Titanium alloy is a typical difficult to machine material, but it has excellent comprehensive mechanical properties and occupies an irreplaceable position in the aerospace field. Therefore, in cutting titanium alloy, higher requirements are put forward for tool materials. Ultra fine grained cemented carbide and high performance high speed steel are typical tool materials for titanium alloy finishing and rough machining respectively. Ultra low temperature treatment (or cryogenic treatment) is a green production technology, which plays an important role in improving the mechanical properties of materials, in line with the development trend of the times. The main content of this paper is to investigate the effect of different ultra-low temperature treatment on the mechanical properties of yg12 and M2A1 and the strengthening mechanism.
Firstly, the ultra-low temperature treatment technology and mechanism analysis of yg12 ultra-fine grain cemented carbide were studied, including processing time, times, methods and post annealing treatment. The results show that: ultra-low temperature treatment can improve the mechanical properties of materials, with the extension of treatment time, the mechanical properties of materials are also improved; many times of short-term cryogenic treatment can improve the mechanical properties of materials, when the cryogenic treatment for three times, the bending strength of the material decreases, and there are microcracks at the fracture surface. The effects of two cryogenic methods, immersion in liquid nitrogen and holding at a cooling rate of 3 ℃ / min to – 196 ℃ were investigated. The results showed that the properties of the material would not be reduced by immersion in liquid nitrogen directly in a cryogenic process. The effect of residual thermal stress on the mechanical properties of materials was studied by combining cryogenic treatment with annealing treatment, The reduction of residual stress is beneficial to improve the mechanical properties of the material. After repeated cryogenic and annealing treatment, the micro defects of the material can be repaired, and the mechanical properties of the material can be greatly improved. The bending strength of the material is increased by about 40% compared with that in the non cryogenic state. Comprehensive analysis shows that cryogenic treatment can improve the mechanical properties of materials, which is the result of the transformation from α – CO to ε – CO and relaxation of residual thermal stress. Secondly, the cryogenic treatment process and mechanism of m2ai high-speed steel were studied, including the treatment time, times, methods and cryogenic and heat treatment process sequence. The results show that: ultra-low temperature treatment can also improve the mechanical properties of M2A1 material and promote the precipitation of more secondary fine carbides; the effect of cryogenic treatment on M2A1 is not obvious after 20 hours of cryogenic treatment, and the carbides precipitated after quenching and cryogenic are all diamond structure fe3w3c; after two times of short-term cryogenic treatment, the mechanical properties of the material can be improved, and the bending strength of the material decreases sharply after three times of cryogenic treatment, The results show that there are many microcracks on the fracture surface, which can be reduced to – 196 when the material is immersed in liquid nitrogen at a speed of 3 ℃ / min. The results show that the properties of the material will not be reduced by directly immersing in liquid nitrogen in a cryogenic process; tempering treatment before cryogenic treatment can improve the stability of austenite and reduce the effect of cryogenic treatment. After tempering after cryogenic treatment, the strength of the material is greatly increased, and the bending strength is increased by about 60% compared with that in the quenched state, The secondary hardening temperature of M2A1 high speed steel is reduced to 500 ℃ by cryogenic treatment, and the hardness is increased by 15% to 1180hv. The main reason why cryogenic treatment improves the mechanical properties of M2A1 high speed steel is that the cryogenic process promotes the transformation of retained austenite into martensite, and there are a lot of fe3w3c precipitated with diamond structure. This kind of carbide has very high hardness and strength. The diamond structure is very stable and not easy to be damaged, which plays a role of dispersion strengthening.