Carbon steel is an alloy of iron and carbon, with a carbon content of up to 2.1 wt.%. Unlike other types of steel, carbon steel does not have a minimum requirement for other alloying elements, but it often contains manganese. The maximum allowed content of other elements in carbon steel is 1.65 wt.% for manganese, 0.6 wt.% for silicon, and 0.6 wt.% for copper.
Carbon steel manufacturing process:
Carbon steel is a widely used material that is essential to many industries due to its unique properties, which include high strength, good ductility, and excellent machinability. The production of carbon steel can be done using a variety of methods, but one of the most common ways to produce it is through the use of virgin steel.
Virgin steel is produced by combining iron ore, coke, and lime in a blast furnace. The process starts by crushing the iron ore into small pieces and mixing it with coke and limestone. The coke is used as a fuel, and it burns in the furnace, producing the heat necessary for the process to proceed. The limestone acts as a flux, and it helps to remove impurities from the iron ore during the smelting process.
Once the materials are in the blast furnace, they are heated to temperatures of around 1650°C. At these high temperatures, the coke reacts with the oxygen in the air to produce carbon monoxide. This carbon monoxide then reacts with the iron ore, reducing it to molten iron. The molten iron is then enriched with carbon from the burning coke to produce molten steel, which typically contains around 4 wt.% carbon.
To produce carbon steel with the desired carbon content, the molten steel is subjected to a process called decarburisation. During decarburisation, oxygen is introduced into the melt, which oxidises the carbon in the steel and produces carbon monoxide and carbon dioxide. This reduces the carbon content of the steel to the desired amount, typically less than 2 wt.%.
Overall, the production of virgin steel is an important process that allows for the production of high-quality carbon steel with a wide range of properties, making it a versatile material used in many different industries.
Types of carbon steel and their properties
Carbon steel is a versatile and widely used material that comes in a variety of types, each with its own unique properties. Some of the most common types of carbon steel include:
- Low Carbon Steel: Also known as mild steel, this type of carbon steel contains a low amount of carbon (up to 0.3%) and is easy to shape and weld. It’s commonly used for structural applications, such as buildings and bridges.
- Medium Carbon Steel: With a carbon content of 0.3% to 0.6%, medium carbon steel is stronger than low carbon steel but still easy to machine and weld. It’s often used for gears, axles, and other machine parts.
- High Carbon Steel: This type of carbon steel contains a carbon content of 0.6% to 1.4%, making it strong and hard but also less ductile and difficult to weld. It’s commonly used for cutting tools, knives, and springs.
- Ultra-High Carbon Steel: With a carbon content of more than 1.4%, ultra-high carbon steel is extremely strong and hard but also brittle and difficult to work with. It’s used in applications that require extreme hardness, such as drill bits and saw blades.
Understanding the properties of each type of carbon steel is important in selecting the right material for a particular application.
| Examples | Carbon content (wt.%) | Microstructure | Properties | |
| Low-carbon steel | AISI 304, ASTM A815, AISI 316L | < 0.25 | Ferrite, pearlite | Low hardness, high ductility, toughness, machinability and weldability |
| Medium-carbon steel | AISI 409, ASTM A29, SCM435 | 0.25 – 0.60 | Martensite | Low hardenability, medium strength, ductility and toughness |
| High-carbon steel | AISI 440C, EN 10088-3 | 0.60 – 1.25 | Pearlite | High hardness, strength, low ductility |
| Ultra-High carbon steel | AISI 1095, AISI 1080, W1 | 0.9 – 1.4 | Ferrite, pearlite | High hardness, strength, toughness, edge retention, machinability, weldability |
Low carbon steel
Low-carbon steel is the most commonly used form of carbon steel due to its affordability and versatility. These steels typically contain less than 0.25 wt.% carbon and cannot be hardened by heat treatment to form martensite. Instead, they are strengthened through cold work or through the addition of other elements.
Carbon steels are generally soft and have low strength, but they exhibit high ductility, making them excellent for machining, welding, and other applications where formability is important.
High-strength, low-alloy (HSLA) steels are a type of low-carbon steel that contain small amounts of other elements, such as copper, nickel, vanadium, and molybdenum. These elements, which can make up to 10 wt.% of the steel content, help to increase the strength and hardness of the material while retaining ductility.
HSLA steels are often heat-treated to achieve their high strength and are more resistant to corrosion than plain low-carbon steels. They are easily formable and machinable, making them ideal for use in a range of industries, including construction, automotive, and aerospace.
Medium Carbon Steel
Medium-carbon steel contains between 0.25 and 0.60 wt.% carbon and 0.60 to 1.65 wt.% manganese. The addition of manganese improves the strength and hardenability of the steel. Heat treatment, which involves austenitizing followed by quenching and tempering, can improve the mechanical properties of medium-carbon steels, giving them a martensitic microstructure.
However, heat treatment can only be performed on thin sections of the steel. To improve the ability of medium-carbon steel to be heat treated and hardened, additional alloying elements such as chromium, molybdenum, and nickel may be added.
Hardened medium-carbon steels have greater strength than low-carbon steels, but this comes at the expense of ductility and toughness. Medium-carbon steels are often used in applications that require a balance of strength and ductility, such as shafts, gears, and axles in automotive and machinery industries. Understanding the properties of medium-carbon steel is important in selecting the right material for a particular application.
High-carbon steel
High-carbon steel contains between 0.60 and 1.25 wt.% carbon and 0.30 to 0.90 wt.% manganese. It is the hardest and toughest of the carbon steels but has the lowest ductility. Due to its high carbon content, high-carbon steel is typically hardened and tempered, making it very wear-resistant.
Tool steels and die steels are specific types of high-carbon steels that are used in applications where high wear resistance and toughness are critical. These steels contain additional alloying elements such as chromium, vanadium, molybdenum, and tungsten, which contribute to the formation of carbide compounds such as tungsten carbide (WC). This results in a very hard and wear-resistant steel that is well-suited for cutting tools, dies, and molds.
Despite their excellent wear resistance, high-carbon steels have limited use in applications where toughness and ductility are important. The brittleness of these steels makes them prone to fracture and failure under certain conditions. As with all steels, selecting the appropriate high-carbon steel for a given application requires careful consideration of the desired properties and the operating environment.
Ultra-high carbon steel
Ultra-high carbon steel is a type of steel that contains a very high percentage of carbon, typically between 1.25% and 2.0%. This high carbon content gives the steel exceptional hardness and wear resistance, making it ideal for use in cutting tools, knives, and other applications that require sharpness and durability. Ultra-high carbon steel also has high strength, making it well-suited for applications that require high levels of strength and durability.
One of the key characteristics of ultra-high carbon steel is its hardness. With a hardness typically above 60 HRC, ultra-high carbon steel is one of the hardest materials available. This makes it ideal for use in cutting tools and other applications where hardness and wear resistance are important. However, this high hardness also makes ultra-high carbon steel more brittle and less ductile than other types of steel, which can make it more difficult to work with.
Another important characteristic of ultra-high carbon steel is its wear resistance. Ultra-high carbon steel has excellent wear resistance, which makes it well-suited for applications that involve high levels of abrasion or impact. This makes it an excellent choice for use in machine parts, gears, and other industrial applications where wear resistance is important. However, it is important to note that ultra-high carbon steel may not be suitable for all applications, particularly those that require high levels of ductility or machinability.
Applications of Carbon Steel
Low-Carbon steel
Low-carbon steel is widely used in various applications due to its ductility, toughness, and affordability. Some common uses of low carbon steel include:
- Construction: Low carbon steel is often used in the construction industry to make structural components such as beams, columns, and girders.
- Automotive: It is used to manufacture car bodies, chassis, and other components due to its high strength and malleability.
- Pipes: Low carbon steel is used to make pipes for various applications, including water supply, gas transmission, and oil pipelines.
- Furniture: It is also used to manufacture furniture due to its strength and durability.
- Appliances: Low carbon steel is used in the production of various household appliances such as washing machines, refrigerators, and dishwashers.
- Manufacturing: It is used in the manufacturing of a wide range of products, including tools, machinery, and equipment, due to its excellent machinability and weldability.
Overall, low carbon steel is a versatile material that is used in many different applications due to its combination of strength, durability, and affordability.
Medium-carbon steel
Medium-carbon steel has good strength and toughness and is often used in applications where high strength and wear resistance are required. Some common uses of medium-carbon steel include:
- Automotive: Medium-carbon steel is used to manufacture parts such as gears, crankshafts, and axles due to its high strength and wear resistance.
- Machinery: It is used in the production of machinery and equipment components such as shafts, couplings, and sprockets.
- Construction: Medium-carbon steel is used in the construction of bridges, buildings, and other structures due to its strength and durability.
- Railway tracks: It is used to manufacture railway tracks and other rail components due to its wear resistance and strength.
- Tools: Medium-carbon steel is used to manufacture various types of cutting tools, including knives, saw blades, and drill bits, due to its hardness and toughness.
- Springs: It is also used to make springs and other components that require high strength and toughness.
Overall, medium-carbon steel is a versatile material that is used in many different applications where high strength, wear resistance, and toughness are required.
High-carbon steel
Some common uses of high-carbon steel include:
- Cutting tools: High-carbon steel is used to make cutting tools such as knives, saw blades, and drill bits due to its hardness and wear resistance.
- Springs: It is used to make springs and other components that require high strength and durability, such as in automotive suspension systems.
- Automotive: High-carbon steel is used in the manufacture of various automotive components such as crankshafts, axles, and gears.
- Rails: It is used to manufacture railway tracks and other rail components due to its high strength and wear resistance.
- Wire ropes: High-carbon steel is used to make wire ropes and other cables that require high strength and durability.
- Construction: It is used in construction applications such as reinforcement bars and cables for bridges and high-rise buildings.
Overall, high-carbon steel is a specialized material that is used in applications where high strength, hardness, and wear resistance are critical. It is not as widely used as low or medium-carbon steel due to its brittleness and difficulty in working with, but it is essential for specific applications where its unique properties are necessary.
Ultra-high carbon steel
Ultra-high carbon steel is primarily used in applications that require high levels of hardness, wear resistance, and strength. Some common applications of ultra-high carbon steel include:
- Cutting tools: Ultra-high carbon steel is commonly used to make cutting tools such as knives, saw blades, and drill bits. Its high hardness and wear resistance make it well-suited for cutting and drilling applications that require sharpness and durability.
- Industrial machine parts: Ultra-high carbon steel is often used to make machine parts such as gears, bearings, and shafts. Its high strength and wear resistance make it ideal for use in industrial settings where parts are subjected to high levels of stress and wear.
- Automotive parts: Ultra-high carbon steel can also be used to make automotive parts such as springs and suspension components. Its high strength and toughness make it well-suited for these applications, where durability and reliability are key.
- Mining equipment: Ultra-high carbon steel is often used in mining equipment such as drills and cutting tools. Its high hardness and wear resistance make it ideal for use in harsh mining environments where equipment is subjected to high levels of abrasion and impact.
- Musical instruments: Ultra-high carbon steel is sometimes used in the production of musical instruments such as guitars and cymbals. Its high density and unique acoustic properties make it well-suited for these applications, where tone and resonance are important.
Overall, ultra-high carbon steel is a versatile material that is well-suited for a wide range of applications where hardness, wear resistance, and strength are important. Its unique properties make it a valuable material in many industrial and manufacturing settings.
Properties of Various Grades of Carbon Steel
| Type | AISI/ASTM name | Carbon content (wt.%) | Tensile strength (MPa) | Yield strength (MPa) | Ductility (% elongation in 50 mm) |
| Ultra-Low | 1010 | 0.10 | 325 | 180 | 28 |
| Low | 1020 | 0.20 | 380 | 205 | 25 |
| Low | A36 | 0.29 | 400 | 220 | 23 |
| Low | A516 Grade 70 | 0.31 | 485 | 260 | 21 |
| Medium | 1030 | 0.27 – 0.34 | 460 | 325 | 12 |
| Medium | 1040 | 0.37 – 0.44 | 620 | 415 | 25 |
| High | 1080 | 0.75 – 0.88 | 924 | 440 | 12 |
| Ultra-High | 1095 | 0.90 – 1.04 | 665 | 380 | 10 |
