Common Materials And Properties of Shaft Forgings

Core Tip: Shaft forgings are a widely used type of forging. This type of shaft has good machining performance. In practical applications, it has no porosity or other defects, so it not only has good shaft forgings are a widely used type of forging. This type of shaft has good machining performance. In practical applications, it has no porosity or other defects, so it not only has a good appearance guarantee, but also has excellent performance. Let's introduce shaft forgings that meet the requirements to be popular among people.

There are various types of gear shaft forgings. The commonly used materials for gear forgings include 40Cr, 42CrMo, 20CrMnMo, and 20CrMnTi. 42CrMo and 40Cr forged gears are mostly large gear forgings in the lifting industry, while 20CrMn molybdenum and 20CrMnTi are mostly used for forging gears in transmission machinery, without main small parts (reference). Most gears require gear lifting. The heat treatment hardness of the gear reaches good performance at 38-42HRC. The toughness of 42CrMo is much better than that of 40Cr because the former has good heat treatment hardenability, which is closely related to its material. Similarly, the strength under the same hardness is very similar. Under good performance, the tensile strength of 40Cr is 60-75kg/mm2, and the yield strength is 35-55kg/mm2; The tensile strength of 42CrMo is 110kg/mm2, and the yield strength is 95kg/mm2. The performance is much better than 40Cr.

40Cr material has good hardenability. Water quenching can harden to a diameter of 28-60mm, while oil quenching can harden to a diameter of 15-40mm. After quenching and tempering, the material has good comprehensive mechanical properties, with good low notch sensitivity and low-temperature impact toughness. 40Cr gear forgings are usually subjected to surface high-frequency quenching or nitriding treatment after quenching and tempering. When the hardness is between 174~229HBS, the machinability is good, with a relative machinability of 60%. The carbon content of 40Cr material forgings is maintained at around 0.40%, which ensures 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 and heating, the chromium element is completely dissolved in the austenite, which improves the hardenability of the steel. After quenching, the Cr element solid solution strengthened the matrix structure and improved the tempering stability of the matrix structure. During high-temperature tempering, some Cr elements diffuse from the matrix structure to 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, ≤ 0.035% P, ≤ 0.035% S.

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

The initial forging temperature of 40Cr gear forgings is 1100~1150 ℃, and the forging temperature is 800 ℃. After forging, sizes above 60mm require slow cooling.

Gear shaft manufacturers remind that the material of gear shaft forgings must first meet the requirements of the working conditions. When selecting gear forging materials, the requirements of working conditions should be considered first. Alloy steel is commonly used to manufacture gear forgings that work under high-speed, heavy-duty, and impact loads. High reliability is required, therefore alloy steel with high mechanical properties must be selected. If the gear size is required to be as small as possible, high-strength alloy steel that has undergone surface hardening treatment should be used. Gear transmission in mining machinery usually 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 with little or no lubrication. Therefore, engineering plastics are often used as gear materials.