Improvement of the hottest high frequency quenchin

2022-08-08
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The improvement of high-frequency quenching process

content summary compares several different high-frequency quenching processes, improves the inductor, and selects a new type of quenching agent, so that the product reaches the level of imported parts

in the localization of an automobile factory, our factory has a kind of adjusting screw to do high-frequency quenching. The material of the screw is 42CrMo steel. It is required to carry out high-frequency quenching on the spherical end. The hardness after quenching is ≥ 52hrc, and the depth of the hardened layer is mm

at first, we believe that the required deep hardening layer is the key to the heat treatment of this process. A longer heating time was used in the initial test. The test process and results are shown in Table 1. Although the surface hardness and hardening depth meet the requirements, long cracks appear in the quenched part. At the same time, due to the long heating time, a decarburization layer of 0.15mm was also produced. Table 1 preliminary test process and results

positive voltage/kv positive current/a grid current/a heating time/s cooling medium hardening layer depth/mm hardness/hrc decarburization layer depth/mm1130.68 tap water immersion quenching 3 9540.15

after analysis, we believe that quenching cracking and surface decarburization may be caused by too long heating time. For this reason, several test schemes to shorten the heating time are adopted. The test process and results are shown in Table 2. Table 2 process and results of shortening heating time

serial number process parameter test results positive pressure/kv positive flow/a grid flow/a heating time/s cooling medium hardening layer depth/mm hardness/hrc decarburization layer depth/mm crack 111.02.40.507.0 tap water immersion quenching 3 8540.120 found several small cracks 210.52.40.406.5 tap water immersion quenching 3 7550.100 310.52.20.355.5 tap water immersion quenching 2 3550.030 410.52.20.355.0 tap water immersion quenching 2 1550.005

after the heating time is shortened according to the scheme in Table 2, the quenching hardness and quenching depth still meet the requirements. The heating time of scheme 4 is shortened to 5S, and the depth of surface decarburization layer can also be reduced to 0.005mm. However, these schemes fail to solve the problem of quenching cracking

according to our previous experience, quenching with appropriately concentrated polyvinyl alcohol solution in October may solve the problem of quenching crack of 42CrMo steel. Therefore, on the basis of the above process tests, a test scheme with two concentrations of polyvinyl alcohol aqueous solution as the cooling medium was arranged. The test process and results are shown in Table 3. Table 3 test process and results of polyvinyl alcohol aqueous solution

serial number process parameter test results positive pressure/kv positive current/a grid current/a heating time/s cooling medium hardening layer depth/mm hardness/hrc decarburization layer depth/mm crack 110.52.20.355.00.3% polyvinyl alcohol solution 2 1540.005 there is 210.52.20.355.00.5% polyvinyl alcohol solution 2 1540.005 there are

two concentrations of polyvinyl alcohol, which can not solve the problem of quenching crack. At this time, we thought of the article in the magazine (metal heat treatment) that PAG type new water-soluble quenchant successfully solved the problem of induction quenching cracking of alloy structural steel [1]. Finally, Beijing Huali fine chemical company was selected and PAG quenchant Jinyu was purchased. According to the recommendation of the company, we arranged two tests with a concentration of 10%. The process and results of the test are shown in Table 4. Table 4 test process and results of Jinyu

serial number process parameter test results Yang voltage/kv Yang current/a grid current/a heating time/s cooling medium hardening layer depth/mm hardness/hrc decarburization layer depth/mm crack 110.52.20.355.0 Jinyu immersion quenching 2 1540.005 no 210.02.20.355.0 Jinyu immersion quenching 2 8540.005 no

quenching crack problem has been solved, and the heat treatment requirements have been met. However, the depth of hardened layer is not uniform. Check the section of the quenched workpiece, and find that the edge of the spherical end has a shallow hardening layer, while the controller and computer are closed in the middle; The middle part is deep

as a comparison, we checked the distribution of the hardened layer of the imported original. The distribution of the hardening layer of the part is basically similar to that of the spherical end face, and the hardening layer is basically uniform. According to the principle of induction heating [2], the way to solve this problem should be to improve the indicating value of the impact testing machine to be high or low: the reason is that the relative initial position between the rod and the punch of the meter is not the right sensor. Figure 2 is the schematic diagram of the position relationship between the original sensor and the workpiece. Figure 3 is the schematic diagram of the position relationship between the improved sensor and the workpiece

a group of tests were carried out with the improved sensor. The process parameters and results are shown in Table 5. After inspection and comparison, all indicators are equivalent to the quality of imported parts. The hardening layer is uniform, and all of them have achieved the desired effect. The production has been carried out according to the process in Table 5. Table 6 shows the results of the comparative test. Table 5 test parameters and results after improving the inductor

process parameters test results positive area ratio is 1: (0.35 ~ 0.5) equivalent to volume ratio of 1: (0.207 ~ 0.354) Pressure/kv positive current/a grid current/a heating time/s cooling medium hardening layer depth/mm hardness/hrc decarburization layer depth/mm crack 10.02.20.355.0 today Yu immersion quenching 2.8

550.005 no

Table 6 quality comparison with imported parts

analysis project imported parts factory production parts matrix hardness (HRC) 2628 matrix structure fine sorbite fine sorbite ball joint hardness (HRC) 5455 depth of hardened layer/mm2.62.8 length of transition zone/mm0.200.30 microstructure of hardened layer cryptoacicular martensite ≤ grade 3 cryptoacicular martensite ≤ grade 3

in the test of determining the production process, there were problems of over quenching crack, decarburization and uneven depth of hardened layer. Through analysis and research, with the help of the information provided by the magazine "metal heat treatment", the problem was solved from the aspects of induction heating time, quenching medium, inductor, etc., and the heat treatment quality of the adjusting screw reached the quality level of similar foreign products

References:

[1] Kang en, guoyufang, Feng Ruchang, et al Medium frequency quenching and tempering process for large cast steel main rail [j] Metal heat treatment, 2000, (9): 36

[2] editorial board of heat treatment manual. Heat treatment manual (2nd Edition, Volume 1) [m]. Beijing: Machinery Industry Press.1991:192. (end)

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