Nitriding steel - Theoretically, all iron and steel materials can be nitriding. However, only those steels which are suitable for nitriding treatment and can obtain satisfactory results are referred to as nitriding steels. All low and medium carbon alloy structural steel, tool steel, stainless steel containing Cr, Mo, V, Ti, Al and other elements (stainless steel nitriding before the removal of passivation film on the surface of the workpiece, stainless steel, heat resistant steel can be directly treated with ion nitriding method), nodular cast iron can be nitriding.
Although the parts after nitriding have high hardness, high wear resistance and high fatigue strength, but only the surface of a very thin layer (chromium-molybdenum-steel at 500--540℃ through 35--65h nitriding layer depth of only 0.3--0.65mm). It is necessary to have strong and tough core tissue as the solid base of nitriding layer to give full play to the maximum effect of nitriding. In general, most nitriding parts work under friction and complex dynamic loading conditions, regardless of the surface and heart performance requirements are very high.
Fe4N and Fe2N are less stable if carburized with carbon steel. The higher the temperature, the easier the aggregation coarseness, the surface can not obtain higher hardness, and its heart can not have higher strength and toughness. In order to obtain high hardness and wear resistance on the surface, as well as strong and tough core tissues, it is necessary to add to the steel to form stable nitride with nitrogen on the one hand, and to strengthen the core alloying elements on the other. For example, Al, Ti, V, W, Mo, Cr, etc., can form stable compounds with nitrogen. Among them, Cr, W, Mo, V can also improve the structure of steel, improve the strength and toughness of steel.
At present, 38CrMoAlA is a kind of steel specially used for nitriding. Aluminum has a great affinity with nitrogen and is the main alloying element to form nitrides and improve the strength of nitriding layer. AlN is stable and does not dissolve in steel to about 1000℃. Due to the good nitriding properties of steel due to the role of aluminum, the surface hardness of the steel after nitriding up to 1100--1200HV(equivalent to 67--72HRC). The decarburization tendency of 38CrMoAlA steel is serious, each process must leave a large machining allowance.
For nitride parts with high hardness and wear resistance, carbon steel and general alloy steel are not suitable. Carbon steel and alloy steel can be used to improve the corrosion resistance of ammoniated parts.
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