关键词: 25Cr2MoVA, 螺栓断裂, 力学性能, 金相组织, 热处理

Abstract: A bolt on the channel head flange of the feed heat exchanger in an S-Zorb unit fractured at a refinery.To identify the cause of the bolt failure and fracture, thereby formulating effective protective measures to prevent disruption to normal production and ensure operational safety of the equipment, an indepth investigation was conducted through macroscopic inspection, material composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy (SEM), and energydispersive Xray spectroscopy (EDS) analysis.The results indicate that the fracture surface of the bolt presents a quasicleavage morphology. It is therefore concluded that the bolt fracture occurred due to the following causes: insufficient heat treatment led to a coarse and unevenly distributed grain structure in the metallographic microstructure. After prolonged service, component segregation occurred within the alloy, which resulted in reduced hardness and impact toughness of the base material.In addition, prolonged exposure to stress concentration in the fracture region resulted in fatigue crack initiation. Under the action of tensile stress and torque, brittle fracture occurred. Based on the above analytical findings, restorative heat treatment should be implemented for the bolts, specifying appropriate thermal processes to refine the grain structure, thereby improving the mechanical properties of the material.

Key words: 25Cr2MoVA steel, fracture failure of bolts, mechanical properties, metallographic microstructure, heat treatment