In addition to economic aspects (availability, machinability, etc.), important prerequisites for a material to be used in vacuum technology are above all factors such as a low inherent vapor pressure and magnetic permeability as well as high mechanical strength and corrosion resistance. In vacuum technology, austenitic stainless steels have become established as standard materials. These stainless steels are also used for fasteners such as our vacuum screws. One advantage of using the same materials in a vacuum system is that the same expansion behavior of the materials means fewer uncertainties in the process. In addition, the use of stainless steels in fasteners does not entail the risk of material fatigue as a result of hydrogen embrittlement, as is the case with alloyed steels of strength class 8.8 and higher. The risk of cold welding (“galling”) can be avoided by a suitable coating or by selecting an alternative material.
Typical stainless steels and non-ferrous metals, from which our vacuum-optimizing screws are also made, have the following material properties:
|Material||Strength class||Tensile strength Rm |
|0,2% Yield strength Rp0,2 [N/mm²]*||Density|
|Relative magnetic permeability*|
|Austenitic stainless steel A2 & stainless steel A4||70||700||450||7.9/8||≤1.3**
|Austenitic stainless steel A2 & stainless steel A4||80||800||600||8||≤1.3**
|Titanium Gr. 2||-||480||340||4.51||≤1.00005|
|Titanium Gr. 5||-||950||880||4.51||≤1.00005|
* at room temperature 20°C
** Due to cold deformation during the manufacturing process, the value for screws can deviate considerably (folding martensite))
A2 stainless steel is the all-rounder material in vacuum technology. Due to its high availability, low inherent vapor pressure and good corrosion resistance, A2 has established itself as the standard in vacuum technology.
A4 stainless steel has a higher content of molybdenum than A2, which translates into better corrosion resistance and lower magnetizability.
Titanium screws are characterized by their low weight (approx. -45% of the density of stainless steel), excellent mechanical properties (titanium Gr.5 > stainless steel strength class 80) and very low magnetizability.
Special screws from Bumax® combine the excellent properties in terms of magnetizability of titanium screws and resistance to corrosive media as well as the mechanical properties of stainless steels (strength class 80).