H13热作模具钢冲头的早期断裂原因

Early Fracture Cause of H13 Hot Die Steel Punch

某H13热作模具钢冲头在锻打钻杆管端后,抽出时发生早期断裂。通过断口形貌观察、化学成分分析、显微组织观察、微区成分分析等方法探讨了冲头断裂的原因。结果表明:该冲头断裂的性质为疲劳断裂;冲头工作部位外壁区域存在的大尺寸Al2O3、MnS、VC等夹杂物以及气孔、疏松等缺陷处易产生应力集中而成为疲劳裂纹源,在热应力、拉应力、压应力和弯曲载荷的反复作用下,横向微裂纹萌生并以发散形式快速失稳扩展,导致冲头断裂;该冲头中钼、钒的含量远低于标准值下限,导致冲头的高温力学性能降低,从而造成了冲头的疲劳断裂。

An H13 hot die steel punch fractured during extracting after drilling and forming of drill pipe.The reason for the fracture of the punch was studied by fracture morphology observation,chemical composition analysis,microstructure observation and micro-area composition analysis.The results show that the fracture type of the punch was early fatigue brittle failure.The locations of large inclusions of Al2O3,MnS,VC and defects such as pore and porosity in the outer wall area of the punch work site were easy to produce stress concentration,and became the fatigue crack source.Under cyclic thermal stress,tensile stress,compressive stress and bend load,the lateral microcracks intiated and extended rapidly in divergence form,which eventually led to the fracture of the punch.The content of Mo and V of the punch was far below the lower limit of standard values,resulting in decrease of high temperature mechanical properties of the punch,and then the fatigue fracture of the punch was accelerated.