A Brief Analysis of the Failure of the Spring Ring of a Missile Calibration Unit
Hydrogen content determination: The hydrogen content of the fractured spring washer was measured, and the average value was found to be 17×10â»â¶. These test results indicate that the metallurgical quality of the failed material meets the required standards, and thus, the failure cannot be attributed to poor raw material quality. Although the hardness of the failed washer is slightly higher than usual, it is within acceptable limits for 65Mn steel, which typically requires a high hardness to ensure sufficient elasticity. The measured hardness exceeded the upper limit by only 0.5–1.0 HRC, which does not affect its normal performance. Hydrogen source analysis: Based on the manufacturing process, the primary source of hydrogen in the spring washer is the electroplating procedure. During electroplating, hydrogen evolution occurs simultaneously, contributing to hydrogen absorption. Prior to plating, the workpiece undergoes pickling, during which the surface is cleaned. In addition to chemical reactions between the oxide layer and the acid, some metal also reacts with the acid, releasing hydrogen that penetrates into the metal. Factors such as the composition of the pickling solution, temperature, duration, and alloy type all influence the amount of hydrogen absorbed. As a result, both the plating layer and the internal structure of the component may contain significant amounts of hydrogen after the process. Fracture analysis of the spring washer: The fracture morphology indicates that the failure is due to hydrogen embrittlement. Hydrogen present in the metal matrix accumulates under applied stress, leading to embrittlement. Microscopically, hydrogen atoms have the smallest atomic radius (RH = 0.053 nm), making them highly mobile and capable of diffusing into the metal's crystal lattice. Under stress, these atoms cause dislocations, leading to rapid hydrogen accumulation at regions of high stress. When hydrogen atoms combine to form molecules, they produce a volume expansion effect, resulting in crack initiation at grain boundaries or dislocation sites. Once cracks form, they propagate rapidly, with propagation rates varying depending on the material and hydrogen concentration. In some cases, crack growth can reach the speed of sound. Generally, when the hydrogen content in steel exceeds (5–10) × 10â»â¶, hydrogen-induced cracking may occur. In this case, the average hydrogen content in the failed washer reached 17 × 10â»â¶. When hydrogen in the matrix encounters stress, it accumulates and eventually leads to hydrogen embrittlement and fracture. Conclusion: The fracture mechanism of the spring washer is classified as hydrogen embrittlement. Improper hydrogen removal after plating led to residual hydrogen, which caused embrittlement and fracture during assembly. Based on the failure analysis of the 65Mn steel spring washers, the following recommendations are made: (1) Replace the material of the spring washer. It is known that the Shanghai Spring Washer Factory was commissioned by the former aerospace industry to address hydrogen embrittlement issues in 65Mn steel spring washers. In November 1996, the factory began developing stainless steel spring washers and successfully completed the project in the same month. That year, the product passed acceptance tests by the Aerospace Corporation and Shanghai Standard Parts Corporation. Carbonation Stone,Titanium Rod,Inner Thread Titanium Rod,Thread Beer Carbonation Stone Ningbo Wenhan Fluid Equipments Co., Ltd. , https://www.wenhanvalves.com