X70大变形管环焊接头及断裂机制研究

X70 Large Deformed Pipe Ring Welded Joint and Fracture Mechanism

目的基于应变设计大变形管线环焊接头热影响区的软化问题,解决制约管线安装质量和服役寿命等难题。方法通过显微硬度测试、微观组织分析,研究了X70大变形管接头热影响区的软化原因,并利用数字相关法研究了焊接接头拉伸过程中的断裂机制,还对焊接接头热影响区进行了激光增强探索。结果 X70焊接接头热影响区粗晶区的最大硬度损失达HV0.239;软化区最大应变达到37%以上;经过热影响区激光重熔后,X70钢焊接接头抗拉强度可提高10%以上,断裂位置均位于母材。结论 X70焊接接头热影响区粗晶区存在明显的软化;拉伸过程中在软化区出现了明显的应变集中,是X70焊接接头断裂于近缝区的主要原因;焊接接头热影响区粗晶区粗大的粒状贝氏体和铁素体导致了焊接接头热影响区的软化。

The work aims to solve the problem restricting the installation quality and service life of pipeline for the softening of heat affected zone of ring weld joints of large deformation pipelines based on strain design. The softening causes of the heat affected zone of X70 large deformation pipe joints were studied by microhardness test and microstructure analysis, and the fracture mechanism during the welding process was studied by digital correlation method. The laser enhancement of the heat affected zone of welded joints was also explored. The maximum hardness loss in the coarse-grained zone of the heat-affected zone of X70 welded joints was HV0.239;the maximum strain in the softened zone was above 37%;after laser remelting in the heat-affected zone, the tensile strength of X70 steel welded joints could be increased by over 10%;and the fracture position was located in the base material. The coarse-grained zone in the heat-affected zone of X70 welded joints is obviously softened and obvious strain concentration appears in the softened zone during stretching, which is the main reason for X70 welded joints to fracture in the near-seam zone. The coarse grained bainite and ferrite in the zone cause softening of the heat affected zone of the welded joint.