High Temperature Vacuum Atmosphere Electric Furnace Application
1. Heat treatment in GWL vacuum atmosphere furnace.
1) In the development trend of less oxidation and no oxidation heat treatment technology, GWL vacuum atmosphere furnace and GWL vacuum atmosphere furnace have developed rapidly. At present, in the production of few varieties and large quantities, especially in the bright quenching, annealing, carburizing quenching, carbonitriding quenching and gas nitrocarburizing of carbon steel and general alloy structural steel, controllable atmosphere is still the main means. Therefore, GWL vacuum atmosphere furnace heat treatment is still the main component of advanced heat treatment technology.
2) The source of preparation atmosphere. In the process of mastering and promoting controllable atmosphere, China has gone a long way to solve the problem of atmosphere. The earliest endothermic atmosphere producer was mainly liquefied gas, i.e. propane or butane with high purity. In recent years, it has been proved that China has abundant natural gas resources, which create good conditions for the preparation of endothermic atmosphere from methane. The use of direct atmosphere without furnace is also a way that can not be ignored.
3) Heating equipment. The production line of sealed multi-purpose furnaces and multi-purpose furnaces is highly automated, flexible and applicable, so they are widely used.
4) Heat treatment process of GWL vacuum atmosphere furnace. Carburizing. High temperature carburizing is one of the development trends of carburizing technology. Increasing carburizing temperature can significantly increase productivity and save energy consumption. For this reason, it is urgent to research and develop materials for electric radiation tubes which can be used above 1000 C. The development and improvement of low-pressure carburizing technology create conditions for high-temperature carburizing (1040 C). The depth of carburized layer of steel is generally conservative and sometimes blind. It seems necessary to study the mechanical factors that determine the depth of the carburized layer and explore the possibility of reducing the stipulation of the carburized layer. Carbonitriding. The temperature of Carbonitriding is lower than that of carburizing, and the distortion of workpiece is smaller. When the penetration depth is below 0.6 mm, the penetration rate is close to 930 C. The abnormal structure is easy to occur during carbonitriding of steel, and the surface hardness decreases after quenching. There are more retained austenite in the carburizing layer. How to reasonably select the process and give full play to the potential of Carbonitriding is still a problem worth discussing. In the past, high concentration carbonitriding has been advocated, and there have been reports that the surface carbon content of steel is 0.6% during carbonitriding, which has the best comprehensive mechanical properties. It seems necessary to grasp these rules, which will be helpful to the optimization of production process. Carbonitriding has been reported in the past and now to improve contact fatigue strength of rolling bearings. For example, balls and rollers made of AISI52100 (equivalent to GCr15) steel have been changed from quenching and tempering to carbonitriding, quenching, tempering and bearing failure life by 2.42 times. It seems that there is still much work to be done to give full play to the potential of carbonitriding process.
2. GWL vacuum atmosphere furnace.
1) The advantages of GWL vacuum atmosphere furnace. GWL vacuum atmosphere furnace is a widely used non-oxidizing heat treatment technology which can keep pace with controlled atmosphere. It is also one of the main marks of the advanced degree of heat treatment production technology. GWL vacuum atmosphere furnace can not only realize the non-oxidation and decarbonization of steel parts, but also realize the non-pollution of production and less distortion of workpiece. Therefore, it belongs to the category of clean and precise production technology. At present, it has become an irreplaceable advanced technology in the production of tools and dies.
2) GWL vacuum atmosphere furnace process. Small distortion of workpiece is a very important advantage of GWL vacuum atmosphere furnace. According to experience at home and abroad, the distortion of GWL vacuum atmosphere furnace is only one third of that of salt bath quenching. It is of great significance to study the vacuum heating mode of various materials, parts with different complexity and the distortion law under various cooling conditions, and to simulate them by computer for popularizing GWL vacuum atmosphere furnace technology. The uniformity of air flow during vacuum heating, atmospheric pressure or high pressure air-cooled quenching has a great influence on the hardening effect and quality dispersion of parts. It is of great significance to study the law of gas flow circulation in the furnace by means of computer simulation for improving the structure of the furnace. Vacuum carburizing is the most possible way to achieve high temperature carburizing. However, the austenite grain size of most steels will grow very large when heated for a long time at high temperature. For specific steels carburizing at high temperature, it is necessary to study the effect of reheating and quenching on the properties of materials and workpieces, and to optimize the vacuum carburizing, cooling and heating quenching process and equipment. In recent years, there is an international trend of research and development of combustion vacuum furnace using gas fuel. There are too many difficulties in using gas fuel to heat in vacuum furnace. Although there is a view of saving energy, it is not necessarily an important development direction.
3) GWL vacuum atmosphere furnace.
Modern GWL vacuum atmosphere furnace refers to a cold-wall furnace which can be heated in vacuum and then quenched in oil or in atmospheric pressure and pressurized gas. Research and development of this type of equipment is a comprehensive, interdisciplinary work involving many scientific and technological fields. The application prospect of GWL vacuum atmosphere furnace for tool and mould materials is very great. Most die steels are heated in vacuum and then cooled and quenched in gas. In order to obtain satisfactory mechanical properties both on the surface and inside of the workpiece, vacuum high pressure gas quenching technology must be adopted. At present, the pressure of vacuum gas quenching has increased from 0.2 MPa and 0.6 MPa to 1-2 MPa or even 3 MPa in the world. Therefore, the gradual increase of cooling gas pressure in high pressure gas quenching vacuum furnace is an important development trend. In addition to high-pressure gas quenching, convective heating after vacuum extraction followed by high-pressure inert gas filling can more than double the speed of traditional vacuum radiation heating, thus significantly improving the heating efficiency is also one of the important directions of vacuum heating technology. Developing to multi-function is also one of the trends of vacuum furnaces. The semi-continuous GWL vacuum atmosphere furnace equipped with oil quenching in the front chamber, atmospheric or high pressure gas quenching in the back chamber and vacuum heating or plasma carburizing in the middle chamber is one of the typical examples. At present, the domestic market has already reflected the demand for this type of furnace. Various continuous vacuum carburizing, high pressure, air-cooled, quenching and tempering production lines which can satisfy mass production have been published one after another. It can be predicted that in the near future, it will cause a major change in heat treatment of automotive parts. In view of the characteristics that vacuum heating is easy to achieve high temperature carburization, the development of vacuum high temperature carburizing, slow cooling, reheating, oil quenching, cleaning and tempering production lines should be put on the agenda as soon as possible.