Heat treatment Process of High Precision Steel Pipe

Process
Vacuum quenching vacuum quenching furnaces are divided into two types according to cooling methods: oil quenching and gas quenching, and are divided into single chamber and double chamber types according to the number of stations. The 904 Mountain/Weidao furnace belongs to the periodic operation furnace. Vacuum oil quenching furnaces are double chamber, with electric heating elements installed in the rear chamber and oil grooves located below the front chamber. After the work piece is heated and insulated, it is moved into the front chamber. After closing the middle door, inert gas is filled into the front chamber to approximately 2.66% 26times; LO~1.01% 26times; 10 Pa (200-760mm mercury column), add oil. Oil quenching can easily cause surface deterioration of the work piece. Due to its high surface activity, significant thin layer carburization can occur under the action of a brief high-temperature oil film. In addition, the adhesion of carbon black and oil on the surface is not conducive to simplifying the heat treatment process. The development of vacuum quenching technology mainly lies in the development of gas cooled quenching furnaces with excellent performance and single station. The aforementioned dual chamber furnace can also be used for gas quenching (air jet cooling in the front chamber), but the operation of the dual station type makes it difficult to produce large quantities of furnace loading, and it is also easy to cause work piece deformation or change the orientation of the workpiece to increase quenching deformation during high-temperature movement. A single station air-cooled quenching furnace is cooled by jet cooling in the heating chamber after heating and insulation is completed. The cooling speed of air cooling is not as fast as that of oil cooling, and it is also lower than the isotherm and graded quenching of molten salt in traditional quenching methods. Therefore, continuously increasing the pressure of the spray cooling chamber, increasing the flow rate, and using inert gases helium and hydrogen with Molar mass smaller than nitrogen and argon are the mainstream of the development of vacuum quenching technology today. In the late 1970s, the pressure of nitrogen cooling was increased from (1-2)% 26times; Increase 10Pa to (5-6)% 26times; 10Pa, making the cooling capacity close to oil cooling under normal pressure. In the mid-1980s, ultra-high pressure gas quenching appeared, using (10-20)% 26times; Helium at 10Pa, with a cooling capacity equal to or slightly higher than oil quenching, has entered industrial practice. In the early 1990s, 40% 26times was adopted; The 10Pa hydrogen gas, which is close to the cooling capacity of water quenching, is still in its early stages. Industrial developed countries have advanced to a high pressure (5-6)% 26times; 10. Pa gas quenching is the main part, while the relationship between Vapor pressure (theoretical value) and temperature of some metals produced in China is still in the stage of general pressurized quenching (2% 26times; 10Pa).

The result is a vacuum carburization quenching process curve. After heating to the carburizing temperature in vacuum and holding it for surface purification and activation, a thin carburizing enrichment gas (see controlled atmosphere heat treatment) is introduced, and the infiltration is carried out at a negative pressure of approximately 1330Pa (10T0rr). Then, the gas is stopped (depressurized) for diffusion. The precision steel pipe quenched after carburization adopts a one-time quenching method, which first cuts off the power, passes nitrogen to cool the workpiece to the critical point A, below, causing internal phase change, and then stops the gas, starts the pump, and raises the temperature.