Vacuum heat treatment is a newly-developed heat treatment in recent years. Its features meet the requirements of mould making, like preventing heating oxygenation, non-decarburization, vacuum degassing, and eliminating hydrogen embrittlement, which highly improve plasticity, tenacity and fatigue strength of materials. Due to slow vacuum heating and low temperature difference between inside and outside of parts, parts heated by vacuum have less deformation.
According to different cooling media, vacuum hardening can be classified into vacuum oil hardening, vacuum gas hardening, and vacuum water hardening. Vacuum oil hardening, gas hardening and tempering are mainly applied in vacuum heat treatment of mould. For keeping good properties of mould during vacuum heating, coolant and cooling process choosing are vital.
For the mould which does not need machining after being heated, vacuum tempering should be adopted as far as possible after quenching, particularly vacuum hardened mould. It can improve the mechanical properties having closed relationship with surface quality, such as fatigue strength, surface brightness and corrosion resistance.
Successful development and application of computer analog technology during heat treating realize intelligent heat treatment of mould. For limited quantities, multispecies high requirements for heat treating and non-wastes, mould intelligent treating is necessary. Mould intelligent heating treatment includes confirming the structure, materials and heating properties of mould, simulating distribution of temperature field and stress field during heating and cooling, formulating simulate hardening during cooling and heating. In develop countries, such as the U.S. and Japan, vacuum high-pressure gas hardening has been developed, focusing on mould.