Tool materials: increasing ability to retain hot hardness (red hardness) Arrange the given tool materials in order of increasing ability to retain hardness at elevated temperature (lowest → highest): carbide, ceramic, cermet, borazon (CBN). Choose the correct sequence.

Concept/Approach
Hot hardness (red hardness) is a tool material's ability to retain hardness and resist softening at high cutting temperatures. In general across common cutting materials: carbide < ceramic < cermet < cubic boron nitride (borazon) in hot-hardness capacity.

Reasoning
Tungsten-carbide tools are strong but lose hardness sooner than ceramics/cermets at higher temperatures. Advanced cermets and ceramics perform better at elevated temperatures, while CBN (borazon) exhibits excellent hot hardness, second only to diamond and preferred on hardened steels.

Final Answer
carbide, ceramic, cermet, borazon