Carborundum is used as an abrasive, because it

Carborundum, the commercial name for silicon carbide (SiC), is primarily used as an abrasive due to its extreme hardness. It is a synthetic material created by fusing silicon and carbon at high temperatures, resulting in a crystalline structure that is exceptionally hard, sharp, and resilient. On the Mohs scale, silicon carbide reaches a value of 9.2 to 9.5, making it one of the hardest known materials, second only to diamond and a few other substances like boron carbide [1]. This mechanical property allows it to effectively cut, grind, and polish a wide variety of tough materials, including metals, ceramics, stone, and glass [1]. While it also possesses high thermal conductivity and chemical stability, its primary functional advantage in abrasive applications is its ability to resist wear and maintain sharp edges under high pressure.

Sources

1. [1] https://www.sciencedirect.com/topics/materials-science/silicon-carbide