The coupling involves a variety of heat treatment methods, such as surface rust black, tempering for changing the overall hardness of the steel, hardening and tempering for increasing the local hardness, etc. This time is mainly about the rarely used nitriding treatment.

Nitriding is a process of nitriding to steel surface layer. At present, gas nitriding method is widely used, that is, active nitrogen atoms decomposed when heated by ammonia gas are used to infiltrate into steel. Nitriding temperature is usually in the range of 500-600℃, generally need 20-50 hours, and the depth of nitriding only 0.3-0.5mm, no longer for heat treatment after nitriding.

Nitriding has the following different purposes:

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

1. Nitriding to improve the hardness and wear resistance of such 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 department reaches HV1000-1110(equivalent to HRC65-70), and its hardness can be supported to 600-650℃ without decreasing. Its disadvantages are that the nitriding time is longer and the nitriding layer bears less load.

After nitriding, the fatigue limit of steel will be significantly increased (often by 25-35%). This is mainly because of the formation of compressive stress on the steel surface, so commonly used in the variable load work of structural parts, such as internal combustion engine crankshaft and various gears. Ordinary structural alloy steel can be used. Such as 18Cr2Ni4WA and 34CrNi3Mo steel for this nature of nitrification.

3. Nitriding to improve corrosion resistance if only to improve the corrosion resistance, any kind of steel can be nitriding, low carbon steel usually at 620-700℃, nitriding layer depth is 0.025-0.06mm. High carbon steel at 620-800℃, the depth of nitriding layer is 0.01-0.04mm. In many cases it can be substituted for nickel plating, zinc plating and bluing. General processing of the parts are instrument parts, screw, small shaft and pinion gear.

Nitriding treatment of coupling