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）选择合理的焊接规范和线能，改*焊缝及热影响区组织状态，如焊前预热、控制层温度、焊后缓冷或后热等以加*氢分子逸出。

(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）采用碱性焊条或焊剂，以降低焊缝中的扩散氧含量。

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

（3）焊条和焊剂在使用前应严格按照规定的要求进行烘干（低氢焊条300℃～3 50℃保温lh；酸性焊条l 00℃～l50℃保温lh；焊剂200℃～250.C保温2h），认真清理坡口和焊丝，去除油污、水分和锈斑等脏物，以减少氢的来源。

(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）焊后及时进行热处理。一是进行退火处理，以去除内应力，使淬火组织回火，改*其韧性；二：是进行消氢处理，使氢从接头中充分逸出。

(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#圆钢质量，减少钢材中的层状夹杂物。

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

（6）采取可降低应力的各种工艺措施。

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

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