The structure, temperature control, heating process and furnace atmosphere of high-temperature vacuum furnace, muffle furnace and tubular furnace will directly affect the product quality after the production of resistance furnace. In muffle furnace (experimental electric furnace and resistance furnace), increasing the metal temperature can reduce the melting resistance, but too high temperature will cause grain oxidation or over-burning, which will seriously affect the product quality in vacuum furnace, In the process of heat treatment, if the steel is heated to a point above the critical temperature, and then suddenly cooled by the cooling method, the hardness and strength can be improved. If the steel is cooled slowly to a point below the critical temperature, the steel will be more ductile.
In order to obtain the workpiece with smooth surface and accurate size, or to reduce metal oxidation to protect the mold. For the purpose of reducing processing allowance, various kinds of low and non-oxidation muffle furnaces can be used. In the open-flame low and non-oxidation heating muffle furnace, the incomplete combustion of fuel can be used to produce reducing gas, in which the oxidation burning loss rate can be reduced to less than 0.6% by heating the workpiece. This muffle furnace is often used in the experimental stage of products. After trying various heat treatment processes, the process curve can be obtained, so that the large heat treatment furnace can be used successfully in the future.