锥裙锁表面疑似裂纹磁痕显示原因分析

飞机机尾罩与机体连接用ZG0Cr14Ni5Mo2Cu不锈钢锥裙锁铸钢件,在磁粉检测时,其表面有多条疑似裂纹状线性磁痕显示,后采用荧光渗透检测方法进行辅助检测,原磁痕显示处未见异常荧光显示。采用表面形态-组织特点-成分分布-磁性变化相结合的研究思路,开展表面形态电镜观察、显示区剖面金相检查、组织微区成分能谱分析、材料硬度测试、XRD相分析以及模拟热处理等试验。结果表明:锥裙锁磁痕显示区未见表面缺陷,铸钢的枝晶间存在较粗大条状分布的残余奥氏体组织,这种组织差异破坏了材料磁性的连续性,导致其表面出现磁痕显示;锥裙锁宏微观组织不均匀,存在奥氏体富集区,其产生与C、S、P类元素偏析有关,研究为该材料零件在磁粉检测时的磁痕判定提供了依据和借鉴。

Causes Analysis of Crack-like Magnetic Trace Display on Conical Apron Locking Surface

ZG0Cr14Ni5Mo2Cu stainless steel cone skirt lock castings are used for connecting the aircraft tail cover with the body. During the magnetic powder detection, there were a number of suspected linear magnetic cracks on the surface, and then the fluorescence penetration detection method was used for auxiliary detection. There was no abnormal fluorescence display at the original magnetic trace display. The surface morphology, microstructure characteristics, composition distribution and magnetic changes were studied, and the experiments were carried out, such as surface morphology observation by electron microscopy, metallographic examination of the section of the display area, energy spectrum analysis of the components at the microstructure area, hardness test of materials, XRD phase analysis and simulated heat treatment. The results show that there are no surface defects at the magnetic trace display area of the cone skirt lock, and there are residual austenite structures of thick and large strips between the dendrites of the cast steel. This difference in structure destroys the magnetic continuity of the material, resulting in the appearance of magnetic traces on its surface. The macro and microscopic structures of the cone skirt lock are not uniform, and there are austenitic rich areas, which are related to the segregation of C, S and P elements. This study provides a basis and reference for the determination of magnetic trace during magnetic powder detection.