超高温金属铸锻件缺陷电磁超声在线检测方法研究

The application of Electromagnetic Acoustic technology into non-destructive testing of metal castings and forgings with ultra-high temperature (>800℃) in forging process, is vital significant for improving the yield rate and the economy of the castings and forgings manufacturer in our nation. Upon on this technology, the defects can be detected and repaired in early stage of manufacture, and those components with excessive defects are removed in time..In this project, theories and methods for the application of Electromagnetic Acoustic technology into on-line detection in the castings and forgings with ultra-high temperatures are carried out. The circuit-field coupling numerical model of the progress for Electromagnetic Acoustic testing is established. Using theoretical analysis, numerical calculation and experimental testing, the transmitting and receiving mechanisms of the normal beam bulk wave Electromagnetic Acoustic Transducer (EMAT) and the line-focusing shear vertical wave EMAT applied in the castings and forgings with evaluated temperatures, rough surface and oxide layers are investigated. The patterns of defect evaluation error and its real-time compensation method with respect to rough surface, oxide layers and lift-off with high temperature are also analyzed. The numerical model and ray-tracing mathematical model for the propagation of ultrasonic waves in the castings and forgings with non-uniformed high temperature are established, and the characteristics of the propagation path and energy attenuation of ultrasonic waves in non-uniformed temperature is investigated. The features of scattering and waveform conversion for the interaction between ultrasonic waves and defects in non-uniformed temperature are analyzed. The compensation method for the estimating deviation of the defect sizing and positioning in non-uniformed temperature is also provided..The project employs the potential to form the independent innovation of the key technology in this field with important academic significance and application value.

采用电磁超声技术对锻造过程中超高温(>800℃)金属铸锻件进行无损检测，在制造初期发现并修复缺陷，及时剔除缺陷超标件，对提高我国铸锻件成品率和制造经济性水平有着至关重要的意义。.本项目提出开展超高温铸锻件电磁超声在线检测理论与方法研究。建立脉冲电磁铁式电磁超声检测的场路耦合数值模型，通过理论分析、数值计算和实验测试，研究表面粗糙形貌、金属氧化层、高温铸锻件的直入射P&S波/线聚焦SV波电磁超声换能器激励/接收机理，研究高温状态下，表面粗糙形貌、金属氧化层和提离对缺陷定量评价偏差的影响机制及其在线补偿方法；建立超声波在非均匀高温铸锻件中传播数值模型和射线追踪数学模型，研究超声波在非均匀温度场中的传播路径和能量衰减特性，分析超声波在非均匀温度场中与缺陷的散射和波形转换特性，提出非均匀高温缺陷定量/定位偏差补偿方法。.本项目具有在该领域关键技术上形成自主创新的可能，具有重要的学术意义和应用价值。

在高温连铸和锻造过程中实时检测大型铸锻件裂纹、夹杂和空洞等缺陷，提高制造质量和水平是我国装备制造业、核电工业急需解决的重要课题。本课题研究工作如下：.(1) 研制了chirp脉冲压缩技术的1MHz螺旋线圈EMAT探头，在720℃、3mm提离、无同步平均时，与tone-burst激励相比，脉冲压缩的SNR提高了5.4dB，主瓣宽度减小了58.8%。当碳钢平底孔埋深为80mm，500℃时可检出Φ4平底孔，730℃时可检出Φ6平底孔。.(2) 建立chirp脉冲压缩技术的螺旋线圈EMAT激励过程的场路耦合有限元模型，通过对导线直径、阻抗匹配方式以及匹配参数进行优化后，主瓣幅值提高了3.16倍，主瓣宽度减少了24%。.(3) 建立了chirp脉冲压缩技术的0.5MHz跑道线圈EMAT有限元模型，经优化后，在3.5mm提离、无同步平均时，Φ4平底孔的SNR可达8.0dB。.(4) 研制了基于chirp脉冲压缩技术的0.2-0.4MHz跑道线圈EMAT探头，对于反射式，提离可达4mm，SNR为13.6 dB。在碳钢为730℃时，无同步平均的脉压信号的SNR相当于64次同步平均。.(5) 将Barker码和组合Barker码脉冲压缩技术应用于跑道线圈EMAT，以800℃高温锻件和铸件为对象，比较了Chirp信号、Barker码和组合Barker码脉冲压缩技术的检测优势。.(6) 搭建了激励频率为0.2MHz-2MHz、峰值功率为24kW的EMAT激励电路和频率为0.2MHz-2MHz、增益为60dB-110dB的EMAT接收电路。.(7) 建立了高温铝合金EMAT场路耦合有限元模型，研究了温度对换能效率、激励/接收电路功率分配、超声扩散衰减和回波幅值的影响。.(8) 建立了凸面/凹面/平面构件的线聚焦/传统斜入射SV波EMAT辐射声场有限元模型，研究了曲率半径、EMAT参数对辐射声场的影响。当采用线聚焦SV波EMAT，裂纹回波幅值提高1倍以上。.(9) 建立了直入射/斜入射超声波在非均匀高温铸锻件中的传播有限元模型和三角形追踪射线数学模型。三角形前向展开法对直入射超声波温度重建的误差在3%以内。当采用斜入射超声波时，传播声线路径受温度梯度、入射角度影响较大。.本课题所形成的高温EMAT可以实现高温连铸和锻造过程中的缺陷在线检测，据此调整制造工艺参数，实现缺陷控制与消除。