Steel is a malleable iron/carbon alloy containing from 0.10 to as much as 2% carbon, which determines the level to which it can be hardened. It is sometimes further alloyed with manganese, molybdenum, chromium, nickel, etc. to improve the ease with which it can be hardened and other characteristics such as corrosion resistance. Iron/carbon alloys having carbon in excess of 2% are called cast irons and are not malleable except in special forms known as malleable and ductile cast iron. As a metal, steel is characterized as being strong; fatigue-, impact-, and creep-resistant; electrically- and thermally-conductive; heavy; temperature-resistant; and fairly hard as compared with other materials such as wood, polymers, or ceramics. Steel is fabricated by removing impurities from pig iron in a furnace.
Steel is an alloy made from iron and carbon. There are several distinct grades of steel that have unique chemical compositions based on the different amounts of carbon and added alloys.
According to the World Steel Association, there are over 3,500 different grades of steel, encompassing unique physical, chemical, and environmental properties.
In essence, steel is composed of iron and carbon. However, it is the amount of carbon, as well as the level of impurities and additional alloying elements that determine the properties of each steel grade.
The carbon content in steel can range from 0.1%-1.5%, but the most widely used grades of steel contain only 0.1%-0.25% carbon. Elements such as manganese, phosphorus, and sulphur are found in all grades of steel, but. In contrast, manganese provides beneficial effects; phosphorus and sulphur are deleterious to steel’sstrength and durability.
When determining the type of steel that you want to buy, it is important to know four different types of steel are classified based on their chemical structure and physical properties: carbon steels, alloy steels, stainless steels, and tool steels. We’llWe’ll outline each of the following steel types below.
The majority of steel produced every day is called carbon steel. It is the most basic kind of steel. Depending on its carbon content, it can still be subdivided into more categories.
Steel with a maximum of 0.3% carbon is known as low-carbon steel. It is the most common out of all the kinds of carbon steel. It is cheap and very flexible with its numerous applications. Compared to the other kinds of carbon steel, it has relatively low tensile strength, but it is malleable and ductile. This is made into flat-rolled sheets and strips that are used for shipbuilding, wires, vehicle bodies and some domestic appliances. It can also be used for fencing, gates, and railing because it is hard, but not brittle.
When the carbon content is around 0.3% to 0.6%, it is called medium-carbon steel or mild steel. It is a bit stronger than low-carbon steel and is trickier to form, weld, and cut. Its quality can be easily enhanced by adding small amounts of silicon and manganese. Mild steel is primarily used for buildings and bridges as axles, gears, shafts, rails, pipelines, couplings, as well as cars, fridges and washing machines.
High-carbon steel is also called carbon tool steel and has 0.6% to 1% carbon content. It can easily be exposed to heat treatment; however, it is vulnerable to impurities, particularly sulphur, which makes the steel brittle and crumbly when worked on. It has better tensile strength than the previous two and is used in making cutting tools like blades, punches, and springs and high-strength wire.
Lastly, ultra-high carbon steel contains 1.25% to 2% carbon and is brittle yet very hard. It can’t be cold-worked and is usually utilized to make extremely hard components for cutting tools, large machine parts, hot water radiators, and industrial castings. It is also more commonly known as “cast iron”.
Carbon steel is dull and matte in appearance and is vulnerable to corrosion. Carbon steel can contain other alloys, such as manganese, silicon, and copper. There are three main types of carbon steel: low carbon steel, medium carbon steel, and high carbon steel. Low carbon steel is the most common and typically contains less than .30% of carbon. Medium carbon steel contains up to .60% of carbon as well as manganese and is much stronger than low carbon steel. High carbon steel contains up to 1.5% carbon steel and is the strongest of the categories and can often be hard to work with.
Carbon steels contain trace amounts of alloying elements and account for 90% of total steel production. Carbon steels can be further categorized into three groups depending on their carbon content:
- Low Carbon Steels/Mild Steels contain up to 0.3% carbon.
- Medium Carbon Steels contain 0.3-0.6% carbon
- High Carbon Steels contain more than 0.6% carbon.
Alloy steels are a mixture of several metals, including nickel, copper, and aluminium. Alloy steels tend to be cheaper and are used in mechanical work, car parts, pipelines, and motors. The strength and property of alloy steels depend on the concentration of elements they contain.
Alloy steels contain alloying elements (e.g. manganese, silicon, nickel, titanium, copper, chromium, and aluminium) in varying proportions in order to manipulate the steel’ssteel’s properties, such as its hardenability, corrosion resistance, strength, formability, weldability or ductility. Applications for alloys steel include pipelines, auto parts, transformers, power generators and electric motors.
Stainless steels are shiny, corrosion-resistant, and used in many products, including home appliances, backsplashes and cooking utensils. It has a low carbon content Stainless steel contains the alloy chromium and can also include nickel or molybdenum. Stainless steel is strong and can withstand high temperatures. There are more than 100 grades of stainless steel, making it an extremely versatile material that is customizable depending on your purpose.
Stainless steels generally contain between 10-20% chromium as the main alloying element and are valued for high corrosion resistance. With over 11% chromium, steel is about 200 times more resistant to corrosion than mild steel. These steels can be divided into three groups based on their crystalline structure:
- Austenitic: Austenitic steels are non-magnetic and non-heat-treatable, and generally contain 18% chromium, 8% nickel and less than 0.8% carbon. Austenitic steels form the largest portion of the global stainless steel market and are often used in food processing equipment, kitchen utensils, and piping.
- Ferritic: Ferritic steels contain trace amounts of nickel, 12-17% chromium, less than 0.1% carbon, along with other alloying elements, such as molybdenum, aluminium or titanium. These magnetic steels cannot be hardened by heat treatment but can be strengthened by cold working.
- Martensitic: Martensitic steels contain 11-17% chromium, less than 0.4% nickel, and up to 1.2% carbon. These magnetic and heat-treatable steels are used in knives, cutting tools, as well as dental and surgical equipment.
Tool steels are hard and heat and scrape-resistant. They have named tool steels because they are often used to make metal tools, such as stamping, cutting, and mould-making tools. Tool steels are made up of vanadium, cobalt, molybdenum, and tungsten in different amounts, which improve its durability and heat resistance properties. They are also commonly used to make hammers. There are several different grades of steel that can be used for distinct applications.
Tool steels contain tungsten, molybdenum, cobalt and vanadium in varying quantities to increase heat resistance and durability, making them ideal for cutting and drilling equipment.
Steel products can also be divided by their shapes and related applications:
- Long/Tubular Products include bars and rods, rails, wires, angles, pipes, and shapes and sections. These products are commonly used in the automotive and construction sectors.
- Flat Products include plates, sheets, coils, and strips. These materials are mainly used in automotive parts, appliances, packaging, shipbuilding, and construction.
- Other Products include valves, fittings, and flanges and are mainly used as piping materials.
Plain Carbon Steel
Plain carbon steel contains no appreciable alloying element other than carbon itself, and, depending on the carbon content, is classified as low-, medium-, or high-carbon. Low-carbon steel (< 0.3% C) is used for making rivets, cold-drawn parts such as wire, stampings, etc. in the lower ranges and structural shapes, gears, cold-forged parts, and welded tube in the middle and upper ranges. Medium-carbon steel (0.3-0.5% C) is used for gears, shafts, connecting rods, seamless tubing, etc. and is sometimes called machinery steel. High-carbon steel (> 0.5% C) is used for springs, knives and handtools, taps and milling cutters, wire-drawing dies, etc. and is sometimes called tool or spring steel.
A simple AISI 4-digit numbering system designates plain carbon steel as 10xx, with the last digits approximating the percentage of carbon in the metal. A plain carbon mild steel designated as 1010 would contain 0.08-0.13% carbon, for example. Free-machining steel would be designated as 11xx.
To harden plain carbon steel, it must be cooled rapidly. This can lead to high residual stresses, distortion, diminished ductility, etc.
While it is the carbon content of steel that determines the degree to which it can be hardened, certain alloying elements added to the steel can make heat treatment less traumatic, a benefit when it comes to reducing quenching distortion in complex, thin-walled parts, for example. The term hardenability refers to how deep steel can be hardened, and alloy steels loosely fall into two camps around this measure: carburizing steel, which mostly hardens near the surface, and through-hardening steel, which can extend the hardening down into the metal’s core.
In the AISI numbering system, manganese steels are designated 13xx, nickel steels, 2xxx, nickel-chromium steels, 3xxx, molybdenum steels, 4xxx, and so on up to 9xxx for silicon-manganese steels.
Hardening of alloy steels can usually be done in oil for a slower quench than with water as required for plain carbon steels. This can reduce distortion and permit hardening to penetrate deeper into the material’s core.
Low Alloy Steel
Sometimes called HSLA, or High-Strength Low-Alloy, steel, this metal offers improved strength over plain carbon steels and is used in settings where weight is a factor such as mobile equipment. It cold-forms well and is readily welded. It has better resistance to corrosion than plain steel, with good impact, fatigue, and abrasion resistance as well.
Other low alloy steels, with designations such as HY 80 and HY 90, are used for ship hulls and off-highway equipment. Still, other low alloy steels are available for specific conditions such as low-temperature toughness or to produce protective, weathering layers on decorative steel used for building facades.
Stainless steel is an iron/chromium alloy that contains anywhere from 10 to 30% chromium which gives the metal high resistance to corrosion. Although there are many grades of stainless steel, only a dozen or so are used with any regularity. For example, AISI Type 304 SS, having a chromium-nickel constituent and low carbon, is popular for its good corrosion resistance, cleanability, and formability, making it popular for many everyday items such as kitchen sinks. AISI Type 316 SS, containing the alloying element molybdenum, is even more resistant to chemical attack than Type 304, making it useful for exposure to seawater, brine, sulfuric acids, and other corrosives found in the industrial environment.
Alloy steel products and their applications
There are hundreds of products that can be manufactured with alloy steels of varying compositions. These include alloy steel pipes and tubes, alloy steel plates, sheets and coils, alloy steel bars, rods and wires, alloy steel forged fittings, alloy steel buttweld fittings, alloy steel flanges, fasteners and more. Alloy steels have many uses in various industries such as automobiles, mining, machinery and equipment, railways, road.
The Three Main Categories of Stainless Steel
While there are thousands of different alloys of stainless steel, they can all be divided into three broad categories:
Austenitic Stainless Steels
These are the most frequently used types of stainless steels. Austenitic stainless steels tend to have a high chromium content compared to other steel alloys, giving them a higher resistance to corrosion. Another common characteristic of austenitic stainless steel alloys is that they tend to be non-magnetic—though they may become magnetic after cold working.
Ferritic Stainless Steels
The second most common form of stainless steel after austenitic alloys. As the name implies, ferritic stainless steel is magnetic. These alloys can be hardened through cold working. They also tend to be less expensive because of their reduced nickel content.
Martensitic Stainless Steels
The least common category of stainless steel alloy. Their corrosion resistance tends to be lower than either ferritic or austenitic alloys, but they have a high hardness. Martensitic stainless steel alloys are often ideal for applications requiring extraordinarily high tensile strength and impact resistance. When said applications also require corrosion resistance, these alloys may be used with a protective polymer coating.
There are numerous grades of stainless steel within each category—here are the breakdowns of the most common varieties of each:
Common Types of Austenitic Stainless Steels
Grade 304 Stainless Steel
The most common variety of stainless steel, and one that is frequently used in Marlin Steel’sSteel’s custom wire basket designs because of its versatility. Even among steel alloys, grade 304 stainless steel is noteworthy for its high tensile strength—roughly 621 MPa (90 ksi). Like most stainless steels, grade 304 has a high maximum operating temperature (about 870˚C). This combination of high tensile strength, temperature resistance, and corrosion resistance makes grade 304 stainless steel ideal for a wide variety of applications.
Grade 316 Stainless Steel
Another common variety of austenitic stainless steel, grade 316 stainless has a high tensile strength of 579 MPa (84 ksi) and maximum use temperature of around 800˚C (1,472˚F). While having lower tensile strength and temperature tolerance than grade 304 stainless steel, grade 316 stainless has better resistance to chlorides (like salt) than 304 alloy does. This makes it a preferred choice for any application involving exposure to salt or other chlorides.
Ferritic Stainless Steels
Grade 430 Stainless Steel
While not as strong as either of the austenitic alloys highlighted above, grade 430 stainless steel does have an especially good resistance against nitric acid. Although the tensile strength of 450 MPa (65 ksi) is lower than the austenitic stainless steels, it’sits still more than strong enough for many heavy-duty applications.
Grade 434 Stainless Steel
The stronger alternative to grade 430 stainless, 434 stainless steel has a tensile strength of 540 MPa (78 ksi) and a maximum operating temperature of 815˚C (1,499˚F). This makes grade 434 stainless steel slightly better for high-temperature applications than 316 stainless while being tougher than grade 430 stainless. Grade 434 stainless also has excellent pitting resistance compared to 430-grade stainless steel.
Martensitic Stainless Steel
Grade 420 Stainless Steel
If annealed, grade 420 stainless steel has a tensile strength of around 586 MPa (85 ksi). When hardened and stress relieved, this material’smaterial’s tensile strength jumps to roughly 1,586 MPa (230 ksi). While not as chemically resistant as the austenitic and ferritic stainless steels mentioned above, grade 420 stainless steel does have good resistance to mild acids, water, some alkalis, and food compounds—which is why it is often used for cutlery. When tensile strength and impact resistance are the primary concerns for an application, 420 stainless is a top choice.
Steel is something that has taken over many industries. It is the foundation of many things because it makes up most of the equipment people use. With the variety of kinds of steel, there will surely be something that will satisfy your every need.