How to deal with aging of multi-purpose carburizing furnace?

How to deal with aging of multi-purpose carburizing furnace?

The aging of nitrile furnace means that after the nitriding tank is used for a long time, the decomposition rate of ammonia in the furnace increases significantly, resulting in partial loss of nitriding capacity. Its essence is that the tank wall (including the ammonia tube in the furnace) increases ammonia consumption due to the catalytic effect of ammonia decomposition rate, and may even make nitriding out of control, and nitriding products can not meet the technical requirements. How to deal with aging of multi-purpose carburizing furnace?

General household carburizing multi-purpose furnace and ammonia pipe are 18-8ti stainless steel. The passivation film on the surface of the new nitriding tank will prevent the penetration of nitrogen, but due to the low nickel content of 18-8ti, there will still be penetration (penetration is generally slower and uneven). With the increase of the number of carburizing multipurpose furnace and nitriding time, the inner wall is nitriding gradually. Under the same process, temperature, time and load, the decomposition rate of ammonia increases gradually. In order to ensure the nitrogen potential NP required for the process, nitrogen removal is required. The basic law of furnace life is that the flow rate in the furnace increases from slow to fast to uncontrollable NP stage in a certain time. According to the actual production data of a furnace, the loading capacity of the furnace is very different from the loading capacity specified by the equipment.

Therefore, the influence of the workpiece on the ammonia decomposition rate is the main factor, and the furnace suction gradually slows down, reflecting the actual situation. As we all know, the lower the ammonia decomposition rate, the higher the np, and the stronger the nitriding ability. However, it should be noted that the nitrogen atoms produced by the decomposition of ammonia molecules are very active. If not absorbed, it will bind with stable nitrogen molecules at a very fast rate, but the steel surface cannot be absorbed. When the ammonia decomposition rate is high, that is, the smaller the proportion of ammonia in the atmosphere, that is, the smaller the ammonia concentration, the fewer the number of ammonia molecular contact plates, the fewer nitrogen atoms, and the lower the nitridation capacity. The higher the ammonia decomposition rate, the higher the hydrogen concentration in the furnace, and the absorption of nitrogen atoms will be affected. If the atmosphere is full of ammonia, that is, the decomposition rate is zero, and no nitrogen atoms are formed, then nitridation must not exist.

Therefore, a reasonably low decomposition rate will inevitably lead to a rapid increase in ammonia consumption, the impact of air flow on the workpiece will lead to temperature imbalance and uncontrollable, resulting in uneven deformation of the workpiece and layer, and even some people will cause difficulties in nitride control. The decomposition rate and NP are also controlled by the composite layer. Under reasonable nitriding conditions, the nitriding rate can be improved.