3 Development direction of advanced heat treatment technology Liquid carburizing, carbonitriding and nitrocarburizing with large amounts of cyanide salts should be prohibited. Gas carburizing and gas carbonitriding and carbonitriding after carbonizing with carburizing gas and ammonia are ignited and can be discharged harmlessly. Do not use the drug diborane (B2H6) when ionizing boron. Use yellow blood salt and red blood salt carefully in the salt bath, because it will produce cyanide after decomposition. Do not put urea or biuret in the salt bath containing carbonate, otherwise it will react with cyanate and then decompose into cyanide salt. The cyanide salt bath containing S and Li can keep the cyanide at a low level of 0.1% to 0.5%. The Sul2surf of France HEF and the LT sulfuritriding method of China all belong to this category. The addition of the organic polymer melon to the cyanide salt bath also reduces the cyanide content to 2% to 3%, with the remainder being non-toxic cyanate. The QPQ treatment salt bath belongs to this category. The energy saving potential of heating equipment is great, and the continuous heating furnace is more energy efficient than the periodic furnace. The order of energy efficiency of the four types of furnaces (from large to small) is: vibrating bottom furnace, pit furnace, box furnace and conveyor belt furnace. The furnace must use a high-efficiency heat exchanger to preheat the air and reasonably control the combustion coefficient (α) in the range of 111 to 113. Promoting burners and radiant tubes with lateral combustion of cellular heat storage cycles are good equipment energy saving measures. Metallic materials have been subjected to non-oxidative annealing in hot wall vacuum furnaces for nearly a hundred years. In the cold-wall vacuum furnace with water-cooled sandwich furnace shell, no oxidation annealing, quenching, tempering, brazing, sintering, etc. have been processed for nearly 40 years. The furnace is evacuated to a vacuum of 0.1 Pa to achieve oxidation-free heating of most metals. In order to increase the heating rate of the metal in the furnace, an inert or neutral gas of about 0.8 x 105 Pa is often introduced into the furnace after evacuation. From this point of view, vacuum and atmosphere heating have certain in common. The fastest growing in modern times is a variety of vacuum heat treatment equipment. The current vacuum heat treatment equipment has single chamber, double chamber, three chamber, multi-chamber, oil quenching, gas quenching, oil and gas quenching, high pressure gas quenching, low pressure carburizing high pressure gas quenching furnace, multi-chamber low pressure carburizing and high pressure gas quenching. Production line. A flexible production line for low-pressure carburizing, high-pressure gas quenching and tempering similar to gas carburizing multi-purpose furnace production line. At present, due to the relatively expensive equipment, the one-time investment is too large, and the vacuum heat treatment equipment suitable for mass production has yet to be perfected. At present, it cannot be said that the vacuum heat treatment will largely replace the atmosphere heat treatment. Previous Next Metallurgical Equipment,Metallurgical Supplies,Metallurgy Lab Equipment,Metallurgical Testing Equipment Shanxi KathayTech Co.,ltd. , https://www.jdsmachine.com
As mentioned above, modern heat treatment technology has developed rapidly due to the high attention of the manufacturing industry. Its main development direction can be summarized as 8 aspects, the author said as 8 Less (LessorNon), that is, less pollution-free, less distortion-free, less (quality) dispersion, less waste (energy), less oxidation, Less decarbonization, less waste, and no labor.
3.1 Less pollution free
Heat treatment produces exhaust gas, waste water, waste residue, dust, noise and electromagnetic radiation. If it is not noticed, it will pollute the work site and the surrounding environment. Advanced heat treatment technology should first be a technology that does not pollute the environment. These include cleaning processes, cleaning equipment, cleaning materials, and more. Controlled atmosphere, vacuum, and inductive heat treatment with good shielding are typical cleaning processes for a wide range of applications. Plasma heat treatment, low pressure carburizing, high pressure gas quenching, laser electron beam strengthening, spray quenching, vacuum cleaning, etc. are also among the less polluting technologies. Vacuum furnaces, atmosphere furnaces, ion nitriding furnaces, low NOx, SOx combustion furnaces, and fluid furnaces corresponding to these processes are non-polluting equipment. Polymer quenching agents, non-HCFC solvents, fluid bed particles such as Al2O3 and SiO2, nitrogen and various inert gases are clean materials.
The cyanide content in the wash water has been diluted to provide harmless emissions. The strontium chloride salt residue and the excessive wastewater containing barium chloride are harmful to the human body and must be discharged after being harmlessly treated. Barium chloride is a medium that cannot be replaced by quenching heating of high-speed steel cutting tools, but it must ensure the harmless discharge of barium salt and barium chloride-containing wastewater.
The quenching oil for heat treatment is not completely replaceable at present. The fumes formed during quenching have an impact on the job site and the environment. At present, enterprises in China are directly venting air to the outside, causing pollution to the atmosphere is also an urgent problem to be solved.
The US 2020 heat treatment target must first achieve zero pollution.
3.2 Less distortion free
The shape and dimensional changes of metal parts during heat treatment are unavoidable, and excessive and uneven distortion can increase the machining allowance or scrap it. After the heat treatment of the gearbox of the automobile, the machining is generally not performed, and the distortion will make it lose the interchangeability or increase the gap and increase the noise of the vehicle. Therefore, minimizing distortion is the goal of many heat treatment workers.
Workpiece distortion mainly occurs during the cooling phase, especially during the quenching and cooling process. Uniform cooling, reducing the temperature difference between the workpiece surface and the core are the main measures to reduce distortion, so the choice of cooling medium and cooling method is crucial. There are many kinds of quenching media in modern times, and there are various quenching methods, which can be selected according to the requirements of cooling speed and distortion technology. Cyclic agitation is 1 to 3 times greater than static cooling capacity. The direction change cycle can improve the uniformity of cooling. Isothermal and graded quenching can reduce the temperature difference between the surface of the workpiece and the core, make the phase change close to synchronization, reduce the thermal stress and the tissue stress. It is still the quenching distortion of the international famous brand gear after carburizing. The main measure.
The controlled cooling technique that uses the adjusted spray parameters to simulate the change of the workpiece temperature field brings hope to reduce the heat treatment distortion of the simple shape workpiece. After the large bearing ring is carburized, the hot oil is circulated in the spring oil sump, and the quenching method of moving the workpiece left and right can replace the pressure quenching on the press. After the low-pressure carburizing of the automobile gear, the variable-direction high-pressure (2MPa) gas quenching can be performed to control the synchronizing ring gear distortion to a very narrow range. Complex shape distortion-prone workpieces can be straightened on an automatic straightener using a tempering residual heat after pressure quenching or quenching on a press.
The uniformity and stability of the chemical composition of the material and the guarantee of hardenability can keep the quenching distortion of the workpiece stable, so as to specify the exact machining allowance and take reliable and less distortion-free measures.
In the US 2020 heat treatment target, it is proposed that the workpiece heat treatment should reach zero distortion.
3.3 Less (quality) dispersion
Due to the inconsistency of the chemical composition of the material and the effective heating zone temperature of the furnace, the difference in heating and cooling conditions and the influence of human operating factors may cause the quality of the heat treatment parts of the same heat (hardness, structure, distortion, surface state, depth of infiltration, infiltration of elements). The surface concentration and the concentration gradient along the layer) cause significant differences, or the non-reproducibility of the quality of the different heat products. The use of scientific management and advanced technology can minimize this difference. In the report of the Heat Treating Technology Roadmap Workshop organized by the American Institute of Metals (ASM) and the Department of Energy in 1997, the goal of 2020 is to reduce the mass dispersion of heat-treated workpieces to zero. In order to achieve this goal gradually, the reliability of the equipment, the advancement and stability of the process, the uniformity of the temperature of the furnace, the uniform circulation of the furnace gas, the qualification and stability of the material composition of the workpiece, the online control of the automatic production and quality can be eliminated. The influence of human factors is a very important issue. To this end, the heating furnace uses the temperature field inside the furnace, the circulation route of the furnace gas, the flow condition of the quenching agent, the heat exchange of the workpiece and the quenching agent, and the computer simulation of the temperature field and the stress field change during the cooling process of the workpiece. It is very important. Statistical process control is used in quality management measures in production. (Statistical Process Control) can gradually reduce the quality dispersion to a very narrow range.
Scientific production management, ISO9000 series standard certification, raw material inspection, coordination and connection of heat treatment processes, the implementation of various process standards and general quality standards are also closely related to the dispersion of product quality. It can be seen that there are many factors affecting the quality dispersion. It is necessary to use technology and management as a systematic project to achieve long-term, meticulous and practical work, in order to achieve good results in this aspect.
3.4 Less waste (energy)
Energy conservation is also one of the main features of advanced heat treatment technology. The energy-saving heat treatment process is the most effective energy-saving measure. Increasing the carburizing temperature from 930 ° C to 1050 ° C can reduce the process cycle by 40%. In general resistance furnaces, this temperature increase is difficult to achieve due to the limitation of the heating element and the heat resistant material, while low pressure carburizing in the vacuum furnace Execution at 1050 ° C is a breeze. Substitution of carburizing and carbonitriding by nitrocarburizing, sulfur-nitrocarburizing and oxygen-nitrogen co-infiltration can reduce the process temperature from 850 °C to 930 °C to 550 °C to 580 °C instead of general gas nitriding. The nitrogen time was reduced from 30h to 70h to 1.5h to 3h. The quenching and quenching of the forging billet by using the residual heat after forging can save the heat energy required for reheating, and can also obtain the deformation heat treatment effect for improving the structure and performance. The calculation of the heat treatment heating time of steel parts is too conservative and must be changed. It is feasible to perform zero-insulation heating and uneven austenite quenching of carbon steel and low-alloy steel and incomplete quenching to the FA two-phase zone.
Japan Tokyo Heat Treatment (now Tonghe Mining) 20 years ago, an energy-saving carburizing, quenching, cleaning and tempering push rod production line, the front cleaning changed to combustion degreasing, degreasing waste heat can be used as part of the heat source of the tempering furnace, carburizing furnace The exhausted atmosphere can be used as a degreasing furnace and an alkali cleaning tank as well as heating of the quenching oil, and the result of comprehensive utilization of various waste heat can save 40% of the fuel cost. The heat dissipation of the furnace has a great relationship with its external surface area. The circular section furnace is about 14% smaller than the rectangular section furnace surface, and the outer wall temperature is reduced by 10 °C, which reduces the heat dissipation through the furnace wall by 20%. At present, Japan's sealed multi-purpose furnaces and push rod continuous furnaces have been changed to circular sections.
The energy efficiency of heat treatment in the 2020 heat treatment target proposed by ASM in the United States will generally increase to 80% by then.
3.5 Less oxidation free
Oxidation of most metals when heated in air causes a large loss of metal and also destroys the surface condition and processing accuracy of the part. Less oxidation-free heating is also one of the main signs of the development of advanced heat treatment technology in modern times.
Techniques that fall into the category of less oxidative heat treatment include atmosphere, vacuum, induction, fluid bed, salt bath, laser, electron beam, coating, packaging heat treatment, and reductive conditioning of the furnace flame. Atmospheric heat treatment in an inert, neutral atmosphere and a multi-component controlled atmosphere is still the most widely used non-oxidizing heating method. To achieve complete non-oxidative heating in inert (Ar, He) and neutral (N2) gases, the gas must be dried to reduce the dew point below -60 °C. Heating in H2-H2O, CO-CO2, N2-H2-CO-CO2-H2O mixed atmosphere must control the H2/H2O, CO/CO2 ratio to a certain extent, so that the atmosphere can be reduced at a given temperature to achieve no Oxidation. In the past 30 years, due to the increase in fuel prices, the development of nitrogen-based pressure swing adsorption nitrogen separation and membrane separation nitrogen production using carbon molecular sieves, nitrogen-based atmospheres have been promoted, and liquid nitrogen evaporation supplied by gas companies has also been widely used. A portion of the synthesis atmosphere mixed with pure nitrogen and methanol cracking gas replaces the endothermic atmosphere prepared with natural gas or propane. A single gaseous nitrogen is supplied to the furnace, which requires a high purity (>99199%), and the non-oxidative heating of the steel must be achieved under the condition of a stainless steel furnace. Usually, 9918% of the nitrogen is used in the production, and a certain amount of methanol is added to the furnace. The residual oxygen in the nitrogen can be removed by H2 and CO after the methanol cracking. In recent years, due to the large-scale use of methanol, the price of methanol in the United States in 1995 was 215 times that of 1994, which made the preparation cost of N2 methanol atmosphere 100% higher than that of 1994, and 215 times that of natural gas to prepare an endothermic atmosphere. Therefore, the use of exothermic and endothermic atmospheres is the most economical non-oxidizing heating method with sufficient natural gas supply.