The Influence of HH Type Steel Microstructure on the Distortion Behavior of Grate Bar Part in the Indurating Machine of Pelletizing Plant

Document Type : Research Paper


1 Department of Materials Engineering, Isfahan University of Technology, P.O. Box 84156-83111, Isfahan, Iran

2 Nanotechnology and Advanced Materials Department, Materials and Energy Research Center, P.O. Box 31787- 316, Karaj, Iran


Grate bar is an industrial part which is used in the indurating furnace of an iron ore pelletizing plant. Steel part of
the grate bars are expected to have high resistance to atmospheric oxidation because of its contact with hot gases
(up to 920 °C) during the normal operation of the process. In this study, different samples from several sections of
used grate bars with apparent defects were selected. The microstructure of the selected samples from the affected
areas was studied via optical and scanning electron microscopy with EDS analysis. The results showed that the
internal oxidation would occur through the oxygen diffusion into the chromium carbide nets and caused the change
of chromium carbide to chromium oxide. Furthermore, internal oxidation led to the separation of the grains from
the steel matrix and resulted in the dusting phenomenon. In order to modify the steel microstructure, Ti element
was added to the melt in different levels during the casting process and the results showed that the presence of
Ti could modify the carbides structure and consequently improve the oxidation resistance of the steel. The grate
bars with new composition were placed in the furnace and the monitoring of the consumption of the grate bar
in Mobarakeh Steel Company pelletizing plant. In a six -month period revealed that the grate bar consumption
decreased about 30%.


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