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针对340MPM机组(Multi-Stand Pipe Mill限动芯棒连轧管机组)芯棒服役过程建立三维有限元模型,研究芯棒在服役过程中温度场变化规律.同时,通过对热应力的研究,分析了芯棒热疲劳裂纹萌生机理及裂纹在芯棒内部的扩展规律.对比实测数据与模拟结果,认为所建立的有限元模型能够反映芯棒温度变化趋势.芯棒首次脱管后表面最高温度为630℃,此后经历三次反复的水冷降温和空冷返温过程,冷却结束后表面最高温度为98℃.脱管后,芯棒表面轴向和环向压缩热应力均达到900 MPa,第三次水冷结束时刻,轴向拉伸热应力达到186 MPa,环向拉伸热应力达到221 MPa.芯棒的拉压交变热应力使其表面出现热疲劳裂纹并逐渐扩展,环向裂纹扩展至距表面17.5mm深、轴向裂纹扩展至距表面20mm深时会显著受阻,热应力对轴向裂纹的促进作用强于环向裂纹.
A three-dimensional finite element model was established for the mandrel service of 340MPM unit (Multi-Stand Pipe Mill), and the variation of temperature field during the service of mandrel was studied. At the same time, through the study of thermal stress, The crack initiation mechanism of the mandrel and the propagation of the crack in the mandrel were compared.The measured data and the simulation results show that the established finite element model can reflect the trend of the mandrel temperature.The maximum surface temperature of the mandrel after the first de- 630 ℃, and then subjected to repeated water-cooling and air-cooling to return temperature process three times, the maximum surface temperature after cooling is 98 ℃, the axial and circumferential compressive thermal stress of the mandrel surface reaches 900 MPa, At the end, the axial tensile stress reached 186 MPa and the circumferential tensile thermal stress reached 221 MPa. The hot tensile stress of the mandrel caused thermal fatigue cracks on the surface and gradually expanded, and the circumferential crack extended to the surface 17.5mm deep, the axial cracks extended to 20mm deep from the surface will be significantly blocked, thermal stress on the axial crack promotion role is stronger than the circumferential crack.