The fracture observation and analysis diagram after washing is the front and side topography of the fracture after acid cleaning. The crack distribution on the fracture surface and the fracture side is clearly visible. Stress Corrosion Bolt Heat Exchanger Diagram Failure Bolt Natural Fracture Morphology Work. Partial structure diagram of the floating head heat exchanger. Front view of the fracture after cleaning. Front and side topography of the fracture after cleaning, lateral view, longitudinal failure, failure of the transverse and longitudinal microstructures of the broken bolts Bolt chemical composition analysis results and standard comparison, chemical element failure bolt 40Cr steel standard value application square version of a crack at a certain angle with the axis. The crack is initiated by the source of the crack on the outer surface of the bolt and extends as a dead branch toward the core of the bolt. It can be seen from the figure that there is a pattern in the entire fracture surface that is radially expanded from the source of the surface crack to the inside (the arrow in the figure is the surface crack source), so that the fracture is divided into the initial crack formation zone, the rapid expansion zone and the instantaneous fault zone. three parts.
No original material defects were found in the transverse cross section and the longitudinal outer surface of the bolt after acid cleaning. Based on the results of the comprehensive macro-low test, the preliminary analysis shows that the bolt break time has been longer. The cracks causing the fracture originate from the outer surface of the bolt and expand radially toward the center of the bolt at a relatively fast speed. The chemical composition analysis was carried out on the failed bolts for chemical composition analysis. The results of the chemical analysis showed that the chemical composition of the failed bolts did not meet the steel standard values ​​and met the steel standards. Therefore, it can be confirmed that the steel for manufacturing bolts is steel. The hardness test is carried out at the fracture point of the failed bolt and the intact end to test the Rockwell hardness. The test result is shown in the table. It can be seen from the results of the hardness test: as the bolt type fastener, the hardness of the failure bolt is too high. This will reduce the toughness of the material. Metallographic examination will break the failure bolt in the central fracture table. The Rockwell hardness test results of different parts of the failure bolt test position near the fracture near the bolt end Rockwell hardness average HRC and the end of one end intercept the transverse and longitudinal specimens for metallographic examination . The transverse and longitudinal microstructures at the fracture are the coarse tempered troostite structures.
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