Source: Internet Release Date: 2007/4/9
Nitriding of steel
XNUMX. Process factors affecting the quality of nitriding
1. As the temperature increases, the surface hardness of the nitrided parts decreases and the deformation of the parts increases; if the temperature is too low, the nitriding speed is very slow.
2. When the time and temperature are constant, the depth of the nitriding layer depends on the nitriding time.The alloying elements in the steel have an effect on the diffusion rate of nitrogen in the steel, so the time required for different types of steel is different, and it needs to be determined by specific experiments.
3. The influence of ammonia decomposition rate during nitriding, the ammonia decomposition rate (nitrogen and ammonia mixed gas in the furnace gas volume percentage) should be controlled within a certain range. At different temperatures, the reasonable range is as follows:
Nitriding temperature ℃ 500 510 525 540 600
Ammonia decomposition rate% 15-25 20-30 25-35 35-50 45-60
38. Preliminary heat treatment before nitriding (take XNUMXCrMoAlA as an example)
调质：950±10℃淬油，620-680℃回火，硬度241-285HBS
Three, gas nitriding
1. Process operation
①Prepare heat treatment for nitriding workpiece.Carry out anti-seepage treatment on parts that do not need nitriding (see the table below for details).Prepare the furnace sample that meets the requirements
②When installing the furnace, the harmful substances on the surface of the workpiece should be cleared, and the furnace should be installed steadily and firmly, paying attention to the distance.Put 3-10 samples in different positions to facilitate quality inspection
③Debug and check whether the pipeline is unblocked, whether the circuit and instrument are normal
④ During the nitriding operation, the ammonia gas is passed to drive the air in the tank and the temperature rises slowly.Gradually increase the amount of ammonia and maintain a positive pressure in the furnace.After rising to the specified temperature, the furnace pressure is maintained at 780-1960Pa.Control the ammonia decomposition rate to the specified range.
In order to ensure the stability of the ammonia decomposition rate in the furnace, the furnace and the spreader are regularly denitrogenated after use
2. Anti-nitriding coating and coating
Coating or paint Thickness mm Remarks
Tin plating 0.004-0.006 The thickness must be strictly controlled. If the tin is thick, the protection effect is not good if the tin is thin.
Copper plating 0.02-0.03 Long electroplating cycle, mainly used for stainless steel and heat-resistant steel
Nickel plating 0.02-0.04 high plating cost
Water glass 0.4 The workpiece is preheated to 70-90℃, repeated coating 2-3 times
Water glass+10%-20% graphite 0.5-1 Preheat the workpiece to 150℃, and repeat coating 2-3 times
3. Gas nitriding process (take 38CrMoAlA as an example)
Steel number serial number process specification infiltration layer
depth
mm surface hardness
Stage Temperature ℃ Time h Ammonia Decomposition Rate%
38CrMoALA 1 I 510±10 17-20 15-35 0.2-0.3 ≥550HV Boring bar
2 I 530±10 60 20-50 ≥0.45 65-70HRC boring bar
3 I 540±10 10-14 30-50 0.15-0.3 ≥88HR15N boring bar
4 I 495±5 15 18-30 0.41-0.43 988-1048HV screw
II 525±5 7 80-100
5 I 495±5 63 18-40 0.58-0.65 974-1026HV gear
II 525±5 5 100
6 I 495±5 17 18-25 0.53-0.57 988-1048HV gear
II 545±5 34 50-75
7 I 525±5 20 25-35 0.35-0.55 ≥90HR15N axis
II 540±5 10-15 35-50
8 I 520±5 19 25-45 0.35-0.50 87-93HR15N-
II 600 3 100
9 I 495±5 63 18-40 0.58-0.65 974-1026HV
II 525±5 5 100
10 I 510±10 20 15-35 0.50-0.75 ≥750HV gear
Crankshaft
II 560±10 34 35-65
III 560±10 3 100
