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- Apr 8, 2016
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the Rat's use Bohler D2. its a bit different than usa made D2. and CPM version isnt that great. its prefered to use psf27 spray formed version of D2 instead. but these are all budget knives.As I understand it the D2 in my blade isn't the powder metallurgy version and so has some fairly large carbides that I expect to not do so well in the rubber trimming.
I look forward to farting around with the Rat on monday.
Even if the Rat D2 is only some what useful in the rubber trimming it has proven to be a totally great edge for general use; well above many.
Who has CPM D2 blades ?
Some D2 info from a master.
http://xf.bladeforums.com/threads/any-experience-with-nathans-d2.1470902/#post-16929136
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.
and...
https://bladeforums.com/threads/is-it-psf27-or-d2.1597897/
The HDFK marked D2 is PSF27
PSF27 is D2
The EDC I've made that are marked D2 are Crucible D2, but the non-particle metallurgy version. CPM D2 carbide is small and rounded and does not enhance edge retention or create a toothy edge like conventional D2, and it is a little more "mushy" and does not respond well to pre-quenching so overall it does not have the edge stability potential (given an optimized HT) or edge retention of their regular D2 though I expect it is very good in tool and die.
D2 can be cheapass Chinese import with impurities, alloy banding and mixed microstructure (this is frequently sold as American D2 because it was cutup and ground here)
It can be high end cross rolled very clean electroslag remelt
It can be spray formed to reduce issues with aggregating alloy and carbide (PSF27) this actually has some advantages over CPM
It can be one of the foreign equivalents with tungsten replacing vanadium and some Chinese maker is calling it D2
edit to add:
The amount of vanadium can vary widely from maker to maker and this greatly effects pre-quenching response. You might find a higher chrome lower vanadium and moly blend that works great in tool and die or reacts well to induction hardening that doesn't play well in a knife edge or increased carbon versions tweaked for drawing dies rather than stamping tools or a lower carbon made to use for injection molding abrasive corrosive plastics like PVC. Some D2 has no manganese and added moly and has a better secondary hardening response and reduced pitting and is used to extrude vinyl siding. D2 is like hotdogs with many makers using different ingredients. Many flavors.
PSF27 is D2
D2 might be my personal favorite steel but I don't use it much because other people value other properties differently than I do and there isn't much demand for it. Also, it was frustrating having one batch behave differently than the next. 3V does so much of what D2 does and does it with much better toughness, and better corrosion resistance and edge stability too that I work in 3V almost exclusively now, and from a manufacturing point of view it is wonderful ordering 3V custom rolled and getting an entire ingot of it with consistent chemistry and microstructure. People tend to think of me as a 3V guy, but I was a D2 person first.
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I might just have to punch my self in the face. But I never cut up boxes with it so I may be OK there .