I believe that the vacuum furnace and the integral-quench furnace have reached the limits of their design effectiveness. Which means to say, that the furnaces themselves cannot progress much further. The growth area in heat-treatment-furnace engineering is and will be even more so in the area of process control and atmosphere developments.
We are seeing emerging developments of the diffusion treatments by the use of fluidized-bed technology and the diffusion (not deposition) of aluminum, vanadium, molybdenum, chromium and others.
This technology is opening up new areas of application potential. For example, if one considers AISI 8620 carburizing material being diffusion carburized followed by the diffusion of aluminum into the surface while controlling the surface potential of aluminum at 1%, the surface of the AISI 8620 now becomes almost the equivalent of AISI 52100. The advantage of the system is that it can be controlled by PC/PLC combinations but with the use of a less-expensive furnace.
So, where are we going with heat treatment? As long as man produces metals, be they ferrous or nonferrous, there will always be a need for heat-treatment processing. The major future developments in metallurgical furnace engineering design will undoubtedly be in the field of process control and the better use of materials of construction for the furnace.