Steel is present in nearly every aspect of modern life, from infrastructure, vehicles, and appliances to advanced technology and aerospace. It stands as one of the world’s most widely used engineering materials. However, not all steels are identical; their compositions and intended applications vary greatly. Selecting the appropriate steel type and grade is a vital decision for any engineering or manufacturing project.
What is Steel?
Steel is an alloy, which means it is made from a mixture of elements rather than a single element. The base element in steel is iron, while other elements such as carbon, manganese, chromium, nickel, and molybdenum are added in small amounts to enhance mechanical and chemical properties. Among these, carbon is the most influential element, providing hardness that pure iron lacks.
The steelmaking process begins with the extraction of iron from iron ore, followed by refining to remove impurities and adjust the carbon content. After refining, additional alloying elements may be added to create steels with specific properties, such as increased strength, toughness, or resistance to corrosion and wear. Steel is also highly recyclable, with a large percentage of global steel production coming from recycled material.
Steel Types
Steel can be broadly grouped into several categories based on composition and intended use:
Carbon Steel
Carbon steel is the most basic and widely used type of steel. It primarily contains iron and carbon, with minimal amounts of other elements. The carbon content determines the steel’s hardness, strength, and weldability. Carbon steel is sub-classified into:
- Low Carbon Steel: Contains less than 0.25% carbon. It is soft, ductile, highly weldable, and commonly used in structures and general fabrication. Common examples include MS (mild steel) pipe and structural plates.
- Medium Carbon Steel: Contains about 0.25-0.6% carbon. It offers a balance of strength and ductility and is often heat-treatable. Commonly used for shafts, axles, and gears.
- High Carbon Steel: Contains 0.6-1% (sometimes up to 1.2%) carbon. It is very hard with excellent wear resistance but is more brittle and less weldable. Used for cutting tools, springs, and high-strength wires.
Alloy Steel
When elements such as chromium, nickel, molybdenum, or vanadium are added to carbon steel, they form alloy steels. These steels are designed for enhanced strength, toughness, or resistance to specific conditions. Alloy steels are further divided into:
- Low Alloy Steel: Total alloy content less than 5%. Offers a good balance of strength, toughness, and cost. Used for machine parts like EN19 and EN24.
- High Alloy Steel: Total alloy content above 5%. Known for superior hardness, wear, and corrosion resistance. Most high alloy steels fall under stainless or tool steels.
Stainless Steel
Stainless steel typically contains at least 12% chromium, which provides corrosion resistance. This category is widely used for applications needing durability and a shiny finish, such as kitchenware, medical instruments, and chemical processing equipment.
Tool Steel
Tool steels are specially formulated for high hardness and toughness, suitable for cutting and shaping other materials. They are used for tools, dies, and high-speed cutting applications, often containing elements like tungsten and molybdenum.
Special Steels
- Cast Iron: Contains more than 2% carbon, making it brittle but excellent in compression and ideal for casting complex shapes like engine blocks and machine beds.
- Bearing Steel: High carbon, high chromium types with great wear resistance, used for bearings and precision components.
- Spring Steel: Designed for elasticity and fatigue resistance, used in springs and measuring tapes.
- Electrical Steel: Contains silicon for improved magnetic properties, used in motors and transformers.
- Weathering Steel: Forms a stable rust layer to protect from deeper corrosion, used in bridges and towers.
- Nickel and Chromium-Molybdenum Steels: Developed for strength and toughness, especially at low or high temperatures.
What is Steel Grade?
A steel grade represents a specific set of chemical composition and mechanical properties. Each grade is designed for particular applications and performance requirements. Grades help engineers and manufacturers specify exactly what kind of steel is needed for a given project.
With hundreds of unique grades defined under various international standards, each steel grade comes with its own designation, reflecting its composition, properties, and sometimes its intended use.
Steel Grade Standards
There are many steel grade standards used around the world, each with its own naming system and specifications:
- AISI/SAE (USA): Popular for automotive and tool steels. AISI and SAE systems have merged, and grade numbers reflect chemical composition (e.g., 1045, D2).
- ASTM (USA): Includes chemical, mechanical, and testing specifications. Used in construction, engineering, and oil industries (e.g., A36).
- EN ISO (Europe): Focuses on chemical composition and delivery condition, widely adopted internationally.
- JIS (Japan): Used for automotive, electronics, and tool steels, with consistent and clear prefixes (e.g., SUS304 for stainless steel).
- BIS (India): The Indian standard, often influenced by British and global standards (e.g., IS 2062 for mild steel).
- DIN (Germany): Previously very popular, now largely merged into EN ISO.
- EN (Old British): Simple codes like EN8, EN19 still widely used in India despite being officially obsolete.
Sometimes steel products in local markets are labeled with legacy or international grades due to familiarity, even if local standards exist.
Steel Grade Chart
| Steel Type | Common Grades | AISI/SAE | EN / Old EN | DIN | JIS | Typical Applications |
|---|---|---|---|---|---|---|
| Low Carbon Steel | 1010, 1020, A36, IS 2062, SS400 | 1010, 1020 | EN3B, EN2 | 1.0038 | SS400 | Structures, auto panels, MS plates/pipes |
| Medium Carbon | 1040, 1045, C45, EN8, EN9 | 1040, 1045 | EN8 (C40), EN9 | 1.0503 | S45C | Shafts, gears, axles, bolts |
| High Carbon | 1060, 1080, 1090, EN42, SK5 | 1060, 1080 | EN42 | 1.1274 | SK5 | Springs, cutting tools, wires |
| Alloy Steel | 4140, 4130, EN19, EN24, 4340 | 4140, 4130 | EN19, EN24 | 1.7225 | SCM440 | Shafts, spindles, machine parts |
| Bearing Steel | 52100, EN31 | 52100 | EN31 | 1.3505 | SUJ2 | Bearings, rollers, precision parts |
| Spring Steel | 5160, 65Mn, SUP9, EN47 | 5160 | EN47 | 1.1273 | SUP9 | Springs, clips, blades |
| Stainless Steel | 304, 316, 410, 420, 430 | 304, 316 | 1.4301, 1.4401 | 1.4301 | SUS304 | Kitchenware, medical, chemical equipment |
| Tool Steel | D2, D3, H13, O1, SKD11, SKS3 | D2, O1, H13 | EN31, EN24 | 1.2379 | SKD11 | Dies, punches, cutting tools |
| Cast Iron | FG200, FG260, A48 | — | — | — | — | Machine beds, engine blocks |
| Weathering Steel | Corten A/B | — | — | — | — | Bridges, outdoor structures |
| Electrical Steel | M19, M27, M36 | — | — | — | — | Transformers, motors, generators |
How To Select Steel Grade for Your Project?
Choosing the right steel grade involves considering several factors:
- Mechanical Requirements: Assess the need for strength, toughness, hardness, ductility, or wear resistance. For example, use low carbon steel for easy fabrication, medium carbon steel for strength, and high carbon steel when wear resistance is a priority.
- Weldability and Formability: If welding is important, opt for steels with lower carbon equivalents for better weldability.
- Corrosion Resistance: For environments prone to rust or chemical exposure, stainless steel or weathering steel may be necessary.
- Availability: Not all grades are available everywhere. It’s practical to check which steel grades are commonly stocked in your region or by your supplier.
- Equivalent Grades: Once a grade is known in one standard, equivalent grades can often be found in other standards. For example, AISI 304 stainless steel is also known as SUS304 in JIS, X5CrNi1810 in ISO, and 1.4301 in DIN.
- Application: Base your selection on the end use—structural work, tool manufacture, springs, bearings, or electrical applications all have preferred steel grades.
- Cost: Alloy content and required processing affect price. High alloy and specialty steels are more expensive, while mild and medium carbon steels are typically more economical.