I probably have more experience with my D2 than anybody, I have them around the shop, my own skinning knife, and my steak knife. I use it all the time, it's probably my favorite steel and it has been running circles around and handing out spankings to the stainless super steels for years.
D2 is probably my favorite steel and I do a very good job with it. My heat treat for it has developed over the years and I feel it represents the best in the industry. I've been very open with other makers about what I'm doing with it and my techniques for it are now widely adopted to the point I see new makers talking about the process and unaware where it came from.
Complex steels like D2 usually have a basic "built in" grain size that results from their alloy and its reaction to an anneal. By default D2 is usually around 12-13 intercept grain size which is relatively fine grain.
Pre-quenching in D2, M2 and other complex steels is a grain refinement step that violates the "only one austenitizing per anneal" rule for these steels meant to avoid the extreme grain growth they're prone to on a second heat which creates a large fish scale style fracture. When done improperly it can have no effect or can lead to intercept grain size as low as 1 (extremely coarse).
Prequenching, when done properly, can refine the grain upwards of 17 or more, which is a very fine grain condition. This is based on research by Teledyne VASCO.
Before going further, let me state that grain refinement to this level serves no purpose in-of-itself and very fine grain, beyond a certain point, doesn't make a better knife. This is a widely misunderstood concept among makers and knife nuts. That's not what this is about.
There are a couple steps about pre-quenching I don't recommend to other makers because they have to be adjusted for each heat batch because the variations in alloy content and material condition effect the heat treat response and can lead to problems if done improperly. This is one reason I don't use D2 much any more, because every single batch needs special attention to be fully optimized. This is particularly true going from one manufacturer to another, because D2 is like hotdogs, they can all put different ingredients into it, and a .8 vanadium will react differently than a 1.2. But, when the time and temp is dialed in it refines the grain (which is not a bad thing) and puts carbon into solution, reducing the soak time and temp for the second heat which I believe may be very significant in minimizing naturally occurring structures that play hell with edge stability such as RA that converts in temper rather than during the quench.
The end result of a fully optimized D2 is a durable knife with outstanding edge retention, good corrosion resistance, and that toothy D2 edge that just keeps cutting. While not as durable as 3V, it's more durable than most, and it just keeps cutting and cutting.
Sometimes D2 can be somewhat brittle, but our final cut testing yesterday of a knife from this batch had a thin D2 knife at 18 DPS at HRC 63 cutting some 4D nails without chipping.
We're using Crucible D2 for this batch, but not their CPM version. This was not to save cost (less than $2 difference per blade) but to avoid the small rounded carbides that fall free from the edge. It's a good process to promote toughness, but it spoils one of the best properties of D2 in a knife, so we use a conventional melt.
If you'll try it, I promise you'll like it.
