What is Stainless Steel and Where is it Used

What is Stainless Steel and Where is it Used?

What is Stainless Steel and Where is it Used? Used in many fields, steel is made by removing impurities such as manganese, sulfur and silicon from iron. They are versatile materials with different qualities and areas of use. However, as it is known, it is prone to rust and corrosion. Stainless Steel was developed to make such an important and useful product more durable.

Stainless Steel, as the name suggests, does not stain or rust easily. Both types of steel contain the base metal iron, as well as carbon and some other trace elements. The difference in the structure of stainless is the addition of chromium, nickel, nitrogen and molybdenum to give it resistance. The addition of these elements makes steel less prone to corrosion and rust. While steel is magnetic, most types of stainless steel are not.

Stainless is an alloy containing around 10-30% chromium, which makes it resistant to corrosion and heat. Stainless also contains other elements such as nickel, molybdenum, titanium, aluminum, niobium, sulfur, copper, phosphorus, nitrogen and selenium. All kinds of items are made with this raw material alloy, which can enter all areas of life and can be easily used in an active way. There are four types of stainless steel: austenitic, ferritic, martensitic and duplex. They are defined by their microstructure based on the elements added to the steel.

Stainless Steel Properties and General Structure

There are many grades and surface finishes of stainless steel available, depending on the environment the metal is expected to withstand. They can be divided into four main categories according to their microstructure. According to these categories, you can determine their place of use.

Austenitic Stainless Steel

Austenitic stainless steel, which has austenite as its primary microstructure, is a solid solution of iron and carbon formed above a critical temperature of 723°C. Seventy percent of stainless steel is austenitic. It contains at least 16% chromium and 6% nickel. Austenite stabilizers are substances added to promote the rapid formation of the austenite microstructure. This type of stainless is a non-magnetic metal and cannot be hardened by heat treatment. Corrosion resistance can be modified depending on the service environment.

Austenitic steel is the most popular of the stainless steel groups. It is frequently used in many industrial and consumer applications such as chemical and power plants as well as food processing and dairy equipment. Austenitic steel is the most weldable of the groups and is divided into three ‘loose’ groups;

Ferritic Stainless Steel

Ferritic steels will usually have only chromium as an alloying element. Chromium content ranges from 10.5% to 18%. Such steels usually have average corrosion resistance and poor fabrication properties. The application of heat treatment methods also does not harden the metal. Generally better than austenitic grades. Unlike austenitic grades, they are magnetic. In addition, they have very high resistance to stress corrosion. This results in lower corrosive material wear. Ferritic steel is an iron-chromium based alloy and is the most flexible and formable of the three types of stainless steel, but does not perform well in high temperature structures. Typical uses for ferritic steel include car exhausts, kitchen sinks and industrial equipment. Ferritic steel is cheaper than austenitic steel.

Martensitic Stainless Steel

Martensitic steel is a steel composition containing chromium, iron and carbon. Tempered martensite is resistant to corrosion and is relatively strong and durable. Untempered martensite lacks toughness and is brittle. Martensitic steels are used in medical equipment, cutlery and aerospace applications such as drive shafts and landing gear. This type of stainless steel consists of high carbon and low chromium content. It is magnetic like ferritic grades. It shows poor weldability compared to other grades, but has higher hardenability and can be heat treated to improve properties. Martensitic stainless has lower corrosion resistance than austenitic and ferritic grades with similar chromium and alloy content.

Duplex Stainless Steel

Duplex is a mixture of austenitic and ferritic stainless. It therefore has the properties of both components. It is formed by a mixture of high chromium and low nickel. With their tensile strength and good weldability, duplex stainless steels offer unique advantages. They show good resistance to stress corrosion. But this resistance is not as high as ferritic grades. Ferritic grades are tougher than products while austenitic grades are inferior. Duplex stainless steels are usually a 50/50 mix of ferritic and austenitic steels. They are used to provide higher corrosion resistance and are stronger than standard austenitic steel. They are used in the petrochemical and oil and gas industries in the form of piping, manifolds, pipelines and pressure vessels.

Precipitation Hardening Stainless Steels

This subgroup contains a mixture of austenitic and martensitic properties. Hardening is achieved by the addition of one or more elements such as aluminum, molybdenum, niobium, titanium and copper. It has the ability to develop high tensile strength by heat treatment. It contains chromium and nickel as alloying elements. These grades are used in the formation of high-speed products such as turbine blades.

Advantages and Disadvantages of Stainless Steel Materials

Advantages and Disadvantages of Stainless Materials

Stainless steel has some disadvantages as well as superior and advantageous features. Depending on the place of use, the functionality of these features has the potential to vary. Especially with its high resistance to corrosion, it is often preferred in kitchenware or outdoor products. Its superior properties and related advantages can be listed as follows;

Steel is easy to clean, so it can be used in the medical and food industries that adhere to strict food hygiene standards. Its high resistance to impact means that small crevices or indentations cannot form in the steel. This means that dirt and germs have nowhere to hide. Cleaning with water, especially after use, is a simple solution. Stainless steel can therefore easily be used in kitchen products.

Stainless steel is a durable alloy. This strength and corrosion resistance make stainless steel an indispensable product for many businesses. Stainless steel is resistant to high temperatures If you maintain stainless steel (which is not very difficult), you can count on it to last a long time.

The main reason for the development of stainless steel is to combat corrosion that occurs in normal steel, such as rust-based or other types of corrosion. The superior properties of the metal alloys used to create stainless steel create resistance to corrosion. It reduces or even eliminates conditions such as rust and mold.

Stainless steel can retain its value for a long time because it doesn’t get damaged or rust quickly. If you use steel temporarily, you can resell it and get back some of the money you paid for it.

The initial cost of stainless steel can be higher than other metals such as aluminum. But if the resale value remains high, you can recoup some of the cost when you sell.

Although steel is easy to clean, it is a magnet for dirt and dust. It therefore needs to be cleaned regularly. Stainless steel knives or utensils can last a long time when well maintained. It is also preferred for equipment in the medical sector due to its potential for hygienic use.

Most stainless steel is made from recycled steel. Impressively, when the metal is recycled, its qualities do not deteriorate. This allows it to be continually reused and benefit the environment.

Stainless Chemical Properties

It is the chemical properties of stainless that make it special and give it its uniqueness. With its durability and other advantages, the usage area of this product expands. Stainless Steel properties can be listed as follows in general;

High oxidation resistance is the most important detail that prevents rust and mold. Oxidation resistance is directly related to the chromium content. The chromium percentage can reach up to 26% in some grades. Although many different anti-corrosion coatings and paints can be used, the main raw material structure is determined as the most influencing factor. In the case of stainless steel, it may be necessary to remove the coating of the natural chromium oxide component due to surface damage and incorporate a more durable material.

When exposed to harsh chloride solutions or environmental conditions such as the seaside or salty roads, many stainless alloys develop pitting that can penetrate the chromium oxide layer and persist underneath. For this type of industrial chemical or automotive situation, a more exotic and expensive stainless alloy or other material such as titanium, which has excellent chloride resistance even at high temperatures, can be used.

Stainless steel is biologically inert, i.e. less reactive. It can therefore behave in harmony with the human body and homeostasis. This makes it an ideal metal for kitchen appliances.

Stainless steel is highly resistant to acids, bases and organic compounds. Its resistance to acids varies, of course, to different degrees. Some grades can withstand high concentrations of acids, while others may only be resistant to low concentrations. Similar low reactivity is observed with basic compounds and organic compounds. This resistance makes it particularly suitable for the chemical industry. Stainless steel also readily resists moisture, salt, sulfur, carbon dioxide and chloride compounds.

Stainless Steel Uses

Stainless steel is 100% recyclable, easy to sterilize and used in many applications. In fact, many people interact with products made of stainless every day. Stainless is used in the kitchen, on the road, in the doctor’s office or in the building. Unlike ordinary steel, stainless is not prone to corrosion, rusting or staining when exposed to water. However, this does not mean that it is completely stain-resistant. In areas with low oxygen, high salinity or poor air circulation, stainless steel is susceptible to staining.

Most often stainless steel is used for applications that require the unique properties and corrosion resistance of steel. You will see this alloy milled into coil, plate, sheet, bar, wire and pipe. Some products where stainless steel is often used;

Products made of stainless steel can benefit from the alloy structure of stainless steel. Stainless steel contains iron and nickel as well as chromium and molybdenum. As a result, products made from stainless can gain unique advantages from these alloy metals, such as a polished surface or the ability to resist corrosion and stress.

Medical Technology

Stainless steel is often preferred for clean and sterile products due to its ease of cleaning and resistance to corrosion. It is used in the manufacture of medical equipment, including surgical and dental instruments. It is also used to make operating tables, kidney cups, MRI scanners, cannulas and steam sterilizers. Most surgical implants, such as replacement joints and artificial hips, are made from stainless steel, as well as some joining equipment, such as stainless pins and plates for repairing broken bones.

Building Materials

Due to its durability and flexibility, the application of stainless steel has become a vital element of the construction industry. It is commonly found indoors in countertops and groves. It is also used externally in cladding for high impact resistant buildings. With the movement towards sustainable building, stainless steel, a highly recyclable metal, is increasingly being used in construction. It has aesthetically pleasing properties with a polished or veined finish and can help improve natural lighting in the building.

Food and Catering Industry

Stainless steel is used in the food and catering industry to produce kitchen accessories, cookware and cutlery. Kitchen utensils such as knives are made using less ductile stainless steel. Softer grades are used to make grills, stoves, cookware and sinks. Stainless can also be used to finish freezers, dishwashers, refrigerators and countertops. In food production, stainless is ideal because it does not affect the flavor of the food. It is also corrosion resistant and can therefore hold acidic drinks, including orange juice. The ease of cleaning stainless steel makes it difficult to harbor bacteria, increasing its usefulness in food storage.

Automotive Industry

Stainless steel is widely used in vehicles because it maintains its structural integrity despite constant exposure to extreme temperatures and vibrations. Gearboxes, transmissions, suspension systems, differential modules and steering systems are automotive parts that are often made from stainless. In addition, stainless steel’s excellent corrosion resistance makes it ideal for use in automotive components such as fuel tanks and catalytic converters. Exterior automotive components such as mufflers and exhausts are often made from stainless steel due to the metal’s distinctive luster.

Energy Production Facilities

Most power generation plants require metals that are corrosion resistant and durable. Due to its corrosion-resistant properties, stainless is widely used in various power generation plants. In the nuclear power industry, stainless steel, especially with low cobalt content, is frequently used for radiation containment and power generation. Turbines used in gas, steam and water plants are also made of stainless steel. It is preferred in these applications due to its corrosion and heat resistance.

Stainless Steel Grades

Stainless Steel Grades

There are hundreds of grades of stainless steel on the market today. It is important to choose the right one for your application because the properties can be quite different. The AISI (American Iron and Steel Institute) system for naming stainless steel is still used by the industry.

Stainless Steel Elemental Content

It is generally the elemental content that determines superior properties and causes qualities to vary. By using various metals, it is possible to produce steel with different quality contents and uses. This also opens up a wide range of uses for stainless steel.

Chromium

Chromium is the defining alloying element of stainless steel. It gives the steel its stainless characteristic. The passive chromium oxide layer protects the internal structure of the metal from corrosion by preventing oxygen diffusion into the metal as well as protecting the surface. Chemically, the oxidized component of chromium can greatly affect the strength of the formula. A minimum of 10.5 percent is required for a steel to be “stainless” and is quite critical. However, it is common to add even more chromium to improve corrosion resistance.

Nickel

Nickel is added to improve corrosion resistance and to promote austenite formation. 8-9% nickel results in a fully austenitic structure with excellent weld properties. Increasing the nickel content offers superior properties in terms of machinability and corrosion resistance.

Manganese

Manganese improves the strength, toughness and hardenability of stainless. Adding manganese in hot working processes of the metal provides better performance. Furthermore, manganese promotes nitrogen dissolution in stainless steel and can therefore be added to stainless steel to replace nickel with nitrogen.

Copper

Copper also acts as an austenite stabilizer and improves corrosion resistance and work hardening properties. The addition produces stainless steel products suitable for the cold working conditions required with screws and nails.

Molybdenum

Molybdenum and tungsten improve general and localized corrosion resistance properties. The former is a ferrite stabilizer. Therefore, when used in austenitic alloys it must be balanced with austenite stabilizers to maintain austenite composition. Molybdenum also improves high temperature strength when added to martensitic stainless steel. The addition of molybdenum with tungsten also improves the properties mentioned above.

Silicon

The addition of silicon material to the mix increases the chemical resistance of stainless steel to high concentrations of nitric and sulfuric acid species. It also accelerates the formation of ferrite and makes the metal resistant to oxidation.

Nitrogen

Nitrogen is an austenite stabilizer and increases strength and localized corrosion resistance. Localized corrosion refers to phenomena such as pitting corrosion, crevice corrosion and intergranular corrosion.
Stainless Grades

Stainless Grades

Stainless steel material with different quality contents creates various areas of use. In this way, it becomes possible to find materials that appeal to every sector.

Type 201 Stainless Steel

Type 201 stainless steel is unique because it was produced in response to rising nickel prices in the market. This means it is cheaper but it also has a much lower nickel content. Without a lot of nickel it is not effective in preventing corrosion. The higher manganese levels help make type 201 one of the strongest types of stainless tape. Industries looking for more durability at a lower cost prefer this type. More manganese and nitrogen are used to compensate for the lack of nickel. Type 201 stainless steel is particularly useful in cold environments as it retains its durability in cold weather. As the cheapest type of stainless steel, type 201 appears to be the most attractive. However, it does not last as long in extremely corrosive environments.

Type 304/304L Stainless Steel

Within the classification of stainless steel there are many different types and grades. By far the most common grade is 304 and this accounts for over 50% of stainless steel used worldwide. Grade 304 stainless is austenitic, a term related to its molecular structure that refers to the addition of nickel to the alloy. Austenitic stainless steels are the most common. Up to 70% of commercially produced stainless is of the austenitic type.
Grade 304 stainless consists mainly of iron, which makes up 66% to 75% of its composition. The alloy mixture also includes 18% to 20% chromium and 8% to 10.5% nickel. With a density measured at about eight grams per cubic centimeter, 304 stainless steel may also contain trace amounts of other elements such as silicon, sulfur, phosphorus and manganese. It has good corrosion resistance and good formability. Grade 304 is non-magnetic.
Austenitic stainless steels such as 304 have a yield strength that represents a relatively low fraction of the tensile strength, between 40% and 45%. The yield strength can be further improved when the material is cold worked. This is particularly useful when making things like spring wire.

Type 309 Stainless Steel

Austenitic chromium-nickel stainless steels frequently used in high temperature applications. Alloys 309 and 309S are resistant to corrosion due to their high chromium and nickel content. They have greater resistance to oxidation and have excellent heat resistance while giving good qualities at room and elevated temperatures. The difference between stainless 309 and 309S is the carbon content.

Machines with this alloy are identical to type 304 stainless steel. The chips of this alloy are fibrous and will harden very quickly. It is imperative that the tool is kept in the cutting state at all times and that chip breakers are used. Most austenitic stainless steels can be welded quickly using the fusion or resistance technique. Oxyacetylene welding is not recommended. Working temperatures of 1177°C and reheating to 982°C are mandatory for this alloy.

Rapid quenching is recommended. Full annealing after working is required to regain maximum corrosion resistance. Although this alloy has a high work hardening rate, it can be drawn, headed, knitted and stamped. Full annealing after cold working is required to eliminate internal stress.

420 Type Stainless Steel

420 grade stainless steel has a chromium element concentration of at least 12%. It also contains a high degree of carbon in its structure. Similar to other stainless steel grades, heat treatment can be ideal for hardening in this grade. It offers good ductility in the annealed condition and excellent corrosion resistance properties when the metal is polished, surface ground or hardened.

It has the highest degree of hardness compared to other grades. It also has a very high impact strength. Under hardened conditions, grade 420 steels are resistant to fresh water, alkalis, air, food and mild acids.

Those with a smooth surface have higher strength. The corrosion resistance properties of grade 420 will tend to decrease under annealed conditions. The corrosion resistance of grade 420 is lower than that of grade 430 Ferritic alloys containing 17% chromium, grade 410 steels and other austenitic grades. This steel grade finds application in cutlery such as carving knives, table knives etc. Grade 420 standards are suitable for food contact, but continuous exposure of these materials to unwashed food products may cause corrosion.

Type 431 Stainless Steel

431, high chromium-low nickel, with high hardenability, high strength and good corrosion resistance, usually 850 – 1000. Martensitic stainless steel is supplied hardened and tempered in the Mpa (T condition) tensile range. Brinell range has values of 248 – 302. It shows high resistance against corrosive factors. It shows resistance in general atmospheric conditions and provides high resistance to light marine and industrial environments.

Resistant to many organic substances, nitric acid and petroleum products. It also has high tensile and yield strength in the hardened and tempered condition, as well as excellent toughness. Due to its excellent hardenability, 431 can be hardened to Rc44, depending on carbon content and section size.

For maximum hardness, small sections can be air cooled and larger sections oil quenched. Pre-hardened and tempered 431 will also readily respond to nitriding, achieving a typical surface hardness above Rc65. However, nitriding reduces corrosion resistance and is therefore generally not recommended except in critical applications where the benefit outweighs all other considerations. It has widespread use among the stainless steel grades.

It is widely used for parts requiring a combination of high tensile strength, good toughness and good corrosion resistance properties. They have the potential to be used in fasteners and equipment suitable for every industry.

Type 430 Stainless Steel

It is a low cost stainless steel. 430 stainless is a type of stainless steel that is hypoallergenic and anti-explosion. It is also resistant to harsh environments and chemicals. This metal can withstand high temperatures and acids, making it an excellent choice for medical devices and food packaging. Here are the benefits of 430 stainless steel:

Super Duplex Type Stainless Steel

Super Duplex Steel with high chromium content provides exceptional resistance to acids, acid chlorides, caustic solutions and other media in the chemical/petrochemical, pulp and paper industries. It often replaces 300 series stainless steel, high nickel element super austenitic steels and nickel-duplexes. Base alloys; chemical composition based on high chromium, nickel and molybdenum content improves intergranular and pitting corrosion resistance.

The addition of nitrogen promotes structural hardening through an intermediate solid solution mechanism that increases yield strength and ultimate strength values without impairing toughness. Since the introduction of the first grade, Duplex steel has steadily grown in popularity.

Recently, the production of high-strength, corrosion-resistant super duplex coil has been applied in the marine and chemical industries, architectural and pole hardware, wire lines, hoisting and spooling equipment and well service lines. In fact, the development of wire processing techniques has enabled the production of steel wires up to 1 mm in diameter.

Type 904L Stainless Steel

The main characteristic of 904L is that it has very good corrosion resistance in dilute sulfuric acid over the entire concentration range up to 35°C. It also has useful resistance to some other inorganic acids, although its performance may be limited when halide ions are used.

Although the nickel content of conventional stainless steels (e.g. 316L) is very susceptible to chloride stress corrosion cracking, the higher level of this element in 904L imparts good resistance to this form of corrosion.

The contents of nitrogen, molybdenum and chromium in stainless steels have a direct influence on their resistance to pitting and crevice corrosion, and in the case of 904L this parameter is good. However, 6% molybdenum austenitic grades or super duplex grades show superior resistance to this type of localized corrosion.

Titanium Type Stainless Steel

Looking at the list of weaknesses of stainless steel, it is clear that Titanium, due to its relatively light weight, high strength and corrosion resistance, can often pick up where rust leaves off; so let’s get to know this top performer a little better. Unlike many common metals that have been reduced using carbon for thousands of years (think iron smelting to produce all steel),

Titanium has only been commercially available since the 1940s. Although now relatively available in many grades, the high melting point and chemical reduction process used to produce Titanium is time and chemically intensive, leading to its high cost. While stainless steel gains its unique properties only when alloyed, Titanium is an element that is available and often used in its “commercially pure” form. However, Titanium is also widely alloyed and even within the definition of commercially pure there are various grades, meaning that like any other useful metal, its properties can be tailored to specific applications.

Like other corrosion resistant materials that oxidize to form a barrier when exposed to oxygen in the air, the surface of Titanium immediately begins to oxidize, forming titanium oxide which forms a thin passivating layer that protects the rest of the material from further corrosion. Unlike some other oxide layers, the titanium dioxide layer continues to thicken over time, reaching 25 nm after a few years, giving it a corrosion resistance almost equal to platinum.

Titanium is a total creepy dude: it’s almost impossible to get it to react with anything at normal temperatures. Combine that with its low density and you have the recipe for the most common hypoallergenic metal used in the medical industry today for joints, bone repair and other delicate body contact applications.

Titanium is a high cost material and only becomes economically viable when unique material properties are required. For things like machining, Titanium can have a cost factor 30 times that of Stainless because it is relatively difficult to machine as well as the material cost.

Titanium and stainless steel face many of the same challenges for the machinist: Instead of the chip breaking cleanly at the cutting edge, the common alloys of both grades break easily. Both have a low coefficient of thermal conductivity, which means it is easy to cause localized work hardening and lead to premature tool wear. Titanium has the additional challenge of being more flexible than most machined materials compared to its hardness, so care must be taken to fix it as rigidly as possible.

Type 303 Stainless Steel

303 gains improved machining and frictional properties with the addition of sulfur. However, this addition also reduces the corrosion resistance of stainless steel and slightly reduces its toughness compared to 304 Stainless Steel. Type 303 stainless shows good corrosion and oxidation resistance in mildly corrosive atmospheric environments. Sulfide residues act as pitting initiation sites, which means it provides much less resistance than 304. It is recommended not to expose grade 303 to marine or similar environments to prevent rapid pitting corrosion.

Type 316/316L Stainless Steel

Type 316/316L is a chromium nickel austenitic stainless steel containing molybdenum. The addition of molybdenum improves corrosion resistance over 304/304L in halide environments as well as in reducing acids such as sulfuric and phosphoric acid. Type 316L can be dual certified as 316 when the composition meets the lower carbon limit of 316L and the slightly higher strength levels of 316. Type 316L should be specified for welded applications as the lower carbon version eliminates chromium carbide precipitation and improves corrosion resistance. It also has excellent corrosion resistance and good formability. Grade 316 is non-magnetic.

Type 316TI Stainless Steel

316 Ti has better high temperature strength and mechanical strength than 316L thanks to Titanium additions; this means that Stainless 316Ti has both corrosion resistance and the ability to withstand high temperatures. Stainless steel 316Ti has high density, melting point, coefficient of expansion, modulus of hardness and flexural strength.

310S Type Stainless Steel

Stainless steel 310S is resistant to high heat and oxidation. The high chromium and nickel content provides comparable corrosion resistance, superior resistance to oxidation and retention of a greater proportion of the strength at room temperature compared to common austenitic alloys such as Type 304. Stainless 310 is often used at cryogenic temperatures, with excellent toughness down to -450 °F and exhibits low magnetic permeability properties. Application areas are shown below;

Type 440M Stainless Steel

Materials in the 440 stainless steel grade are mostly offered in forms. Bars, wires, billets, coils and tubes are the most common, but there may be others. 440 is the highest grade of cutlery steel on the market. Because it has more carbon, it has a stronger edge retention. When properly processed, it has the capacity to reach one of the highest hardness ratings among other steels on the Rockwell scale. It is preferred to be used easily in forks and knives with its affordable price.
Although 440 stainless has a hard structure, its workability increases according to the degree of annealing. Other features include: