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研究了热循环对Ｘ７０管线钢焊接热影响区低温脆性的影响及其断口特征，重点探讨了二次热循环对粗晶区性能的影响。结果表明，随着峰温的提高，低温冲击韧性下降．峰温９５０℃时韧性最好，断口形貌为韧窝状;;峰温１２００℃和１３６０℃时韧性低于母材，发生脆化，断口形貌为解理状。粗晶区再经峰温９５０℃第二次热循环作用韧性提高，断口形貌转变为准解理状;;再经７８０℃第二次热循环作用产生严重脆化，断口形貌为解理状，且存在大量微裂纹。
The effect of thermal cycling on the low temperature brittleness and the fracture characteristics of heat affected zone (HAZ) in X70 pipeline steel were studied. The effects of secondary thermal cycling on the properties of the coarse grain region were discussed. The results show that with the increase of peak temperature, the impact toughness at low temperature decreases. The peak temperature of 950 ℃, the best toughness, fracture morphology of dimple-like; peak toughness at 1200 ℃ and 1360 ℃ lower than the base metal, embrittlement occurs, the fracture morphology cleavage. The coarse-grained region was further heated by the peak temperature of 950 ° C for the second thermal cycle to improve its toughness and transform the fracture morphology into a quasi-cleavage shape. After the second thermal cycle at 780 ° C, severe embrittlement occurred and the fracture morphology was cleaved Like, and there are a lot of micro-cracks.