连轧钢管限动芯棒温度场及热疲劳有限元分析

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.

Finite element analysis on the temperature field and thermal fatigue of the retained mandrel in a multi-stand pipe mill

A finite element model of retained mandrel service process in 340MPM(Multi-Stand Pipe Mill) was built to research the temperature field change of the mandrel.The thermal stress of the mandrel was also studied to analyze the initiation mechanism and propagation law of fatigue cracks in the mandrel.A comparison between the measured data and the simulation results indicates that the model can reflect the temperature change of the mandrel.After the mandrel was detached from the tube,the highest temperature of the mandrel surface went up to 630 ℃.Then the mandrel went through three times of temperature-falling in water-cooling stages and three times of temperature-rising in air-cooling stages.At the end of the whole cooling process,the highest temperature of the mandrel surface was 98 ℃.Both the axial compressive stress and circumferential compressive stress reached to 900 MPa after the mandrel was detached from the tube.At the end of the 3rd water-cooling stage,the axial stress reached to 186 MPa,while the circumferential stress reached to 221 MPa.Cyclic thermal stress could lead to crack initiation and propagation in the mandrel,yet circumferential cracks would be significantly blocked at the place of 17.5 mm away from the surface,while axial cracks would be significantly blocked at the place of 20 mm away from the surface.The impetus for axial cracks which came from thermal stress was stronger than that for circumferential cracks.