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Heat treatment deformation process for controlling thin wall sleeve of coal mine excavator loader
The thin-walled sleeve is a critical component in coal mine excavator loaders, subjected to significant impact and friction during operation. Its performance and durability are heavily influenced by the quality of heat treatment and its geometric accuracy. Due to the thin wall structure, it's particularly prone to deformation during heat treatment, making the process more complex and challenging.
To address this, an optimized heat treatment plan was developed through detailed analysis and testing. This approach effectively controls deformation, ensuring the part meets required specifications and maintains long-term reliability. The technical parameters vary depending on the material used:
- **42CrMo**: Quenched to a surface hardness of 45–50 HRC.
- **38CrMoAlA**: Undergoes quenching and tempering followed by nitriding, achieving a core hardness of 240–280 HBW, a nitride layer depth of 0.2–0.4 mm, and a surface hardness of 970–1100 HV.
The heat treatment process includes pre-treatment, aging, and final hardening. Pre-heat treatment involves quenching and tempering to refine the microstructure and improve machinability. Aging is performed after semi-finishing to relieve cutting stresses and prevent oxidation. For 42CrMo, the quenching temperature is set at 850°C, while 38CrMoAlA undergoes ion nitriding to minimize distortion.
During the test phase, real parts were processed under controlled conditions. Material defects were minimized through repeated forming. Quenching temperatures were carefully selected based on Ac3 values, and cooling was managed to reduce stress and distortion.
Geometric control was strictly maintained. Before quenching, the outer diameter of 42CrMo sleeves was kept within φ99.23–φ99.25 mm, and for 38CrMoAlA, it was φ99.90–φ99.95 mm.
Post-treatment inspections showed minimal deformation: ≤0.12 mm for 42CrMo and ≤0.06 mm for 38CrMoAlA. Hardness met specifications, with 42CrMo showing 47–49 HRC and 38CrMoAlA reaching 987–1003 HV. Metallographic analysis confirmed a fine tempered martensite structure in 42CrMo and a small amount of nitride in 38CrMoAlA.
In conclusion, proper heat treatment is essential for thin-walled components. Quenching and tempering help eliminate forging stress, while nitriding offers high hardness with minimal distortion, making it ideal for high-performance applications.