Abstract
In this work, the fatigue crack growth (FCG) behavior and fatigue damage mechanism of the 2.25Cr1Mo0.25V steel welded joint used in hydrogenation reactors were investigated. The multi-pass welding was carried out to manufacture the welded joint using the combined shielded metal arc welding (SMAW) and submerged automatic arc welding (SAAW) processes. The FCG behavior of different zones in the welded joint, including the base metal (BM), the heat-affected zone (HAZ) and the weld metal (WM), were studied by compact tension tests. Moreover, the acoustic emission (AE) technique was used to monitor AE signals generated from FCG process for further understanding FCG behavior and fatigue mechanisms. Additionally, the microstructures and fracture surfaces of different specimens were observed by optical microscopy (OM) and scanning electron microscopy (SEM). The results revealed that the microstructure of BM is fine granular bainite, while the WM shows coarser bainite grains. The HAZ exhibits the most significant inhomogeneity with large dispersion of grain size. FCG results showed that the HAZ exhibits much higher fatigue crack growth rate (FCGR) at low ΔK values, while the BM shows the most superior fatigue resistance. The AE technique is successful in monitoring and identifying damage evolutions during the FCG process. Moreover, an enhanced AE activity is observed in FCG of the WM specimen, which is attributed to the combined influence of the formation of numerous secondary cracks and coarse-grained microstructures.
Highlights
Hydrogenation reactor plays a crucial role in petrochemical hydroreforming, hydrorefining and hydrocracking industries
An enhanced acoustic emission (AE) activity is observed in fatigue crack growth (FCG) of the weld metal (WM) specimen, which is attributed to the combined influence of the formation of numerous secondary cracks and coarsegrained microstructures
It is obvious that the main microstructure of base metal (BM) is fine granular bainite, while WM exhibits coarse bainite grains, whose grain size are much larger than BM
Summary
Hydrogenation reactor plays a crucial role in petrochemical hydroreforming, hydrorefining and hydrocracking industries. The HAZ and WM are likely to become the weak parts under stress due to microstructural inhomogeneity caused by complex thermal history It has been reported by Tsay et al [12] that the fatigue crack growth rate (FCGR) of HAZ was higher than that of other regions in the 2.25Cr1Mo steel welded joint. Understanding the fatigue behaviors and damage mechanisms of different zones (BM, HAZ and WM) of welded joints is; of great importance in the safety and reliability of hydrogenation reactors. The present work aimed to investigate the FCG behavior and fatigue mechanism of the 2.25Cr1Mo0.25V steel welded joint. FCG were measured to investigate crack growth behaviors and corresponding failure mechanisms of BM, HAZ and WM in the 2.25Cr1Mo0.25V steel welded joint. The microstructures and fracture morphology of specimens were investigated by optical microscopy (OM) and scanning electron microscopy (SEM), respectively, to clarify the fatigue mechanisms
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