通过化学成分分析、力学性能试验、显微组织及开裂形貌观察等方法, 对X70钢直缝埋弧焊管导向弯曲开裂原因进行了分析。结果表明: 开裂钢管焊接接头热影响区存在明显软化; 弯曲过程中塑性变形集中在软化的热影响区, 过量的塑性变形引起粗晶区粗大M/A岛与板条铁素体界面的应力集中程度超过了材料的抗拉强度, 导致弯曲开裂; 建议钢管厂根据钢板的化学成分、组织及力学性能制定相应的焊接工艺。

By the methods of chemical composition analysis, mechanical properties test, microstructure and crack morphology observation, the cracking reasons of X70 steel submerged arc weld pipe during guide-bend test were analyzed. The results show that the heat affected zone (HAZ) of cracked steel pipe erxhibited obvious softening, and the plastic deformation concentrated on softened HAZ during bend test. Superfluous plastic deformation caused the stress concentration on the interface between coarse M/A island in coarse grain zone and lathy ferrite, when the stress exceeded the tensile strength of the material, bending cracking happened. It was suggested that the steel pipe plant should establish corresponding welding process according to the chemical composition, microstructure and mechanical properties of the steel sheets.