Quenching, also called hardening is the process of heating and then cooling of steel (or other alloy) at a high speed that there is a much increase in hardness, either on the surface or throughout. In the case of vacuum Quenching, this process is done in vacuum furnaces in which temperatures of up to 1,300°C can be reached. The quenching methods will differ with regards to the material treated but gas quenching using nitrogen is most common.
Vacuum Gas quenching：
During vacuum gas Quenching, material is heated in the absence of oxygen by convection in the medium of inert gas (N₂) and / or heat radiation in the underpressure. Steel is hardened with a stream of nitrogen, whereby cooling rate can be determined by selecting the excess pressure. Depending on the workpiece shape it is possible also to choose the direction and time of nitrogen blowing. Optimization of time and steel temperature control are carried out during process with the use of pilot thermocouples which can be placed on a workpiece in the heating chamber. Steel that is heat treated in a vacuum furnace obtains the specified properties of strength and hardness throughout the entire cross-section, without surface decarburization. Austenitic grain is fine and it complies with international standards.
Practically all technically interesting steel alloys, such as spring steels, cold-worked steels, quenched and tempered steels, anti-friction bearing steels, hot-worked steels and tool steels, as well as a large number of high-alloy stainless steels and cast-iron alloys, can be hardened in this way.
Vacuum Oil Quenching
Vacuum Oil quenching is cooling the heated materials by Vacuum oil.As the transfer of the charge is taking place under vacuum or inert-gas protection after we vacuum purge the furnace, the part surface is always protected until it is completely immersed into the oil. Surface protection is very similar whether quenching in oil or gas.
The major advantage compared to conventional atmospheric oil-quenching solutions is the precise control of cooling parameters. With a vacuum furnace, it is possible to modify the standard quenching parameters – temperature and agitation – and to also modify the pressure above the quenching tank.
Modifying the pressure above the tank will induce a difference in pressure inside the oil bath, which changes the oil-cooling efficiency curve defined at atmospheric pressure. Indeed, the boiling zone is the phase during which the cooling speed is the highest. The change in oil pressure will modify its vaporization due to the heat of the load.
The reduction of pressure will activate the vaporization phenomena, which initiates the boiling phase. This will increase the cooling efficiency of quenching fluid and improve hardening capacity versus atmospheric condition. However, the massive generation of steam can cause sheath phenomenon and incurs potential deformation.
The increase of pressure in the oil inhibits the vapor formation and retards evaporation. The sheath sticks to the part and cools down more uniformly but less drastically. Oil quenching in vacuum is therefore more uniform and incurs less distortion.
Vacuum water quenching
Process like vacuum oil quenching,It is the ideal solution for hardening heat treatment of aluminum, titanium or other materials which need to be cooled at a sufficiently rapid rate.
Post time: May-07-2022