Precision Carburizing Heat Treatment of Gears and Requirements For Control Accuracy

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1. Precision carburizing heat treatment requirements

(1) The precision heat treatment of gear includes the microstructure, hardness, effective hardening depth, residual stress of carburized layer, and the quality dispersion of tooth profile and tooth direction.

(2) Basic conditions required for precision heat treatment of gears

① Material uniformity. The material is required to have good composition and organizational uniformity, that is, including the consistency of material hardenability. The fluctuation of material hardenability will inevitably lead to the dispersion of microstructure, hardness and deformation after heat treatment. The composition uniformity of advanced steelmaking has strict internal control indicators, and the composition uniformity expressed in carbon equivalent can reach ±(0.01%~0.02%) stably.

② Well-distributed temperature field and fluid field (including carburizing, nitriding, carbonitriding airflow field and quenching liquid fluid field).

2. Precision carburizing heat treatment control accuracy requirements

(1) Temperature control accuracy

GB/T 9452 puts forward different requirements for the temperature control accuracy and the maximum allowable deviation of the temperature in the furnace according to 6 types of heating furnaces. Generally, the heating furnace for the final heat treatment should meet the requirements of Class I to III, that is, the maximum allowable deviation from the furnace temperature is ±3 °C, ±5 °C and ±10 °C, and the corresponding control accuracy is ±1.0, ±1.5 and ±5.0. The accuracy class is not lower than 0.25, 0.3 and 0.5.

(2) Carburizing atmosphere control accuracy

The use of oxygen probes as sensors and various types of carbon control instruments, as well as databases and process software suitable for various steels and different carburizing processes can realize timely control at the moment of the process, so that the carbon content on the surface of the steel can be controlled within ± Within the range of 0.03% to ±0.05%, the depth of the seepage layer is controlled within the range of ±0.1mm.
Precision carburizing heat treatment technology

(1) Control accuracy requirements. The furnace temperature control accuracy is ≤±1℃, the multiple points in the effective heating zone are ≤±5℃, the carbon potential of the carburizing furnace gas is controlled at ≤±0.05%, and the carburizing layer depth fluctuates ±0.1mm. Therefore, under continuous production conditions, furnace temperature uniformity and effective heating area measurements should be carried out according to GB/T 9452 at least twice a year.

(2) Quality online control. The precise and sensitive sensor control system can be used to accurately control the quality of heat-treated workpieces online, so as to achieve a 100% pass rate.

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