Cold-drawn steel pipes are mostly medium and high carbon alloy steels. After quenching, some undercooled austenite does not transform into martensite, and retains as retained austenite in service state, which affects service performance. Preventive measures: (1) Boiling cold-drawn steel tube in boiling water for 30-60 minutes before quenching can eliminate 15%-25% internal stress and stabilize retained austenite, then conventional cooling treatment at - 60 degrees Celsius or deep cooling treatment at - 120 degrees Celsius. The lower the temperature, the more retained austenite transforms into martensite, but it is impossible to complete the transion. The experiment shows that about 2% retained austenite transforms into martensite. The retained austenite retains between%-5% and retains a small amount of residual austenite to relax stress as needed. Its cushioning effect is that retained austenite is soft and tough, which can partly absorb the rapidly expanding energy of martensitization and alleviate the phase transion stress. If the retained austenite is cooled below zero, the martensitic transion of retained austenite can occur. Therefore, the essence of cooling treatment is to continue quenching. The superposition of quenching stress at room temperature and quenching stress at zero degree results in the ion of cold treatment cracks when the superposition response exceeds the strength limit of the material.
(2) After the cold treatment, the cold-drawn steel pipe is taken out and heated in hot water, which can eliminate 40%-60% of the cold treatment stress. When the temperature rises to room temperature, it should be tempered in time. The cold treatment stress should be further eliminated to avoid the ion of cold treatment cracks, obtain stable structure and properties, and ensure that no distortion occurs in the storage and use of cold-drawn steel pipe products.
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