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

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%.