Low, medium, and high-carbon steel: everything you need to know
We’ve put together this guide to help you understand the differences in these steels. Their very names tell you something about their carbon content. But what does that mean for the characteristics of low-carbon steel? Medium-carbon steel? And high-carbon steel? We’ll look at each individually and then see how they compare. We’ll cover:
- What is low-carbon steel?
- What are the uses of low-carbon steel?
- Types of low-carbon steel
- Grades of low-carbon steel
- Properties of low-carbon steel
- What is medium-carbon steel?
- What are the uses of medium carbon steel?
- Types of medium-carbon steel
- Grades of medium-carbon steel
- Properties of medium-carbon steel
- What is high-carbon steel?
- What are the uses of high-carbon steel?
- Types of high-carbon steel
- Grades of high-carbon steel
- Properties of high-carbon steel
- The differences between low, medium and high-carbon steel
What is low-carbon steel?
Low-carbon steel, also known as mild steel, has a comparatively low radio of carbon to iron compared to other steel types. Typically, its carbon content is within the range of 0.05% and 0.32% by weight. This gives low-carbon steel low strength while making it more malleable and ductile compared to high-carbon steel.
One of the major benefits of mild steel is its cost-effectiveness. As it requires less carbon and other alloying elements, it’s normally less expensive than other types of steel. Moreover, it’s more readily available and simpler to work with than higher-carbon steels, which makes it a popular choice for a wide range of applications.
What are the uses of low-carbon steel?
Despite its low strength compared to other steel types, low-carbon steel is still strong enough for use in structural applications. It’s also used for machinery parts, as it helps to reduce machining costs. It’s easy to shape, which speeds up production times and reduces the cost of machining compared to other materials, such as aluminium.
Mild steel is also used in industrial small components, ranging from fasteners to levelling-feet studs.
Components made of low-carbon steel
Types of low-carbon steel
There are different low-carbon steels with varying amounts of carbon. Below are examples of different types and their applications:
| Type | Industry | Applications |
|---|---|---|
| Low-carbon structural steel | Construction | Buildings, bridges |
| Low-carbon sheet and strip steel | Sheet metal work | Automotive body panels, appliances and other uses that require thin, flat material |
| Low-carbon tubing and piping steel | Construction, automotive, heavy equipment, oil and gas | Mechanical tubes, pipes for fluid transport, and structural tubing |
| Low-carbon pressure vessel steel | Heavy equipment, machinery manufacturing | Boilers, pressure vessels and other uses where material must withstand high internal pressures |
| Low-carbon galvanised steel | Construction, HVAC, automotive | Roofing, automotive body panels, ductwork |
| High-strength low-alloy (HSLA) steel | Construction | Building frames, bridges, support structures |
Grades of low-carbon steel
The most common standard organisation in the UK is:
- BSI: The British Standards Institution, who have adopted ISO standards. On a technical sheet, they use ‘BS’ instead of their full initials.
- EN: The EN designation in BS (British Standard) grades of steel refers to the European standardisation system for steels. EN stands for "European Norm" and is a harmonised system of technical specifications for steel products across the European Union. Sometimes you’ll see a grade listed as BS EN.
One of the most widely used standards is BS 970, which specifies a range of low-carbon steel grades. It covers the chemical composition of steel and the corresponding mechanical properties. The grades are designated by a four-digit number, which represents the chemical composition of the steel. The grades are designated by a four-digit number, which represents the chemical composition of the steel.
For example, let's take the BS 970 080M40 grade.
The first two digits ‘08’ represent the carbon content of the steel (0.8%). The next two characters ‘M40" represent the type of steel and its properties. In this case, ‘M’ stands for ‘manganese’ and ‘40’ indicates the minimum tensile strength of the steel in units of 1,000 pounds per square inch (ksi). So, the minimum tensile strength of BS 970 080M40 is 40 ksi.
Commonly used BS 970 grades and their typical applications include:
| Grade | Application |
|---|---|
| 080M40 | Shafts, axles |
| 070M20 | Bolts, nuts, & other fasteners |
| 080A42 | Gears, pinions, & other machine parts |
| 080A15 | Gears, pinions, & bushings |
| 080M50 | Crankshafts, couplings, spindles, high-strength bolts, gears & cams |
| 150M19 | Bushings, pins, & rollers |
| 605M36 | Gears, crankshafts, axles,high-strength bolts, nuts, & studs |
Commonly used BS 970 grades of medium-carbon steel include:
| Grade | Application |
|---|---|
| 080M30 | Gears, shafts, axles |
| 080M40 | Bolts, studs & gears |
| 605M36 | Crankshafts, connecting rods & bolts |
| 722M24 | Shafts, bolts & gears |
| 080A42 | Cutting tools, eg: saw blades & knives |
| 735A50 | Gears for heavy machinery & equipment, eg: mining equipment, construction machinery & heavy trucks |
| 655M13 | Gears for heavy machinery, connecting rods, fasteners & bolts |
Some of the most commonly used BS 970 grades of high-carbon steel include the following:
| Grade | Application |
|---|---|
| 080A67 | Cutting tools, e.g. saw blades |
| 817M40 | Crankshafts, gears, shafts, & bolts |
| 060A96 | High-stress components, eg: springs |
| 735H51 | Bearings & bushings |
| 826M40 | Gears, shafts, & bolts |
| 070M55 | Ploughs, chisels & hammers |
| 735A51 | Bushings, springs, cutting tools, e.g. dies & reamers |
Properties of low-carbon steel
Each grade has slightly different properties, although the melting point of low-carbon steel is about the same. That said, we can still give a range of values to give you an idea of this material’s overall properties.
| Property | Value |
|---|---|
| Density | 2.85 – 8.08 g/cc |
| Tensile Strength, Yield | 140 – 2400 MPa |
| Fracture Toughness | 33.0 – 115 MPa-m½ |
| Shear Modulus | 70.0 - 80.0 GPa |
| Melting Point | 1430°C |
| Thermal Conductivity | 25.3 – 93.0 W/m-K |
What is medium-carbon steel?
Medium-carbon steel has a carbon content typically ranging between 0.3% and 0.6%. This category of steel offers a balance between the ductility and formability of low-carbon steel and the strength and hardness of high-carbon steel.
Medium-carbon steels are stronger and harder than low-carbon steels. This is due to their increased carbon content, but it also means they’re less ductile and more difficult to form and weld. They often require heat treatment, such as quenching and tempering, to achieve desired mechanical properties. This is possible with its manganese content, which ranges between 0.30% to 0.60%.
What are the uses of medium carbon steel?
Medium-carbon steels are commonly used in applications where higher strength and toughness are needed, as shown in the table below. It’s also used to make small components, such as concealed hinges.
Types of medium-carbon steel
Common types of medium-carbon steel and their applications include:
| Type | Industry | Application |
|---|---|---|
| Medium-carbon structural steel | Construction, Manufacturing | Buildings, bridges, heavy-duty equipment |
| Medium-carbon sheet and strip steel | Sheet metal work | Machinery parts, Automotive parts |
| Medium-carbon tubing and piping steel | Construction, automotive, heavy equipment | Mechanical tubes, pipes for fluid |
| Medium-carbon pressure vessel steel | Oil and gas, food and beverage, pharmaceutical | Pressure vessels |
| Medium-carbon alloy steel | Automotive, Heavy machinery | Gears, shafts, axles, connecting rods |
| Medium-carbon quenched and tempered steel | Automotive, Construction, Heavy machinery | Gears, axles, transmissions, crane booms, excavation arms |
Grades of medium-carbon steel
Products made from medium-carbon steel adhere to specific standards. Within those standards are grades. Commonly used grades of medium-carbon steel – and the standard they fall under – include:
| Standard | Grade | Application |
|---|---|---|
| SAE J403 | 1045 | Gears, shafts, machine parts |
| SAE J404 | 4140 | Gears, axles, aircraft landing gears, and drilling equipment |
| ASTM A29 | 1045 | Axles, bolts, studs, and other machinery parts |
| ASTM A576 | 1045 | Bolts, studs, couplings, bushings, shafts and gears |
| ASTM A29 | 4140 | Gears, axles, and shafts |
| ASTM A434 | Class BD (AISI/SAE 4140) | Bolts and other fasteners, connecting rods, gears and shafts |
| ASTM A829 | 4140 | Gears, axles, and drilling equipment |
Properties of medium-carbon steel
Each grade has its own properties that distinguishes it from other medium-carbon steel grades. The table below gives you a range of values for medium-carbon-steel properties.
| Property | Value |
|---|---|
| Density | 7.75 - 7.89 g/cc |
| Tensile Strength, Yield | 245 - 1740 MPa |
| Fracture Toughness | 80.9 – 143 MPa-m½ |
| Shear Modulus | 72.0 - 82.0 GPa |
| Melting Point | 1425-1540°C |
| Thermal Conductivity | 21.9 - 52.0 W/m-K |
What is high-carbon steel?
High-carbon steel contains a carbon content ranging between 0.60% – 1.5%. It’s the most corrosion resistant of the steels due to its high amount of carbon. This increased carbon significantly enhances the steel's hardness, tensile strength, and wear resistance. In turn, that makes it suitable for applications that demand high strength and wear resistance.
However, the higher carbon content also makes these steels more brittle and less ductile, which makes it more susceptible to cracking under certain conditions. High-carbon steel is also more challenging to weld than lower-carbon-content steels, due to the risk of cracking and brittleness in the heat-affected zone.
What are the uses of high-carbon steel?
High-carbon-steel uses include anything needing wear resistance and durability, as shown in the table below. A note about plain high-carbon steel, which is often used to mean high-carbon steel. They are different. Plain high-carbon steel consists mostly of carbon and iron, without any significant amounts of alloying elements.
High-carbon steel is often used to manufacture springs:
Types of high-carbon steel
High-carbon steel types, and their applications, include:
| Type | Industry | Application |
|---|---|---|
| Plain high-carbon steel | Manufacturing, automotive, construction | Springs, knives, cutting tools, brake components |
| High-carbon tool steel | Manufacturing, metalworking, woodworking | Cutting tools, punches, dies, injection moulding tools, extrusion dies, router bits |
| High-carbon bearing steel | Industrial machinery, automotive, aerospace | Ball and roller bearings for engines; also, transmissions, wheels, heavy machinery, gearboxes, pumps |
| High-carbon spring steel | Electronics, automotive, manufacturing | Leaf springs, coil springs, machinery, springs for electronic devices |
Grades of high-carbon steel
Grades of all carbon steels are subsets of specific standards. Some of the most commonly used grades of high-carbon steel include the following:
| Standard | Grade | Application |
|---|---|---|
| ASTM A29/A29M | AISI/SAE 1060 | Springs, gears, axles, heavy-duty machinery components |
| ASTM A29/A29M | AISI/SAE 1065 | Springs, cutting tools, industrial knives and blades |
| ASTM A29/A29M | AISI/SAE 1070 | Springs, automotive suspension components, agricultural machinery parts |
| ASTM A29/A29M | AISI/SAE 1080 | Heavy-duty springs, automotive components, heavy machinery parts |
| ASTM A295 | AISI/SAE 52100 | Bearing steel used in the manufacture of ball and roller bearings |
| ASTM A600 | AISI/SAE M2 | High-speed tool steel used for cutting tools, drills, and taps |
| ASTM A686 | AISI/SAE W2 | Water-hardening tool steel used for cutting tools, dies, punches, and woodworking tools |
Properties of high-carbon steel
Because standards and grades vary between each other, there is no one value for the properties of high-carbon steel. Below is a broad range of what you can expect.
| Property | Value |
|---|---|
| Density | 0.451 – 8.26 g/cc |
| Tensile Strength, Yield | 245 – 1740 MPa |
| Fracture Toughness | 13.2 – 165 MPa-m½ |
| Shear Modulus | 78.0 – 82.7 GPa |
| Melting Point | 1540 – 1590°C |
| Thermal Conductivity | 19.0 – 52.0 W/m-K |
The differences between low, medium and high-carbon steel
The essential difference is in the steels’ carbon content, which gives each different characteristics.
| Low-carbon steel | Medium-carbon steel | High-carbon steel | |
|---|---|---|---|
| Carbon Content | 0.05% to 0.32% | 0.30% to 0.60% | 0.60% to 1.5% |
| Characteristics | Ductile Malleable Tough Easily joined and welded Poor corrosion resistance |
Stronger Harder Less ductile Less malleability Good corrosion resistance |
Very strong Very hard Poor ductility Poor malleability Better corrosion resistance |
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