Nitriding treatment for shaft couplings
Shaft couplings involve many heat treatment methods, the common ones are surface anti-rust and blackening, quenching and tempering, nitriding, etc.
Nitriding is the process of nitriding the surface layer of steel. At present, gas nitriding is widely used, that is, the active nitrogen atoms decomposed when heated by ammonia gas penetrate into the steel. The nitriding temperature is usually in the range of 500-600 ℃, usually takes 20-50 hours, and the nitriding depth is only 0.3-0.5mm, no longer 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. Improve hardness and wear resistance: Generally, materials containing alloy elements such as aluminum, chromium, molybdenum, manganese, etc. adopt this type of nitriding treatment, such as 38CrA1A, 38CrMoA1A, etc. After treatment, the surface hardness can reach HV1000-1110 (equivalent to HRC65-70), and its hardness can be supported to 600-650℃ without reduction. The disadvantage is that the nitriding time is longer, the nitriding layer is thin and the load is less.
2. Improve fatigue strength: After nitriding, the fatigue limit of steel will be significantly improved (often increased by 25-35%). This is mainly due to the formation of compressive stress on the steel surface, so it is commonly used in structural components that work under changing loads, such as internal combustion engine crankshafts and various gears. Ordinary alloy structural steel can be used. Such as 18Cr2Ni4WA and 34CrNi3Mo steel.
3. Improve corrosion resistance: If only to improve the corrosion resistance, any steel can be nitrided, low carbon steel is usually carried out at 620-700 ℃, the depth of the nitride layer is 0.025-0.06mm. High carbon steel at 620-800 ℃, the depth of nitride layer is 0.01-0.04mm. In many cases, it can replace nickel plating, zinc plating and bluing treatment.
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