ABSTRACT Low-temperature reduction disintegration is a critical factor governing the blast furnace burden performance of sinter. In this study, ultrasonic attenuation was evaluated as a nondestructive parameter associated with reduction-induced microstructural damage in synthetic Fe 2 O 3 -CaO-SiO 2 -MgO-Al 2 O 3 sinter systems. Phase evolution was analyzed by XRD and thermodynamic calculations, and the resulting crack development after reduction was characterized by SEM and image analysis. In the ternary system, increasing SiO 2 promoted Ca 2 SiO 4 formation and reduced the fraction of reducible ferrite and hematite phases, which was accompanied by lower crack density and lower ultrasonic attenuation. At low SiO 2 contents, the disintegration tendency varied non-monotonically with CaO content, with the most severe cracking observed at intermediate CaO levels. In the quinary system, excessive Al 2 O 3 favored the formation of fine acicular SFCA-type phases, which exhibited poor interfacial bonding with the Fe 2 O 3 substrate and promoted interfacial delamination. In contrast, MgO addition promoted spinel and SFCA-III formation, thereby reducing crack development; this effect was particularly pronounced when MgO/Al 2 O 3 ratio exceeded 1. Within the investigated composition range, ultrasonic attenuation showed a consistent relationship with crack density, suggesting its potential as a supplementary indicator for assessing reduction-induced damage in sinter.