Nitriding method of stainless steel
The key to the nitriding of stainless steel is to remove its passive film, which is the reason why stainless steel is rust-proof and cannot be nitrided. Therefore, the key to nitriding stainless steel is to remove the passive film on the surface. The purpose of nitriding stainless steel is to increase its hardness, improve its wear resistance and corrosion resistance. There are chemical and mechanical methods to remove the passivation film.
(1) Sandblasting. Before nitriding, the workpiece is sandblasted with fine sand at a pressure of 0.15%26mdash; 0.25MPa until the surface is dark gray, and the surface dust is cleared and immediately enter the furnace.
(2) Phosphating. Phosphating treatment on the workpiece before nitriding can destroy the oxide film on the metal surface and form a porous and loose phosphating layer, which is conducive to the infiltration of nitrogen atoms.
(3) Chloride bubble. The blasting or finishing work piece is bubbled or coated with chloride, which can effectively remove the oxide film. Commonly used chlorides are TiCl2 and TiCl3.
The ferritic, martensitic and austenitic stainless steels and heat-resistant steels that are usually nitrided.
The chemical method is to soak the workpiece in 50% (volume) hydrochloric acid (temperature 70 degrees), and then clean it with water;
Nitriding of high speed steel
Generally, the nitriding of high-speed steel should not have three phases, otherwise the infiltrated layer will become brittle. According to the above rules, high-speed steel should be nitrided at low temperature and short time. Because the thickness of the infiltration layer increases slowly at a lower temperature, it is easy to control, and the nitrogen concentration on the surface of the infiltration layer is lower. The short-term low-temperature nitriding concentration is lower and the toughness is better. High-speed steel (w18cr4v) generally uses 510% 26 mdash; 520 degrees Celsius) with a diameter of 15 mm, 15% 26 mdash; 20 minutes, larger ones use 25% 26 mdash; 32 minutes, and large ones use 60 minutes.