Today, iron is the most widely used metal. It’s durable, versatile, and abundant in the earth’s crust (which makes it cheap). However, in its pure form, iron is very sensitive to oxygen – it rusts quickly. Stainless steel provides a solution to this problem.
The world as we know it would not be possible without stainless steel. It is a material that combines strength, flexibility and durability at an affordable cost. This alloy makes an appearance in everything from high-rise, high-performance cars to spoons and baby monitors. To a fairly large extent, our world is built on stainless steel. So let’s learn more about it.
What is Stainless Steel?
“Stainless Steel” is a generic, generic term for a wide range of metal alloys — cocktails of metals — based on iron. Like all other types of steel, it also contains carbon.
It has excellent resistance to corrosion (oxidation or rust), is relatively unreactive with most chemicals, has high durability and good hygienic properties. It is widely used today in products ranging from cutlery to medical devices to building materials.
Aesthetically, stainless steel is a shiny, silvery metal, which can take a very high polish. From a practical point of view, stainless steel is a solid and very resistant material; its exact properties depend on the composition of the alloy, but it can be tailored to meet a wide range of needs, having the potential to be very flexible, scratch resistant, mechanically strong or any other property needed in a certain application . It can be recycled practically indefinitely, as its recovery rate during recycling is close to 100%
Although more difficult and expensive to produce than metallic iron, stainless steel has virtually replaced iron in all but the most specialized cases due to its advantages over unalloyed metal. Almost every “iron” product you’ve come across in your life was made of stainless steel.
What is stainless steel made of?
Stainless steel differs from other types of steel by adding a handful of elements to the mix. The exact elements added vary by alloy type but, as a general rule, stainless steels contain chromium (Cr), in amounts ranging from 10.5 to 30% by weight.
Chromium is what gives these alloys their high corrosion resistance. When it interacts with corrosive agents in the air, chromium forms a passive layer — a “film” of chromium oxide — on the surface of the metal that protects the alloy. Oxygen and moisture cannot penetrate this film, so it protects the iron from rust throughout the steel body.
Other elements added to stainless steel include nonmetals such as sulfur, silicon, or nitrogen, metals such as nickel, aluminum, copper, or more exotic metals such as selenium, niobium and molybdenum. Although the exact composition of the alloy is decided based on its desired properties – each element added and its proportion changes the characteristics of the alloy – some of the most common additional elements seen in stainless steel alloys are nickel and nitrogen. These improve its hardiness and its ability to resist corrosion in certain conditions, but also increase its price per kilo.
There are currently over 100 types (called “grades”) of stainless steel produced and used, each with its own ISO number, many of which are for specialist applications. The five most common types are called “austenitic”, “ferritic”, “martensitic”, “duplex” and “precipitation hardening” steels.
- austenitic stainless steels are the most used grades. They have very good corrosion and heat resistance, offering good mechanical properties over a wide temperature range. It is used in household items, industrial applications, construction and decorations.
- ferritic stainless steels have lower mechanical strength – they resemble mild steels in terms of strength – but are better able to resist corrosion, heat and are more difficult to crack. Any washing machine or boiler you have at home is probably made of ferritic steel.
- martensitic stainless steels are much harder and stronger than their peers, but they are not as capable of resisting corrosion. This is the type of steel that makes high quality knives, and is also used for turbine blades.
- Duplex stainless steel is a mixture of austenitic and ferritic steels, and their properties are, likewise, a happy medium between these two grades. Typically, it is used in applications where strength and flexibility are required, and corrosion resistance is a plus; shipbuilding is a prime example.
- Precipitation hardening stainless steels are a subclass of alloys, somewhere in the overlap between martensitic and austenitic steels. They offer the best mechanical properties of the lot (they have very high material strength), thanks to the addition of elements such as aluminum, copper and niobium.
What is stainless steel used for?
With a material as versatile as stainless steel, it is difficult to cover all its uses in great detail. Suffice it to say, it is used in virtually every product and application where strength, flexibility, beauty and hygiene are needed, at relatively low cost, and weight is not a major concern. .
Household items and appliances make heavy use of stainless steel, especially kitchen utensils or other products intended to come into contact with water. Knives and cutlery, household appliances such as washing machines, bathroom fixtures, piping, kitchen utensils use stainless steel because of its corrosion resistance, beauty, ease of washing and its great durability. Different grades of stainless steel are used depending on the intended role and use of each product.
Medical tools also widely use stainless steel. Items such as surgical and dental instruments, scissors, trays and a wide range of other items for medical use are made from this alloy. Here, it is the chemical inertness and corrosion resistance of stainless steel that are most important. Medical devices also contain stainless steel, particularly structural elements and coatings, due to their strength and ease of cleaning. Medical implants, such as those used in knee or hip replacement surgery, are also made of stainless steel.
Stainless steel is also used in the construction of vehicles, mainly ships, trains and cars. Aircraft manufacturers tend to prefer aluminum alloys because they are lighter. That being said, stainless steel is essential in the production of aircraft frames and various structural elements of the landing gear. For all vehicles, however, stainless steel combines good mechanical properties with long life (due to its resistance to corrosion), making it durable and long-lasting parts.
Construction and architecture are two other areas that love stainless steel. The combination of strength and high chemical inertness makes this alloy ideal for structural elements of buildings such as skyscrapers, or in exposed elements, such as fire escapes or service ladders.
Jewelry manufacturers also use stainless steel in their products, where it is preferred due to its hypoallergenic properties (it does not trigger metal allergies).
Stainless steel is an indispensable alloy today. Our societies rely heavily on it, using it in everything from small trinkets around the house to the most powerful skyscraper. Its unique combination of strength, longevity and relatively low cost means that stainless steel will most likely not be replaced anytime soon.