A Brief Analysis of the Failure of the Spring Ring of a Missile Calibration Unit
Hydrogen content analysis was conducted on the fracture spring washer, and the average hydrogen content was found to be 17@10â»â¶. The test results indicate that the metallurgical quality of the failed material meets the required standards, thereby ruling out the possibility of failure due to substandard raw materials. Although the hardness of the failed washer is slightly higher than usual, as it is made from 65Mn steel, which requires a relatively high hardness to ensure sufficient elasticity, the measured value only exceeds the upper limit by 0.5–1.0 HRC. This minor deviation does not affect its normal performance or service life. Analysis of the hydrogen source in the spring washer indicates that the primary source of hydrogen is the electroplating process. During electroplating, hydrogen evolution occurs simultaneously, and prior to plating, the workpiece undergoes pickling, which involves chemical reactions between the acid and surface oxides. In addition, some metal reacts with the acid, releasing hydrogen that can penetrate into the metal structure. Factors such as the composition of the pickling solution, temperature, duration, and the alloy's properties all influence the amount of hydrogen absorbed. As a result, significant amounts of hydrogen may remain in both the plating layer and the internal structure of the component after plating. The fracture morphology of the spring washer suggests that the failure resulted from hydrogen embrittlement. Hydrogen present within the metal matrix accumulates under applied stress, leading to embrittlement and eventual fracture. Microscopically, hydrogen atoms, being the smallest in size (with a radius of 0.053 nm), can easily diffuse into the metal's crystal lattice. Under stress, these atoms move toward regions of high stress, causing dislocation and rapid hydrogen concentration. When hydrogen atoms combine to form molecules, they generate a significant volume expansion, which can lead to crack initiation at grain boundaries or dislocation sites. Once a crack forms, it propagates rapidly, with the growth rate depending on the material type and hydrogen concentration. In some cases, the crack propagation speed can reach that of sound waves. Generally, hydrogen-induced cracking occurs when the hydrogen content in steel exceeds (5–10)@10â»â¶. In this case, the failed washer had an average hydrogen content of 17@10â»â¶. When hydrogen in the matrix encounters stress, it accumulates and eventually leads to embrittlement and fracture. This mechanism aligns with known causes of hydrogen embrittlement in high-strength steels. In conclusion, the fracture of the spring washer was caused by hydrogen embrittlement, resulting from inadequate post-plating hydrogen removal. This led to hydrogen accumulation during assembly, ultimately causing failure. Based on the failure analysis of the 65Mn steel spring washers, several recommendations are proposed: (1) consider replacing the spring washer material. It is noted that the Shanghai Spring Washer Factory was commissioned by the former aerospace industry to address hydrogen embrittlement issues with 65Mn spring washers. In November 1996, the factory began developing stainless steel spring washers and successfully completed the project by the same month. That year, the product passed acceptance tests by the Aerospace Corporation and Shanghai Standard Parts Corporation. Check Valve,Stainless Steel Check Valve,Quick Installation Check Valve,Quick Installation Stainless Steel Check Valve Ningbo Wenhan Fluid Equipments Co., Ltd. , https://www.wenhanvalves.com