Steel is used in a wide variety of industries and is considered the backbone of modern infrastructure. The ability to add other elements and, in doing so, manipulate the properties of steel is what makes it such a widely used resource. This article will examine the most common elements that make up the wide range of steel grades and explore their impact on material properties.
Iron alone is not enough
In its purest form, iron is neither exceptionally strong nor hard – in fact, a block of pure iron could be cut with a knife. The addition of carbon and the removal of oxygen give iron-based steel its incredible strength.
An alloy is a metal made by combining two or more metallic elements. Adding more metallic and non-metallic elements to iron and carbon allows the properties to be manipulated to meet a specific need or application.
Even changing the amount of carbon combined with iron can affect the properties of the material. High carbon steel contains between 0.60% and 0.95% carbon (as a percentage by weight) and is incredibly strong and hard, but is less ductile and more difficult to machine and weld. As the carbon content is reduced, the material is more like pure iron and therefore softer and more ductile.
The maximum carbon content of steel is 2.1%, as anything above that is not really classified as steel. As the carbon content is reduced, the material falls into one of four categories:
1. Ultra high carbon steel (0.96% to 2.1% carbon)
High carbon steel is extremely strong and able to withstand localized deformation under high tension. It is produced through a specialized process. Therefore, machining, welding or bending this material is almost impossible.
2. High carbon steel (0.55% to 0.95% carbon)
High carbon steel is quite strong and offers more ductility than very high carbon steels and until recently was used in railway applications. Other applications include chiseling and cutting tools.
3. Medium carbon steel (0.30% to 0.54% carbon)
Medium carbon steel balances strength and hardness with ductility and is primarily used in machine parts i.e. gears, bolts and axles.
4. Low carbon steel (0.05%-0.25%)
Low carbon steel offers incredible strength at a lower weight compared to other grades of steel. Adding alloys can give low carbon steel different properties without a massive impact on weight.
Although all grades of steel can use alloys and non-metallic elements to modify their properties, this article will focus on how certain elements modify the properties of low carbon steel.
Elements that harden
Before looking at items that harden, it is important to note the difference between hardening and strengthening.
The hardness of steel refers to the level of impact a material can absorb before it hits and is usually measured by a Charpy impact test. Hardness can be greatly affected by temperature, as the material can generally absorb less impact in colder temperatures.
On the other hand, steel strength focuses on yield strength and tensile strength. A yield point is the point at which a material is stressed and deforms but does not break. Tensile strength is the amount of stress required for the material to fail or break.
Elements that harden steel increase the amount of impact a material can absorb. The most common hardening elements are:
- Phosphorus*
- Silicon*
- Manganese*
- Nitrogen
- Nickel
- Chromium
- Boron
These hardening elements are common in quenched and tempered grades (eg ASTM A514 or ASTM A710) and offshore grades (eg ASTM A633). Nickel can be added to carbon steel alloys, but is more common in stainless steel grades.
*Phosphorus, silicon and manganese are the most common elements added to steel. ASTM A752-50 (a low alloy high strength steel) and ASTM A36 (a mild steel) are two of the most widely used grades in North America and contain all three of these elements.
Elements that reinforce
Elements that strengthen the steel increase the load that the material can withstand. Therefore, it is common for these elements to be present in infrastructure such as roads, bridges, and buildings. The most common reinforcing elements are:
- Silicon
- Chromium
- Vanadium
- Phosphorus
- Titanium
- Nitrogen & Aluminum Combo
- Niobium (Columbia)
These reinforcing elements are common in quenched and tempered grades (eg, ASTM A514) and high-strength, low-alloy grades (eg, ASTM A656 and ASTM A5720-50).
Elements that increase ductility
In projects that require drilling, welding, machinery or bolting equipment, ductility is an important factor. Common elements added to steel alloys that improve ductility include:
- Niobium (Columbia)
- Sulfur
- Phosphorus
- Chromium
These softening elements are common in quenched and tempered grades (e.g. ASTM A514) and are used in dozens of others.
Elements that resist corrosion
Elements that promote corrosion resistance are essential to steel alloys for use in applications that require resistance to atmospheric conditions. Common elements used include:
- Zirconium
- Nickel
- Phosphorus
- Copper
- Chromium
Corrosion resistance is important for structural steel used in exterior applications, for example bridges, and offshore or marine applications.
The power of chemistry
Iron and carbon are the simple building blocks of steel. However, a wide range of metallic and non-metallic elements can alter the properties and behavior of steel, making it a viable resource for many applications.
Leeco Steel specializes in supplying carbon steel plate in the United States, Canada and Mexico. A wide variety of alloy steel grades are available. After determining the ideal steel grade for your project, you can get the steel plate you need, when you need it.
This information was obtained, reviewed and adapted from materials provided by Leeco Steel, LLC.
For more information on this source, please visit Leeco Steel, LLC.
