Carbides - The Nitty Gritty

[Sandow]

I'd guess that the electronegativity has less of an effect than the orientation of the bonds due to the valence electrons, the size of the metal ions, and the kinetics of bond formation vs the equilibrium states of the different carbides.

Ion size seems to be the compelling factor within each shell category. Found a great paper on it for those that are interested:
http://www.tribology.fink.rs/journals/2010/2010-2/2.pdf

Page 15 sums it up reasonably simply.

-Sandow

 

[james terrio]

{re: S35VN} ... why not limit the V to .5 as well and let a third carbide former soak the surplus carbon...

The small amount of Niobium is already doing what a small amount of V would... controlling grain growth.

It's not really a question of soaking up "surplus" carbon. It's there for a reason, and I'm pretty sure it's because they want the vanadium carbides for wear-resistance. Without it, S35VN wouldn't really be much different than other common stainless steels. Likewise, without the extra V (and CPM process itself), CPM-3V is not massively different chemically from good old A2 and other tool steels (although being just over the hypoeutectoid line does have a lot to do with its toughness).

As I understand it, the main point of powder/particle metallurgy is to control grain size and carbide distribution without relying entirely on chemistry. That allows a lot more control when tweaking the amounts of alloying elements (including carbon).

If you don't require the carbides for extra wear-resistance, and are only concerned with very fine grain and good toughness, you can just stick with simple ingot steels like 52100 or AEB-L and save a whole lot of money.