Discussion on cryogenic treatment technology of low temperature valve

Cryogenic treatment technology of low-temperature valve cryogenic treatment of low-temperature valve body can greatly reduce the retained austenite in metal materials The cryogenic treatment of low temperature valve body can produce uniform, fine and dispersed carbide precipitation on the metal matrix structure Low temperature mechanical properties of materials refer to the mechanical properties of materials tested in low temperature environment! Some materials used at low temperature must be tested for their low-temperature mechanical properties, for example, refrigerated containers need to be tested for their low-temperature mechanical properties Low temperature treatment is the extension of conventional heat treatment (quenching + tempering), which aims to eliminate the retained austenite (high alloy steel: die steel, high speed steel, etc.) and improve the service performance Deep cooling technology is to use the refrigerant medium as the cooling medium to continue the cooling process of the quenched metal materials, so as to achieve a temperature far lower than the room temperature (- 196 ℃), so as to achieve the purpose of exerting the properties of metal materials In recent years, cryogenic technology is a new technology to develop the performance of metal parts, which is an effective and economical technology for Zui
In the process of deep cold working, a large number of residual austenite in metal is transformed into martensite, especially the supersaturated metastable martensite, which will reduce the supersaturation from - 196 ℃ to room temperature, precipitate the dispersed ultra-fine carbide whose size is only 20-60a and keeps the same lattice relationship with the matrix, which can reduce the lattice distortion of martensite, reduce the micro stress, and fine dispersed carbide The dislocation movement can be hindered during plastic deformation of the material, thus strengthening the matrix structure At the same time, the ultra-fine carbide particles are evenly distributed on the martensite matrix after precipitation, which weakens the role of grain boundary embrittlement The refinement of the matrix structure not only weakens the degree of segregation of impurity elements on the grain boundary, but also plays the role of grain boundary strengthening, thus improving the performance of the tool and die, making the hardness, impact toughness and wear resistance significantly improved The improvement effect of the cryogenic technology is not the same as that of the working surface It penetrates into the workpiece and reflects the overall effect Therefore, it can be used repeatedly to regrind the workpiece and reduce the quenching stress and enhance the dimensional stability of the workpiece The finer dispersed carbide precipitated from the cryogenic and ultra cryogenic treatment refers to the picture under the microscope: the size of the martensite lath after the cryogenic and ultra cryogenic treatment is obviously small, which means that the original coarse martensite lath will be crushed in the process of the cryogenic and ultra cryogenic treatment, and the fragmentation of low carbon martensite is related to the martensite micro decomposition caused by the cryogenic treatment In the process of cryogenic and ultra cryogenic treatment, the lattice constant of volume shrinkage Fe tends to decrease at - 190 ℃, while the decrease of solid solubility at low temperature increases the supersaturation of martensite and decreases the plane concentration of vacancy All of these increase the driving force of carbon atom precipitation and segregation, but at low temperature, the movement of atoms is difficult and the diffusion distance is very short The supersaturated carbon atoms in martensite tend to gather on the nearby dislocation line, and gradually form the ultra-fine carbide core in the subsequent temperature return process After falling off, the martensite will undergo micro decomposition, and the internal sub unit size will be smaller: the low-carbon martensite will be During tempering, some of the carbon atoms are partially segregated and precipitated with fine carbides, but they are still supersaturated solid solutions of carbon in α - Fe The cryogenic and ultra cryogenic treatment can promote the dispersion and segregation of carbon atoms, form the ultra-fine carbide core, decompose the martensite, increase the interface of martensite and break it up The diffusion ability of carbon atom increases greatly in the temperature rising stage of cryogenic and ultra cryogenic treatment, and the equilibrium concentration of vacancy increases with the temperature rising, thus accelerating the diffusion of carbon atom The micro carbides produced by self tempering promote the polymerization and growth of carbides, and the super micro carbides formed by cryogenic and ultra cryogenic treatment gradually aggregate and grow in the process of temperature return and room temperature maintenance Therefore, the amount and size of carbide particles in martensite increased after cryogenic and ultra cryogenic treatment Data: Bolei valve technology (Kunshan) Co., Ltd - a reliable low temperature valve solution