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Analysis and Preventive Measures of Cold Treatment Cracks on Seamless Steel Pipes

Date:2019-12-19    keywords:seamless steel pipe,cold treatment,cracks
Most of the seamless steel tubes are medium and high carbon alloy steels. After quenching, some supercooled austenite has not been converted into martensite, and remains in the use state as residual austenite, which affects the performance. If it is cooled below zero, it will 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 degrees are superimposed. When the superimposed stress exceeds the strength limit of the material, it will form a cold treatment crack.

Precaution: 
(1) Seamless steel pipes are boiled in boiling water for 30-60 minutes before quenching after quenching, which can eliminate 15% -25% quenching internal stress and stabilize residual austenite, and then perform conventional cold processing at -60C, or After -120C cryogenic treatment, the lower the temperature, the more the amount of retained austenite is transformed into martensite, but it is impossible to complete the transformation. Experiments show that about 2% -5% retained austenite is retained and retained as required A small amount of residual austenite can relax the stress and play a buffering role. Because the residual austenite is soft and tough, it can partially absorb the rapid expansion energy of martensitization and ease the phase transition stress;
(2) After the cold treatment is completed, the seamless steel pipe is taken out and heated in hot water, which can eliminate 40% -60% of the cold treatment stress. It should be tempered in time after warming to room temperature.The force is further eliminated, and the formation of cracks during cold treatment of rabbits is avoided to obtain stable structural properties and ensure that no distortion occurs during storage and use of seamless steel pipe products.

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