Nitriding is a heat treatment method that diffuses N elements into the surface of metals to form a hardened layer. It is mainly used for heat treatment of steel, and its typical applications include gears, crankshafts, camshafts, valves, bolts, die-casting parts, forging fixtures, die drawing fixtures, nozzles, and plastic mold fixtures.
For gas nitriding, a nitrogen-containing gas, usually NH3, is used. When NH3 comes into contact with the surface of the workpiece, it decomposes into N and H, and then the active N element infiltrates the material surface to form a nitride. The depth and composition of nitrides can be changed by selecting process parameters.
Advantages of gas nitriding:
Control the concentration of N by regulating the flow rate of gas;
The effect of overall nitriding (which has certain advantages compared to plasma nitriding);
• Can process larger quantities of parts at a time, influenced by the size of the nitriding furnace and the flow rate of gas;
By computerizing the atmosphere, the effect of nitriding can be controlled
Temperature: 500-550 ° C Time 10-70h
Gas nitriding can be used for nitriding steel and cast iron. Generally speaking, materials need to undergo quenching and tempering treatment before nitriding, and the nitriding temperature should be lower than the tempering temperature.
For the gear ring, after years of experience, the most suitable material is 42CrMo, which undergoes quenching and tempering treatment before machining.
After nitriding, the following can be obtained:
• High surface hardness;
Wear resistance and friction resistance (this nitride layer is particularly used in the field of tribology);
• Improve fatigue performance (forming compressive stress on the surface);
• Improve corrosion resistance;
Small deformation (low temperature): reduces problems that may occur during part fitting and reduces noise.
• No need for grinding after nitriding: No machining is required after nitriding, resulting in better material uniformity on the surface of the part.
