Good question.
Best answer I can come up with is "it's a known quantity and offers good bang for the buck in a slicing type knife".
D2 Pros:
P1. inexpensive
P2. heat treat methods are tractable and known
P3. fair sized dose of Vanadium helps resist abrasive wear
P4. brittleness is "ok" for a slicing type knife when run at Rc61, D2's optimum
P5. may be a bit easier to sharpen than ATS-34 at a given hardness, depends on heat treat method I think.
D2 Cons:
C1. doesn't take much of a finish (orange peel effect unless you try REAL hard, ala Walter Brend)
C2. not tough enough for a big knife that will see any rough use
C3. grain structure is pretty "big" even with a decent heat treat, despite vanadium content (what I hear anyway, I get a great toothy edge on my D2 stuff so this is only a toughness, not sharpenability, issue).
C4. corrosion resistance is marginal ... but quite manageable
So, where does ATS-34 / 154CM differ?
P3... lots of Molybdenum helps abrasive wear but makes ATS-34 hard to sharpen by some accounts (I have no trouble with diamonds).
C1. ATS-34 takes a decent finish
C3. depends on heat treat though
C4. ATS-34 wins corrosion battle, but not by a whole lot
So by my tally, ATS-34, given a good heat treat and treated to run around Rc61, wins by a bit. D2 is simply an old workhorse. Somehow, I suspect Goddard's testing (slicing rope) is probably right on.
I'd take BG-42 before either actually, since it is basically ATS-34 with an added dose of 1.2% Vanadium on top of what ATS-34 offers, but again the margin is small. BG-42 might be a better steel if the moly was backed down from 4% to near 1-2% and the Vanadium was bumped up to 4%. But of course, that's S30V.
In today's market, for a stock removal knife, I'd take 3V or S30V over all of the above depending on what the intended use of the knife was. But now we're back to a price premium.
