The vapor pressure of grease, lubricant, etc. adhering to the metal surface is high. When heated in vacuum, it volatilizes or decomposes into water, hydrogen and carbon dioxide and other gases, which are pumped away by vacuum pump and chemically react with different metal surfaces. Oxidized, corrosion-free very smooth surface
When the metal is smelted, the liquid metal must absorb gases such as H2, O2, N2, CO, etc. Because the cooling rate is too fast, these gases remain in the solid metal, resulting in various metallurgical defects such as pores and white spots, which make the material's resistance, magnetic properties and magnetic properties. Conductivity, hardness, strength, plasticity, toughness and other properties are affected. According to the solubility of the gas in the metal, it is proportional to the square root of the partial pressure of the surrounding environment. Solubility in , the released gas is pumped away
3. Oxide decomposition
The oxide film, rust, oxide and hydride on the metal surface are reduced, decomposed or volatilized and disappeared during vacuum heating, so that the metal surface is smooth and clean. When the vacuum degree of steel parts reaches 0.133~13.3Pa, the surface purification effect can be achieved. After the metal surface is purified, the activity is enhanced, which is conducive to the absorption of atoms such as C, N, and B, which makes the chemical heat treatment speed faster and more uniform.
4. Protective effects
The vacuum heat treatment is essentially carried out in a very thin atmosphere, and the trace gas remaining in the furnace is not enough to make the treated metal material produce oxidative decarburization, carbon increase and other effects. Keep the chemical composition of the surface of the metal material and the brightness of the original surface unchanged
5. Evaporation of alloying elements
Various metals have different vapor pressures at different temperatures. When the vacuum degree increases, metals with high vapor pressures (Mn, Cr) are easy to evaporate and contaminate other metal surfaces, causing adhesion between parts or between parts and the material basket. junction, causing electrical short circuit, material modification and other defects, usually parts are heated to 800ºC under high vacuum, and inert gas should be passed above 800ºC