When Fasfa Says Try Again Later How Much Later
Thanks to Saptak Dutta, Bill Clancy, Cap Hayes, Electro_Static, Coll Gomila, Kody Ekstrom, Nico, Tom Ewing, Ken Johnson, Brent Stark, Jesse Warren, Malachi Chou-Green, Luke Haag, Bill Harrison, John Geelhoed, and Julian Hamilton for becoming Knife Steel Nerds Patreon supporters!
My Steel Past
S30V was developed by Crucible and released at the end of 2001. As I began to be interested in knives and steel in my teens the idea of developing a new steel was very interesting to me. Not necessarily as something I would do myself, but development of new products, knowledge of the metallurgy required to do so, the trial and error necessary to find an optimal balance, etc. was all intriguing. S30V was touted as a steel developed specifically for knives, and I was curious about what that meant exactly; what properties were they trying to balance for a knife steel as opposed to tool and die, or high speed steel, injection molding steel, etc. I talked to Crucible metallurgists at every knife show I attended and even called them up frequently with many questions and they always did their best to answer. I was hooked.
Matthew Gregory chopper in CPM-MagnaCut
After ~10 years and 2 kids later I was working at United States Steel developing automotive sheet steels. It is a fun job but because of my original passion for knife steels I began writing for this website and doing research on the properties of various steels. As part of this I write articles about the history of different steels including how they were developed and what gives them their properties in terms of composition and processing. However, this doesn't necessarily qualify one to design a new steel. It's sort of like the difference between offering commentary on a football game and actually playing in one. I had considered attempting to come up with my own unique steel compositions, but just wanting to do so doesn't mean that you have something unique to offer. However, spending all this time on writing about different knife steels eventually led to a series of epiphanies about possibilities in steel design that have not yet been explored.
Epiphanies
Orange dots are PM non-stainless, blue dots are PMstainless
Early powder metallurgy stainless steels used high chromium content (17-20%) for corrosion resistance in combination with vanadium for wear resistance. These included steels like S60V, Elmax, and M390. However, these steels have relatively low toughness from the relatively coarse microstructure that results from a large percentage of chromium carbides. Non-stainless powder metallurgy steels like CPM-4V, CPM-3V, and Vanadis 8 have smaller vanadium carbides only which give them a superior combination of toughness and wear resistance. The small, but very hard, vanadium carbides, offer superior wear resistance for a given amount of carbide. And less carbide means higher toughness. Crucible later developed steels like S90V and S30V which had less chromium (14%) for less chromium carbide which improved properties relative to the higher chromium stainless steels. The corrosion resistance was not necessarily reduced when compared with the higher chromium steels because only so much of the chromium is "in solution" to contribute to corrosion resistance. Somewhere in the range of 10-13% in solution is common, with the rest tied up in carbides. Which means a stainless steel can be developed with only about 10% chromium as long as all of it is in solution after heat treatment. Actually, it could be a little bit less because some of the steel is carbide. If the steel has 10% carbide, that leaves 90% matrix, so the 10% chromium could end up being as high as 11.1% in solution (10 divided by 0.9).
Devin Thomas chef's knife in stainless san-mai with CPM-MagnaCut core steel. Devin says this is his new favorite kitchen knife steel.
So if the properties were improved by reducing the chromium content down to 14%, why couldn't they be improved by reducing the chromium content further? Is it possible to balance the composition to ensure that any chromium carbides are dissolved during heat treating so that we get a microstructure of only small hard carbides rather than the larger, softer chromium carbides? Modeling of steel in Thermo-Calc did not initially look promising. Reducing the chromium content of a steel like S30V would result in less chromium in solution and lower corrosion resistance but not much less chromium carbide. The carbon content would also have to be reduced so that chromium carbide would dissolve at a reasonable temperature. But in those cases the steel may not have enough hardness.
I found that if I kept the carbon content into a relatively narrow range, a sweet spot would be found where there would be enough carbon (for hardness) and chromium (for corrosion resistance) in solution while also having a combination of hard vanadium and niobium carbides for the optimal balance of wear resistance and toughness. At least, according to the software. There are never any guarantees that software is going to be right. You can read more about my stainless steel design ideas in this article.
Darrin Thomas folder in CPM-MagnaCut
Property Target
But eliminating the chromium carbide is only one part of the equation. I then had to pick a toughness-edge retention balance. After all, the non-stainless PM steels extend all the way from Z-Tuff (very tough but relatively low edge retention) up to 15V (very high edge retention but relatively low toughness). To me the sweet spot is around the steel CPM-CruWear, 4V/Vanadis 4 Extra, and CPM-M4. Those steels are known for their excellent balance of properties. CPM 4V is very popular with everything from competition chopping knives to fine cutting knives. Its fine microstructure and medium-high toughness in combination with above average edge retention makes it very versatile. It has very good ease in grinding and sharpening along with its balanced properties because of the fine microstructure. And since the stainless PM steels are so crowded in the high edge retention group, going a bit higher in toughness gives more differentiation with the currently available products. So my target was CPM-CruWear/CPM-4V but stainless. Possible? Maybe.
Phil Wilson "Sprig" in CPM MagnaCut
Options for Testing my Idea
So now I had a composition I wanted to try but had no way of testing it. I called a research facility that does small batch powder metallurgy production and they quoted me an obscene amount of money for 50 lbs of steel. Too much for me to justify spending. I decided that the best way to do it would be to convince a steel company to make it. The worst that could happen would be that they say no. There are only a few steel companies making powder metallurgy tool steels, so it wouldn't take many rejections to reach the end of the list. I have never heard of an independent metallurgist offering a steel design to a company out of the blue. Almost universally the designs come from internal metallurgists that are being paid a salary. Sometimes a University Professor is brought in for certain things, but often those projects come as suggestions from the steel company itself, usually to be part of a Graduate student thesis.
I decided to contact Crucible Industries first. They were the company that got me excited about knife steel to begin with. They have had the best availability of knife steel in a range of sizes and in reasonable prices. In part because of the partnership with Niagara Specialty Metals who do the hot rolling and distribution of knife steels for Crucible. So they have shown commitment to the knife industry in the past. However, Crucible is not the same company they were when developing S30V and S90V. At that time they had a dedicated research facility where Pilot-sized heats of steel would be produced to test out different designs before full production. Now to test out a new steel concept you have to make a full heat of several thousand pounds. The costs add up quickly if you want to try more than one composition. I likely have only one shot to get this right.
Triple B "Cruiser" knife in MagnaCut by Shawn Houston
Convincing the Powers that Be
I put together a PowerPoint presentation summarizing my steel design idea and why I thought it would work. I showed all of my experiments comparing the modeling of Thermo-Calc compared with my measured hardness, toughness, wear resistance, and corrosion resistance of different steels to demonstrate the reliability of the modeling. And the presentation showed that we could match the properties of non-stainless powder metallurgy steels like CPM-4V and CPM-CruWear if my design would do what it is predicted to do. I first talked to Bob Shabala of Niagara Specialty Metals and he was very excited. He offered to help me how he could with convincing Crucible to try the steel. With Bob in my corner I went to Crucible with the same presentation. They were intrigued but reticent. John Shiesley, then the head of Sales (and now the CEO), wanted to know how this would work in terms of distribution, etc. I assured him it would be sold as a normal Crucible grade and that I wasn't interested in warehousing and selling steel myself. Bob Skibitski, the lead metallurgist at Crucible, had several questions designed to test my knowledge of steel and to discover if I knew anything practical or was just a research nerd with my head in the clouds. I convinced them that I knew what I was doing and they agreed to produce a heat of the steel.
Big Chris "Ranger" in MagnaCut
Sleepless Nights
It took just over a year for the first melt of steel to be "atomized" to powder. I woke up at 3am most nights unable to sleep worried about the steel. Should it have a little more carbon? A little less silicon? Am I being too aggressive in how much nitrogen I want? Chromium is one of the main elements that allows more nitrogen to enter liquid steel and I was reducing the bulk chromium content. Finally after that year I got an email from Bob Skibitski early in the morning that the steel was currently liquid and that some of the elements had already been added. He said that the melt was "mushy" from partially solidifying and asked if he could add more carbon to reduce the melting temperature. I did not want to increase carbon because that would increase the amount of chromium carbide. I asked him to wait until the remaining elements were added and gave him permission to bump up the carbon by 0.1% if necessary. After the further elements were added the melt became liquid and that minor emergency was averted. The remaining production proceeded without issue. Fortunately, the target composition was largely reached, extremely close for the first attempt. Even the target nitrogen was reached despite the lower chromium.
I was excited that the target composition was achieved, and simulations in Thermo-Calc confirmed the steel would be very close to the target. It then took another six months for the steel to be HIPed, given the initial forging, and delivered to Niagara for hot rolling. There were many more sleepless nights. Did it meet expectations? Let's find out.
Naming the Steel – CPM MagnaCut
I wanted a name that made it clear that it is a knife steel and also calls back to the history of steel. One of my favorite parts of Knife Steel Nerds has been researching the history of steel development and which companies and people contributed to the most significant breakthroughs. One company that was very influential was Vanadium Alloys Steel Company (VASCO) which developed steels that are still in use today in various forms, like M4 (CPM-M4), Vasco Die (CPM-3V), Vasco Wear (CPM-CruWear), and VASCO-MA (CPM-1V). One of their major developments was M42, one of the earliest steels capable of 70 Rc. VASCO named the steel Hypercut, fitting a theme of other high speed steels with cut in the name like Van Cut, Telecut, Red Cut, Grey Cut, etc. So as a nod to VASCO I named the steel MagnaCut, Magna being the Latin word for great or awesome.
Testing of CPM-MagnaCut
I ran the steel through my battery of tests, of course, though steel was also sent to several knifemakers for testing, including Phil Wilson, Shawn Houston, Devin Thomas, Darrin Thomas, Big Chris, Matthew Gregory, and Andrew Demko. These knifemakers were selected because they have experience with other high alloy steels and with testing of their knives. Darrin shared some steel with Chad Nell and Jared Oeser. I will be reporting some of their testing and experiences in the appropriate sections below. Some steel was also sent to Brad at Peters' Heat Treating to test the response to vacuum furnace hardening.
Composition
The composition of MagnaCut is not particularly complicated. The nitrogen and niobium additions help make the steel a bit better but it could have even been made without significant additions to those elements. The main challenge was in balancing the carbon and chromium to ensure sufficient hardness and corrosion resistance while also dissolving the chromium carbide at a reasonable heat treating temperature. I also have the composition of other previous steels that show the approximate evolution of composition to lead to MagnaCut.
This is a classic example of how it is difficult for a "lay person" to assess the properties of a steel based simply on composition. The 4% vanadium plus 2% niobium the steel may look like it is higher wear resistance than it is. Instead it is designed to have similar wear resistance to CPM 4V which has just under 4% vanadium with no niobium. The higher heat treating temperature required for a stainless steel means that the two have a similar amount of carbide. Also I am sure that people will look at the Cr content and immediately call it a "semi-stainless" despite the steel's excellent corrosion resistance. So hopefully word of the steel's performance travels faster than initial reactions to the composition. I might be putting too much faith in humanity.
Microstructure
The carbide structure of MagnaCut is much finer than the common powder metallurgy stainless steels such as CPM-154, M390, Elmax, S35VN, etc. The only stainless PM steel I have imaged which is competitive in terms of carbide/nitride size is Vanax. MagnaCut is even somewhat finer than CPM-4V and Vanadis 4 Extra, the non-stainless steels that MagnaCut was modeled after. This is an excellent result and should lead to excellent properties. Compare with more steels with this article on micrographs of knife steels.
MagnaCut
CPM-154
M390
Elmax
S30V
Vanax
CPM-4V
I also imaged the steel with SEM using backscatter imaging to see if I could differentiate between different carbide types. I wasn't sure if there would be separate vanadium-rich and niobium-rich carbides or if it would all be a complex niobium-vanadium carbide. The backscatter imaging confirms that there are both types. Niobium carbides are white and the vanadium carbides are grey in the image below. The niobium carbides are finer which brings down the average carbide size. Also there is a smaller amount of vanadium carbide when compared with 4V (more vanadium carbide means a larger average size for the vanadium carbides). So the partial replacement of vanadium carbide with niobium carbide leads to a smaller average carbide size vs 4V even though the overall volume of carbide is similar. Nitrogen can also slow down coarsening of carbide in PM steels but I don't know for sure if the 0.2% is enough to make a measurable difference. Regardless, the carbide structure is excellent.
Grain Size
I got some decent images of the grain boundaries of MagnaCut from Bob Skibitski at Crucible. Typically we don't need to worry too much about the grain size of high alloy steels because they have plenty of carbides that "pin" the grain boundaries, preventing excess grain growth. And revealing grain boundaries with etching can be surprisingly difficult. However, austenitizing up to 2200°F is recommended in the datasheet so I was curious if it was possible for the grains to grow at those temperatures. Metallography after a 2150°F austenitize confirmed the same fine grain size as at lower austenitizing temperatures. The average grain diameter is about 5.5 microns, for an ASTM grain size of about 12 (bigger number is better for ASTM grain size). This is in the "ultra fine" range for grain size. The grain size was not significantly different with a 2050°F austenitize. I also looked at the fracture grain appearance for 2200°F specimens and it had a completely smooth appearance, indicating ASTM 10 or better. This may be helped by the decreasing hold time I recommend at higher temperatures, but either way the grain size is very fine across the recommendations.
Grain boundaries visible in a 2150°F heat treated MagnaCut coupon. A few of the largest grains are measured with red lines. The average grain size is in the "ultra fine" range.
Hardness
Hardness was measured both by myself and Robert Skibitski of Crucible. I rounded the values to the nearest 0.5 Rc because there is going to be small variability even if I were to heat treat a set of three coupons exactly the same way. I used shorter austenitizing times for higher temperatures, as the steel heats through more quickly and the carbides dissolve more quickly at higher temperature. 30 minutes hold time for 1950°F, 25 minutes for 2000°F, etc. up to 2200°F with only 5 minutes. This is a standard austenitizing time range used in Crucible datasheets in steels like CPM-M4 and CPM-10V. I tested the hardness with cold treatments as well, one set with my basement freezer and another set with liquid nitrogen. I placed the samples in the freezer or liquid nitrogen directly after quenching because that makes the cold treatment more effective than tempering first or letting it sit around and measure hardness of it first.
The steel can reach relatively high hardness, over 63 Rc without cold treatment, and over 64 Rc with a cold treatment, even reaching 65 Rc, at least with the small coupons I heat treated. This is what I was targeting with the steel and I am happy with the result. There is a tradeoff between hardness and corrosion resistance, explained in this article on Vanax. Steels like Vanax and LC200N have excellent corrosion resistance but are limited to about 60-61 Rc even with cryo treatments. This steel was targeted for a good combination of high hardness and corrosion resistance, though the corrosion resistance ended up better than expected as will be discussed further on. Hardness is pretty similar regardless of cold treatment up to about 2050°F, indicating retained austenite is not excessive up to that temperature. So 2050°F would be a good general austenitizing temperature from that standpoint.
Shawn Houston heat treated one of his MagnaCut knives to 65.5 Rc, confirming the potential hardness of the steel. Reported hardness from knifemakers using the steel has been relatively similar, though occasionally up to 1 Rc lower than the values I obtained. Large knives quench more slowly with a plate quench than small coupons. So hardness results may be somewhat lower than shown in the table depending on the size of the knife and the quenching speed. A gas quench also leads to lower hardness. This is of course normal with any knife steel.
Brad at Peters' Heat Treating tested a series of coupons using their vacuum furnaces. Larger heat treating operations used by knife companies and some knifemakers, generally use vacuum furnaces. And the heat treatment response is somewhat different than with plate quenching or oil quenching in a home shop. So these hardness values are important to heat treating companies. Peters' used a 2 bar gas quench with these coupons and performed heat treatments both with and without a cryo heat treatment. The hardness values are also about 0.5-1 Rc lower than the oil or plate quench coupons. One point lower in hardness vs rapidly quenched coupons is promising, demonstrating excellent "hardenability" so that properties are consistent across different heat treating methods, whether industrial vacuum furnaces or plate/oil quenching individual blanks.
Toughness
The main goal of this steel design was to have much greater toughness than previous powder metallurgy stainless steels. I also tested a range of heat treatment variables to narrow down the optimal toughness. Peak toughness was found with austenitizing temperatures of 2000-2050°F, though toughness was similar for the two while hardness was higher with 2050°F. Therefore, 2050°F had a superior toughness-hardness balance. So 2050°F is my general recommendation for heat treating in terms of optimal toughness.
The toughness for 350°F tempering was higher than 300°F, though at lower hardness, of course. Toughness at 400°F was very similar to 350°F, occasionally a bit higher but they were close enough that sometimes an individual result for 350°F could be higher here or there. The potential improvement in toughness by tempering higher than 350°F doesn't seem worth it for the drop in hardness that you get. So a 350°F temper is also my recommendation for best balance of properties.
Plotting out the best hardness-toughness combinations you get the following plot where you can pick your target hardness for strength and edge retention and select the best heat treatment to achieve it. However, using other combinations of austenitizing and tempering will not lead to much worse toughness for a given hardness.
In terms of comparisons with other steels, MagnaCut looks very similar to CPM-4V and Vanadis 4 Extra as was expected (labeled V4E with a tan line on the non-stainless chart). This is even better than non-stainless steels that are well regarded in terms of toughness such as CPM-M4 and A2. And the steel did significantly better than the common powder metallurgy stainless steels such as 20CV, M390, S30V, S35VN, CPM-154, S90V, etc. It is not as tough as a steel like AEB-L at 61 Rc because AEB-L has less carbide and therefore higher toughness and less wear resistance. However, somewhat surprisingly, MagnaCut matches the toughness of AEB-L at high hardness. At maximum hardness (~65 Rc), MagnaCut matches the toughness of the best PM stainless steels when they are at only 60-61 Rc, like S35VN and Vanax. And significantly better toughness than steels like M390 and S30V at their typical hardness levels. This means that intriguing combinations of strength/hardness and toughness are possible vs those stainless PM steels.
Knifemakers that have used MagnaCut have also reported excellent toughness thus far. Phil Wilson put the steel through his battery of cutting tests designed to put significant force on the edge, cutting through increasingly harder materials, and twisting out of the cuts. The knife made it through seasoned fir and deer antler, though it saw some mild chipping and rolling with bocote, a very hard wood. This behavior was also seen when he tested CPM 4V. You can see an example of the way he tests (with different knives) in the video below. He tests cutting a couple different woods at different points in the video, though the first test with bocote on a CPM-154 knife starts around 10:55.
Big Chris chopped through a 2×4 with a knife with "near chef knife" edge geometry, which was a very tough test when compared with heavier choppers. He chopped through four 2×4's without any loss of sharpness, as it was still cleanly slicing through newspaper afterward.
Shawn compared a knife head-to-head with an ESEE 6, a knife known for its excellent toughness, made in 1095 steel. In chopping and batoning of wood both knives performed well with no loss in sharpness. The big difference came in the nail chop test where the 1095 had significant deformation; a typical resharpening was unable to take the edge back. Significant edge repair is necessary. However, the MagnaCut knife had only minor edge damage and was back to shaving sharp quickly.
Edge Wear
I tested two knives in MagnaCut at two different hardness levels with my standard CATRA slicing edge retention test. I heat treated the knives and Shawn Houston ground the bevels and did the initial sharpening. I tested each knife 3 times. The steel matched the approximate edge retention of S35VN, CPM-4V, and CPM-CruWear as expected.
Edge retention from knifemakers has also been excellent. Phil Wilson did his standard test with 3/4″ manilla rope where he uses a consistent edge geometry to compare steels. A MagnaCut knife at 62.5 Rc made 45 cuts, which compares with 40 cuts for 61 Rc S30V and 60 cuts for S90V or S110V. You can see an example of Phil's rope cutting in the video I linked to in the toughness section. Shawn Houston reported in his rope cutting testing it slightly outperformed a Z-Wear (CPM-CruWear) knife at similar hardness and edge geometry, measuring better sharpness with the Edge on Up BESS test after cutting the same amount of rope. Big Chris did a cardboard cutting test comparison with CPM-3V and found that after cutting twice as much cardboard with the MagnaCut knife that it was still significantly sharper than the 3V comparison.
Corrosion Resistance
The biggest surprise in testing of MagnaCut was how good its corrosion resistance is. It was expected to have corrosion resistance in between S35VN and S45VN, "good" or even "great" but not spectacular. However, the corrosion resistance ended up being even better than 20CV and just under stellar steels like Vanax or LC200N. With my standard 1% saltwater test, there was no corrosion visible on the steel after 72 hours, while a couple small spots were visible on 20CV and significant rusting on everything else but Vanax. MagnaCut is listed as "new steel" in the image below.
The test above used a 2100°F heat treatment. To see how the steel compared to Vanax and to test the effect of heat treating I also did a range of coupons with austenitizing of 1950, 2000, 2050, and 2100°F. Lower austenitizing temperatures typically lead to slightly reduced corrosion resistance so I wanted to see if there was a big dropoff. In the retest I used 3.5% saltwater for 72 hours, which will rust just about anything outside of Vanax or LC200N. The 1950 and 2000°F samples showed no rust spots, while the 2050 and 2100°F had a couple very small rust spots. This is probably due to inconsistent finishing in the corners (notice the location of the rust spots), or perhaps some minor contamination of iron particles there. There is no reason for those samples to have lower corrosion resistance compared to the 1950 and 2000. So it seems the steel is on the border of being a "saltwater" steel but not quite there I think. It could be used in knives that see occasional saltwater exposure but is not really for diving knives. This is excellent corrosion resistance for general purpose knives.
The surprisingly excellent corrosion resistance of MagnaCut is due to the lack of chromium carbides when compared with other stainless steels. The chromium carbide leads to locally lean regions of chromium surrounding the carbides, as the carbides form by taking chromium out of the surrounding matrix. I first saw this in testing of 420 stainless, which did better than expected for corrosion resistance which is because of the lack of chromium carbides in that steel as well. In low carbon stainless steels they go to great lengths to eliminate chromium carbide to improve corrosion resistance. Typically this isn't something that stainless tool steel developers talk about because the chromium carbides are generally seen as unavoidable. Removing chromium carbides in MagnaCut led to an improvement in corrosion resistance that makes sense in retrospect but was a surprise when I first tested it.
Shawn Houston told me that MagnaCut had no rust issues when wet grinding, while ZDP-189 and AEB-L have rusted on him if not being very careful. Big Chris also reported in grinding a CPM-4V knife that it was rusting while MagnaCut wasn't, as expected based on 4V being non-stainless. If I receive any other reports of corrosion testing I will update this article to include them.
Recommended Heat Treatment
From the above experiments the "general recommendation" for heat treatment is 2050°F austenitize, plate/oil quench, and 2×2 hour 350°F temper. The hardness is somewhat higher if a cryo step is added after the quench. A home freezer can also be used for a small improvement in hardness, but only if the steel is placed directly into the freezer after quenching. Don't temper first. Don't measure the hardness before going into the freezer; you don't need to know what the hardness is before and after. The 2050-350 heat treatment results in around 61-62.5 Rc and offers balanced properties including good edge retention, toughness, and corrosion resistance. Higher hardness can be achieved with increased austenitizing temperature and/or decreased tempering temperature. Higher hardness can be used when maximum strength is desired for improved stability and edge retention in fine cutting knives. For example, many Japanese kitchen knives are in the range of 62-64 Rc and MagnaCut would be very well suited to that hardness range for those types of knives.
I also have a new video about the recommended heat treatment of MagnaCut and optimal hardness that answers questions I have gotten frequently:
Sharpening and Grinding
I don't have any standardized tests of grindability, finishability, or sharpenability so I am reliant on anecdotal experiences. A fine microstructure means improved grindability, but MagnaCut also has a significant amount of high hardness vanadium and niboium carbides so I didn't know where the grindability and finishability would end up. Initial reports from knifemakers are very positive, with Matt Gregory and Shawn Houston reporting that it finishes and grinds easier than S35VN or S45VN. Those steels have a relatively small amount of vanadium and niobium carbide so I assumed they would be easier to work with. The finer microstructure of MagnaCut apparently helps in that regard. Big Chris ground a CPM-4V knife side by side with a MagnaCut knife and reported that the MagnaCut was significantly easier to grind, even though the two knives were at the same hardness. Matt Gregory said, "This stuff grinds so easily with coarse belts that you think something is wrong with it." So the somewhat finer microstructure of MagnaCut has made an improvement in grinding. Finishing is not as easy as CPM-154 according to Matt Gregory and Darrin Thomas, which is to be expected probably since CPM-154 has no vanadium carbides. With polishing, the closer the abrasive size is to the carbide size the more apparent the harder carbides are. Matt says that grinding is easier than CPM-154 until about 240 grit where the vanadium carbides start to make the MagnaCut somewhat more difficult. Chad Nell said that grinding MagnaCut is similar to CPM-154 but is more difficult to finish. However Shawn reported that MagnaCut was easier to finish than Z-Wear at similar hardness which was surprising. Z-Wear has a similar amount of carbide but a good portion of it is the softer chromium carbide. Apparently the finer carbide size of MagnaCut makes the difference between the two.
Sharpening was also reported to be relatively easy by all of the knifemakers that commented on it to me. Devin Thomas reported that it sharpened well even with Shapton Glass stones, which have the standard aluminum oxide abrasive, as opposed to CBN or diamond which is harder than vanadium carbide. He found the Shapton stone to sharpen better than diamond plates on MagnaCut, perhaps due to the finer scratch pattern. Shawn Houston also said that putting on the initial bevel and burr removal was very easy to do. Some steels can have issues with "stubborn burrs" particularly with heat treatments that lead to excess retained austenite, but that does not seem to be an issue with normal heat treatments of MagnaCut. Shawn found steel removal easier with a 62 Rc knife while 65 Rc felt a bit more glassy, as expected by the higher hardness. However, he also said the higher hardness knife was easier to deburr. The steel is capable of very high sharpness, of course, as most knife steels are. Chad Nell liked how MagnaCut sharpens better than CPM-154 and thought the edge that it took was better. Big Chris said that MagnaCut "gets incredibly scary sharp; best part is it has great feedback on the stones and is very responsive to stropping (the burr is not difficult to remove)." He even said it is easier to sharpen than CPM-4V.
Balancing Properties
Two of the major balancing acts in stainless tool steel design are edge retention-toughness and hardness-corrosion resistance. Higher edge retention typically means reduced toughness and vice versa. The new design eliminating chromium carbides gives MagnaCut a much better edge retention-toughness balance than previous PM stainless steels, and gives performance similar to the best non-stainless PM steels.
The unexpectedly high corrosion resistance from the elimination of chromium carbide also means that an excellent combination of hardness and corrosion resistance was achieved. MagnaCut reaches hardness levels as high as most any stainless steel while being more corrosion resistant. Steels like Vanax or LC200N typically can only reach 60-61 Rc while this steel can reach 64+ Rc while being more corrosion resistant than even steels like 20CV and S45VN. On the other end of the spectrum is ZDP-189 which can reach 68+ Rc but is in fact not stainless. The only steel that has a similar hardness-corrosion resistance balance to MagnaCut is S110V though its hardness is higher in part from high carbide volume. MagnaCut does not have to be heat treated to 65 Rc, but has the potential for certain knives, and heat treating to hardness levels such as 62-64 Rc is relatively easy since the steel has some headroom. And even if the target is only 60-61 Rc it has excellent corrosion resistance to go with it.
In my book Knife Engineering when providing steel recommendations I suggested CPM S35VN as the best "balanced" stainless knife steel for a combination of edge retention and toughness. MagnaCut is better in most every category including toughness and corrosion resistance so it is now my recommendation for balanced stainless knife steel.
Edge Retention is More than Wear Resistance – It's Time for Thinner Edges
Steels can lose sharpness due to deformation (strength/hardness is needed), chipping (toughness), wear (wear resistance such as measured by CATRA or rope cutting), or corrosion (see this article on acidic fruit and sharpness loss). Therefore this steel has an excellent combination of properties to suppress dulling in a wide range of applications. For example, Phil Wilson tells me that corrosion resistance is very important to the edge retention of his fillet knives that are used around salt water, which makes him excited about MagnaCut in those applications.
Some have asked what toughness has to do with thin slicing knives like folders and kitchen knives. However, high toughness means that you can have thinner edges at more acute angles with less susceptibility to chipping which improves cutting ability and edge retention. Therefore, a combination of high toughness, hardness, and wear resistance can provide improved cutting performance if the edge is tuned correctly for the steel. This concept is sometimes called "edge stability." Of course for knives that see impacts such as chopping knives the toughness is well suited for those applications. So MagnaCut can be used in everything from thin slicers and kitchen knives to large chopping knives.
Availability
CPM MagnaCut is produced by Crucible and hot rolled and distributed by Niagara Specialty Metals. This is the same production and distribution path used by other CPM steels like S45VN, S30V, S35VN, 20CV, S90V, etc. So the steel will eventually have full availability through steel suppliers and to knife companies. For now there is limited stock available through Niagara Specialty Metals starting on April 1, 2021. No, this is not an April fools! A further 15,000 lbs are on order and will be ready to sell by mid-July. Niagara is ready to take orders but are requesting patience.
Summary and Conclusions
CPM MagnaCut is the result of my passion for knives and steel. I used a new approach to stainless tool steel design to eliminate chromium carbides from the microstructure. This led to a combination of properties which is better than previous stainless knife steels, and has similar toughness and edge retention to non-stainless steels like CPM-CruWear, CPM-4V, and Vanadis 4 Extra. The corrosion resistance was also excellent, even better than I was expecting, which means that the hardness-corrosion resistance balance of MagnaCut is very impressive, with achievable hardness being 64+ Rc and corrosion resistance being even better than steels like S110V, S45VN, and M390. The recommended heat treatment is 2050°F austenitize and 350°F temper, and a cold treatment after the quench means somewhat higher hardness. The steel has limited availability from Niagara Specialty Metals which will expand in the coming months.
Source: https://knifesteelnerds.com/2021/03/25/cpm-magnacut/
0 Response to "When Fasfa Says Try Again Later How Much Later"
Post a Comment