Analysis of heat treatment technology development and heat treatment industry market (2)
2.1.2 Main signs of foreign advanced heat treatment technology: In view of the above-mentioned strategic goals of foreign advanced heat treatment development, the main signs of development can be summarized as 8 “lessâ€: less pollution, less distortion, less dispersion, less waste, Less oxidation-free, less decarbonization, less waste and less man-made. Here we discuss the current level of advanced foreign heat treatment in the following four aspects.
2.1.2.1 Clean production and zero pollution: Some heat treatment production will form environmental pollution, mainly refers to waste gas, waste water, waste residue, noise and electromagnetic radiation generated during the production process. Advanced heat treatment technology should use cleaning equipment to clean the cleaning materials.
Vacuum equipment, controlled atmosphere equipment, ion osmosis equipment, low NOx, SOx fuel combustion equipment, fluid bed equipment, etc. are non-polluting cleaning equipment; N2 and various inert gases, polymer quenching agents, no chlorofluorocarbon cleaning solvents, Materials such as Al2O3 and SiO2 fluidized bed particles (with dust removal conditions) are clean materials; vacuum treatment, controlled atmosphere treatment (to minimize CO2 emissions), and a well-shielded induction heat treatment process is a cleaning process; thus, vacuum heat treatment, low pressure Carburizing, plasma heat treatment, high pressure gas quenching, vacuum cleaning, three beams (ion beam, laser beam, electron beam) heat treatment, spray water quenching, etc. are obviously less pollution-free clean heat treatment technology.
Exhaust gas from gas carburizing and gas carbonitriding and nitrocarburizing with carburizing atmosphere should be ignited before being harmlessly discharged; highly toxic B2H6 (diborane) should not be used in ionizing boron ); in the salt bath, yellow salt and red blood salt which are decomposed by heat to produce cyanide should not be used; for carbonate-containing salt bath, urea or biuret should not be used because it will react to form cyanate and then decompose. It is a cyanide salt. The cyanate-carbonate salt bath containing S and Li can keep the cyanide at a low level of 0.1-0.8%, the nitriding performance of the treated parts is good, and the treatment cycle is shortened. This process is in the United States, Europe and Europe. There are quite a lot of applications in Japan. The SURSULF process of French HEF company and the process of entering the oxidation salt bath after treatment belong to this technology (the LT sulfur-nitrogen co-infiltration method in China is also). The addition of the organic polymer melon to the cyanate bath can also reduce the cyanide content to 2% to 3%, the majority of which is non-toxic cyanate, the German company Durferrit (formerly Degussa) of HEF, France. The Tufftride / Melonite / Tenifer / QPQ treatment salt bath belongs to this type of technology, (the QPQ compound salt bath treatment of Chengdu Institute of Tools in China is also). The cyanide content in the wash water has been diluted to provide harmless emissions. Despite this, France, Germany and Japan are very strict with the pollution-free treatment of these processes and study the regeneration of waste salts. The BaCl2 salt bath and the BaCl2-containing wastewater still used for the quenching of high-speed steel cutting tools are allowed to be discharged after being harmlessly treated, and Germany has adopted special techniques and devices to solve them.
For some non-cleaning and non-cleaning materials that should be used, they should be completely enclosed throughout the treatment process and disposed of in a closed system to achieve pollution-free emissions. The treated slag should be studied for regeneration or special treatment.
2.1.2.2 Accurate production and zero distortion: heating and cooling in the heat treatment process will cause the shape and size of the metal workpiece to change after processing. The machining allowance will be eliminated by the reprocessing method, and the deformation will be scrapped. Loss of materials and resources that have been invested. Deformation of the workpiece also affects interchangeability and reduces the precision of operation, resulting in reduced efficiency, increased energy consumption and noise. For this reason, zero distortion of heat treatment is very important, which is guaranteed by the precise production of the heat treatment process. Accurate production depends on heat treatment equipment with high precision and reliable operation (precise control and reproducibility control of process parameters such as temperature, pressure, time, etc.), composition of materials (content deviation, impurity content and segregation, original organization consistent) and corresponding The material thermal physical properties and process performance deviations are small to ensure that the mass (tissue, hardness, deformation, surface state, depth of the layer, concentration of the layer, etc.) of the same batch of parts is reduced (or in technical requirements) Within the control range) and improve the reproducibility of different batch batch products.
The deformation of the workpiece mainly occurs in the cooling stage. During the quenching process, the workpiece is uniformly cooled. It is important to reduce the temperature difference between the surface of the workpiece and the core to reduce distortion. Therefore, the cooling medium and cooling method should be selected reasonably. Use polymer quenching medium, adopt cycle and agitation mode and speed to control cooling, reasonably select quenching oil temperature, control quenching oil surface pressure (to reduce workpiece quenching deformation), carry out salt bath grading or isothermal cooling, perform gas cooling, spray Water spray cooling, application of computer simulation of cooling field technology, pressure quenching, use of tempering residual heat on the straightening machine and other techniques to create conditions to reduce distortion.
The main measures for quenching and reducing deformation after carburizing in international famous brand automobile gears are to achieve isothermal and stepwise quenching, reduce the temperature difference of the gear heart watch and the different time of phase change, and reduce the difference between thermal stress and tissue stress. It has also been reported that automotive gears are subjected to variable-direction high-pressure (2 MPa) gas quenching after low-pressure carburizing, which can cause the synchronizing ring gear distortion to fall within a very narrow range.
It should be pointed out that strict management, scientific and advanced technology, reliable equipment, precise sensors, and complete control engineering systems (including instrumentation, cutting, pumping, executing motion components, computers, programming and implementation, etc.) ) is the guarantee to ensure accurate production, to achieve production without waste and zero mass production.
2.1.2.3 Less oxidation and less decarburization: Generally, the metal will be oxidized and decarburized when heated in air, which will cause a large loss of metal and also damage the surface state and processing accuracy of the workpiece. The performance of the steel workpiece with decarburization on the surface will be reduced after heat treatment: hardness reduction, wear resistance, tensile stress on the surface, fatigue resistance, corrosion resistance, etc. This necessitates further processing to remove the oxidative decarburization layer or to perform a "recarbonization" process, which inevitably increases production costs, wastes materials, increases energy consumption, and reduces yield.
Heat treatment technologies that are less oxidizing mainly include application atmosphere, vacuum, induction, fluid bed, salt bath, laser beam, electron beam, ion beam, coating, packing, and furnace heating technology under reducing flame. The application atmosphere includes inert (mainly Ar) and neutral atmosphere (in N2 gas) and a controlled atmosphere (controlling H2/H2O, CO/CO2 ratio to a certain extent). The first two gases should be dried to reduce the dew point to below -60 °C. The latter atmosphere is reductive at the temperature of use, and it controls the atmospheric carbon potential in order to prevent decarburization. Applied atmosphere In the past 30 years, there has been a nitrogen-based atmosphere, which can be applied to the production of nitrogen by the pressure swing suction air of carbon molecular sieve and the separation of nitrogen by film separation. For carburizing, a synthetic atmosphere mixed with pure nitrogen and methanol cracking gas can be used instead of natural gas or propane to prepare an endothermic atmosphere. Usually, 99.8% of the nitrogen can be added to the methanol in the production, and the residual oxygen in the N2 is removed by the H2 and CO in the methanol cracking gas. This method is simple, but in the United States due to the price increase of methanol, the cost has increased a lot. In fact, it is more feasible to use natural gas to prepare an exothermic or endothermic atmosphere under the guarantee of natural gas supply.
The vacuum is applied to the furnace to a vacuum of 0.1 Pa, which can achieve the oxidation-free heating of most metals, but since the heating in the vacuum is radiant heating, the heating rate is slow. It is often re-introduced with an inert gas or atmosphere of about 0.8 x 105 Pa to increase the convection to increase the heating rate, which has been gradually promoted in vacuum heat treatment furnaces. The current vacuum heat treatment equipment has a single chamber, double chamber, three chambers, multiple chambers, oil quenching, gas quenching, oil and gas quenching, high pressure gas quenching, low pressure carburizing high pressure gas quenching, multi-chamber low pressure gas quenching and high pressure gas quenching. Continuous production line and flexible production line for low pressure carburizing, high pressure gas quenching and tempering.
Induction heating is rapid due to the heating rate. At this time, the oxidation of the workpiece is not serious. It is also a non-oxidative heating method. In the case where oxidation is not allowed at one point, the atmosphere can be protected by induction heating. The Japanese electronics industry has provided similar Technology. Induction heating has been reported for carburizing chemical heat treatment. Non-oxidative heating can be achieved by using a fluidized bed (passing protective gas under necessary conditions) and a normal deoxidized salt bath furnace. In the absence of an atmosphere furnace, anti-oxidation coatings and heating in an air furnace after packaging with stainless steel foil can be used, but it is noted that these heating methods cause a small amount of decarburization on the surface of the heated workpiece.
The decarburization is caused by the heating of steel in air or an oxidizing atmosphere containing CO2 and H2O. Decarburization is more serious than oxidation, and the requirements are stricter. For heating quenching, CO-CO2, N2-CO-CO2-H2-H2O mixed atmosphere is applied, the carbon potential of the furnace gas must be consistent with the carbon content of the workpiece surface. For the heating of medium and high carbon steel, carbon must be applied to the furnace gas. Potential control. In the application of vacuum heating, when the degree of vacuum is not oxidized, decarburization does not occur. The advanced heat treatment technology in foreign countries is quite strict in controlling decarburization.
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