Abstract
The high temperature intergranular corrosion behavior of SCH2 heat resistant steel in a waste incinerator was investigated by scanning electron microscopy, electron probe micro-analysis, and X-ray analysis. Specimens were exposed in a waste incinerator where plastics and used tires were burned under thermal cycling conditions of heating at 1423K for 6.2ks and 1150K for 17ks and then cooling to room temperature.
A Cr carbide network structure was identified, but there was no intergranular corrosion near the surface of SCH2, SiO2 down to about 20μm and 2μm diameter Mn sulfide were observed at the top of the alloy. There was no Cr carbide network about 100μm from the scale/alloy interface. Cr diffused into the substrate during the exposure and then formed a Cr2O3 scale at the alloy surface by rapid diffusion in ferrite. It is suggested that intergranular corrosion was not the cause because of the disappearance of Cr carbide near the surface. The EPMA analysis showed that Cr was depleted while Ni was concentrated at the top of the alloy. The Fe-Cr-Ni phase diagram shows that the γ-phase appears at 1423K and it is assumed that this area was changed from ferrite to austenite.
It is concluded that SiO2 formed due to diffusion of oxygen (O) through the austenitized area, while Cr and Mn sulfides were formed under it.
