某NC38钻杆接头在调质处理后的车外圆、内孔工序中发现内壁存在横向裂纹。通过宏观观察、化学成分分析、金相分析以及能谱分析等方法，对钻杆接头内壁裂纹产生原因进行了分析。结果表明：用于生产该钻杆接头的钢锭在切除冒口时未切除到位，钢锭中有缩孔残余没有切除干净，使得用于生产该接头的圆棒料内部存在缺陷，并导致接头在后续的加工工序中产生开裂。最后提出了相关建议以避免此类缺陷造成的损失。

An NC38 drill pipe joint was found to have transversal cracks in the inner wall during machining outer circle and inner hole after quenching and tempering treatment. The causes of cracks in the inner wall of the drill pipe joint were analyzed by macro observation, chemical composition analysis, metallographic analysis and energy spectrum analysis. The results show that the steel ingot for the production of the drill pipe joint was not cut enough from the top and left residual shrinkage in the ingot, which caused defects in the round bar for the production of the joint and then resulted in cracking of the joint in the subsequent processing. Finally, relevant suggestions were put forward to avoid losses caused by such defects.