Metallurgical investigation into the failure of an iron ore sintering car pallet

• Detailed microstructural characterization of a prematurely failed sintering car pallet was done.
• A degenerate graphite (flake and vermicular) layer at the casting surface acted as stress raisers.
• Cracks initiated under severe external dynamic load and thermal cycling.
• Sudden impact loading at the discharge end led to the catastrophic failure of the component.

A failure analysis on premature cracking of a sintering car pallet in an integrated steel plant is presented. A detailed study on the microstructural and mechanical properties of the failed component has been carried out. Microstructurally, the amount of pearlite in the ferritic–pearlitic matrix was found to be significantly higher (~ 65.8%) than normally expected in materials used for elevated temperature application. A thin layer of flake and vermicular graphite (degenerate graphite) was found just beneath the casting skin although interior of the matrix contained normal spheroidal graphite. In few occasions, the presence of undesirable spiky and exploded graphites was also noticed. The material exhibited lower yield stress (312 MPa), tensile strength (457 MPa) and Charpy impact energy (3.4 J) indicating poor strength and toughness of the casting. The improper graphite morphologies in the sinter car pallet acted as stress raisers and produced cracks under dynamic thermal cycling and external loads experienced during the sintering process resulting in its premature failure.