通过宏观检验、金相检验、能谱分析、现场跟踪了解,讨论分析了NC40钻杆接头产生裂纹的原因.结果表明:母接头外壁的裂纹为锻造折叠缺陷,接头圆棒料长径比过大,在大钳中部易形成凹陷折叠,是造成接头表面出现横向裂纹的主要原因;另外接头局部存在偏析,在加热时发生相对过热现象,晶界易达到熔点而弱化,使得折叠继续沿晶界延伸扩展.最后笔者结合实际生产提出了相应的改进措施和建议.

Through the macroscopic inspection,metallurgical structure inspection,energy spectrum analysis,and on-site tracking,crack formation reason of NC40 joint of drilling pipe was analyzed.The results show that the crack on the outer wall of the female joint was considered as the forging folding defect.Relatively too large length-diameter ratio of the joint round bar would be prone to the depression and fold in the middle of the tong,which was the main cause of the transverse crack on the joint surface.In addition,partial over heating caused alloy elements melting and segregating along the grain boundary.The folding defect extended along the weakened grain boundary.Finally,the corresponding improvement measures and suggestions were proposed combined with practical production.