Classification of Quality Grades of Steel
Steel is an essential material for a variety of applications in industries ranging from infrastructure to consumer products. Due to the different properties of steel, the steel quality grades are classified according to their chemical composition, mechanical properties, and corrosion-resistant properties. The most commonly used classification of steel grades is the one developed by the American Iron and Steel Institute (AISI).
The AISI steel grades are referenced using numbers, each corresponding to a different set of properties. For example, the carbon steels are classified as 1018, 1020, 1022, 1030, 1035, 1045, and higher grades. These grades are grouped according to the carbon content, i.e., low, medium, or high. The low carbon steels, such as 1018 and 1020, contain only 0.18-0.23% carbon, and the medium carbon steels, such as 1035 and 1045, contain 0.29-0.45% carbon and 0.30-0.60% manganese. The high carbon steels, such as 1050 and 1541, contain up to 0.95% carbon and 0.60-1.65% manganese.
Steel with a low alloy content, such as 1021 and 1025, is also classified as a medium carbon steel as they contain 0.25-0.29% carbon. The alloy steels, such as 4130 and 8620, are classified as low and medium alloy steels having 0.15-0.30% alloy content such as chromium, molybdenum, and nickel. The other types of steel grades include the special purpose grades such as SAE 4130 (chromoly low alloy), AISI 4140 (chromoly medium alloy), and AISI 4400 (high alloy).
The mechanical properties of steel are also important for its classification. These properties depend on the chemical composition of the steel. Generally, steels with a low carbon content are more ductile and do not need to be heat-treated before use. The medium and high carbon steels, however, require heat treatment to make them more ductile so that they can be used for various applications. Additionally, the alloy steels require some form of heat treatment to improve their strength and ductility for use in applications demanding higher strength and wear resistance.
The corrosion resistance properties of steel depend on the element content, surface preparation, and type of environment. For example, the carbon steels have superior corrosion resistance when compared to the alloy steels due to their low chromium content. The stainless steels, however, have superior corrosion resistance as they contain high amounts of chromium and nickel. The low alloy steels have moderate corrosion resistance, while the high alloy steels have superior corrosion resistance due to their high chromium and molybdenum contents.
The steel quality grades are also classified based on the standards they comply with, such as ASTM, EN, and JIS. Each standard offers different steel grades and corresponding quality requirements. The American Society for Testing and Materials (ASTM) AISI standards cover carbon, alloy, stainless, and tool steels typically used for specific applications. The European Standards (EN) provide quality grades for all types of steel. The Japanese Industrial Standard (JIS) covers both carbon and alloy steels.
In conclusion, the quality grade of steel is an important factor that should be considered when selecting steel for a specific application. The most commonly used classification is the one developed by the American Iron and Steel Institute (AISI). The grades are based on their chemical composition, mechanical properties, and corrosion-resistant properties. Additionally, the quality of steel can also be classified according to the standards they comply with, such as ASTM, EN, and JIS.
