Metallers hårhedsgrad

[Bjørn H._phpbb3_import15705]

Case materials and their relative hardness (Minimum figures)
18 carat red gold - 165 HV.
Grade 2 titanium - 165 HV. ( IWC Porsche 2000 - presumably with some sort of nitriding )
90/10 Platinum / Iridium - 190 HV.
18 carat white gold - 200 HV.
316L stainless - 200 HV. (common case material)
904L stainless - 200 HV. (rolex case material)
Grade 5 titanium - 350 HV. (IWC Aquatimer)
HV = hardness Vickers
You have to be careful with the precious metal figures, tiny
differences in alloy & degree of cold-rolling can have a big
impact on the final hardness.
Also, wear resistance & hardness do not always follow each other,
abrasive particles tend to embed in the softer metal and then
happily grind away on any hard parts they contact.
The stainless steel grades 316L & 904L are very nearly
equal regarding hardness & tensile strength , they are
both cleared for biomedical purposes in spite of the
high nickel content (15% / 26% )
What separates the two steels is the resistance to
chemical stress - if you wear your watch while swimming
in boiling acid , the 904L will come out slightly
superior to 316L.
The titanium grades you are likely to encounter in the
watch business is gr.2 (aka "commercial pure")
and gr.5 (al6v4)
There seem to exist a myth about titanium parts
"welding" together in time - one explanation might
be that gr.2 is notorious for seizing / galling
particularly in a "blue on blue" encounter, i.e.
a gr.2 case with a gr.2 screw-on back.
The good and the bad news is that it will NOT
work loose - - -
Anti seize paste or no anti seize paste !
Grade 5 will usually cause no problems in that respect,
it is not more prone to seizing on itself than stainless
steel.
Always use a light film of anti seize (copperpaste etc.)
on the threads when assembling parts that are supposed
to be dismantled sometime !