Zhengzhou Gou's electromagnetic induction heating equipment m

The gas nitrogen carbon treatment of the workpiece is to improve the surface hardness, wear resistance and fatigue resistance of the surface layer of the workpiece, while also having good anti-seize and corrosion resistance. It can be seen that gas nitrocarburizing treatment is an important process in the heat treatment of workpieces. What defects will occur during the gas nitrocarburizing process of the X60 milling machine table lifting screw? How should we solve it? Let's wait and see.

1. Causes of red or rusty spots on the surface of the workpiece:

a. The workpiece comes out of the furnace at too high a temperature and is oxidized in the air. The workpiece is cooled in the furnace to below 200°C and then cooled out of the furnace, or oil-cooled. The remedial measures: clean the workpiece after rust removal, and then process it according to the normal nitrocarburizing process.

b. There is too much water in the penetrating agent used, which is caused by the failure of the liquid ammonia desiccant. Dehydrate the penetrating agent and replace it with a new desiccant.

c. During the falling process of urea, it adheres to the workpiece; we should pay attention to the position of the workpiece in the furnace and avoid the blanking port.

2. The reason for the appearance of troostite structure on the surface of the workpiece: oxidation of alloy elements on the surface of the workpiece.

Precaution:

a. Improve the sealing of the furnace, accelerate exhaust, control the content of furnace gas components, and ensure the nitrogen concentration of the infiltration layer.

b. Speed up the stirring of the quenching cooling medium or change the medium, and use tungsten-molybdenum steel with low oxidizing tendency.

3. Causes of large deformation of the workpiece and preventive measures:

a. The residual stress of mechanical processing (such as turning or grinding, etc.) is too large, and stress relief annealing is not performed before co-penetration or the annealing is insufficient; in view of the defect of large residual stress, we should perform stress relief treatment after rough machining. It is (590~620)℃×(2~3)h, which should be higher than the normal nitrocarburizing temperature.

b. The ammonia gas circulation is not smooth, the furnace is improperly installed and the furnace is installed properly. Overlapping pressure is not allowed when installing the furnace. It should be conducive to the circulation of gas in the furnace and the fan should operate normally.

c. The cooling rate after co-infiltration treatment is too fast. Select the cooling medium or reasonably control the cooling speed according to the requirements

d. The temperature inside the tank has poor uniformity; we should formulate a heat treatment process to slowly heat up or heat in stages. Above 300°C, keep the temperature for 1 hour for every 100°C increase, and control the heating and cooling rates to ensure uniform furnace temperature.

e. The workpiece is heated too fast, and the temperature difference between the inside and outside of the complex workpiece is too large, resulting in increased thermal stress.

f. The workpiece is large in size, complex in shape and cross-section, is not hung or placed vertically, and is affected by the workpiece’s own weight; improve the design, pay attention to the center of gravity when hanging, and place it stably and firmly.

g. If the workpiece is asymmetrical or partially treated, we can use bundling, filling or other methods to maintain the uniform symmetry of the workpiece, or remove the hardened layer after co-penetration.

4. The brittleness of the infiltration layer is caused by: the supply of ammonia is too large, and the nitrogen concentration on the surface of the infiltration layer is too high to form a large number of shell-like nitrogen and carbon compounds. Preventive measures: increase the co-infiltration temperature and reduce the supply of ammonia.

5. Causes and preventive measures for the loose surface of the workpiece seepage layer:

a. It is mainly caused by the high nitrogen content on the surface of the infiltration layer; therefore, we must strictly control the amount of ammonia.

b. The raw materials used are deoxidized with aluminum, which is prone to such defects. We must correctly choose raw materials that meet the requirements.

c. Too high co-infiltration temperature or too long time can also cause it; we should correctly formulate and implement co-infiltration process parameters, especially reasonably control the co-infiltration temperature and time.

6. Causes of excessive residual austenite in the carburized layer:

a. The co-infiltration temperature is too high and the carbon concentration is too high; to address this cause of defects, we should adjust the furnace temperature and carbon potential of the atmosphere.

b. The co-infiltration temperature is too low and the nitrogen concentration is too high. Adjust the furnace temperature and ammonia supply amount.

7. Causes of surface spots:

a. The workpiece is not cleaned before co-infiltration; we should clean the workpiece before entering the furnace.

b. The workpieces are in contact with each other, or with fixtures, tooling, etc. For this reason, we should install the furnace reasonably to ensure that there is a certain gap between the workpieces.

8. The hardness is low and the seepage layer is shallow. Causes and measures:

a. The cross-sectional size of the workpiece is too large or the furnace installation is unreasonable; we can prevent this defect by changing the design, installing the furnace reasonably, and improving the fluidity of the atmosphere in the furnace.

b. The furnace tank is leaking or the pressure in the furnace is low. We should check the equipment regularly to ensure the sealing performance of the equipment.

c. The co-infiltration time is short or the temperature is too low; select the correct co-infiltration temperature and time, and re-perform the co-infiltration treatment.

d. Surface roughness of the workpiece; the workpiece should be inspected to ensure that the surface roughness of the workpiece is controlled below the specified range.

e. There is insufficient nitrogen potential in the furnace atmosphere

f. The cooling speed after infiltration is low; the disadvantage of low speed is to increase the cooling speed appropriately.

g. Improper selection of raw materials. We should select materials reasonably to ensure that the co-penetration quality meets technical requirements. Remedy: Re-process according to the normal nitrocarburizing process.

h. There is cutting fluid adhesion or rust on the surface of the workpiece, and the surface is decarburized; the workpiece should be cleaned thoroughly, no traces of cutting fluid and rust should be left, and the decarburized layer should be removed.

i. The nitrogen potential and carbon potential on the surface of the workpiece are low, the nitrogen content of the carburizing layer is too low, and the gas circulation in the furnace is poor.

The gas nitrocarburizing process is widely used. Workpieces made of alloy structural steel, non-alloy structural steel, alloy tool steel, etc. can be nitrocarburized. Precisely because it has so many applications, it is helpful and necessary to understand some common defects and prevention methods of nitrocarburizing in heat treatment for heat treatment work.