I wish I had known about the "holiday inn express" learning method. Instead I wasted my time getting a PhD. I work in the petrochemical industry and have spent many years specifying alloys and fabrication methods for process equipment. And my family owns a large metal fabricating business that serves automotive and aerospace industries. So I get my dose of metallurgy talk at family gatherings too.
I think the discussion comparing Sinn's tegimenting (very hard shell on a soft core) to Damasko's ice-hardening (medium hardness all the way through) has been well covered on the watch forums. Some damage scenarios will mess up a Sinn, but not a Damasko -- and vice versa. It just depends on the nature of the unfortunate watch accident. Both are great watch cases that can look new for many years if there are no severe accidents.
Damasko was smart to patent their choice of steel alloy for all watch case applications. They use Cronidur 30 (X30CrMoN15 1). They did not invent this steel, nor did they develop its ice hardening process. But they were brilliant in finding novelty in order to secure a patent. Here is their explanation of novelty from their US patent:
"these materials have heretofore been regarded by experts as unsuitable for the manufacture of wrist watches, due to the fact that such steels are highly magnetizable, especially by external magnetic fields, so that they function as permanent magnets whose magnetic field strongly impairs the highly sensitive clockwork of a wrist watch. The invention is based on the realization that the aforementioned hardenable steel surprisingly is suitable for wrist watch cases, and especially if in the interior of the case a ring or plate enclosing the clockwork is made of a diamagnetic metal."
So Damasko is saying that nobody thought to use this type of steel because it can become magnetic and screw up the movement. They solve this problem by putting in a diamagnetic inner cage around the movement. This might seem obvious to a WIS in hindsight, but probably was quite impressive to the patent examiner.
The Damasko ice-hardening is a complex process. I haven't yet seen it described anywhere on the web, so here it is: First the metal is heated to above 1000°C, then rapidly quenched to room temperature in oil. This is followed by deep freezing at – 80 °C for 1 hr, then tempering for several hours at 160°C to give hardness >710 HV. The Pitting Resistance Equivalant is 30 points which is similar to 316L. The nickel-free composition is great for people with allergies.
So what about Bremont watches? Here is a quote from QP magazine: http://www.jurawatches.co.uk/PDF/bre...ingyarnQP1.pdf
"Furthermore, all the cases and buckles are brought back to England to be treated for hardness with B-EBE2000 technology, a process used on the turbine blades of jet engines. The cases are heated to high temperatures and carbon diffusion is used to increase the overall underlying hardness of the case to 1,200 Hv on the Vickers scale (normal watch-grade stainless steel is more like 280 Hv in hardness). Argon electron ions then prepare the surface of the case followed by a metallic ceramic coating at temperature, bringing the case hardness up to 2,000 Hv – the same hardness as sapphire crystal.
Based on this info, Bremont is kolsterizing, then plasma spray coating. Since this is done in England, they are probably using Poeton Apticote 800/24. This is a tungsten carbide and cobalt coating applied with an argon plasma torch. That gives hardness of 2000HV, and is used on jet turbine blades. Poeton does work for Airbus and Rolls Royce.
DLC (Diamond Like Carbon) coating is starting to get used by lots of watch companies in the last couple years, like Glycine, Ball, Bremont, Linde Werdelin, MKII, Perrelet, Richard Mille, Panerai, Montblanc, Citizen, and Casio. The quality of DLC coating is highly dependent on the coating vendor. If done right, these will be >2000HV and will take a beating. I have found these coatings to be highly variable in ultimate hardness. And some have even delaminated around part edges.
If I had my own watch company I would use Nirosta 4565 for the case. It has a Pitting Resistance Equivalent >50 for ultimate corrosion resistance in seawater. I would harden it with the Swagelok SAT12 process (low temperature colossal supersaturation) to get above 1500 HV.
Don't get me started on ceramic cases...