I came accross the following review of the N690 steel used in ER knives:
"The knives Extreme Ratio are in steel N690.
This steel, used for all the blades of the Extrema Ratio since 1998, is a martensitic chromium one, enriched with molybdenum and vandadium cobalt. It has excellent skills of corrosion resistance guaranteed from the high content of chromium (17.00%) but its main feature is the elevated hardness which can be reached with the temper (60HRC) without influencing negatively on the resistance towards the sollicitacions. The result is a blade with a very hard edge (therefore sharp and longlasting) and an elastic and though body. It is used for the production of industrial blades of high quality, installed for example on industrial meatchoppers where the holding of the edge is important (for a minor maintainance) and the stainlessness, seeing that they have to work in presence of air, water and biological acids, and the oxidation would result very polluting for treated alimentary products. It is as well used for the production of milling tools to work steel, thanks to its hardness, to which fragility is exceptionally not accompanied. Another tipical usage is the production of razorblades or bistouries for the above mentionned characteristics."
http://www.afcoltelli.it/newseng5.html
It surprises me that a steel with 17% chrome would show any pits, regardless of the damp summer swingshot reports in his post.
I wonder if swingshot used the knife to cut something unusual, such as a particularly acidic or alkaline fruit or vegetable.
The other thing I noticed about this steel from this review had to do with the high hardness in conjunction with the remarkably high chrome content.
The review above describes the blade steel as retaining "springiness" despite the hardness and the chrome content.
Hardly a scientific review, and while I don't doubt it, I'd like to hear more from some other source.
Some years ago, Buck Knives submitted a knife to the US Navy to test for possible use by the SEAL's (I have one of those knives).
The knife steel had an abnormally high chrome content in order to withstand constant exposure to salt water, and an unusually high hardness for edge retention.
The Buck knife beat out all other candidates until they tested it for resilience, or flexibility.
They put it half way into a vise and a 200lb man put his weight on the handle.
Not surprisingly, it broke cleanly at the juncture with the vise.
Incidentally, the Navy finally chose a knife made of O-1, with chrome plating, as the winner of the competition.
This made no sense to me since I suspected that corrosion would creep under the chrome plating from the unplated edge of the blade.
In a very short period of time, as expected, these O-1 knives began to break in service as the result of corrosion.
Anyway, I would not expect a truly corrosion-resistant knife, heat-treated to 60HRC, to withstand a 200lb side load at mid-blade, and so it would not disappoint me if a corrosion-resistant knife failed from such abuse (I might get upset if a low-alloy blade steel failed due to this type of side load).
And I certainly wouldn't abuse a folder in this manner with any expectations other than failure, regardless of type of steel.
Still, I find myself wondering whether any reliable figures exist regarding the side load tolerance of N690 at 60HRC that would put it into perspective, especially in comparison to some of the other "stainless" steels.
Like I said, I don't have very high expectations, except that the corrosion reported by swingshot surprises me, given 17% chrome.
