Note: I have a new article on ApexUltra that shows properties of the final product (as opposed to these experiments with “lab scale” production). And also heat treatment recommendations on the final steel. Click here to read the newer article.
In March 2021 I was contacted by Marco Guldimann and Tobias Hangler about a steel they wanted to develop for forging bladesmiths. They had a few compositions in mind and wanted to know if I would analyze them to see if they would meet their design goals. Marco and Tobias are both knifemakers and have a particular interest in metallurgy and steel. Tobias is a metallurgist and Marco had previously designed his own steel called Guldimann steel. They wanted to make a new forging steel with high wear resistance, toughness, and hardness through W alloying. There have been a few steels with W alloyed to them in the past but availability has been poor and some sources have been drying up. I analyzed the compositions they proposed and said they would work fine but that I felt that an alternative composition could be better. Coincidentally I had proposed a steel at the end of the CruForgeV article which involved taking the 1.5Cr-0.3Mn-0.3Si base composition of 52100 and adding W and V to it for increased wear resistance. This fit the original goals of Marco and Tobias to have a higher performance forging steel with relatively high edge retention and potential hardness.
Alloy Design
Cr-alloying
The relatively high Cr of 52100 gives it a very intriguing set of properties. The Cr gives 52100 better control over carbon in solution to avoid tempered martensite embrittlement so that it has better toughness than other high carbon low alloy tool steels used by forging bladesmiths. The chromium also increases the hardness of the iron carbide which gives 52100 superior edge retention for a given amount of carbide. The 1.5Cr-0.3Mn also gives the steel a nice intermediate level of hardenability. Hardenability is how slow you can cool the steel and still get full hardness. 52100 will form pearlite during air cooling rather than martensite. Oil hardening steels like O1 and L6 will form some martensite during air cooling which increases the chances of cracking after forging. And those steels can be difficult to anneal without a slow cool in a furnace. But 52100 has enough hardenability where you can use a wide range of oils during the final quench and still achieve full hardness. Low hardenability steels like 1.2562, Blue Super, 1095, 26C3, etc. require a thin cross-section with a very fast oil. Or a water quench which is very severe and can lead to warping and/or cracking.
ApexUltra knife from Devin Thomas
W + V alloying
Tungsten was the first alloying element used in tool steels to contribute to wear resistance. Very early on there were steels like O7 and F2 which were low alloy steels with 1-4% W. Tungsten carbides are among the hardest that can form in steel. But the biggest benefit to a forging steel is that the tungsten carbides can be dissolved at forging temperatures which makes forging easier and means the carbides can be kept small without powder metallurgy production. In previous analysis of 1.2562 I found that with its ~3.1% W there were still some larger carbides that were not eliminated during forging, but that Blue Super and 1.2442 with about 2% W the carbides were fine. So this provides some guidance on the amount of tungsten to use.
Vanadium can also be used if the amount is not too great. While V, Nb, and Ti tend to influence each other and form around themselves leading to larger carbides, V and W carbides tend to form independently. Nb and Ti also will form at high temperatures making the size of the carbides difficult to control. Blue Super has a vanadium addition of ~0.4% which is about as much as you can get away with before the carbides will no longer dissolve at forging temperatures. While that amount is significantly less than tungsten, tungsten is a much heavier element so the two alloys actually contribute a similar amount of carbide, because you need about 6 times more W to get the same effect as V. CruForgeV has a vanadium addition of 0.75% though that steel has some larger carbides in it that aren’t dissolved in forging.
ApexUltra knife from Tobias Hangler
Laboratory Development
So, I proposed a final composition which was made with vacuum induction melting in a small ingot of about 20 kg. In general, the composition was very close to what was intended. The final composition will be shown closer to the final release of the steel. Tobias then forged the steel down to stock thickness and we performed experiments on this material to see if it was working as designed. At this stage it is not necessarily guaranteed that the properties of the final material will behave in exactly the same way as the steel will be made in larger ingots and then forged to a greater degree.
Microstructure
The microstructure of the material is quite fine with occasional “primary” carbides that were not broken up in forging. However, these carbides are less common and smaller in size than those found in 1.2562 and Blue Super. Also, both 1.2562 and Blue Super exhibited grain boundary carbides which were not found in the new steel. Below I have example micrographs from an area with primary carbides and from an area without.
ApexUltra – area without primary carbides
ApexUltra – area with primary carbides
1.2562
Blue Super
CruForgeV
Toughness
So far, we have only tested the toughness of the new steel at high hardness, 65 Rc and above. However, the toughness in this hardness range is stellar. It is significantly better than 26C3, Blue Super, and 1.2562. And above 66 Rc the toughness of 52100 drops down sharply with increasing hardness while ApexUltra maintains toughness all the way up to 68 Rc. It is likely that the tungsten and vanadium carbides are helping to maintain a fine grain size at the higher temperatures necessary for achieving the high hardness levels.
In fact, ApexUltra is the highest toughness steel I have tested in the 67-68 Rc range, exceeding even the PM high speed steels like Rex 45, Rex 76, Z-Max, and Maxamet.
More complete toughness experiments will be completed when there is final production material. I am especially interested in what it can do in the 60-63 Rc range. Because of the 1.5Cr based design we expect it to perform similarly to 52100 in that lower hardness range (yellow dots below) but this will of course have to be confirmed experimentally.
Edge Retention from Wear
In my previous CATRA testing, 52100 had unexpectedly high edge retention when compared with other low alloy steels and I proposed that this was due to the chromium-enriched iron carbides. Those enriched carbides are higher in hardness than typical iron carbide found in other low alloy steels. Apparently enough of an increase in hardness to better handle the abrasion from the silica in the cardstock used in the CATRA test. When compensated for hardness, 52100 even had higher edge retention than Blue Super and 1.2562. ApexUltra, however, with its combination of chromiuim-enriched iron carbides, tungsten carbides, and vanadium carbides, has significantly better edge retention than other low alloy steels typically used by forging bladesmiths. See this article for more information about the CATRA edge retention test and to compare with more steels.
Ease in Forging
Initial reports from knifemakers who have used the steel indicate that ApexUltra is similar to forging 52100 or 1.2562. So not the very easiest steel to forge, but significantly easier than high alloy tool steels and stainless steels.
Ease in Heat Treatment
Our experiments thus far have focused on furnace heat treating of ApexUltra to ensure that specific temperatures are tested. Furnace heat treating is the best method for any steel, even very simple steels like 1084. However, forge heat treating is also possible for ApexUltra though we have not specifically tested that aspect of the steel. ApexUltra will heat treat very similarly to 52100, and I recently showed that 52100 can be heat treated in a forge easily when using a normalized, pearlitic microstructure. For furnace heat treating, annealed steel is better because it gives more control over the final properties.
Knife in ApexUltra by Benjamin Kamon
What is Next?
Next, the steel is on order to be produced with ESR (Electro-Slag Remelting). This production process leads to greatly reduced impurities (phosphorus, sulfur, oxygen, etc) and also has a much faster solidification rate to help maintain fine carbides. Those two factors will ensure that the toughness of the steel remains high. The steel is scheduled to be ready in March 2022. At that point we will be thoroughly testing the steel including the final microstructure, full heat treatment recommendations and hardness measurements, and toughness and edge retention in the low and high hardness ranges. If all is successful then the steel can be sold to suppliers and makers. Updates on the new steel are being provided on its new website, ApexUltraSteel.com, and its Instagram page @ApexUltraSteel.
Summary
ApexUltra is thus far a laboratory developed steel by Larrin Thomas, Tobias Hangler, and Marco Guldimann. It uses a design combining 1.5Cr with W and V for increased wear resistance. The steel maintains good toughness up to very high hardness and has superior wear resistance to other low alloy steels used by forging bladesmiths. The steel is designed to maintain good forgeability and grindability despite the increase in wear resistance. Final production is planned for ESR to ensure the excellent laboratory properties are maintained in larger quantities.
Fantastic news. It’s great to see low alloy steel that has significantly better edge retention than the current options (adjusting for RC of course). I know the current data is somewhat limited but at this point can you comment on a possible mechanism(s) that contribute to it having such a large increase in edge retention per HRC pt?
Chromium-enriched cementite (iron carbide) is higher in hardness so contributes more to wear resistance.
So does the amount of Chromium-enriched cementite increase as hardness increases? I would have figured if anything it decreases due to increasing austenitization temperatures.
No, the amount of chromium-enrichment comes from the amount of chromium.
That’s what I thought. My question is this: why does Apex ultra have a larger increase in edge retention when it goes from 66-67 Rc than predicted by the standard 15.8mm/RC as indicated by the dotted lines on the chart?
That I can’t say for sure.
Wow. Initial testing looks extremely promising.
Really looking forward to getting my hands on some to compare. As an amateur with limited tools and machinery, steel choice makes a huge difference lol.
I wish this steel fell under my hammer. Very interesting
Hello,
really nice and interesting project.
I am really interested about the mechanical properties after the electro-slag-remelting. I am not sure if you really get finer carbides after the ESR-Process if you compare it you your small scale labortory melt (i guess there was a very fast solidifaction rate). In which remelting unit size do you plan the remelting?
Do you have any experience of how the steel cleanliness affects the edge retention and toughness?
For example, if you compare a steel with 100ppm S and O to a steel with 10ppm S and O each. Do you think there is a noticeable difference in TCC?
Best Regards
Daniel David
As the article said there is no guarantee that doing a full size heat will match the properties of the lab steel. Cleanliness does not affect edge retention.
Sounds like a cool new steel! Any plans to make flat stock for us stock removal makers? Either way itās awesome to see a new blade steel go through the development process.
Yes stock removal will also be possible though initial stock will be on the thick side.
Excellent news! Iāll look forward to giving it a try in the future. Iām a fan of 52100 and this looks like even more fun!
This is really exiting. Iāve been hoping for quite some time now that a forgeable (easily by hand) steel with higher edge holding then what is already available would come out.
If it works out as intended I will definitely be buying!
This looks like another amazing achievement and could give bladesmiths an exceptional top of the line material option.
I’m guessing this approach has been unexplored because it won’t produce the high temperature tempering characteristics of high speed steels. Nonetheless I have to think this combination of hardness and toughness would have to have some application beyond knives, perhaps machining soft thermoplastics?
It so seems like this alloy should be relatively affordable to produce – if only there was much of a market for mass produced non-stainless cutlery.
Finally I noticed that all of your beautiful pictured example knives in apex ultra seem to have a visible hamon line, do you know what hardnesses were achieved at the edge and back? (Or were they laminated?)
Those are laminated blades. While I wouldnāt say that ApexUltra is impossible to get a hamon with it is definitely not ideally suited for that, since it is designed to harden in oil.
You have an interesting point. However, I think at the end of the day it’s easier to use the production lines for high-speed steel tools rather than make new infrastructure for new steel. In addition, even machining thermoplastics can get components hot and I think it’s just too much of a liability using steel that could become embrittled due to heating up past 450f.
So if this works out, what shapes and sizes might we see? Any chance of round bar like we saw with Cru Forge V?
We are looking at there being a larger square/rectangle size for part of the first batch but final sizes are not yet decided.
Cool. l guess with steel like this where you are unlikely to etch for a hamon, you can dry weld some pieces together and it won’t show……in theory. š
Please get razor thickness bars in thereā¦ 1/4ā 1.75-2ā wideā¦ pretty pleaseā¦
Primary carbides shown in one of the pictures will vex people honing a razor, and the super high hardness will be problematic with strops.
How is the corrosion resistance by the way?
As good (or as bad) as 52100.
My limited experience with 80crv2 appears and performs like the new forging steel your developing. I believe 80crv2 is very underrated. Keep it oiled though.
80CrV2 is not similar to ApexUltra, but I’m glad it is working well for you.
Is 1.5%Cr enough? As far as I know, some matrix high speed steels have great hardness and toughness and are better for making long weapons.
With too much Cr it would no longer be well suited for a steel designed for forging bladesmiths.
Thanks for your reply. Cr can improve the hardenability until the content reaches 5%. And I’ve already read your test for edge retention and it shows a 5-7.5% of Cr is the best option for edge retention. So what do you think is the upper limit content of Cr for home forging? Can it be over 5%? In factories some kinds of steel with a 7% of Cr can be forged without gas protection.
5, 7, 12, or even 20% Cr steels can be forged at home just fine but it doesnāt have the advantages of low alloy steels like ease in forging, low hardenability, etc.
Fascinating!just getting back into smithing after years away. think I’ll use mostly 52100. apex iltra sounds very good. Bu-at Rc 66 or 68, ow do you sharpen it?
With a sharpening stone. Sharpens easy.
It always amazes me when people think the harder a steel, the more difficult to sharpenā¦ the harder the steel, the easier to sharpen really really wellā¦ and the more flexible your choice of edge finish isā¦ the only things that make sharpening hard is fat edges and retained austeniteā¦
what do you think of 8670? I was thinking of making a couple of 10″ blades. only 3/16″ thick or one 8-9″ long and 1/8″ thick. Would you use 8670, 52100 or somethng else? They are unlikely to see heavy use.
8670 is good for high toughness applications
If this hits a retailer that I can buy from in the next year, I’ll sample some and see if I can get a reliable heat treat after an anneal (something I don’t usually do, so maybe some learning curve).
if I can snap samples and get a hardness that stones won’t touch without big grain or other baddies, I’ll send a couple for testing.
there may be some interest in this for woodworkers who are hardness chasers. I’ve been disappointed with anything that has the words “japanese and blue” in it together due to the supposed potential for fine grain, but in practice, I see edge voids – even in blue #1.
Any news about the production batch?
There have been a couple updates on the official instagram page: https://www.instagram.com/apexultrasteel/
What about the precise heat treatment processes (hardening, normalizing, stress-relief annealing, tempering)? Thank you for your work (research, explanation)!
Galaxis MTG
Final heat treatment recommendations have to wait for tests on the final material.
Well, it’s in stores. They have it in 5mm thickness. Ordering for fun.:)