，
Steel occupying a major role in the modern world, it is essential to have a comprehensive understanding of the different types of steel, their grades and standardization. In the US, the American Iron and Steel Institute (AISI) is responsible for classifying and grading the different types of steel available in the US market. There are four main grades: AISI C, AISI D, AISI S and AISI H.
AISI C-grade steel has the most common types of mild steel. It is characterized by medium and low alloyed carbon, an average yield strength of 60,000 psi, and a moderate ductility. This grade is primarily utilized in the construction of industrial buildings, cars, and appliances and is popular for its resistance to wear and tear.
AISI D-grade steel is preferred for its high strength, flexibility, and compliance with international standards. It is most commonly used for heavy duty applications, such as for bridges, oil and gas tanks, heavy machinery and construction, due to its durability and strength.
AISI S-grade steel stands for the Specialized grade of steel. It is composed of different alloy elements, such as chromium and molybdenum, and strives to offer the absolute highest strength and stability. AISI S-grade steel is typically used in the manufacture of automotive parts, jet engines, high-pressure boilers, aircraft and aerospace components.
Finally, there is AISI H-grade steel, which is a type of high strength low alloy steel that is heat treated to achieve a greater strength and dominate its low corrosion resistance. This grade of steel is especially suitable for demanding applications, such as offshore platforms, oil and gas pipelines, heavy machine tools and others.
In order to guarantee quality, most American manufacturers use the American Society for Testing and Materials (ASTM) for quality control and product verification. ASTM has a wide range of standards for steel structures, strength, ductility, hardness and other physical characteristics. The set of standards tests are designed to ensure the steel meets quality and safety standards.
Generally speaking, ASTM or AISI grades serve as a reference to the quality and performance of a certain steel type. The most common type is Grade A, which is the “tensile strength” grade for structural steel. Grade A steel is a structural use only product and should not be used for other applications, such as fertilizer or economic chemicals.
On the other hand, Grade B is used for high-strength, low-alloy (HSLA) steel and is known for its higher strength and lower machinability. It is used to fabricate steel parts with increased durability and strength, making it popular in industries such as the defense, transportation and construction. Grade C is corrosion resistant steel, used for applications such as storage tanks, chemical equipment, etc.
All US steel products must also go through the ASTM A370 test in order to guarantee that the individual pieces of steel have the same physical characteristics across different production batches. The A370 test is designed to measure the materials hardness, tensile and yield strengths, elongation, chemical resistance, toughness and chemical composition.
In the US, the National Product Number (NPN) is used to identify and track multiple steel products throughout different processes of production. This number is assigned by the US government and is unique to each different type of steel product. The NPN allows manufacturers to quickly and easily identify the steel they are working with, as well as any additional information needed.
In conclusion, steel is an essential part of modern industry and it is important to be familiar with the different grades, standards and quality control measures in the US. It is essential to use the correct type of steel for the application, and to be aware of the NPN when tracking batches of steel.
