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Ion Nitriding vs Gas Nitriding

Nitriding refers to a surface treatment technology in which nitrogen exists in the surface layer of the processed workpiece in the form of iron compounds and interstitial solid solutions at a temperature not higher than A1, so as to improve the hardness of the surface layer and improve the wear resistance of the material. At present, the nitriding processes commonly used in industrial production include ion nitriding, gas nitriding and soft nitriding.

Process introduction

(1) Ion nitriding

Put the workpiece as the cathode into the negative pressure container of nitrogen-containing gas, electrify the nitrogen-containing medium to ionize into nitrogen ions, and under the action of a strong electric field, the nitrogen ions bombard the surface of the workpiece, absorb and diffuse into the surface of the workpiece, thus obtaining excellent surface properties.

(2) Gas nitriding

The gas nitriding process is to place the workpiece in a sealed container, pass through the flowing ammonia-containing gas, and heat it to a certain temperature, so that the ammonia gas is heated to decompose into active nitrogen atoms, and then adsorbed to the surface of the workpiece and diffused into the surface of the workpiece. Thereby changing the chemical composition and organization of the surface layer to obtain excellent surface properties.

(3) Nitriding

Soft nitriding is also called nitrocarburizing. In addition to nitrogen, there is also a small amount of carbon in the co-infiltration medium of soft nitriding. They undergo thermal decomposition reactions at high temperatures to produce activated carbon and nitrogen atoms, making the surface of the workpiece in the main When nitrogen is infiltrated, carbon is also infiltrated. The carbides formed after carbon infiltration can promote the diffusion of nitrogen and accelerate the formation of high-nitrogen compounds. These high-nitrogen compounds can in turn increase the solubility of carbon. In addition, carbon in nitrides reduces brittleness.

Advantages and disadvantages

(1) Production efficiency: Due to the sputtering effect of high-energy nitrogen ions on the surface of the workpiece, ion nitriding activates the surface, accelerates the infiltration speed of nitrogen ions, and has the highest production efficiency. Activated carbon and nitrogen atoms in nitrocarburization can accelerate the mutual infiltration speed of the two, and the production efficiency is high. However, the gas nitriding time is longer and the production efficiency is lower.

(2) Environmental hazards: Both gas nitriding and soft nitriding will produce a certain amount of undecomposed ammonia gas, which needs to be treated by cracking and incineration, otherwise it will pollute the environment; while ion nitriding uses ionized Nitrogen-containing gas, and the nitriding pressure is low, the gas consumption is small, and the amount of undecomposed ammonia gas discharged is small (if the mixed gas of nitrogen and hydrogen is used as the nitrogen source, no toxic tail gas will be produced), and the impact on the environment is small. However, it is also necessary to treat the tail gas by adsorption and other methods.

(3) Nitriding layer control: Ion nitriding can control the structure of the surface compound layer and diffusion layer by adjusting the composition of the nitriding atmosphere, air pressure, electrical parameters, temperature and other factors.

(4) Nitriding effect: Compared with gas nitriding, the deformation of the workpiece in soft nitriding is small, the brittleness of the carburized layer is small, but the hardness is low; the deformation of the workpiece in ion nitriding is extremely small, and the carburized layer is hard and thick.

(5) Production cost: Compared with gas nitriding, ion nitriding and soft nitriding consume less energy, have a higher utilization rate of nitriding media, and lower production costs.

(6) Scope of application: The nitriding efficiency of gas nitriding is low, and it is widely used in steel materials containing nitriding elements such as Al, Cr, and Mo. However, ion nitriding and soft nitriding have a wide range of applications, and can also be used on the surface of stainless steel, low alloy steel and other materials.

(7) Equipment investment: The equipment for gas nitriding and soft nitriding is relatively simple, and the investment in equipment is small. Difficulty of operation: The process of ion nitriding is relatively complicated, and the requirements for workers’ operation skills are relatively high.

Practical application

(1)Die-casting steel SDDVA, the matrix hardness is 47±1HRC, after gas nitriding treatment or soft nitriding treatment, the infiltrated layer structure without white and bright layer can be obtained, and the infiltrated layer thickness is greater than 0.14mm, which greatly improves the quality of SDDVA steel. resistance to thermal fatigue cracking.

Microstructure of SDDVA steel after nitrocarburization

(2)SDCM for hot stamping, the hardness of the substrate is 53±1HRC, after ion nitriding treatment, the infiltrated layer structure with a white layer thickness of 12μm and a diffusion layer thickness of 250μm can be obtained, and the surface hardness reaches 1023HV0.2, which is greatly improved By improving the wear resistance of SDCM steel, the predicted service life can be increased from 168849 pieces without nitriding to 336394 pieces.

Diagram structure of SDCM steel after ion nitriding

Summarize

Therefore, according to different service conditions, we need to adopt different nitriding treatment processes. When the die-casting mold adopts gas nitriding (or soft nitriding), it is necessary to strictly control the nitrogen potential and nitriding time to avoid white and bright layers, so as not to deteriorate the service life of the material. As for the hot stamping die, the ion nitriding process is adopted to ensure the brittleness of the nitriding layer, and try to form a thicker white layer on the surface of the die to improve the wear resistance.

Ion Nitriding Furnace Selection

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