Reproduction of decarburization caused by overheating in fire tube boiler material

One of the non-destructive testing methods for analysing fire tubes is the replica technique. This technique allows the investigation of microstructure, cracking, and high-temperature creep under operational circumstances without the cutting of the components. A cellulose-acetate foil was used to make a copy from the topography of the surface, which was suitable for microscopic analysis. In this paper, decarburization was generated in P355N fire tube material. The aim of the reproduction was to investigate the effect of overheating in boilers. The decarburization of the fire tube was made at different temperatures (300 – 900 °C) in an electric heating furnace. General deterioration and decarbonization began at 700 °C. A preliminary step of the decarburization was the transformation of the pearlite, which can be easily detected by scanning electron microscope. Grain growth could not be observed, and the particle size was unrelated to the thickness of the decarbonized layer. © 2024