某42CrMo钢三棱螺旋钻杆接头在进行煤层钻采过程中发生断裂。采用宏观观查、化学成分分析、力学性能测试、硬度测试、金相检验、应力分布有限元模拟等方法对钻杆接头断裂的原因进行了分析。结果表明：该42CrMo钢三棱螺旋钻杆热处理时因回火温度过低，使其硬度偏高，造成冲击吸收能量偏低，韧性较差，在扭转、弯曲等交变载荷作用下，于螺纹牙底的应力集中处发生早期疲劳断裂。

A 42CrMo steel triangular spiral drill pipe joint fractured during the coal seam drilling. The fracture causes of drill pipe joint were analyzed by means of macro observation, chemical composition analysis, mechanical property test, hardness test, metallographic examination and finite element simulation of stress distribution. The results show that the hardness of the 42CrMo steel triangular spiral drill pipe was too high because of low tempering temperature during heat treatment, resulting in low impact absorption energy and poor toughness. Under the action of alternating loads such as torsion and bending, the early fatigue fracture occurred at the stress concentration of the thread bottom.