Hot-work steels range from high to extremely high in hardenability, so it is possible for them to achieve full hardness by cooling in still air. However, this is not recommended, because intense embrittlement occurs after slow cooling from hardening temperature.
Even with those types having the highest hardenability, sections of die blocks may be so large that insufficient hardening results. In such instances, pressurized nitrogen gas (in vacuum furnaces) or an oil quench is required to achieve full hardness. Hot-work steels are never water-quenched. The figure shows the Continuous Cooling Transformation (CCT) diagram for AISI 6F3.
Volume 4D, Heat Treating of Irons and Steels ⇒Tool Steels ⇒ Heat Treating of hot-Work Tool Steels ⇒ Heat Treatment of H Series and Low-Alloy Hot-Work Steels
