| It has been very common to use internal thread in current machinery industry. Its quality has become an important indicator of evaluation of machine reliability; a high quality tap not only improved the production efficiency, but also an important guarantee for the accuracy of internal thread. Nowadays, HSS taps market is utilized widely in our country, but there are some toubles with HSS taps, such as low reliability, easy to wear and short service life, this caused a large area of HSS waste in our country, the development of industrialization will be seriously constrained if things go on like this. It is extremely urgent to improve taps service life.Under the support of the national natural fund(51275333),the research object of this paper is M2 high speed steel tap, cryogenic treatment after conventional heat treatment on tap. By using uniform design method, the tap's tempering parameters and cryogenic parameters will be optimized, and the optimized tap will be passivated. Finally, through the hardness test, torque test, life testing and metallographic analysis to explore the optimal combination between the cryogenic treatment and passivation treatment. According the microstructure of tap flank surface, the conclusions can be obtained that the precipitation of carbides and the blade shape change is the main reason for the increase of tap's service life. The research results provide some reference value for improving the service life of high speed steel complex cutter. The main contents and results in the paper were described as follows:(1) Optimization of heat treatment process for tap. According to the uniform design method, 5 factors are selected as the test variables. They are tempering temperature, tempering times, cryogenic temperature and cooling speed, cryogenic insulation time. Test data are analyzed by the method of two degree polynomial regression. At last, the result shows that cryogenic temperature for-76?, cryogenic time for 16 h, cryogenic speed for 1?/min, tempering temperature for 211? and tempering 3 times the tap have longest service life.(2) Study on tap's service life in different conditions. The result shows that cryogenic treatment can improve tap's service life, but the effect of repeated cryogenic treatment is much better than a long time cryogenic treatment. Before tempering to have a cryogenic treatment is much better than afer and the tap without tempering is the worst.(3) Study on strengthening technology of cutting edge. Electrolytic strengthening technology had been used to deal with taps. The result shows that tapping torque fluctuation is small and can easily pass early wear take tap into the stable wear stage so as to improve reliability. After observation the surface of passivation tap by scanning electron microscopy, find the cutting tool edge is smooth and surface grinding marks is abated. It plays an important role in resistance crack formation and spread. According life test it is discovered that passivation treatment need the material have certain toughness. Taps with cryogenic and high temperature tempering after passivation using life than ordinary tap is increased by 2.7 times.(4) Wear mechanism Analysis. SEM was used to observe the flank surface of tap. Found the tool surface has many broken pits, through the XRD analysis of its composition shows that abrasive wear, oxidation wear, adhesive wear is the main wear form. Abrasive wear and oxidation wear occurred in front of the cutting cone, while the adhesive wear mainly occurs at last few tooth of cutting cone. Compared with the conventional tap, it had stronger ability of anti adhesive after cryogenic passivation treatment. |
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