. Metals are melted down and reused more than any other type of material. anon88997 Post 5 I am in the process of buying a pvc fence for my backyard privacy type. However when I speak to different companies they have stated the PVC fences come in different grades some with mental at the bottom for sturdiness.

Do different manufacturers make different fences have this mental inserts? Thank you. Lorraine anon57554 Post 4 birgitte: You cannot add (plate) a layer of stainless steel. Stainless steel is an alloy and cannot be plated. A fairly reliable test for stainless steel is to use a magnet and compare how well it sticks to ordinary steel and the s/s metal you are testing. The higher grade stainless has no magnetic properties. The best magnet to test with is a rare earth magnet, which is the strongest magnet available. anon21981: 18/8 stainless steel means 18 percent Chrome and 8 percent Nickel. Steel should only be called stainless if it has at least 10 percent chrome. Stainless steel is good for cooking but not for storing food. It is the oxygen in the air that keeps stainless steel from corroding and it will begin to corrode if covered continuously with food etc. lamaestra: Stainless steel is not recommended for the storage of wet foodstuff. Too complicated to explain here.

birgitte Post 3 I am sanding my dishwasher to paint with black epoxy to match my new black and stainless steel appliances, but underneath the paint appears a beautiful brushed stainless steel surface, created by the fine grained sandpaper. So I am thinking: Why don't I just sand over the whole thing? Well, I did, and it looks great, but I am concerned about rust. I wonder if the metal panel is rust-resistant like stainless steel or if you have to treat it, and if that is even possible? Any ideas? Based on this article I wonder if the metal in a dishwasher has enough chromium etc. and whether you can add a film of chromium on top? anon21981 Post 2 I see a lot of food container specify made by 18/8 stainless steel, what is 18/8 stainless steel? Is it better than regular stainless steel? Does it harmful when use as food container for hot/cold? Thanks. Stainless Steel Information Knowledge | 18-8 | 304 | 316 “What you need to know” (Probably more than you ever wanted to know!) The following is a discussion of the various types of stainless steel.

For other terms and their definitions you will encounter when dealing with stainless steel click here . 18-8: 300 series stainless steel having approximately (not exactly) 18% chromium and 8% nickel. The term "18-8" is used interchangeably to characterize fittings made of 302, 302HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the "18-8" types, but slight differences in chemical composition do make certain grades more resistant than others do against particular chemicals or atmospheres. "18-8" has superior corrosion resistance to 400 series stainless, is generally nonmagnetic, and is hardenable only by cold working. 304: The basic alloy. Type 304 (18-8) is an austenitic steel possessing a minimum of 18% chromium and 8% nickel, combined with a maximum of 0.08% carbon. It is a nonmagnetic steel which cannot be hardened by heat treatment, but instead.

must be cold worked to obtain higher tensile strengths. The 18% minimum chromium content provides corrosion and oxidation resistance. The alloy's metallurgical characteristics are established primarily by the nickel content (8% mm.), which also extends resistance to corrosion caused by reducing chemicals. Carbon, a necessity of mixed benefit, is held at a level (0.08% max.) that is satisfactory for most service applications. The stainless alloy resists most oxidizing acids and can withstand all ordinary rusting. HOWEVER, IT WILL TARNISH. It is immune to foodstuffs, sterilizing solutions, most of the organic chemicals and dyestuffs, and a wide variety of inorganic chemicals. Type 304, or one of its modifications, is the material specified more than 50% of the time whenever a stainless steel is used. Because of its ability to withstand the corrosive action of various acids found in fruits, meats, milk, and vegetables, Type 304 is used for sinks, tabletops, coffee urns, stoves, refrigerators, milk and cream dispensers, and steam tables. It is also used in numerous other utensils such as cooking appliances, pots, pans, and flatware.

Type 304 is especially suited for all types of dairy equipment - milking machines, containers, homogenizers, sterilizers, and storage and hauling tanks, including piping, valves, milk trucks and railroad cars. This 18-8 alloy is equally serviceable in the brewing industry where it is used in pipelines, yeast pans, fermentation vats, storage and railway cars, etc. The citrus and fruit juice industry also uses Type 304 for all their handling, crushing, preparation, storage and hauling equipment. In those food processing applications such as in mills, bakeries, and slaughter and packing houses, all metal equipment exposed to animal and vegetable oils, fats, and acids is manufactured from Type 304. Type 304 is also used for the dye tanks, pipelines buckets, dippers, etc. that come in contact with the lormic, acetic, and other organic acids used in the dyeing industry. In the marine environment, because of it slightly higher strength and wear resistance than type 316 it is also used for nuts, bolts, screws, and other fasteners. It is also used for springs, cogs, and other components where both wear and corrosion resistance is needed.

Type Analysis of Stainless Type 304 Carbon Stainless steel corrosion Stainless Steel Corrosion The main reason for the existence of the stainless steels is their resistance to corrosion. Chromium is the main alloying element, and the steel should contain at least 11 %. Chromium is a reactive element, but it and its alloys passivate and exhibit excellent resistance to many environments. Higher Cr contents may be necessary for to improve the corrosion resistance of stainless steels in more aggressive media. Among other alloying elements, Nickel is the most important : it is added to control the alloy microstructure and to improve the corrosion resistance in acidic or caustic media. The addition of other elements such as Molybdenum, Tungsten, Copper, Silicon, Titanium, Niobium, Nitrogen , … enables a wide range of properties to be obtained. All stainless steels contain some carbon. Even though it is difficult to get much less than about 0.03 % and sometimes carbon is deliberately added up to 1.00% or more, modern melting processes allow to reduce the content below 0.015 or even 0.010%, providing stainless steels with superior resistance to intergranular corrosion .

The more carbon there is, the more chromium must be used, because carbon can take from the alloy about seventeen times its own weight of chromium to form carbides. Chromium carbide is of little use for resisting corrosion. The carbon, of course, is added for the same purpose as in ordinary steels to make the alloy stronger. Nitrogen is often added in modern stainless steels (especially in duplex grades or in highly alloyed austenitics); this element provides high mechanical properties, better resistance to pitting initiation and more generally improves the corrosion resistance thanks to a better microstructural stability. From a microstructural point of view, alloying elements may be classified as either Austenite formers (Nickel, Nitrogen, Carbon, …) or Ferrite formers (Chromium, Molybdenum, …). Depending upon the ratio between austenite former elements and ferrite former elements, the resulting microstructure may be Ferritic (Body-Centered-Cubic crystal) or Austenitic (Face-Centered-Cubic crystal). The Martensitic structure (Close-Packed Hexagonal crystal) is the result of the transformation of austenite to martensite during cooling or during strong cold working.

The Duplex microstructure is a mixture of Austenite and Ferrite (generally about 50/50%) which is the result of an accurate balance between Austenite and Ferrite former alloying elements. A large number of stainless steels are available. Their corrosion resistance, mechanical properties, and cost vary over a broad range. For this reason, it is important to specify the exact stainless steel desired for a given application. A modern and comprehensive document on the subject is the second edition of the classic CORROSION BASICS textbook. The new interactive software CorrIntel™ covers the topic of the Corrosion Resistance and Metallurgy of Stainless Steels and Nickel base Alloys. There are five main types of stainless steel: ferritic, martensitic, austenitic, precipitation hardening and duplex. The ferritic and martensitic grades are so named because of their crystal structures. Both are iron-chromium-based alloys and were the type of stainless steel first developed in the early 1900’s. The ferritic and martensitic stainless steels are fully magnetic; duplex stainless steels are partly magnetic.

The martensitic stainless steels can be hardened by a heat treatment similar to that used to harden ordinary steel, namely, heating to a high temperature, quenching, then reheating to an intermediate temperature (tempering) to achieve the desired balance of hardness and ductility. Stainless and heat resisting steels possess unusual resistance to attack by corrosive media at atmospheric and elevated temperatures, and are produced to cover a wide range of mechanical and physical properties for particular applications. All About Stainless Steel Home --> Learning Center --> All About Stainless Steel All About Stainless Steel The many unique values provided by stainless steel make it a powerful candidate in materials selection. Engineer, 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, corrosionresisting 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.

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, therefor cost savings. Properties Stainless steel is defined as a ferrous alloy with a minimum of 10% chromium content. The name originates from the fact that stainless steel does not stain, corrode or rust as easily as ordinary steel. This material is also called corrosion resistant steel when it is not detailed exactly to its alloy type and grade, particularly in the aviation industry. Stainless steels have higher resistance to oxidation (rust) and corrosion in many natural and man made environments; however, it is important to select the correct type and grade of stainless steel for the particular application. High oxidation resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments. The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, meaning the metal stays shiny.

It is, however, impervious to water and air, protecting the metal beneath. Also, when the surface is scratched this layer quickly reforms. This phenomenon is called passivation by materials scientists, and is seen in other metals, such as aluminium. When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off causing the parts to weld together. When disassembled, the welded material may be torn and pitted, an effect that is known as galling. Commercial value of stainless steel Stainless steel's resistance to corrosion and staining, low maintenance, relative inexpense, and familiar luster make it an ideal base material for a host of commercial applications. There are over 150 grades of stainless steel, of which fifteen are most common. The alloy is milled into sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, hardware, surgical instruments, major appliances, industrial equipment, and building material in skyscrapers and large buildings. See "Use in sculpture and building facades", below, for more. Stainless steel is 100% recyclable.

In fact, over 50% of new stainless steel is made from remelted scrap metal, rendering it a somewhat eco-friendly material. Types of stainless steel There are different types of stainless steels: when nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels non-magnetic and less brittle at low temperatures. For higher hardness and strength, carbon is added. When subjected to adequate heat treatment these steels are used as razor blades, cutlery, tools etc. Significant quantities of manganese have been used in many stainless steel compositions. Manganese preserves an austenitic structure in the steel as does nickel, but at a lower cost. Stainless steels are also classified by their crystalline structure: Austenitic stainless steels comprise over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy.

A typical composition is 18% chromium and 10% nickel, commonly known as 18/10 stainless is often used in flatware. Similarly 18/0 and 18/8 is also available. "Superaustenitic" stainless steels, such as alloy AL-6XN and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion due to high Molybdenum contents (>6%) and nitrogen additions and the higher nickel content ensures better resistance to stress-corrosion cracking over the 300 series. The higher alloy content of "Superaustenitic" steels means they are fearsomely expensive and similar performance can usually be achieved using duplex steels at much lower cost. Ferritic stainless steels are highly corrosion resistant, but far less durable than austenitic grades and cannot be hardened by heat treatment. They contain between 10.5% and 27% chromium and very little nickel, if any. Most compositions include molybdenum; some, aluminium or titanium.

Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni. Martensitic stainless steels are not as corrosion resistant as the other two classes, but are extremely strong and tough as well as highly machineable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12-14%), molybdenum (0.2-1%), no nickel, and about 0.1-1% carbon (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic. It is also known as "series-00" steel. Precipitation-hardening martensitic stainless steels have corrosion resistance comparable to austenitic varieties, but can be precipitation hardened to even higher strengths than the other martensitic grades. The most common, 17-4PH, uses about 17% chromium and 4% nickel.

Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim being to produce a 50:50 mix although in commercial alloys the mix may be 40:60 respectively. Duplex steel have improved strength over austenitic stainless steels and also improved resistance to localised corrosion particularly pitting, crevice corrosion and stress corrosion cracking. They are characterised by high chromium (19-28%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. History A few corrosion-resistant iron artifacts survive from antiquity. A famous (and very large) example is the Iron Pillar of Delhi, erected by order of Kumara Gupta I around the year AD 400. However, unlike stainless steel, these artifacts owe their durability not to chromium, but to their high phosphorus content, which together with favorable local weather conditions promotes the formation of a solid protective passivation layer of iron oxides and phosphates, rather than the non-protective, cracked rust layer that develops on most ironwork.

The corrosion resistance of iron-chromium alloys was first recognized in 1821 by the French metallurgist Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery. However, the metallurgists of the 19th century were unable to produce the combination of low carbon and high chromium found in most modern stainless steels, and the high-chromium alloys they could produce were too brittle to be of practical interest. This situation changed in the late 1890s, when Hans Goldschmidt of Germany developed an aluminothermic (thermite) process for producing carbon-free chromium. In the years 1904-1911, several researchers, particularly Leon Guillet of France, prepared alloys that would today be considered stainless steel. In 1911, Philip Monnartz of Germany reported on the relationship between the chromium content and corrosion resistance of these alloys. Harry Brearley of the Brown-Firth research laboratory in Sheffield, England is most commonly credited as the "inventor" of stainless steel.

In 1913, while seeking an erosion-resistant alloy for gun barrels, he discovered and subsequently industrialized a martensitic stainless steel alloy. However, similar industrial developments were taking place contemporaneously at the Krupp Iron Works in Germany, where Eduard Maurer and Benno Strauss were developing an austenitic alloy (21% chromium, 7% nickel), and in the United States, where Christian Dantsizen and Frederick Becket were industrializing ferritic stainless. Already in the year 1908 Krupp had built a famous sailing-yacht featuring a chrome-nickel steel hull, or so it seems its wreck being currently investigated by the Bureau of Archaeological Research of the State of Florida. Stainless Steel Grades Type 301-highly ductile, for formed products. Also hardens rapidly during mechanical working. Type 303-Free machining version of 304 via addition of sulfur Type 304-the most common; the classic 18/8 stainless steel. Type 316-the next most common; for food and surgical stainless steel uses; Alloy addition of molybdenum prevents specific forms of corrosion.

Also known as "marine grade" stainless steel due to its increased ability to resist saltwater corrosion compared to type 304. SS316 is often used for building nuclear reprocessing plants. 400 Series-ferritic and martensitic chromium alloys Type 408-heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel. Type 409-cheapest type; used for automobile exhausts; ferritic (iron/chromium only). Type 410-martensitic (high-strength iron/chromium). Type 416 Type 420-"Cutlery Grade" martensitic; similar to the Brearley's original "rustless steel". Also known as "surgical steel". Type 430-decorative, e.g., for automotive trim; ferritic. Type 440-a higher grade of cutlery steel, with more carbon in it, which allows for much better edge retention when the steel is heat treated properly.

500 Series-heat resisting chromium alloys 600 Series-martensitic precipitation hardening alloys Type 630-most common PH stainless, better known as 17-4; 17% chromium, 4% nickel Metallurgy of Mo in Stainless Steel Metallurgy of Mo in stainless steel Metallurgy of Mo in stainless steel Molybdenum adds corrosion resistance and high temperature strength Molybdenum primarily increases the corrosion resistance of stainless steels (see Grades and Properties ). Molybdenum containing grades of stainless steels are generally more corrosion resistant than molybdenum-free grades. They are used in applications that are more corrosive, such as chemical processing plants or in marine applications. There are many grades of stainless steels with different molybdenum (and chromium, nickel, nitrogen, etc.) contents. The best grade for a given application is selected based on the corrosivity of the service environment. As a large atom, molybdenum increases the elevated temperature strength of stainless steels through solid solution hardening. This effect is used in heat exchangers and other elevated temperature equipment such as in automotive exhaust systems.

Molybdenum is a ferrite former To discuss the influence of molybdenum on the metallurgy of stainless steels it is useful to look at the metallurgy of stainless steels in general. Based on their microstructure, stainless steels are divided into the following families: austenitic duplex precipitation hardenable The division based on microstructure is useful because the members within one family tend to have similar physical and mechanical properties. However, the properties for one family can be very different from the properties for another family. For example, austenitic stainless steels are non-magnetic, while ferritic and duplex stainless steels are magnetic. The difference between the families is fundamental on an atomic level. The arrangement of atoms in the ferrite crystal is different from the one in the austenite crystal: In the ferritic stainless steel, the iron and chromium atoms are arranged on the corners of a cube and in the center of that cube. In the austenitic stainless steels the atoms, here iron, chromium and nickel, are arranged on the corners of the cube and in the center of each of the faces of the cube. This seemingly small difference profoundly affects the properties of these steels.

Fig 1: The ferritic stainless steel on the left has a body centered cubic (bcc) crystal structure. By adding nickel to this stainless steel the structure changes from bcc to face centered cubic (fcc), which is called austenitic. Select properties of austenitic and ferritic stainless steels Properties Copper Molybdenum is a ferrite former. That means that when molybdenum is added to improve the corrosion resistance of an austenitic stainless steel, there has to be an austenite former such as nickel or nitrogen added in order to keep the structure austenitic. Duplex stainless steels have a mixture of austenitic and ferritic grains in their microstructure; hence they have a “duplex” structure. This effect is achieved by adding less nickel than would be necessary for making a fully austenitic stainless steel. Molybdenum is mainly used for added corrosion resistance in austenitic and duplex stainless steels. In austenitic stainless steels between two and seven percent are added, in duplex stainless steels, between three and five percent.

The addition of one or two percent molybdenum to ferritic stainless steels also significantly increases the corrosion resistance and the elevated temperature strength of these stainless steels. Fig 2: Adding 8% nickel to a ferritic chromium stainless steel makes an austenitic chromium-nickel stainless steel, for example Type 304 stainless steel. If less nickel is added to a chromium steel, about four or five percent, a duplex structure, a mixture of austenite and ferrite, is created as in 2205 duplex stainless steel. Simplified Process for Making Stainless Steel Simplified Process for Making Stainless Steel Melting, Slab Casting and Grinding To make ferritic stainless steels, one needs iron and chromium, and to make austenitic stainless steels, nickel is added to the mixture. This raw material mixture is melted in an electric arc furnace. The molten metal is refined and decarburised in an Argon-Oxygen Decarburiser (AOD) vessel by blowing oxygen, argon and nitrogen into the molten steel. The refined stainless steel is processed through a continuous casting machine to produce stainless steel slabs. The slabs can go through a surface grinding process to remove any possible surface defects.

This is our first saleable product. The slabs are typically between 900mm and 1 600mm wide, 200mm thick, and can be cut to lengths of between 4 and 12m. Hot Rolling The hot rolling process begins at the reheat furnace where the slabs are heated to between 1 100 and 1 300°C, depending on the stainless steel grade. The slabs are then rolled on a reversing four high mill to gauges between 65 and 25mm. Thinner gauges are rolled down further on the Steckel mill. Once the predetermined gauge is reached, the material can either be coiled (black coil, also known as hot band, HR or HRA) or cut into plate (black plate (HRA)). This is our second range of saleable products. Coil mass is between 20 and 30 tons and the thickness is generally between 3mm and 8mm. Plate thickness can range between 3 mm and 65 mm. Annealing and Pickling The hot rolled products are softened (annealed) and descaled (pickled with acids) to produce a No.

1 finish product. This product has a light grey matt surface finish. No. 1 coil and plate are also saleable products. Cold Rolling and Finishing Cold rolling of the No. 1 coils takes place on one of our four Sendzimer mills (Z-mills), which produce smooth, shiny finished, cold rolled stainless steel. The thickness range of the cold rolled product is between 0,2mm and 6mm. The material is then annealed (softened) and pickled (and passivated), before it is processed through the skinpass mill, to ensure a smooth surface, known as a 2B finish. Alternatively, the cold rolled material can be processed to a bright annealed (BA) finish. This is achieved by annealing in a vertical furnace with an inert atmosphere, to retain the bright surface imparted by the cold rolling process. These cold rolled stainless steel coils can then be cut into smaller coils or sheets, or slit to narrower widths before being packed and shipped to our customers. Polishing Following the cold rolling, annealing and skin passing processes, a material can be given a uniform scratch finish by polishing with abrasive belts.

Click here to view a full description of stainless steel finishes Producing stainless steel | More stainless | Products & properties | Global | Outokumpu Producing stainless steel ​​​​​Outokumpu Handbook of Stainless steel​ ​​View full copy of Outokumpu Handbook of Stainless Steel​ Polished and brushed Page Content ​Steel is not a single product. There are many thousands of different grades of steel with a variety of properties – physical, chemical, and mechanical. Added to that, each grade can be produced in several different forms. Stainless steel product forms Starting from a geometrical point of view, steel product forms can be divided into flat and long products. An alternative way to describe product forms is to follow the production route, starting with semi-finished products, rolled products, and products finished by additional operations. Flat products A flat product is a plate product or a (hot or cold) rolled coil product. Typically, it is rolled in a rolling mill to produce the final thickness. Plate products vary in thickness from 5 mm to 200 mm and thin flat rolled products from 50 μm to 5 mm. In addition there is an intermediate thickness range covered by hot-rolled coiled flat products.

Plate products are used for construction, large diameter welded pipes, and boiler applications. Thin flat products are used in the chemical process industry, domestic white-good products, welded tubes, and a host of other products, from minute springs to huge heat exchangers and storage tanks. Long products The long products include a variety of forms such as rods, bars , wires, rails, tubes, and sections. Many of the products originate from hot-rolled rod coil that is further processed into wires or cold-drawn bar. The rod coil itself can have a round, square, hexagonal, or octagonal shape. Final products include reinforcing bars for concrete, engineering products such as gears, and tools. Semi-finished products Steel products such as ingots, billets, blooms, and slabs fall into the semi-finished product category. These forms can be made by direct continuous casting of liquid steel or by pouring the liquid steel into ingots, which are then hot-rolled into semi-finished products. Raw materials Stainless steel is the most recycled material in the world and it is estimated that 82% of the stainless steel in use today will be recycled into new steel.

When recycled, the stainless steel is not downgraded – recycled steel has the same quality and properties as the original steel. That’s why, on average, recycled steel makes up around 60% of the raw material used to make new stainless steel. For Outokumpu the recycled steel content of our raw material is between 85 and 90%. To handle such large volumes of steel scrap, rigorous purchase routines are needed. At arrival, before entering the melt shop site, the steel scrap is tested to ensure that no radioactive components are present. It is then tested, analyzed, and sorted according to its alloying content to ensure that as little virgin material as possible is needed to get the right chemical composition of the stainless steel produced. The melt shop Processing steel scrap and alloys in the melt shop is the first step in the production of stainless steel.

The configuration of the melt shop depends on the capabilities of the steel works, but typically there are four main steps: 1) Melting of raw materials in an electric arc furnace (EAF) The most conventional method is to melt the raw materials, scrap (alloyed and unalloyed) and ferro-alloys in an electric arc furnace, where powerful electric arcs start to melt the scrap and alloys. During the melting process, the arc reaches temperatures of up to 3,500 °C, and the molten steel can reach up to 1,800 °C. The additional injection of chemical energy, in the form of carbon, ferrosilicon, oxygen, or fuel gas mixtures, speeds up the melting process. 2) Removal of carbon, sulfur, and possibly nitrogen, in a steel converter After melting, the steel is further processed in an AOD ( Argon Oxygen Decarburization ) converter. The main objective of this step is to reduce the carbon content to a target amount by injecting an oxygen-argon mixture, but also to supply additional alloying elements. After the AOD treatment, the molten material is poured into a ladle.

When liquid ferrochrome is used, an iron-rich scrap mix with low alloy content is melted in the arc furnace. Nickel and molybdenum, together with the liquid ferrochrome, are then added to the AOD converter. An alternative decarburization process is VOD ( Vacuum Oxygen Decarburization ), which is especially suitable when very low carbon or nitrogen content is required, for instance in the case of some high chromium ferritic stainless steels. 3) Tuning of the steel composition and temperature in ladle treatment The quality requirements for most stainless steels make a secondary metallurgical treatment necessary. This is done in a ladle station, ladle furnace, or as a vacuum treatment of the liquid steel. The goal of this process step is to make the final adjustment to the chemical composition. The steel is slowly stirred to remove unwanted inclusions and to homogenize both the temperature and chemistry of the molten material, maintaining a tightly specified composition within exact temperature limits. 4) Casting of slabs or ingots The liquid steel ladle is then transported to the continuous casting machine or, in some cases, to the ingot casting area.

Continuous casting is a process in which molten steel is converted into slabs of manageable size. From the ladle, the molten steel is tapped into the tundish – an intermediate vessel designed to maintain a constant weight and allow for flying ladle changes during casting. The steel then flows into the water-cooled copper mold. The flow is often automatically controlled to maintain a constant level in the mold as the bottom of the mold is slowly retracted. Arc-shaped top and bottom rollers support the solidified strand shell. Molten casting powder is used to reduce friction and ensure good contact between the mold and the shell. Starting immediately below the mold and between the rollers, intensive water spray cools the shell, solidifying the hot melt inside to form a solid strand of steel. The strand is continuously cooled and shrinks in volume as it is passed to the cutting station. At this stage, the steel is still hot and glowing, but is sufficiently solid to enable the strand to be cut with movable oxygen lances into manageable pieces called slabs. Slabs serve as the feedstock for flat hot rolling mills. The process is similar for the semi-finished casting products like blooms and billets, which are feedstock for long product production.

Every slab is given a unique identity number and is carefully tracked. This identity (slab/coil number) follows the material through the whole production line and is written in the material certificate. This makes it possible to track the material all the way back to the melt shop. Recorded production parameters are linked to the identity number to ensure that the individual end product fulfills the customer’s requirements. All slabs are inspected to ensure a high quality. Hot rolling Hot rolling is a metalworking process that occurs at a temperature above the recrystallization temperature of the material. The starting material is usually semi-finished casting products, such as slabs, blooms, or billets. The cast microstructure is broken down and deformed during processing and the deformed grains recrystallize, which maintains a microstructure in which the grains have approximately the same dimensions in all directions and prevents the steel from hardening. While the finished product is of good quality, the surface is covered in mill scale , which is an iron- and chromium-rich oxide that forms at high temperatures. It is usually removed in the annealing and pickling line, which restores the smooth metallic surface.

Cold rolling, annealing, and pickling The cold rolling of stainless steel is predominately carried out in cluster mills. These mills have small-diameter working rolls, each backed by two or three layers of supporting rolls, and are very suitable for cold-rolling wide sheets of stainless steel to close tolerances and improved surface finishes. The mills are equipped to measure strip thickness, profile, and flatness, and have various actuators to control the strip profile and flatness. The rolling schedule defines the number of passes the strip has to go through and which thickness reduction per pass will be used when rolling from the starting gauge to the desired final gauge. During the cold rolling process, the material deforms and strain hardens to the extent that only a few percent of the original tensile elongation remains. Typical cold rolling reduction is 50–90% and depends on the work hardening behavior of the steel grade. To restore the material properties after cold rolling, a heat treatment is needed to recover and recrystallize the deformed microstructure. This is done in a continuous annealing and pickling line.

The majority of the cold rolled products have a 2B/2BB surface , which means that no mechanical scale breaking is used; all oxide scale is removed by chemical means. This is achieved by passing the strip through several consecutive mixed acid pickling baths, and then finishing off with high pressure water rinsing. Many of these lines also have some type of flatness improvement equipment installed. Another route after cold rolling is to use a bright annealing line (BA-line) to restore the material properties. In such a line, the strip is heat treated in a protective atmosphere, often hydrogen or a mixture of hydrogen and nitrogen. As no oxygen is available inside the furnace, no additional oxide scale is formed and whatever oxide remains on the strip is reduced to metal. If the cooling is also done in a protective environment, the strips can, after skin pass rolling, exhibit a mirror like finish, referred to as 2R or BA ( Bright Annealed ) . Skin pass rolling (also called temper rolling) is a very light cold-rolling treatment that involves the least amount of reduction (0.5–1%).

The purpose of skin passing is to improve the strip shape and remove minor surface blemishes, create the desired surface finish, and to produce the appropriate mechanical properties. Final processing The final operations before sending the product to the customer are called finishing. This is where coils and plates are tailored to customer requirements, which can include: Leveling a plate or coil with a roller leveler or a stretch leveler, or a combination of both techniques Edge trimming of the coil to the desired width Slitting a coil into several narrow coils Cutting a coil into tailored or standard length sheets/plates in dedicated cut-to-length (CTL) lines Shearing or cutting into an order-sized square/rectangular plate or customized specially shaped plate from a larger quarto mother plate . Applying a plastic film coat to provide surface protection for further processing by the customer Edge preparation for special welding requirements Surface preparation such as grinding, brushing, pattern rolling, or embossing

Question: What is added to steel to make stainless steel?
Answer: Chromium