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Precautions for the carburizing process and diffusion process stage of the pit furnace

Industry news
Release time:
2019/10/29 15:15
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After the temperature of the well furnace reaches the carburizing temperature, record the temperature to the temperature, change the amount of carburizing agent
Carburizing stage:        
1. After the temperature of the well furnace reaches the carburizing temperature, record the temperature to the temperature, change the amount of carburizing agent, continue to keep the exhaust gas for 30~45min, and take the gas analysis. When the volume fraction of the CO2 in the furnace gas is <0.5%, it will enter the infiltration. In the carbon stage, change the amount of osmotic agent to drop, close the venting hole, make the length of the burning flame reach 100~150mm, the burning flame is bright yellow, no bright Mars is thrown out, open the U-type pressure gauge, so that the furnace pressure is controlled at 250~400Pa
2. Two external samples are placed from the outer sample hole. The outer sample is placed in a depth of 100~200mm from the furnace. The outer test bar hole is tightly packed with asbestos rope to prevent air leakage and heat dissipation.
3. Check the temperature of the well furnace and the pressure of the furnace to check the drop amount of the drops every 15 minutes. The fluctuation range shall not exceed ±5 drops/min of the specified value, and the carburizing atmosphere shall be analyzed, and the values ​​of CO2, H2O and O2 in the atmosphere shall be strictly controlled. When methanol or kerosene is used as the osmotic agent, the composition of the furnace gas is controlled at:
ФCnH2n+2 ФCnH2n ФCO ФH2 ФCO2 ФO2 ФN2
5~15 ≤0.5 15~25 40~60 ≤0.5 ≤0.5 balance
4. The gas potential of the well furnace gas in the strong infiltration stage can be higher than 0.2%~0.4% of the mass value of the required surface carbon.
Diffusion stage:
  1. The percolation rate in the strong infiltration stage can be estimated from 0.15~0.25mm/h, the lower limit of the low carbon steel is taken, and the upper limit of the chrome molybdenum steel is taken. When the carbonization layer is estimated to reach the middle and lower limits of the technical requirements, an external test rod is obtained. Based on the mass of the outer layer and the mass fraction of the surface carbon, it is determined whether or not the diffusion amount and the amount of the osmotic agent at the time of diffusion can be entered. For workpieces that do not need to be diffused, you can start cooling down
  2. When diffusing, the carburizing gas is reduced, and the amount of shielding gas is increased. The diffusion time is in principle 1/3~1/4 of the infiltration time and the carbon steel is 1/4~1/5, but the specific situation is analyzed.
3. The furnace pressure during the diffusion period is generally controlled at 50~100Pa.
4. The carbon potential of the furnace gas is slightly higher than the lower limit of the surface carbon concentration (mass fraction) value specified by the technical requirements.
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