X70管线钢焊接热影响区的局部脆化

Local Brittleness of Weld Heat-Affected Zone of X70 Pipeline Steel

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 effects of thermal cycles on the low temperature brittleness and impact fracturemorphology of pipeline steel X70 were studied with the emphasis on the influence of the secondthermal cycles on the properties of coarse crystal zone. The results of experiments show that thelow temperature toughness goes down with the peak temperature increasing' The toughness isthe best at peak temperature of 950℃ and the fracture is dimple rupture. At peak temperatureof 1200℃ and 1360 ℃ the toughness is lower than the base metal's, and the fracture is cleavage. The toughness of the coarse crystal zone is improved at the second peak temperature of950℃, and the fracture is quasi-cleavage, but at the second peak temperature of 780 ℃, thefracture is cleavage and there are lots of micro-cracks.