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Analysis and Preventive Measures of Seamless Steel Tube Cold Treatment Cracks

Date:2021-07-23    keywords:seamless steel tube, cold treatment

The seamless steel tubes are mostly medium and high-carbon alloy steels. After quenching, some of the subcooled austenite is not transformed into martensite, and it remains in the service state to become retained austenite, which affects the service performance. If it is placed below zero to continue cooling, it can promote the martensite transformation of retained austenite. Therefore, the essence of cold treatment is to continue quenching. The quenching stress at room temperature and the quenching stress at zero are superimposed, and when the stack response force exceeds the strength limit of the material, cold treatment cracks are formed.


seamless tube


Precaution:
(1) After the seamless steel tube is quenched and cold treated, the seamless steel tube is placed in boiling water for 30-60 minutes, which can eliminate 15%-25% of the internal quenching stress and stabilize the retained austenite, and then perform the conventional cold treatment at -60°C. Or carry out -120℃ cryogenic treatment, the lower the temperature, the more the amount of retained austenite transformed into martensite, but it is impossible to complete the transformation. Experiments show that about 2%-5% of retained austenite remains. Press It is necessary to retain a small amount of retained austenite to relax the stress and play a buffering role. Because the retained austenite is soft and tough, it can partially absorb the energy of the rapid expansion of martensitization and ease the transformation stress;

(2) After the cold treatment is completed, the seamless steel tube is taken out and put in hot water to heat up, which can eliminate 40%-60% of the cold treatment stress. After the temperature is raised to room temperature, it should be tempered in time. The cold treatment stress is further eliminated to avoid the formation of cold treatment cracks and obtain stable tissue performance. Ensure that the seamless steel tube products are not deformed during storage and use.


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