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Update: Artisan Cutlery posted to their Instagram confirming our findings:
Video
There is also a video of the following information:
AR-RPM9 Announcement and Name
AR-RPM9 was first announced in June 2020 on the CJRB Instagram, though oddly their Instagram doesn’t seem to go back that far now. I have a screenshot of it here:
CJRB is another brand owned by Artisan Cutlery. AR-RPM9 stands for “Artisan-Rare Powdered Material 9 Element Steel.” That is a very odd name so let’s break it down one element at a time. Artisan makes sense, it refers to Artisan Cutlery. But why “Artisan-Rare”? Just to have an oblique reference to AR rifles? I honestly don’t know. Then “Powdered Material” is odd, generally when we say “PM” steel that means “Powder Metallurgy” or “Particle Metallurgy” but not “powdered material.” In my original Patreon post about this steel I hypothesized that perhaps they were using weasel words for some other process that isn’t powder metallurgy but then they released a video in September 2020 where they specifically called it “powdered metallurgy” process, but we will come back to that. Then “9 Element Steel” which is a good lead-in to the composition discussion.
Composition of AR-RPM9 (Why it should actually be called AR-RPM7)
Artisan Cutlery revealed the composition of the steel in that September 2020 video. I was excited to see what it might be since they claimed to have designed a “new exclusive steel” designed specifically “with our…knives in mind.” Plus nine elements is quite a bit, so they must have gotten very creative in the design of the steel. Unfortunately, the reveal was quite underwhelming. The composition they specified was identical to the common 9Cr18MoV, the same steel as the European 1.4112, and very similar to American 440B. There were a few oddities in the description. One of the elements the video said was part of the 9 was “less than 0.4% nickel.” That is the same maximum allowable nickel content in 9Cr18MoV. Having a maximum allowable content means that it isn’t intentionally added; there is no minimum requirement. This is because nickel is present in a lot of recycled stainless steel. For example, I measured between 0.16 and 0.28% nickel in stainless powder metallurgy steels from Crucible, Carpenter, Bohler, and Uddeholm. So we are already down to 8 elements not nine.
Measurements of nitrogen, copper, nickel, cobalt, and tungsten in a range of powder metallurgy steels
Another oddity in the Instagram video was that he said there were “rare earth elements” in the steel, with elements plural so potentially we are back up to 9 or maybe even more. Before saying what those rare earth elements were, the Instagram video cut off. Rare earth elements are used in some steels and include elements like lanthanum and cerium, used for a couple different reasons in the steelmaking process. So a pretty unusual addition, especially to announce publicly, as often they are used without advertising to the public, in part because it is a trade secret and in part because they are used in very small amounts. Fortunately, Artisan Cutlery later clarified to Knife Newsroom shortly after what these elements are, and even later in December they uploaded a full version of the cutoff instagram video to YouTube. The answer was baffling: phosphorus and sulfur. Phosphorus and sulfur are not rare earth elements. I have never heard anyone say they are rare earth elements. Those are common impurity elements that are often specified with a maximum allowable content. They are not desirable, and are not considered an addition to the steel. So now we are down to 7 elements. We need to rename the steel AR-RPM7.
The only potentially relevant change is cobalt, which they said is 0.3%. 9Cr18MoV doesn’t have a cobalt specification, and 0.3% is a very small amount, so an argument could be made that it would still fit under the 9Cr18MoV spec. Cobalt is also present in a lot of recycled steel, so there is generally at least a small amount of it, though usually less than 0.3%. Furthermore, an addition of 0.3% cobalt to a steel would have a very minor effect on properties. Even with controlled testing of properties with and without 0.3% cobalt I’m not sure a metallurgist could come up with which is which. So maybe this is the change to 9Cr18MoV that they thought was enough to be a “new steel.”
I measured the composition of the steel with Optical Emission Spectroscopy (OES) and the elements were within expected ranges. Of course other trace elements were present which is also expected but I have not included them so as to not confuse anyone.
Powder Metallurgy? (Why we can’t call it AR-RPM7 either)
In my original Patreon article in June 2020 I expressed skepticism about AR-RPM9 being powder metallurgy. Artisan Cutlery already misunderstood how many elements were in their steel and apparently have no idea what a rare earth element is, so the chances they know what powder metallurgy is seemed small. Furthermore, there are several steels made in China using “Sprayform” which is a different technology than “Powder Metallurgy.” One example that has come out since AR-RPM9 is Twosun Knives YJ01-V1 which is a sprayform version of a slightly modified M390. This steel is made by Foshan Fenghe PSF (Precision Spray Form).
What is Spray Form?
Sprayform is an intermediate technology in between conventional casting and powder metallurgy. In conventional casting, the liquid steel is slowly cooled in a mold to form an ingot. The slow cooling leads to alloy segregation and large carbides. With powder metallurgy the liquid steel passes through a nozzle and is sprayed with nitrogen gas to rapidly solidify (gas atomization) the steel into fine particles (powder), which is then placed in a canister under high pressure and temperature called hot isostatic pressing (HIP) to create a solid ingot. The steel is then forged and rolled like normal. I previously wrote about powder metallurgy in this article.
Sprayform is somewhat similar to powder metallurgy in that the liquid iron is sprayed with nitrogen gas, but instead of fully solidifying, the partially solidified steel is sprayed onto a table which lowers during processing to create the entire ingot. This leads to an intermediate microstructure which is not as fine as powder metallurgy but also not as coarse as conventional steelmaking. I have an article comparing D2, sprayform D2, and powder metallurgy D2. Below are micrographs showing the difference in D2 microstructure with the three different technologies:
Conventional D2
Sprayform D2
Powder Metallurgy D2
As one more example, here are micrographs from Fenghe PSF showing their ripoff of M390 made with sprayform (right) compared with the powder metallurgy version (left):
Powder Metallurgy M390 (left) and Sprayform M390 (right)
You can see that the carbides in a sprayform steel are in between powder metallurgy and conventional. Sprayforming is done because it is lower cost vs powder metallurgy, eliminating the HIP step.
What Technology is Used for AR-RPM9?
So Shawn Houston of Triple B Handmade and I bought a couple knives from Artisan Cutlery to investigate the microstructure.
High Magnification (same as prior D2 micrographs)
AR-RPM9 Medium Magnification
Here is Sprayform D2 for comparison:
Sprayform D2 Medium Magnification
It is evident immediately that this is certainly not a powder metallurgy steel. There are many large carbides that I have never seen in any PM steel. I don’t believe that it would be possible to make a PM steel with carbides that large. With the largest carbides being around 10 microns I think sprayform is the most likely, though I could almost be talked into it being a conventionally produced steel. To compare the carbide size with 9Cr18MoV, the conventional version of this steel, we looked at edges of knives in both steels:
AR-RPM9 knife with relatively small carbides visible
9Cr18MoV knife with relatively large carbides visible
The carbides appear larger in the edge of the 9Cr18MoV knife when compared with the AR-RPM9. And the carbides in the AR-RPM9 look much too large to be powder metallurgy. So I think sprayform is the most likely production technology.
Changing the Name of AR-RPM9 to ASF7
We already discussed how the “9” should actually be a “7” in AR-RPM9, but let’s analyze the rest of the name: “Artisan-Rare Powdered Material 9 Element Steel.” We can leave the “Artisan” since that is the company selling the knives. The “rare” part I take some issue with, so we can drop that from the name. And I have discussed how “Powdered Material” is misleading so we can drop that. So we will rename the steel “Artisan Spray Form 7 Element Steel” or ASF7 for short. There, we fixed it. No more false advertising.
Properties of AR-RPM9
So now that we have discussed what AR-RPM9 likely is (and what it isn’t), what are the properties of the steel? Sprayform technology does improve toughness, though not to the extent of powder metallurgy. You can see an example with D2, sprayform D2 (PSF27), and powder metallurgy D2 (CPM-D2):
So we would expect a similar improvement over 9Cr18MoV, which would have similar toughness to 440C which I have already tested:
With 440C being around 6 ft-lbs at 59 Rc, we would expect AR-RPM9 to be in the 8-12 ft-lbs range. Nothing too spectacular but that’s what the main improvement would be over 9Cr18MoV. In terms of hardness, edge retention, and corrosion resistance, any differences would be minimal. You can read an article where I compared the edge retention of conventional and powder metallurgy 154CM to see why I think so (they performed the same). If you want to estimate the edge retention of AR-RPM9 vs other steels in my big CATRA chart you can look at 440C, or possibly a bit less.
Summary and Conclusions
AR-RPM9 is very poorly named, having only 7 elements and likely being made with sprayform but not powder metallurgy. It is essentially a sprayform version of 9Cr18MoV. Despite their claims, this steel isn’t “new” nor is it particularly exciting. The sprayform technology likely improves the toughness somewhat but wouldn’t impact much else.
Very interesting article! Artisan’s sales must have dropped and they made a desperate attempt to get things rolling again.
Absolutely fabulous work here, and done in a way that it’s complete but we don’t have to be metallurgists to understand and get a dead clear understanding of the situation and conclusion.
Follow-up comment to above. I don’t know who is responsible for not having good answers here on the company’s part, but they’re selling a fairly large folding knife that’s not horrible looking (not a knife guy, but I’ve seen worse), and it’s $98 at the moment.
What’s my point? if they actually said it was Sprayform 9Cr18MoV, I can’t see how it wouldn’t sell in the first place. We don’t deal with much of this in woodworking other than one company calling XHP “V11”, and euro tool makers not specifying which drill rod they’re forging tools from (but they make no real outlandish claims).
If I were a knife guy and someone made a sprayform large folder that was actually 60 hardness, I’d hardly balk at spending $97 on it. I don’t see the point for making unneeded claims.
Hi David Weaver,
are you refering to the Veritas PM-V11 they make chisels and plane blades out of? And when mentioning XHP, are you refering to Carpenter CTS-XHP? If so, I would have never thought they were the same… big surprise to me!
Thanks!
makes sense though, considering they claim it’s both high edge retention and easy to sharpen, which didn’t make sense and never sat right with me… until you realize… ah yes, only chromium carbides. So, vs. a steel with similar abrasion resistance that contains vanadium carbides, it will be easier to grind, machine, polish, sharpen, etc. Try grinding k390 or 10v on traditional abrasives then do ZDP-189. Both steels have similar abrasion resistance yet one grinds and polishes a heck of a lot easier than the other… thanks to a lack of vanadium.
You sure do a lot of research. Thank you for your efforts. Joe S
Larrin, Thanks for exposing this deception, the knife world is better for your vigilance and science. People have owned and used knives throughout their lives, so they think they know all there is to know about knives. ‘Tain’t necessarily so. Then they buy the hype and don’t know the difference. I unknowingly purchased some 52100 made in CHINA, it was highly contaminated with impurities, including copper.
Similar to this article, do you have plan to compare PMC27 vs 12c27? I wonder how much toughness/wear resistance improvement is possible for relatively low carbide PM steel.
As far as I know PMC27 is only available as part of a Damasteel mix with RWL34.
I’ve always wondered why Damasteel bothers making a PM version of 12C27 as it already has a finer microstructure than most PM Stainless Steels… It’s like making a PM AEB-L or PM 52100… The only thing increased is the cost!
Probably because it has pretty much exactly the properties they need for damasteel.
Considering it’s main selling point is its looks that probably was the main criterion besides good performance in combination with rwl34 – and it’s hard to make damasteel from an ingot block after all.
Well done. I wonder if Artisan Cutlery will make any changes in their marketing based on your review.
On a personal note, In wonder if you have looked at Japanese steels. They have a legendary reputation.
Thanks for your continuing metallurgy work and writing about it so that even a layman can understand most of it.
I still have some of the original Hitachi ATS-34, has a high Vanadium content and at the right finish, the grain appears “wootz-like.” I have been experimenting with Japanese mud tempers in ATS-34 and like the results of the first few blades. Temperlines (Hamon) are there but elusive to bring out in polishing. Too bad Hitachi discontinued this alloy!
I’m fairly certain ATS-34 is just Japanese 154CM. Though word on the street was that folks always said it was better than the American stuff, but word on knife street means absolutely nothing, often less than nothing.
Jeff, you’re right, ATS-34 is pretty much the same as 154 CM, but in my experience-not exactly- there’s a difference. But, I work the other side of that street, people still claim “You can’t forge stainless.” And I’ve been doing it successfully for 40 years. So have it your way! “Hit Don’ make S**t to me.”
Thank you. Excellent work, both in isolating the metallurgy in question and the bullshittery surrounding it.
Having bought a CJRB knife with this questionable metal as its blade, i’ve been wondering on and off as to what it was (ashamed to say, without research or asking the question of anyone “in the know”) mainly due to the fact that it performed… or to be more precise, it didn’t particularly.
And now I know why, thanks guys, you rock.
Dr. Thomas
This is an excellent review and explianation of AARP9. Thaks for revealing the false advertising. I have a few of the knives in this steel and consider it D2 performance.
Great work as always.
Thank You
Ah what a refreshing and well written article!
Thank you Larrin for cutting so articulately through the crap!
Having been a knife and steel nerd most of my life, this is a breath of fresh air.
Also extremely stoked that one of my favourite brands, Leatherman, is now sporting an ACTUAL custom, amazing super steel- CPM Magnacut!!! #actualwishlist 🙌
Interesting I thought powdered metallurgy was just when you ended up with a powdered form of a metal.
I didn’t realise it could be reformed in process into an ingot.
I’m guessing to get the pure powder form they skip the last step.
Fascinating videos, Chanel & website I just came across it recently.
When I was looking up RWL-34 used in the Norseman by Grimsmo Knives out of Canadia.
Thanks for the awesome resources.
Thank you Tomas for the great work. I learned about this article on Ukrainian YouTube 🙂
Great article – but if spray-form D2 is allowed to call itself PSF27, surely this can be called AR-PSF7?
In terms of performance, it seems like a slightly more corrosion resistant CPM-154, which is very respectable.
The article makes references and comparisons to 9cr18mov and 440B but I can’t find any performance data on these… Have you published any I could look at?
Thanks a lot for all your work in this field.
Outstanding work and delivery with this information, as is the norm with any of Dr. Thomas’ work. I wanted to read this article because my next knife purchase will likely be the CJRB Pyrite Bowie in S90V, but now I’m hesitant. For a company to put out a product release description without a complete understanding of the product they are releasing leads to a couple of conclusions, the first being what you have led to in this article, the company is misleading its customers to drive sales, and got caught, which is despicable enough, but maybe more alarming is they put products and information to the public not fully understanding what they are making or how they are making it, which most definitely hinders the quality control of their products. Neither trait is a sought after one in this industry for sure. Should I be confident that I when I buy a knife from this company, I’m getting what they say I’m getting? I remember a few years ago the rumors that Mantis Knives was lying about the steel variants they were using in their knives. Thanks again for all you do , Dr. Thomas. I have learned so much from your site, your knowledge and delivery of it to the public is second to none.
– Bryan M.