Toolmaker’s clamps are designed for maximum strength and rigidity, and so they are typically made of case hardened steel.
Case hardening is the process of diffusing carbon and/or nitrogen into the outer layer of the steel at high temperatures. The carbon combines with the steel to make its hardness almost like glass. The centre of the metal stays soft, with a thin layer of harder steel (called the case) at the surface.
This process gives you a piece of metal that cannot be cut with a saw and will not shatter.
