The so-called cryogenic treatment is to use liquid nitrogen as a cooling medium to continue the cooling process of the quenched metal material to a temperature far below room temperature, which promotes the further transformation of the retained austenite existing after the conventional heat treatment, thereby improving the metal. Material properties. In 2008, we began to study the process of using cryogenic treatment to improve tool life.
The precipitation of fine carbides during cryogenic treatment is an "atomic extrusion" mechanism. When the tool is quenched to -120 °C, macroscopic volume shrinkage occurs, which causes the internal micro-domain deformation to cause lattice distortion, so that the interstitial carbon atoms inside the martensite are further subjected to compressive stress and are "extruded" into the gap position. The thermal shock of carbon atoms is very weak at temperatures of -120 ° C, so carbon atoms do not "diffuse escape". When the tool is returned to room temperature 20 ° C after the end of deep cooling, there is a temperature difference of nearly 150 ° C, so the tool is equivalent to a low temperature tempering, so the extruded carbon atoms can be formed by segregation near the defect. Diffuse distribution of fine carbides. The dispersion of fine carbides can also hinder dislocation motion, resulting in dispersion strengthening effect, improving the wear resistance and toughness of the tool, and increasing the service life of the tool.
We first cut four pieces of 130mm long from a 25mm × 35mm × 600mm M42 forging material, and made four 20mm × 30mm × 120mm planing knives, labeled 1 # , 2 # , 3 # , 4 # , Among them, 1 # and 2 # planing knives were subjected to cryogenic treatment, and 3 # and 4 # planing knives were subjected to conventional heat treatment. The tool wear test of CrWMn steel was carried out on a planer with four heat-treated tools. The service life results of the two sets of tests are shown in the attached table. From the tool life comparison table and the wear state of the tool surface after use, the cryogenic treatment can significantly improve the wear resistance of the tool and increase the cutting life of the tool.
Therefore, we chose to process the combined cutter of the flame stabilizer on the XX engine for on-site physical test. The flame stabilizer material is GH625, which is difficult to process. At the earliest, there is a 50% scrap rate. By improving the tool size, the scrap rate is reduced. Up to 20%, but the service life of the milling cutter is very short, a set of combined milling cutter can only process 2 to 3 flame stabilizers, and the processing cost continues to climb.
We put 15 sets of cryogenically treated combination milling cutters and 15 sets of conventional heat-treated combined milling cutters into the field. It can be clearly seen from the operator's recorded data that the number of combined milling cutters processed by cryogenic treatment is not deep. The cold processing cutter is twice as long, the service life is greatly improved, and the tool size stability is good, and the product rejection rate is reduced from 15% to 5%. Feedback from another batch of cryogenic treatment reamer shows:
(1) Without the deep-cooling reamer, the number of reaming holes used for the first time is about 30, and the cutting edge is easy to be gapped after manual grinding.
(2) The reamer for cryogenic treatment, the number of reaming holes can reach 80 or so for the first time, no obvious knives, and the cutting edge is not easy to be gapped during the subsequent manual grinding.
Now all the engine special tools of our factory have added the cryogenic treatment process to the original conventional heat treatment. The main consumables for cryogenic treatment are liquid nitrogen. The power of the equipment is less than 1kW, the power consumption is very small, the operation is simple, and there is no environmental pollution. The application of cryogenic technology is a completely environmentally friendly technology, which has made our company's tool quality a new level as a whole, reducing manufacturing pressure, greatly reducing machine cost and significant economic benefits.
Cobalt, elemental symbol Co, silvery white ferromagnetic metal, slightly silvery white on surface, 4th period in Periodic Table, Group VIII, atomic number 27, atomic weight 58.9332, hexagonal close packed, common valence of +2 , +3. Cobalt is a shiny steel gray metal, relatively hard and brittle, ferromagnetic, magnetic disappeared when heated to 1150 ℃. Cobalt has valences of +2 and +3. It does not interact with water at room temperature and is stable in humid air. Cooled to CoO when heated in air to above 300 ° C, and burned into Co3O4 when whitened. Hydrogen reduction method made of fine metallic cobalt powder in the air can spontaneous combustion of cobalt oxide. Cobalt is an important raw material for the production of heat-resistant alloys, hard alloys, anti-corrosion alloys, magnetic alloys and various cobalt salts.
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