In the heat treatment of forgings, due to the high power of the electric furnace and the long holding time, the energy consumption is huge throughout the process. For a long period of time, how to save energy during heat treatment of forgings has always been a problem.
The so-called "zero heat preservation" quenching refers to the heat treatment process in which the surface and core of the forging are quenched and cooled immediately after reaching the quenching heating temperature, without the need for heat preservation. Traditional austenite theory holds that forgings must have a long holding time during heating in order to complete the nucleation, growth of austenite grains, dissolution of residual cementite, and homogenization of austenite. The current quenching and heating processes of forgings are all produced under the guidance of this theory. Compared with the current quenching process, "zero heat preservation" quenching eliminates the heat preservation time required for homogenization of the austenite structure, which can not only save energy by 20% -30%, improve production efficiency by 20% -30%, but also It can reduce or eliminate the defects such as oxidation, decarburization and deformation during the heat preservation process, which is conducive to the improvement of product quality.
When carbon steel and low alloy structural steel are heated above Ac1 or Ac2, the homogenization process of austenite and the dissolution of carbides in pearlite are relatively fast. When the size of the steel part belongs to the range of thin parts, there is no need to consider heat preservation when calculating the heating time, that is, to achieve zero heat preservation quenching. For example, when the diameter or thickness of the 45 steel workpiece is not more than 100mm, the surface and core temperature are reached at the same time when heated in an air furnace, so the uniform time can be ignored, and the traditional production process with a large heating coefficient ( r = aD), it can shorten the quenching heating time by nearly 20% -25%.
Relevant theoretical analysis and experimental results show that it is completely feasible to use "zero insulation" for structural steel quenching and normalizing heating. In particular, 45, 45Mn2 carbon structural steel or single-element alloy structural steel, the use of "zero insulation" process can ensure its mechanical performance requirements; 45, 35CrMo, GCrl5 and other structural steel workpieces, using "zero insulation" heating can save more than traditional heating Heating time 50%. The total energy saving is 10% -15%, and the work efficiency is improved by 20% -30%. At the same time, the "zero insulation" quenching process helps to refine the grains and improve the strength.