分析冷拔鋼管的冷處理裂紋與預(yù)防措施

冷拔鋼管多為中，高碳合金鋼，淬火后還有部分過(guò)冷奧氏體未轉(zhuǎn)變成馬氏體，保留在使用狀態(tài)中成為殘余奧氏體，影響使用性能。預(yù)防措施：(1)冷拔鋼管淬火后冷處理之前將冷拔鋼管置于沸水中煮30—60min，可消除15%-25%淬火內(nèi)應(yīng)力并使殘余奧氏體穩(wěn)定化，再進(jìn)行-60攝氏度常規(guī)冷處理，或進(jìn)行-120攝氏度深冷處理，溫度愈低，殘余奧氏體轉(zhuǎn)變成馬氏體愈多，但不可能全部轉(zhuǎn)變完，實(shí)驗(yàn)表明，約有2%-5%殘余奧氏體保留下來(lái)，按需要保留少量殘余奧體可松弛應(yīng)力，其緩沖作用，因殘余奧氏體又軟又韌，能部分吸收馬氏體化急劇膨脹能量，緩和相變應(yīng)力;若置于零度以下繼續(xù)冷卻，能促使殘余奧氏體發(fā)生馬氏體轉(zhuǎn)變，因此，冷處理的實(shí)質(zhì)是淬火繼續(xù)。室溫下淬火應(yīng)力和零度下淬火應(yīng)力疊加，當(dāng)疊回應(yīng)力超過(guò)該材料強(qiáng)度極限時(shí)便形成冷處理裂紋。

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 transformation. 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 transformation stress. If the retained austenite is cooled below zero, the martensitic transformation 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 formation of cold treatment cracks when the superposition response exceeds the strength limit of the material. 

(2)冷處理完畢后取出冷拔鋼管投入熱水中升溫，可消除40%-60%冷處理應(yīng)力，升溫至室溫后應(yīng)及時(shí)回火，冷處理應(yīng)力進(jìn)一步消除，避免冷處理裂紋形成，獲得穩(wěn)定組織性能，確保冷拔鋼管產(chǎn)品存放和使用中不發(fā)生畸變。

(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 formation 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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