What are the common materials and properties of shaft-type forgings?

Gear shaft manufacturers remind: The material of gear shaft forgings must first meet the requirements of working conditions. The requirements of working conditions are the factors that should be considered first when selecting gear forging materials. Alloy steel is commonly used to make gear forgings that work under high speed, heavy load, and impact loads, such as gears used in aircraft, which must meet the requirements of low weight, high power transmission, and high reliability. Therefore, high-performance alloy steel must be selected. If the gear size needs to be as small as possible, high-strength alloy steel with surface hardening treatment should be used. In mining machinery, gear transmission generally has a large power, low working speed, and high dust content in the surrounding environment, so materials such as cast steel or cast iron are often chosen. Household and office machinery has very low power requirements but requires smooth transmission, low noise or no noise, and the ability to work normally under little or no lubrication, so engineering plastics are often selected as gear materials.

When selecting materials for gear shaft forgings, factors such as gear size, blank forming method, and heat treatment process should be considered. Large-sized gears generally use cast blanks, and cast steel or cast iron can be selected as gear materials. Medium or smaller-sized gears with higher requirements are often made from forged blanks, and forged steel can be chosen. For smaller sizes with lower requirements, round steel can be used as the blank.

The deformation of forging dies during heat treatment is mainly caused by various reasons such as cracking, cracks, and deformation. Cracking may be caused by the inherent quality of the steel, with various reasons such as coarse original structure, excessively high quenching temperature or prolonged holding time, tempering in the tempering brittleness zone, low tempering temperature or insufficient tempering time.

(1) Cracking

1. Cracking caused by the inherent quality of the steel: Strictly control the inherent quality of the steel.

2. Coarse original structure: Improve the structure through appropriate pre-heat treatment.

3. Excessively high quenching temperature or prolonged holding time: Correctly master the heating treatment to improve the structure.

4. Tempering in the tempering brittleness zone: Try to avoid tempering in the tempering brittleness zone.

5. Low tempering temperature or insufficient tempering time: Select appropriate tempering processes.

(2) Cracks

1. Raw materials have microscopic cracks: Strictly control the inherent quality of raw materials.

2. Improper heat treatment operation (heating speed too fast, improper cooling agent selection, excessive cooling time): Pay attention to preheating and select appropriate cooling agents.

3. Special mold shapes, uneven thickness, sharp corners, and threaded holes: Block threaded holes, fill sharp corners, wrap dangerous sections and thin walls, and adopt graded quenching.

4. Re-quenching without intermediate annealing: When repairing or refurbishing molds, annealing or high-temperature tempering must be performed.

5. Failure to temper in time after quenching: Temper in time.

6. Insufficient tempering: Ensure tempering time, and alloy steel should be tempered the required number of times.

7. Improper grinding operation: Choose the correct grinding process.

8. During electrical discharge machining, high tensile stress and microscopic cracks exist in the hardened layer: Improve the electrical discharge machining process; perform stress relief tempering; remove the hardened layer using electrolysis, corrosion methods, or other methods.

(3) Deformation

1. Presence of carbide segregation and accumulation in the steel: Choose appropriate forging processes.

2. Low hardenability steel used for large forging dies: Correctly select suitable forging steel.

3. Surface decarburization or failure to remove the surface decarburized layer during machining: Pay attention to heating protection and salt bath deoxidation.

4. Excessively high quenching temperature and insufficient heating time: Strictly control the quenching process.

5. Insufficient moisture in the alkaline bath: Strictly control the moisture in the alkaline bath.

6. Insufficient residence time in the coolant: Increase residence time.

7. Excessively high tempering temperature: Choose an appropriate tempering temperature.