D2, S30V rust resistance

R

rayback

Joined
Sep 16, 2006
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D2 -- carbon - 1.40-1.60
chromium - 11-13

S30V - carbon - 1.45
chromium - 14

Both steels are almost identical concerning carbon/chromium content.
What makes S30V stainless, whereas D2 is not stain-resistant at all?

Thanks
Ray
 
Though it's true that the modern powder steel S30V is more stain-resistant than the traditional tool steel D2, there is no absolute stainlessness, and no absolute non-resistance. Many people including myself prefer the latter, unless you live in salt-water environments.
For specific debates on this, you'd be better off in the materials section.
 
I have a couple of D2 knives that I use often and haven't had any rust issues, although it does develop a nice patina with time.

I don't remember who it was, I think it was Scott (Razorback), who told me that D2 looses some of its chromium during heat treat.
 
13% is a cutoff for a steel to be classified as stainless, I believe. D2 is rust resistant, it just can't be called stainless.
 
rayback said:
Both steels are almost identical concerning carbon/chromium content.
Click to expand...

D2 has 1.5:12, S30V is 1.45:14. These are not almost identical because many of the materials properties are not linear in dependance on alloying element, corrosion resistance is one of them. For example the difference in free chroimum between 12C27M and 13C26 is only 2.5% but this is enough to make the steels very different in scope of work and 12C27M is recommended for very harsh corrosive enviroments like repeated machine dishwashing.

What makes S30V stainless, whereas D2 is not stain-resistant at all?
Click to expand...

Stainless isn't an on/off condition, all steels with any free chromium will resist rusting to some degree, as there is more free chromium they will resist it more. The critical part is free chromium this is the chromium that isn't in carbide form but is just hanging out in the steel as that is what prevent rusting.

S30V is austenized much hotter than D2, this is the temperature the steel is raised to during heat treatment. The higher temperature puts more of the carbide into solution (dissolves it) and thus more of the alloying elements which make up the carbides (like chromium) will be free in the steel. The difference between those two common austenizing temperatures will shift free chromium levels by a large percent.

In addition S30V has nitrogen to improve corrosion resistance and the extra vanadium also ties up more carbon which again shift the carbon/chromium ratio. You have to look at all the elements which effect corrosion resistance and carbide formation, not just C/Cr. This is actually not a trivial thing to do precisely because you have to do the required thermodynamical calculations to predict the corrosponding phases.

-Cliff
 
In order for steel to be stainless, it has to have enough chromium to over saturate the iron. Normally chromium is absorbed in the iron particles during heat treating, but when you put too much in then you have all these extra particles that aren’t really doing anything, and end up protecting the metal from oxidization (rust). That’s the simple, not so technical way of saying it (feel free to correct me if I got anything wrong).
The reason D-2 is “semi stainless” is that it doesn’t have enough chromium to produce a lot of these “extra” chromium particles. It has some, but not many.
CPM S-30V on the other hand. On top of having enough chromium has a whole bunch of other stuff to help reach the saturation point, meaning it gets more protective chromium than it would otherwise. That’s why it’s still fairly stain resistant at just fourteen percent chromium.

Tristram, you’re forgetting about H-1
http://spyderco.com/catalog/details.php?product=215
 
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