Vacuum Annealing

Vacuum furnaces provide excellent results when used for annealing steel.  Cooling rates are strictly and easily controlled in a vacuum furnace, this is critical in the process of annealing.   Due to the fact that endothermic atmospheres should not be used below 1400F surface carbon levels can be difficult to control in atmosphere annealing.  This can be a major problem when annealing stainless steels and tool steels due to the fact that stock tends to be limited and most tool steels have relatively high carbon contents.  This problem is eliminated in vacuum annealing.  

Capability

ThermTech has vacuum furnaces up to 72” in length and 10,000 pounds in capacity.  Temperature ranges are up to 2350F for high temperature annealing processes.  ThermTech employees an experienced staff including three metallurgists to assure proper processes and procedures are used to achieve the desired final properties for any application.

Process

There are many different types of annealing processes.  Often a customer is not sure which type of annealing process is required or necessary but it’s important that this is discussed because outcomes and costs are very different.  
Subcritical annealing uses temperatures below the point which austenite forms.  It is a good choice when wanting a relatively low hardness and little to no internal stresses.  Cycle times are relatively short as compared to full annealing therefore it is the least costly process.
Full annealing involves heating above the point at which you form austenite and then slow cooling at some rate to which the austenite phase transforms into ferrite and pearlite.  This tends to be an extremely long process and thus can be very costly.  It does provide low hardness and no internal stresses.
Spherodize anneal is similar to full annealing but has a secondary step at which the part is held at a temperature at which the carbide phase is allowed to assume the shape of a sphere thus the microstructure consists of ferrite and spheroidal iron carbide.  This provides an extremely low final hardness.  This is often used for alloys like AISI 52100 that can be difficult to machine.

Recommendations

Full annealing and spherodize annealing treatments are extremely long; keep this in mind when looking at time schedules.  
It is very important that the correct annealing process is chosen given the costs thus a discussion prior to submission of an order is well worth the time.