Among diamond tools, the grinding wheels are among the most commonly used. The diamond grinding wheels are constructed from very small diamond particles held together by bonding material. As the grinding wheel is used, the dulled ruby fragments on the outside falls off, exposing sharper particles underneath. This peeling process takes place continuously up until the grinding wheel is completely used up.
Overheating disrupts the peeling process. The excessive heat softens the bonding material, making it gummy which prevents the dull diamond particles from falling off and exposing the sharper ones underneath. In some instances, the softened bonding material forms a layer of film over the dull particles and completely preventing it from contacting the work piece.
Another reason for early dulling of diamond grinding wheels is using it on steel. The carbon content of steel can cause the diamond particles to undergo graphitization. This procedure is when the molecular structure of diamond and other carbon compounds transform into soft graphite.