Coupling nitriding treatment

Coupling involves a variety of heat treatment methods, common surface rust blackening, in order to change the overall hardness of the steel and to increase the hardness of the local hardening and tempering and so on, this is mainly about the infrequently used nitriding treatment method.

Nitriding is the process of nitriding to the surface layer of steel. At present, the gas nitriding method is widely used, that is, the active nitrogen atoms decomposed when heated by ammonia gas penetrate into the steel. The nitriding temperature is usually carried out in the range of 500-600 ° C, which generally takes 20-50 hours, and the nitriding depth is only 0.3-0.5mm, and the heat treatment is no longer carried out after nitriding.

Nitriding has several different purposes:

(1) Improve hardness and wear resistance; (2) Improve fatigue strength; (3) Improve corrosion resistance.

1. Nitriding to improve hardness and wear resistance The nitriding steel is made of materials containing aluminum, chromium, molybdenum, manganese and other alloying elements, such as 38CrA1A,38CrMoA1A and so on. After treatment, the surface hardness of HV1000-1110(equivalent to HRC65-70), its hardness can be supported to 600-650℃ without reducing. Its disadvantage is that the nitriding time is longer and the nitriding layer is thin to bear less load.

2. Nitriding to improve fatigue strength After nitriding, the fatigue limit of steel will be significantly increased (often by 25-35%). This is mainly because the compression stress is formed on the steel surface, so it is commonly used in structural parts that work under variable loads, such as internal combustion engine crankshaft and various gears. Ordinary alloy structural steel can be used. Such as 18Cr2Ni4WA and 34CrNi3Mo steels for nitriding of this nature.

3. Nitriding to improve corrosion resistance If only in order to improve corrosion resistance, any kind of steel can be nitriding, low carbon steel is often carried out at 620-700 ° C, and the nitriding layer depth is 0.025-0.06mm. High carbon steel at 620-800℃, nitriding layer depth of 0.01-0.04mm. In many cases, it can replace nickel plating, galvanizing and bluing. General processing parts are instrument parts, lead screw, small shaft and pinion and so on.