Why Kolsterising?
The dilemma with steel is that there is a tradeoff between hardness and corrosion
resistance. Higher carbon content makes for harder steel, but creates a susceptibility
to rust and pitting. Kolsterising[R] solves this problem by transforming the surface of
the steel into a high-carbon layer that is five times harder than the original 316L
stainless steel that is used in our watch cases. Amazingly, the high-carbon layer
created by the process is more corrosion resistant than the original steel.
We start with top-quality German 316L stainless steel for our cases and bezels. After
the steel is precision-milled into the components, the Bodycote company subjects them to
their exclusive Kolsterising[R] process at their facilities in Apeldoorn, Netherlands.
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| Not a mere coating but a diffusion of carbon into the metal to a depth of at least 22 microns (μm) |
The shape and finish of the steel is unchanged. It just becomes much, much harder and
tougher. As a result, our watch cases and bezels are highly scratch-resistant and will
continue to look like new for years. Traditionally, watch owners have had to resort to
periodic repolishing or refinishing to keep their watches looking new. This is expensive
and destroys the original integrity of the watch. Matte finishes are especially
susceptible to scratches and are the most difficult to refinish. However, wristwatches
with matte finishes are essential for scuba diving since polished steel looks like bait
and attracts unwanted predatory fish. Our matte-finished Kolsterised[R] diving watches can
be worn with confidence in the most demanding environments.
A few other watch companies subject their watches to various case hardening processes,
but none of them hardens the steel more than our Kolsterising[R]. Furthermore, no other
watch company is willing to disclose the exact nature of their hardening process;
instead they hide behind meaningless proprietary names. Only with Corvus wristwatches
can you be certain that the case hardening is genuine Kolsterising[R].
Unlike other case hardening processes used in other watches, Kolsterised[R] 316 stainless
steel has been extensively tested by the Oak Ridge National Laboratory for use the
world’s most intense pulsed
accelerator-based neutron source (the Spallation Neutron Source). The SNS is located
in Oak Ridge, Tennessee, USA. When at full power, this one-of-a-kind facility creates
the most intense pulsed neutron beams in the world for scientific research and
industrial development. The intense radiation created by this device required the
toughest materials. After extensive testing, the engineers at Oak Ridge chose
Kolsterised[R] 316 stainless steel, just like we did for our wristwatches.
Kolsterised[R] stainless steel is also used on the Hubble Space telescope, as is our
exclusive Satellite Black dial coating.
For more information about the results of the Oak Ridge Laboratory’s torture testing,
you may download the reports:
HISTORY OF KOLSTERISING
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| Prof. Ben Kolster |
The Kolsterising[R] process was developed by Prof. Ben Kolster at the TNO Institute in the
Netherlands in the early 1980s. Kolsterising[R] is a case hardening process primarily for
austenitic stainless steels. The process involves the diffusion of carbon into the work
piece surface without the formation of chromium carbides. Post treatment hardness is
between 70 and 74 HRc (1000 to 1200 VPN). This carburizing reaches a depth of 22 microns
in depth. There are no additions of chemical elements to the steel during the process.
Complex shapes, such as our watch cases and bezels, present no problem for the process.
Surface property enhancements and benefits associated with Kolsterising
The main property enhancements from the Kolsterising process include:
- Improvement of wear and galling resistance
- Improvement of cavitation erosion resistance
- Increased fatigue strength
- Good dimensional stability
- The magnetic properties of the 316L steel are not affected by the process. This is critical for the proper functioning of a mechanical wristwatch.
- The surface hardened layer also has good toughness properties and there is no risk of delamination or peeling of the surface hardened layer.
- The process can be applied to finished parts with a high standard of dimensional accuracy.
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