What is vacuum hardening?
Vacuum hardening is a method generally used for hardening of tools, molds and martensitic stainless steels. The process is on the same principle as the tempering process, and the main differences are the equipment used, atmospheric environment, and cooling environment. The steel to be applied vacuum hardening is firstly taken into a vacuum environment in the vacuum furnace. Thus, impurities that will diffuse from the atmosphere to the surface of the material during heating are prevented.
After vacuuming, the furnace is brought to process temperature (850-1250°C) and austenitic transformation occurs at these temperatures. After the austenite transformation takes place, the martensitic transformation (hardening) of the steel is completed by switching to the cooling stage. Nitrogen, hydrogen, argon or oil can be used as a cooling medium under high pressure. The martensitic transformed steel is subjected to deep cooling to remove residual austenite, if necessary, and then to tempering, if not required, directly to the tempering process to obtain the desired hardness and to release stress. This process is preferably carried out in an oven with a vacuum environment.
After the tempering process, the material becomes ready for the next stage in its production in a state that has reached the desired hardness and microstructure.
Vacuum Hardening Process at Önerler
There are 5 ovens for vacuum hardening in our company.
We offer flexible charging amount opportunity with vacuum furnaces with charging capacities ranging from 250-600-1300 kg.
4 gas-cooled vacuum furnaces of German origin IPSEN with 600 kg and 1300 kg charging capacities
10-5 mbar high vacuuming ability
With the Vacu-Prof program in the furnaces, high repeatability and traceability is provided by controlling all critical parameters.
Possibility to use nitrogen and argon, helium cooling gas
Vacuum hardening possibility for low alloyed steels with 250 kg capacity oil-cooled vacuum furnace
Maximum 20 bar cooling pressure
Apart from the vacuum hardening process with the vacuum hardening furnaces in our company;
Low pressure cementation under vacuum
Brazing (under vacuum brazing)
Solution and aging processes of precipitation hardenable stainless steels
Softening and stress relieving annealing processes applied to copper alloys such as brass and bronze are also performed.
In our company, after vacuum hardening process, tempering process is applied at high temperature in vacuum furnaces.
Benefits of The Processes
Excellent surface cleaning
High wear resistance
High fatigue resistance
- High toughness
- High impact resistance
- High stability
The main difference of the vacuum hardening process compared to other hardening processes is that the process is carried out in a vacuum environment. For this reason, the heating and cooling steps in the process are very homogeneous, and this vacuum environment ensures that the surface of the material remains very clean at the end of the process.
Steels Applicable to the Process
Since nitrogen gas is generally used as a cooling medium in the vacuum hardening process, the cooling rate is lower than in other processes. For this reason, the steel to which the process will be applied must have high alloy and high hardenability. Frequently in vacuum hardening process; cold work tool steel, hot work tool steel, plastic mold steel, high speed steel and martensitic stainless steels are used.
In the table below, steels that are used extensively in the market and applied vacuum hardening process and the maximum hardness values that can be obtained after the process are given in rockwell.
1.2379 / 60 - 62 HRc
K 340/61 - 63 HRc
Sleipner / 62 - 64 HRc
Vanadis / 4 61 - 63 HRc
Sverker / 21 60 - 62 HRc
1.2080 / 61 - 63 HRc
1.2343 / 54 - 56 HRc
1.2344 / 54 - 56 HRc
1.2367 / 54 - 56 HRc
1.2714 / 55 - 57 HRc
100 Cr 6/62 - 65 HRc
1.4034 / 51 - 54 HRc
1.4057 / 49 - 52 HRc
1.4112 / 59 - 62 HRc
1.4122 / 48 - 51 HRc
Problems That May Occur After The Procedure
Although it is seen much less in vacuum hardening than other processes, the most problematic problem is the size change in the materials, in other words, distortion.
Due to the nature of the heat treatment, it creates stresses in the steel as a result of sudden temperature changes and causes dimensional changes. The main reason for the size changes that occur more than anticipated and can be described as error can be examined in 3 main groups. First, the errors that can be made in the heat treatment process, secondly, the mold design errors (intensive thin-thick section transitions, etc.) and finally the residual stresses in the material during the machining phase. Cracks may also occur as a result of the size change mentioned above.
The manufacturer must correctly determine the cleaning criteria on the part surface before the process. If there is an expectation of a delicate clean surface, cutting fluid, boron oil, etc. in the products sent to our company. Surface residues should be at minimum levels or surface cleaning service should be requested from our company before the process. Otherwise, there may be residue, oil and dirt layers on the surface of the part after the process.