Cold crack generally refers to that the temperature of the weld drops to the martensitic transformation temperature range during the cooling process. It can occur immediately after welding or after a long time, so it is also called delayed crack. How can we prevent the cold crack of 55# round steel?

（1）選擇合理的焊接規范和線能，改*焊縫及熱影響區組織狀態，如焊前預熱、控制層溫度、焊后緩冷或后熱等以加*氫分子逸出。

(1) Select reasonable welding specifications and linear energy, and change the microstructure of * weld and heat affected zone, such as preheating before welding, temperature of control layer, slow cooling or post heating after welding, so as to escape hydrogen molecules.

（2）采用堿性焊條或焊劑，以降低焊縫中的擴散氧含量。

(2) Alkaline electrode or flux shall be used to reduce the diffuse oxygen content in the weld.

（3）焊條和焊劑在使用前應嚴格按照規定的要求進行烘干（低氫焊條300℃～3 50℃保溫lh；酸性焊條l 00℃～l50℃保溫lh；焊劑200℃～250.C保溫2h），認真清理坡口和焊絲，去除油污、水分和銹斑等臟物，以減少氫的來源。

(3) The welding rod and flux shall be dried in strict accordance with the specified requirements before use (low hydrogen welding rod shall be kept warm at 300 ℃ ~ 350 ℃ for 1H; acid welding rod shall be kept warm at 100 ℃ ~ L50 ℃ for 1H; flux shall be kept warm at 200 ℃ ~ 250. C for 2H), and the groove and welding wire shall be carefully cleaned to remove dirt such as oil, moisture and rust, so as to reduce the source of hydrogen.

（4）焊后及時進行熱處理。一是進行退火處理，以去除內應力，使淬火組織回火，改*其韌性；二：是進行消氫處理，使氫從接頭中充分逸出。

(4) Heat treatment shall be carried out in time after welding. One is to carry out annealing treatment to remove internal stress, temper the quenched structure and change its toughness; 2： It is to carry out hydrogen elimination treatment to fully escape hydrogen from the joint.

（5）提高55#圓鋼質量，減少鋼材中的層狀夾雜物。

(5) Improve 55# round steel quality and reduce layered inclusions in steel.

（6）采取可降低應力的各種工藝措施。

(6) Take various technological measures that can reduce stress.

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