Stainless steel is a steel alloy with a minimum of 10.5% chromium content by mass.
In the early nineteen hundreds, metallurgists noticed that chromium had a greater attraction to oxygen than iron did so they added the element chromium to steel. Studies prove that when at least 10% chromium was added, the chrome united with oxygen to form a very tight transparent layer over the steel surface that prevented rusting by precluding further oxidation. This transparent layer is self-healing when damaged by scratches, wear or denting. Stainless steels are materials of enduring beauty. These steels also withstand the corrosive attack of many acids. They possess strength and toughness at both extremes of the temperature scale, yet can be fabricated into intricate shapes for many uses. Because of this outstanding versatility, stainless deserves careful consideration for any product where one or more of the following requirements are involved:
- Corrosion Resistance
- Strength at Elevated Temperatures
- Strength and Ductility at Cryogenic Temperatures
- Oxidation Resistance at High Temperatures
- Abrasion Resistance
Saltwater Resistance – Stainless steel has a low ‘galvanic potential’, while Aluminum’s ‘galvanic potential’ is high. This ‘galvanic potential’ causes galvanic corrosion between dissimilar metals, accelerated by exposure to saltwater.
Stainless steel’s resistance to corrosion and staining, low maintenance and familiar luster make it an ideal material for many applications. Stainless steel is used for a multitude of marine applications including grab rails, bow rails and canvas top frames.
There are over 150 grades of stainless steel, of which fifteen are most commonly used. The alloy is milled into coils, sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, hardware, surgical instruments, major appliances, industrial equipment (for example, in sugar refineries) and as an automotive and aerospace structural alloy and construction material in large buildings. Storage tanks and tankers used to transport orange juice and other food are often made of stainless steel, because of its corrosion resistance and antibacterial properties. This also influences its use in commercial kitchens and food processing plants, as it can be steam-cleaned and sterilized and does not need paint or other surface finishes.
Stainless steel is also used for jewellery and watches with 316L being the type commonly used for such applications. It can be re-finished by any jeweler and will not oxidize or turn black.
Unlike the plating used in some metal finishing processes, the finish is not subject to flaking, peeling, wear-off from rubbing, or rust when scratched.
Stainless steel does not corrode, rust or stain with water as ordinary steel does. It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal’s internal structure.
304L (low carbon) and 316L (low carbon with molybdenum) stainless steel maintains its luster, shine and strength over time. Passivation and electropolishing the stainless remove any surface carbon and iron molecules to provide a very saltwater resistant surface. Aluminum does not resist corrosion well, except by anodizing (building an oxide layer on the surface). Welding removes this oxidation at the most critical points, the joints, which will corrode (by pitting) over time, and fail due to fatigue.
Austenitic, or 300 series, stainless steels make up 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 of 18% chromium and 10% nickel, commonly known as 18/10 stainless, is often used in flatware. 18/0 and 18/8 are also available.