Plasma chemical heat treatment
The fastest growing, most widely used plasma heat treatment method is plasma chemical heat treatment. Compared with conventional chemical heat treatment, plasma chemical heat treatment has the characteristics of high quality, high efficiency, low consumption, clean and pollution-free. However, when this technique is used for large-sized small molds and other small parts (such as bolts, nuts, chains, etc.), it is troublesome to install the furnace, and the quality of the layer is difficult to control. Moreover, when mixing workpieces of different shapes and sizes in the same furnace, it is difficult to uniformly control the temperature of the workpiece.
1.1 ion carburizing
Ion carburization, also known as glow carburizing [l0-11]. Carburizing is a heat treatment in which a low-carbon steel or a low-carbon alloy steel parent material which is inexpensive, has good formability and ductility is heated in a carbon-based atmosphere, and the activated carbon is infiltrated into the base material to form a tough, wear-resistant surface. method. Ion carburizing is based on the fact that activated carbon is obtained by hydrogenation of a hydrocarbon gas in a vacuum plasma zone by DC glow discharge. The principle is similar to that of ion nitriding.
In China, the ion carburizing process has been successfully applied to molds in the automotive, aerospace and nuclear industries. The key to ion carburizing technology is the quality control of the layer and equipment design. When ion carburizing, the predetermined carbon content of the surface of the mold workpiece can be controlled by adjusting the carbon flux and the carburizing time. Carbon flux is a function of gas composition, gas pressure, gas flow rate, ion current density, and carburization temperature. In industrial production, when ion carburizing, the mathematical model of diffusion and transmission of carbon can be utilized, and the process control of the whole process is performed by the microcomputer through the current density sensor, thereby obtaining a predetermined surface carbon content, carbon distribution and depth of the layer. However, the ion carburizing process has a high temperature (850 to 980 ° C), requires a large power supply, and is prone to a phenomenon in which a glow discharge is converted into an arc discharge, which makes the process unstable and complicated. At present, the gas carburizing and vacuum carburizing processes commonly used in industrial molds are mature and the quality is stable, which can better meet the needs of industrial molds. Compared with traditional carburizing, ion carburizing has the following advantages: high carburizing efficiency, good surface quality, uniform distribution of permeation layer, small deformation, small environmental pollution, easy process automation, deep hole blind hole treatment, etc. . In the mold industry, ion carburizing technology is widely used in die and plastic molds. At present, more than 80% of the surface hardening is carburized. Therefore, ion carburizing has broad prospects for development.
1.2 ion nitriding
Ion nitriding is currently the most widely used and most mature ion heat treatment process in industry [1-3]. The process easily obtains a pure diffusion layer, a single phase, a compound layer, etc. by adjusting process parameters such as voltage, current, furnace gas pressure, temperature, time, and working gas composition. The key to ion nitriding technology is how to select the process parameters according to its characteristics, combined with the relevant mold service conditions, and then obtain the optimal permeable layer.
1.3 ionic carbon-nitrogen osmosis
Ion carburizing and nitrogen technology relies on the decomposition of the active components of the furnace gas C3H8 and NH3 on the steel surface, and the precipitated active atoms C and N are absorbed by the surface and diffused into the matrix [2,4], which is also called ion soft nitrogen. It is developed from salt bath and gas soft nitriding. The operation method of ion carburizing nitrogen is basically the same as that of ion nitriding, but the working gas composition is different, and the cooling method can be performed by oil quenching or high pressure gas quenching in addition to slow cooling under vacuum conditions. The ionic carbon-nitrogen co-infiltration time is short, the benefit is high, and a thick compound layer can be obtained, which has excellent wear resistance, anti-gluing and anti-fatigue properties. Compared with the traditional process, the ionic carbon-nitrogen co-infiltration technology applied to the mold not only has the advantages of good quality of the layer and easy control of the phase composition, but also high efficiency, cleanliness and energy saving. The process has strong market competitiveness.
1.4 ion boronizing
Boronizing is a very effective surface hardening process. After the boronizing of the metal parts, the hardness of the compounds such as boride and boron carbide formed on the surface is extremely high. The boronized steel is higher in hardness, wear resistance, heat resistance and corrosion resistance than the carburized or nitrided steel [1] , 4]. Therefore, boronizing plays an important role in mold surface strengthening. There are many methods for boronizing, and conventional methods include gas, liquid, solid, and electrolytic boronizing. Ion boronizing has the advantages of uniform layering, fast permeation rate, and no need to clean the workpiece after infiltration. It is a promising process.
1.5 ion infiltration metal
Metallization on the surface of the mold means that under certain conditions of temperature and vacuum, the reduced active metal atoms or ionized, sputtered metal atoms diffuse into the surface layer of the mold steel to form an alloy layer, thereby changing the chemical composition, structure and properties of the surface layer. Methods. The metallizing technology on the surface of the mold belongs to the chemical heat treatment of steel. It is essentially diffusion through high temperature, so that active atoms such as chromium, vanadium, titanium, tungsten, molybdenum, niobium, cobalt, nickel and aluminum form a solid solution or carbide layer on the surface of the mold. The structure has high hardness and good wear resistance, and has good oxidation resistance and corrosion resistance, which greatly improves the surface properties and service life of the mold [12].
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