Types and Grades of Steels
Steel is an alloy of iron and carbon and other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Steels are iron-based metals to which other chemical elements have been added. The addition of these elements can create new constituents in the metal, altering its mechanical properties, machinability and corrosion/oxidation resistance.
The Total Materia database contains many grades of steel from all countries and standards. The names of steel grades in different standards are confusingly similar. For example, the American Iron and Steel Institute (AISI) designations for steel grades show a basic four-digit number followed by a letters and numbers, indicating the composition of the steel. The Japanese Industrial Standards (JIS) designations show a similar basic four-digit number, followed by a letter and a number that indicate strength levels. The European materials (EN) designations have numbers indicating the nominal composition and the strength grade, followed by a letter that is sometimes used to indicate the quality of surface finish.
There are several different types of steel and various alloys and applications for each type. Generally speaking, most steels, such as SAE mild steel and AISI 300 and 400 series stainless steels, are considered ferrous materials, meaning they contain iron. Non-ferrous materials generally refer to unbonded metals or alloys that are not mainly composed of iron. Non-ferrous materials may include aluminum, copper, brass, bronze and titanium.
Carbon Steels
The most common type of steel is carbon steel, typically composed of 0.60 - 1.65% carbon. The term carbon steel may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels. Popular types of carbon alloys include mild steel, medium-carbon steel and high-carbon steel. Mild steel is 1018, and has a low carbon content (0.18%), while high-carbon steel may contain more than 2% carbon content. These types of steels are great for welding, as the higher carbon content provides greater strength and hardness, but can be brittle.
Alloy Steels
Alloy steels are a type of steel that is alloyed with other elements, usually to increase strength, toughness and/or wear resistance. These types of steels can be further divided into low-alloy and high-alloy steels, depending on the percentage of alloying elements present (typically between 1-5% by weight). Of the large family of alloy steels, some of the most widely used categories include HSLA, low alloy, and tool steels.
• High-Strength Low-Alloy (HSLA) steels are a type of alloy steel which have higher strength than normal carbon steels and are typically used in structural applications. These types of steels are generally composed of a small percentage of alloying elements (less than 5%), and have much improved mechanical properties over carbon steels.
• Low alloy steels are generally composed of small percentages of alloying elements and are intended for use in applications where strength and/or corrosion resistance is required. These types of steels generally contain between 1 and 5% of alloying elements and are resistant to corrosion, but not as strong as HSLA steels. Examples of low alloy steels include AISI 4140, 4130, 4340, and 8620.
• Tool steels are designed to retain their hardness and strength at high temperatures and are suited for cutting tools and dies. These types of steels generally contain more alloying elements (7% or more), making them more expensive to produce than carbon or low alloy steels. Some common tool steels include A2, D2, S7, and H13.
Conclusion
In conclusion, there are many different types and grades of steels that are used in various applications, each possessing unique properties and characteristics. Carbon steels, alloy steels, and tool steels are the most widely used and have various compositions and strengths, making them suitable for different purposes. Understanding the composition of steels and their properties can help in selecting the right type and grade of steel for your project or application.
