Heat treatment process of medium frequency induction heating equipment for steel pipe

12CrlMoV steel pipe (wall thickness > 40mm) used in power transmission and distribution construction was heated. There were some problems such as low cooling speed, low hardness of steel pipe, such as air cooling, water spraying or oil immersion cooling. There were technical problems, large equipment investment and environmental pollution. Therefore, the heat treatment test of medium frequency induction heating equipment for 12CrlMoV steel pipe is carried out, and applied to production practice, and the results with practical value are obtained.

12CrlMoV steel pipe specimens were heated and austenitized, and then cooled in water at about 20 ℃. The heat treatment test of medium frequency induction heating equipment shows that in actual production, the immersion end temperature can be controlled according to the wall thickness and the corresponding immersion time. The microstructure of 12CrlMoV steel pipe after soaking in water and air cooling is characterized by more pearlite and granular bainite, which is beneficial to improve the high temperature rupture strength. The organization meets the technical requirements. At the same time, the hardness and other mechanical properties of the specimens meet the technical requirements, and the properties are excellent.

The effects of soaking cooling time, cooling rate and water temperature on steel pipe were investigated. The results show that the heat transfer per unit time is directly proportional to the temperature difference between the sample and the cooling medium, and the cooling rate of the sample is inversely proportional to the temperature of the cooling medium within a certain range. The heat treatment characteristics of medium frequency induction heating equipment for 12CrlMoV steel pipe are as follows: 1. The heat treatment process of 12CrlMoV steel pipe can improve the cooling rate of high temperature section (above 600 ℃ ± 50 ℃); Increasing the content of granular bainite and pearlite can improve its properties. 2. By controlling the immersion time, the immersion temperature can be controlled, so as to control the occurrence of martensite and avoid tube cracking. After immersion treatment, no martensite structure and crack are found, and the metallographic structure and performance indexes fully meet the technical requirements. 3. The low hardness defect in the production of 12CrlMoV steel pipe with wall thickness more than 40mm has been well solved by using medium frequency induction heating equipment heat treatment process. 4. In production, the soaking time can be determined according to the wall thickness of the steel pipe and the test curve, and the soaking time can also be adjusted according to the change of water temperature.