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通过电子拉伸、硬度测试以及金相组织分析,对X70大变形管线钢焊接接头的力学性能及显微组织进行了深入研究。结果表明,X70焊接接头均断裂于焊缝附近(近缝区);X70焊接接头热影响区粗晶区存在明显的软化,焊接接头上表面硬度损失大于下表面,最大硬度损失达28 HV0.2,但下表面软化区宽度大于上表面。X70焊接接头热影响区粗晶区大量粗大的粒状贝氏体和准多边形铁素体的存在是导致焊接接头热影响区软化并断裂于焊缝附近(近缝区)的主要内因。
The mechanical properties and microstructure of the welded joint of X70 large deformation pipeline steel were studied deeply by means of electronic tensile test, hardness test and microstructure analysis. The results show that the X70 welded joints are all fractured near the weld (near seam area); the HAZ of the X70 welded joints is obviously softened, the loss of the upper surface hardness of the welded joints is greater than that of the lower surface, and the maximum hardness loss is 28 HV0.2 , But the lower softened surface area is wider than the upper surface. The existence of a large number of coarse granular bainite and quasi-polygonal ferrite in the HAZ of the X70 welded joints is the main internal cause of the heat affected zone (HAZ) of the welded joints softening and breaking near the weld (near seam).