Carbon steel is an iron-carbon alloy with a carbon content of 0.0218% to 2.11%. Also called carbon steel. Generally also contains a small amount of silicon, manganese, sulfur, phosphorus. Generally, the higher the carbon content in carbon steel, the greater the hardness and the higher the strength, but the lower the ductility.

SAE certification
The American Society of Automotive Engineers (SAE), founded in 1905, is the world’s largest academic organization of automotive engineering. The research objects are cars, trucks and engineering vehicles, airplanes, engines, materials and manufacturing. The standards formulated by SAE are authoritative, widely used by the automotive industry and other industries, and quite a few are adopted as US national standards.

The SAE motor vehicle standard is a technical standard for the locomotive industry. American Society of Automotive Engineers (SAE) certification: sets standards for automotive parts (SAE certification) sold on the market. These parts are not sold in bulk as a supplier.

SAE 8620 corresponds to the national standard 20CrNiMo. This steel is suitable for processing gears and has a better hardenability.
American standard 8620 is alloy structural steel.

Alloy structural steel is generally divided into quenched and tempered structural steel and case hardened structural steel.

1. Quenched and tempered structural steel: The carbon content of this type of steel is generally about 0.25% to 0.55%. For structural parts of a given cross-section size, when quenched and tempered during quenching and tempering, mechanical properties The performance is good. If the ferrite is not hardened and the free ferrite appears in the microstructure, the toughness will decrease.

For steels with a tendency to temper brittleness, such as manganese steel, chrome steel, nickel-chromium steel, etc., they should be cooled quickly after tempering. The quenching critical diameter of this type of steel increases with the increase in grain size and alloying element content. For example, 40Cr and 35SiMn steels are about 30 to 40mm, while 40CrNiMo and 30CrNi2MoV steels are about 60 to 100mm. Structural components such as shafts and connecting rods with large loads.

2. Surface-hardened structural steel: Used to make hard and wear-resistant components on the surface, such as gears, shafts, etc. In order to make the core toughness of the part high, the carbon content in the steel should be low, generally 0.12 to 0.25%, and there should also be a proper amount of alloying elements to ensure proper hardenability. Nitrided steel also needs to add alloying elements (such as Al, Cr, Mo, etc.) that are easy to form nitrides. After carburizing or carbonitriding steel, after carburizing or carbonitriding at 850 ~ 950 ℃, it is quenched and used under low temperature tempering (about 200 ℃). Nitrided steel is subjected to nitriding treatment (480 ~ 580 ℃) and used directly without quenching and tempering treatment.