Microstructure Characteristics of Fatigue Fracture of Furnace Tube in Convection Section of Slurry Bed Fractionator

In this paper, the fatigue cracks were characterized through visual inspection, optical microscope observation, scanning electron microscope (SEM) observation, and electron backscattering diffraction (EBSD) analysis. It was found that the fatigue cracks tend to expand along a relatively straight path, with many secondary cracks appearing behind the crack tip. The fatigue cracking is transgranular, and the extension is tightly aligned with the primary slip system (i.e., (111) < 110 > ). The Schmidt factor diagram shows that the fatigue crack extension through the grain mainly occurs in the region with a high Schmidt factor, and the region with a high Schmidt factor also has a high KAM value and more low-angle boundaries.