The reason why the nitriding treatment of the stainless […]
The reason why the nitriding treatment of the stainless steel screw is difficult is that it uses 9Cr18Mov as a raw material, and the raw material is easy to produce a passivation film. The nitriding process must first go out of its passivation film in order to succeed.
The role of nitriding
1. The hardness of stainless steel screw
2. Improve the wear resistance and corrosion resistance of stainless steel screws
Key to nitriding
In addition to its passivation film. The passivation film is the reason why the stainless steel screw is rust-proof and cannot be nitrided. Therefore, in order to nitride the stainless steel, the key is to remove the passivation of the surface.
Method of removing passivation film
1. Sandblasting. The workpiece is sandblasted with fine sand at a pressure of 0.15-0.25 MPa before nitriding until the surface is dark gray, and the surface dust is immediately entered into the furnace.
2. Phosphating. Phosphating the workpiece before nitriding can destroy the oxide film on the metal surface and form a porous and porous phosphating layer, which is beneficial to the infiltration of nitrogen atoms.
3. Chloride bubbles. The blasted or finished workpiece is bubbled or coated with chloride to effectively remove the oxide film. Commonly used chlorides are TiCl2 and TiCl3.
Ferritic, martensitic and austenitic stainless steels and heat resistant steels are commonly used for nitriding.
Chemical method for removing the passivation film:
The workpiece was soaked in 50% by volume hydrochloric acid (temperature 70 degrees) and then washed with water.