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Quality control of gas carbonitriding process

The quality control of the gas carbonitriding process is actually to control the carbonitriding potential of the gas carbonitriding process. It is easier to control the carbon and nitrogen potential in furnaces equipped with automatic control devices, but it is more difficult for most factories that do not have automatic control conditions and produce many varieties.

1.Temperature control

The co-infiltration temperature is generally 820~880C. The higher the temperature, the faster the penetration rate, the greater the deformation, and the weaker the nitriding effect. The lower the temperature, the opposite effect occurs. When the temperature is lower than 820C, the kerosene cracking rate becomes significantly smaller and carbon black is easily formed, affecting the quality of co-penetration. The specific temperature value should be determined according to the structural shape and performance of the workpiece. For workpieces requiring good comprehensive performance, the mid-upper limit (850~880°C) should be selected, and for complex parts or thin-walled parts that are easily deformed, the mid-lower limit (820~850°C) should be selected.

2.Time control

Once the co-infiltration temperature has been determined, the co-infiltration time mainly depends on the depth requirements of the co-infiltration layer. For workpieces requiring shallow depth, the co-penetration time is relatively short.

3.Furnace capacity control

The furnace charge for gas chemical heat treatment should be measured according to the total surface area of the furnace workpiece. The larger the surface area, the more penetration agent needs to be added to maintain a more stable carbon-nitrogen potential and penetration rate. The structure and shape of the workpiece are different, and the surface area is greatly different. Under the same weight, the surface area ratios of spheres, columns, square strips, and plates range from 1:1.14:1.125 to 10. Several main cooperative light textile parts such as pedal shafts, shaft bowls, shaft blocks, and guides The surface area ratio of the yarn disc is 1:4.9:3.3:6.8. It can be seen that for the same furnace weight, the surface area varies greatly due to different types of workpieces. In order to prevent the furnace loading amount from being too large or too small, causing the penetration amount to be too large or too small, affecting normal co-penetration, the furnace loading volume should be determined according to the specific workpiece.

4.Oil dripping amount control

The amount of oil dripping mainly depends on the furnace type and workpiece surface. If the amount of oil dripping is too large, carbon black will be deposited on the surface of the workpiece, which will affect the co-penetration quality; if the amount of oil dripping is too small, there will be too few active atoms, which cannot meet the needs of absorption and diffusion on the surface of the workpiece, resulting in a reduction in surface carbon concentration and a slowdown in the penetration rate. The number of kerosene drops in the co-penetration stage can be obtained from D=KS. In the formula, D represents the number of kerosene drops (drops/min), and S represents the total surface area of the workpiece (m²).

5.Ammonia flow control

Ammonia not only serves as a nitriding agent that provides nitrogen atoms, but also plays a role in promoting infiltration (surface purification) in the co-infiltration process. Too little ammonia flow will increase carbon black, slow down the penetration rate, and reduce nitrogen concentration. Excessive ammonia flow will reduce the carbon concentration, intensify oxidation, and form brittle nitrides on the surface of the workpiece. The amount of ammonia flow can be determined based on the amount of kerosene cracking gas in the dripping furnace. For kerosene penetrating agents with high carbon potential, the ammonia flow rate can be appropriately increased, and the ammonia flow rate during the co-infiltration stage can be 60% of the kerosene cracked gas flow rate.