White nitride layer
White hard nitriding surface appear inevitably epsilon multiphase compound layer (Fe2-3 n), brittleness is big, so the grinding layer need to be removed after nitriding
Multiphase compounds on the surface of the soft nitriding white no hard white nitride layer Fe2N high brittleness. Usually Fe3N with Fe4N accounted for about 80% of white layer, carbide accounts for about 20%. The compound white layer is the anti-wear layer. So soft nitriding must get a white layer in order to be qualified.
The usefulness of the nitride
General nitrogen applied to the load is large, relatively high contact fatigue artifacts, emphasizes the deep depth.
And the role of the soft nitriding is faster, commonly used in load small artifacts, permeability of shallow layer requirements.
The nitride concept
1, hard nitride: scientific name 'nitriding, also some people called the conventional nitriding. Into a single 'n' on the surface of the steel elements, on the method of gas and ion method, etc. The steel grade for structural parts usually choose to contain chromium, molybdenum, titanium, aluminum alloy elements such as special steel, and there have been other nitriding of steel grade, such as stainless steel, steel, etc. Nitriding processing temperature is usually in the range of 480 ~ 540 ℃ (both to keep the heart of the workpiece and tempering hardness and the hardness of the nitriding layer up to par value), the processing time of different depth in accordance with the requirements, generally for 15 ~ 70 hours, or even longer. A focal point of nitriding is hoping to get a deep degree (0.1 ~ 0.65 mm, there are also requires deeper) that are dispersion with high hardness alloy nitride layer (that is, the diffusion layer), appear to outside surface of compound layer (white layer) wants as far as possible light book, even hope not.
2, soft nitriding: scientific name 'carbon and nitrogen altogether permeability, early translate the Soviet union (Russia) liquid method for cyanide in low temperature. Now popular domestic gas, no (low) poisonous liquid method and ion method. Infiltration of elements is given priority to with "n" on the surface of the steel, and add the "carbon". The addition of carbon to make the formation of surface compound layer (white layer) and some even obvious improvement in performance. Here to emphasize that different places and nitriding is: a focal point of carbon and nitrogen altogether permeability is hoping to get a certain thickness (generally is 10 ~ 20 microns, also have asked 20 microns above, currently the laboratory is ever reached on carbon steel thickness is 110 microns), high hardness and brittleness of small, little or no loose white layer with excellent properties for the diffusion layer on the surface of The Times, in accordance with the requirements for steel and the use of different although sometimes need to make some adjustment, but in a secondary position. Carbon and nitrogen altogether permeability is used widely, covering almost all commonly used steel and cast iron. In carbon steel, for example, according to the temperature of the carbon and nitrogen altogether permeability treatment consists of permeability of the existing body of the carbon nitrogen (520 ~ 520 ℃) and nitrogen austenitic carbon altogether permeability (600 ~ 720 ℃), the processing time is usually 2 ~ 6 hours, the former white layer of iron compounds, which is fast after cold iron compounds below the layer and a layer of nitrogen austenite + martensite layer (5 ~ 12 microns). In order to strengthen and improve the performance of the white layer, the heat treatment of workers in our country is also used in nitriding and individually or in combination with boron, oxygen, sulfur, rare earth elements, such as do a lot of work, and often can see the results of different level. In the exploration, up to now, is one of the hot heat treatment researchers assiduously seek for.
3, 'soft nitriding' meaning is not the hardness than the so-called 'hard nitriding hardness is low, but with simple, convenient, low cost. Nitriding treatment technology of nitrogen into an important process in heat treatment, it has a variety of forms. Each process corresponds to different performance characteristics, hope here you about their own experiences and opinions, in order to improve together. Compound - QPQ nitride this kind of nitriding processing features are: high wear-resisting, high in antioxidants. It is mainly to overcome the friction and wear, the anti-seizure ability very strong after close to sulfurizing effect. Concept: (soft) nitride is to the steel surface infiltration process of nitrogen atoms, its purpose is to improve the surface hardness and wear resistance, and improve the fatigue strength and corrosion resistance. It is the use of ammonia and nitrogen atoms of organic liquid on the heat decomposition into reactive nitrogen atoms, after being absorbed by steel the nitride layer formed on the surface, also spread to the heart. Usually use specialized equipment or nitride well type permeability (nitrogen) carbon furnace. Suitable for all kinds of high precision gear transmission, machine tool spindle (e.g., boring bar, grinder spindle), high speed diesel engine crankshaft, valves, tools, etc.
Nitrogen chemical process routes: forging, annealing - rough machining - conditioning - finishing - in addition to the stress and coarse grinding - nitride - fine grinding or polishing (usually used directly after nitriding). Because nitride thin and brittle, and therefore requires a higher intensity is the heart of the organization, so need to tempering heat treatment, get tempered sorbite, improving the core mechanical properties, ensure the quality of the nitride layer. Steel after nitriding quenching is no longer needed and has the very high surface hardness and wear resistance. Nitride low processing temperature, the deformation is small, it compared with the carburizing, induction hardening, the deformation is much less.