Common materials and properties of shaft forgings

2024-08-14 15:44:56

Shaft forgings are a widely used type of forging, which also have excellent processing performance. In practical applications, they have no porosity or other defects, so they not only have a good appearance guarantee, but also excellent quality. Below, we will introduce what kind of shaft forgings that meet the requirements are popular among people.

There are many types of materials for Gear shaft forgings, and the commonly used materials for gear forgings are: 40Cr, 42CrMo, 20CrMnMo, 20CrMnTi, etc. 42CrMo and 40Cr forged gears are mostly used in the lifting industry for large-sized gear forgings, while 20CrMnMo and 20CrMnTi are mostly used for forging gears in transmission machinery, and small parts have no owner (reference). Most gears require gear lifting, and the heat treatment hardness of gears between 38-42HRC can achieve optimal performance. 42CrMo has much better toughness than 40Cr because the former has good heat treatment hardenability, which is closely related to its material. Also, the strength under the same hardness is very similar. The tensile strength of 40Cr with excellent performance is 60-75 kg/mm2, and the yield strength is 35-55 kg/mm2; The tensile strength of 42CrMo is 110 kg/mm2, and the yield strength is 95 kg/mm2. Obviously, the performance of 42CrMo is much better than that of 40Cr.

40Cr material has good hardenability, which can be quenched to a diameter of 28-60mm when quenched in water and 15-40mm when quenched in oil. After quenching and tempering treatment, the material has good comprehensive mechanical properties, as well as good low notch sensitivity and low-temperature impact toughness. After quenching and tempering treatment, 40Cr gear forgings are often subjected to surface high-frequency quenching or nitriding treatment. When the hardness is 174-229HSS, the cutting performance is good, with a relative cutting performance of 60%. The carbon content of 40Cr material forgings is maintained at around 0.40%, ensuring that the steel has a good combination of strength and toughness. The addition of Cr element is mainly to improve the hardenability of steel. During quenching heating, the Cr element is completely dissolved in the austenite, improving the hardenability of the steel. After quenching, Cr element solid solution strengthens the matrix structure and improves the tempering stability of the matrix structure. During high-temperature tempering, some Cr elements diffuse from the matrix structure into the precipitated cementite Fe3C, forming alloy cementite (Cr, Fe) 3C.

The main chemical composition (mass fraction) of 40Cr steel used for gear shaft forgings produced by gear shaft manufacturers is: 0.37%~0.44% C, 0.17%~0.37% Si, 0.50%~0.80% Mn, 0.80%~1.10% Cr, ≤ 0.035% P, ≤ 0.035% S.

Its phase transition points are: Ac1770 ℃, Ac3805 ℃, Ms328 ℃.

The initial forging temperature of 40Cr gear forgings is 1100~1150 ℃, and the final forging temperature is 800 ℃. After forging, the size above 60mm needs to be slowly cooled.

Gear shaft manufacturers remind that the material of gear shaft forgings must first meet the requirements of working conditions. The requirements for working conditions are factors that should be considered when selecting gear forging materials. Alloy steel is commonly used to make gear forgings that work at high speeds, heavy loads, and under impact loads. For example, gears used in aircraft must meet the requirements of low quality, high power transmission, and high reliability. Therefore, it is necessary to choose alloy steel with high mechanical properties. If the gear size is required to be as small as possible, high-strength alloy steel with surface hardening treatment should be used. Gear transmission in mining machinery generally has high power, low working speed, and extremely high dust content in the surrounding environment, so materials such as cast steel or iron are often chosen. The power of household and office machinery is very small, but it requires smooth transmission, low or no noise, and can work normally in a state of little or no lubrication. Therefore, engineering plastics are often used as gear materials.

The selection of gear shaft forging materials should consider the size of the gear, the blank forming method, and the heat treatment process. Large sized gears are generally made of cast blanks, and cast steel or iron can be used as gear materials. Gears with high requirements for medium or below size are often made of forged blanks and can be made of forged steel. When the size is small and the requirements are not high, round steel can be used as the blank.