Structure characterization and failure mechanisms of high chromium cast iron grate bar

Abstract

Grate bars represent the main failure components within sintering machine trolleys. The quality of grate bars significantly impacts the production efficiency of the sintering process, and understanding the failure mechanisms of grate bars guides research in grate material development. In this study, we analyze the failure mechanisms of grate bars by comparing the structure of the grate matrix before and after failure and by examining the structural morphology of the failed zones. Our findings reveal that the austenite phase of the grate bars transforms into granular pearlite. The carbide type changes from M7C3 to M7C3 and eventually to M23C6 after extended service. P and S accumulate at the grain boundaries, resulting in the formation of the brittle phase Mx(S,P)y. Additionally, Cr diffuses to the surface, forming an oxide layer at high temperatures. The structural transformation from austenite to pearlite and the diffusion of Cr in the matrix phase increase electrode potential differences, which promote electrochemical corrosion between the matrix phase and the carbide at the grain boundary and within the inner grain. Cl being present in the service environment played an important role in the failure of grate bars by promoting high-temperature oxidation and being involved in crevice corrosion. Grate bar failure primarily results from high-temperature oxidation, electrochemical corrosion, brittle fractures, and compound actions. Finally, we propose recommendations to enhance the performance of grate bars through alloying treatments.