Mild steel is a widely used material in the building and engineering industries. It is a popular choice due to its affordability, ease of fabrication, and reliable mechanical properties. Its excellent weldability, cuttability, and formability make it suitable for a wide range of construction applications. In this Brick & Bolt blog, we’ll explore the various grades, composition, tensile strength, carbon content, and common uses of mild steel.
What is Mild Steel?
Mild steel, also known as low-carbon steel, typically contains 0.05% to 0.29% carbon by weight. Due to its low carbon content, it exhibits lower hardness and tensile strength compared to medium or high-carbon steels, making it relatively soft and ductile. However, this softness is advantageous for processes such as machining, welding, and forming, where material malleability is essential.
Mild steel offers excellent weldability, good machinability, and ease of fabrication, which makes it ideal for applications that require complex forming or extensive modification. Although it does not provide the high tensile strength of alloyed or high-carbon steels, it performs reliably in general-purpose engineering applications where high strength-to-weight ratios are not critical.
Due to its balanced mechanical properties, cost-effectiveness, and ease of availability, mild steel is widely used in structural components, automotive parts, fabrication of frames, pipelines, machinery, and construction materials.
Mild Steel Composition
The primary elements in mild steel are as follows:
- Iron: Iron is the base metal that makes up most of the composition.
- Carbon: Low-carbon steel normally has the carbon content between 0.05% and 0.29%.
- Manganese: Manganese increases hardness and tensile strength up to 1.5%.
- Phosphorus & Sulfur: Low levels of phosphorus are used to maintain hardness and ductility and a small amount of sulfur is added to improve machinability.
- Silicon: Silicon is available in small amounts to increase strength without decreasing ductility.
The well-balanced composition gives benefits like good ductility, moderate strength and good machinability.
Mechanical Properties of Mild Steel
The mechanical properties of the mild steel grade you select for a project should be understood. Some of the properties of mild steel are as follows:
- Tensile Strength: The tensile strength of mild steel is usually between 370 and 620 MPa, but it changes based on grade and treatment. This measures how much pressure steel can take before beginning to stretch or break.
- Yield Strength: Mild steel grades have yield strengths from 200 MPa for lower grades to around 370 MPa for higher grades.
- Ultimate Strength: The ultimate strength of mild steel ranges between 370 and 550 MPa, depending on grade, processing, and heat treatment..
- Elongation and Ductility: Mild steel is suitable for uses that need flexibility because depending on the grade and testing process it can take deformation before breaking with an elongation of 15% to 25%.
- Modulus of Elasticity: The elastic modulus of mild steel is normally around 200 GPa (Gigapascals). This shows its stiffness and ability to return to its original shape after deformation.
- Hardness: Mild steel has a Brinell hardness number (BHN) between 120 and 180, depending on treatment. It is soft compared to high-carbon steels, but this makes it easier to cut and machine.
- Impact Strength: Mild steel has decent impact resistance, especially at room temperature. But it may become brittle in sub-zero temperatures if not properly treated.
- Fatigue Strength: While Mild steel can withstand moderate cyclic loading, its fatigue strength is lower than alloy steels normally between 180 and 260 MPa making it suitable for non-critical load-bearing applications.
Mild Steel Grades Classification Systems
Mild steel grades are divided using different national and international standards, each with its own system to ensure quality and performance. Types of steel grades according to systems are as follows:
- Indian Standards (IS) – BIS (Bureau of Indian Standards)
The Indian Standard for structural steel like mild steel, is specified under IS 2062. It divides steel grades on yield strength, impact resistance and chemical composition, ensuring safe and uniform use in Indian construction and engineering projects. Common mild steel grades are IS 2062, E250, E350 and E410, suitable for various structural applications.
- American Standards – AISI / SAE / ASTM
AISI/SAE: Uses a four-digit numbering system where the first two digits identify the type of steel and the last two digits show the carbon content (e.g., AISI 1018 means carbon steel with 0.18% carbon).
ASTM: The American Society for Testing and Materials develops standards like ASTM A36 which is a common mild steel structural grade in the U.S.
- European Standards – EN (Euro Norm)
EN standards like EN 10025 specify grades like S275 and S355, dividing the steel based on mechanical properties, chemical composition and impact resistance. These are used across Europe and other regions for construction and engineering.
- British Standards – BS
British standards like BS 4360, were used for structural steels before being largely harmonized with EN standards. They still serve as reference points in some industries within the UK.
Types of Mild Steel Grades
There are different types of mild steel designed for special use. Steel grades are divided according to their carbon content and mechanical properties. A list of common mild steel grades can be found below:
- AISI Mild Steel Grades (Used Globally)
| Mild Steel Grade | Carbon Content | Tensile Strength (MPa) | Application |
| AISI 1018 | 0.14% – 0.20% | 440 – 500 | Carbonised parts, gears, pins |
| AISI 1020 | 0.17% – 0.23% | 420 – 480 | Machinery parts, camshafts |
- AISI 1018 Mild Steel
The most common type of mild steel has carbon between 0.14% and 0.20%. Because it has a great balance of strength, hardness and simplicity of machining, it is mostly used in general technical applications.
- AISI 1020 Mild Steel
Because it has a higher amount of mild steel carbon (0.17% to 0.23%) this grade is easier to weld and gives greater strength. Small mechanical parts that don’t need to be very durable, like car shafts and axles, mostly use AISI 1020.
- EN Structural Steel Grades (European Standard, used in India too)
| Mild Steel Grade | Carbon Content | Tensile Strength (MPa) | Application |
| S275 J0 | 0.18% | 370 – 510 | Structural components, construction |
| S355 J0 | 0.20% | 470 – 530 | Heavy-duty structural applications |
- Structural Grades (S275 and S355)
Construction is the primary application for these steel grades. Because S275 has a great mix between strength and weldability it is commonly used in bridges, buildings and general construction frames. This makes it a safe option for routine structural work. S355 can be used in difficult structural applications where greater longevity is needed because of its greater strength.
- IS 2062 Mild Steel Grades (Indian Standard for Structural Steel)
In India, mild steel grades are divided based on their mechanical properties and chemical composition as defined by IS 2062, which is the most widely used standard for structural steel. The main grades under IS 2062 are:
| Mild Steel Grade | Yield Strength (MPa) | Applications |
| IS 2062 E250 (Fe 410W) | 250 | Structural components, bridges, building frames |
| IS 2062 E275 | 275 | Light structural work, support structures |
| IS 2062 E300 | 300 | Medium to heavy structural uses |
| IS 2062 E350 (Fe 490W) | 350 | High-strength structures, pressure vessels |
| IS 2062 E410 | 410 | Heavy-duty construction, critical load-bearing parts |
These grades are further subdivided based on impact properties, represented by suffixes:
- BR – for room temperature impact test
- B0 – for 0°C impact test
- B – for -20°C impact test
- C – for -40°C impact test
IS 1079 is another Indian standard used for cold-rolled mild steel sheets and strips suitable for automobile bodies, appliances and furniture.
Applications of Mild Steel
Mild steel is used in many different industries because of its flexible qualities. Here are a few such uses:
- Building Structures: Building structures like beams, columns and reinforcing bars often use mild steel. Because of its great weldability, structural framework joints are known to be strong.
- Automotive Parts: Mild steel has good strength and flexibility and is used in the automotive industry to make frames, body panels and engine parts.
- Machineries: Mild steel has good strength, machinability and affordability and is a good choice for tools and machinery like gears, shafts and fasteners.
- Pipes: Mild steel is strong and can prevent breakage and it is used in pipes that carry oil, gas and water.
Tips to Avoid Corrosion in Mild Steel
Mild steel is affordable, but in some cases, its low corrosion resistance can be a problem. Normally, to avoid rust, mild steel is painted or coated to prevent it. Common protective methods are:
- Galvanizing means applying a zinc coating to avoid corrosion on steel.
- Dry powder finish is used to give a protective covering, and it is called powder coating.
- To protect the outdoor settings from corrosion, paints are applied.
Conclusion
Mild steel is affordable, easy to manufacture and has durable mechanical qualities, making it an important part of modern engineering and construction. Selecting the right mild steel grade for various uses will be made easier for engineers by their understanding of the grades, their composition and tensile strength. For use in machinery, structures or automobile parts, selecting the right grade of mild steel ensures strength, performance and longevity.
Brick & Bolt, an end-to-end construction services provider in India, offers the best building materials supply to streamline building processes. A patented quality assessment system (QASCON) with 470+ tests also ensures that projects are completed with premium quality. To use top-quality construction materials like steel in your project, connect with Brick & Bolt today!
Hemali Patel