A Tale of 2 Nilakka's

[Mallus]

... I'd be interested if the the splashes of vanadium and niobium contribute compared to AEB-L analogues

AEB-L has < 5% chromium carbides. It would be curious how the steel would behave if it was rebalanced with a C/N split to allow a HRC of 67/68 HRC with < 5% niobium carbides and the same Cr% in solution. It would be much harder, with a higher wear resistance and the same corrosion resistance. The apex stability as well as the long term (low sharpness) edge retention on a slice would also be improved.

Would you have any examples of high hardness C/N stainless steel with Niobium already existing? Or would you just expect such to be possible to make, should somebody choose to do so? I tried to scare up a little literature but, alas, found my search prowess in the field of metallurgy nonexistent...

[Cliff Stamp]

Or would you just expect such to be possible to make, should somebody choose to do so?

There isn't a steel which has the properties/makeup I described that I am aware of, however there is nothing preventing it from bring made. The problem in most stainless steels is the C/Cr interaction. Carbon is what is used to increase hardness, and chromium to increase stain resistance, but they both react with each other to form chromium carbides which means they interfere with each other.

If you take AEB-L for example and increase the carbon content you won't end up with a steel which has the same micro-structure and stain resistance but with a higher working hardness. The higher carbon will cause the formation of a much higher volume of chromium carbides, a more coarse micro-structure and thus produce a significantly lower stain resistance. If you try to compensate for this by raising the chromium amount then the structure will become even more coarse and the carbide volume will raise again.

Nitrogen doesn't have this same kind of tie with chromium however and by using Carbon and Nitrogen to form martensite you could shift the hardness up without effecting the carbide balance. It is then just a matter of reducing the chromium amount to prevent primary carbide formation and increasing Niobium to form it. This can all be calculated through standard thermo chemistry.

The problem is though it is a pretty small market as you are talking about something that not only is developed for the cutlery market, it is a sub-set of that market that is looking to optimize cutting ability and high sharpness edge holding in stainless steel blades. However you are going to see an increase in use of nitrogen in stainless steels and Niobium because of the direct materials benefits and it is an active area of research this is already crossing over into the knife industry with steels like 14C28N, Nitrobe 77, etc. .

[Mallus]

Nitrogen doesn't have this same kind of tie with chromium however and by using Carbon and Nitrogen to form martensite you could shift the hardness up without effecting the carbide balance. It is then just a matter of reducing the chromium amount to prevent primary carbide formation and increasing Niobium to form it. This can all be calculated through standard thermo chemistry.

There are several nitrogen containing steels available with wide spectrum of C/N, but I do not recollect any being advertised for hardness beyond ~62 Rc. Mostly I wonder why 14C28N is not tweaked for higher hardness, were it easily doable. I understand it was meant for increased corrosion resistance over 13C26, but still, capability for higher hardness wouldn't hurt. Is it an inherent limit of the ingot process? Vanax 75 has over 4% of N, but it's made with PM process. On the other hand, it has also lots of Vanadium so the structure is different, even if they advertised ( http://www.uddeholm.com/files/HPS_Steel_for_knives.pdf" target="_blank ) that the vanadium nitrides should be rather small at <1 micron. Maybe the nitrides are small, but won't they still aggregate to form effectively much larger clusters?

What would you estimate to be needed for higher hardness, composition wise, compared to the current offerings?

It would be nice to have some kind of thermodynamic software installed to one's computer to try and cook new über-ultimate blade steels. :) Thermo-Calc seems to be available for short term test drive, I may give it a go one day, when I have less junk on my plate waiting to be dealt with.

[farnorthdan]

Really starting to love the Nilakka, after having it for about a week now I'm really impressed with the fit and finish on this one, its just so smooth, the more I flip it and handle it the smoother it gets, the blade literally falls/glides home when released and the detent is perfect. Oddly enough I like the boxy feel of the construction in hand. I also like the blade shape and grind, this is just such a unique design, I'm really glad I picked this one up. The Taichung plant really has their act together and are producing some of the finest Spydies I've seen.

[MacLaren]

Really starting to love the Nilakka, after having it for about a week now I'm really impressed with the fit and finish on this one, its just so smooth, the more I flip it and handle it the smoother it gets, the blade literally falls/glides home when released and the detent is perfect. Oddly enough I like the boxy feel of the construction in hand. I also like the blade shape and grind, this is just such a unique design, I'm really glad I picked this one up. The Taichung plant really has their act together and are producing some of the finest Spydies I've seen.

Roger that :)

[Cliff Stamp]

Is it an inherent limit of the ingot process?

1095 is an ingot steel, working hardness, after tempering of 67 HRC is possible with the most basic of hardening equipment.

The hardness of a steel (ignoring nitrogen) is dependent on :

-the carbon % in the martensite
-the % of non-martensite phases
-the carbide volume fraction

Ideally you want the minimum about of carbon to achieve maximum hardness (~0.6%) because as more is added it will effect the Ms and Mf points and cause more plate martensite to form (brittle) and raise retained austenite and it also has side effects such as dissolving heavy amounts of primary carbide (reduces wear resistance) which often comes back out in the quench producing embrittlement. Nitrogen will also form martensite hence you can get steels such as Nitrobe 77 which can be 60+ HRC with very little carbon, 0.1 %.

Why don't they make something like 14C28N but have it able to achieve higher hardness levels? Well ask this question - why are so many steels ran far softer than the maximum hardness levels? Why doesn't Maxamet at 71+ HRC obliterate 10V as a knife steel which is commonly ran as low as 60/62 HRC? There are already piles of high hardness steels even designed for knives (the cold work tungsten grades) and some which are stainless even like ZDP-189 / Cowry X (~70 HRC). Why doesn't everyone use ZDP-189 at 70 HRC?

I think there are some interesting questions here, for example Rockstead uses ZDP-189 at a very high hardness, ~67 HRC. There are a lot of reports of praise, few complaints. Is this due to the price/aesthetics causes a lack of serious use, or do the blades really perform? If it is the latter is it due to the grind or the finish or simply how they are hardened. If standard Spyderco in ZDP-189 was ground/finished like a Rockstead would it act the same? How much of a difference does the hardness make?

Some actual numbers showing the effect of hardness on edge retention (slicing hemp) :



Is there a significant difference from 58 to 66 HRC? Yes. If I was using one for that kind of cutting which one would I pick - the harder one. But to see that difference and make that nice/neat trend line too *many* trials to average out the large random smears and a lot of work to ensure they would not be subjected to bias. If you don't do those things it is likely the performance will simply oscillate. Once you start to look at general cutting things get even more complicated.

As a really basic point, yesterday a friend asked for a loan of a knife to cut some cardboard. I gave him a Lum in VG-10 which was ground optomized (6.5 dps edge, 15 dps micro-bevel, x-coarse DMT) for exactly that kind of work. However when he started cutting the blade would hangup and he would power through the cutting. When I got it back as I suspected there were visible pieces taken out of the edge (1/2" mm deep at worst). I checked through the cardboard and it had extremely thick runs of epoxy which the blade was catching in and then being subject to pretty extreme lateral loads to force it through. In retrospect, the 12C27 blade I had on me, which would have far less edge retention (about half) in clean/pure cardboard, would have done the same work with no visible damage as it would not have fractured. Thus even asking what appears to be a very simple question "Which blade has better edge retention for cutting cardboard?" should have a very strong answer of "It depends." .

In short, I would love to see a steel as I described, however I can understand how a maker/manufacturer might look at it and not jump on it and even if it was used drop the hardness ~10 HRC points to enhance durability and at that point what did you get for all of that work? Note when Kershaw came out with AEB-L a lot of people were excited and then when they started using it at 55 HRC everyone started saying "What, this is what Roman Landes is always talking about?" Well no, that isn't, that is a gummy mess. But there is a difference between writing on a piece of paper what you have to do to get optimal cutting performance and what you can do on the factory floor and what you are willing to risk in factory returns.

This is one of the real benefits to custom knives because custom knifemakers will risk anything if you ask them politely. I get custom knives made all the time with experimental grinds, steels, heat treatments, etc. . I had this blade made with an experimental hardening (which went wrong in the doing of it, severe warpage) and the edge set at 0.015" thick :



But its my knife, if it exploded then so what. I explode knives all the time anyway.

[Mallus]

Is it an inherent limit of the ingot process?

1095 is an ingot steel, working hardness, after tempering of 67 HRC is possible with the most basic of hardening equipment.

The hardness of a steel (ignoring nitrogen) is dependent on :

-the carbon % in the martensite
-the % of non-martensite phases
-the carbide volume fraction


Is there a significant difference from 58 to 66 HRC? Yes. If I was using one for that kind of cutting which one would I pick - the harder one. But to see that difference and make that nice/neat trend line too *many* trials to average out the large random smears and a lot of work to ensure they would not be subjected to bias.

Thanks for the clarifications! What I meant with my question regarding the ingot process, was not whether it allows high hardness, but (sufficiently) high nitrogen to be infused to the steel; hence the comparison to Vanax 75 (a particle process steel).

I see the points with regard to maximizing hardness; its not always what the manufacturer wants to do and may not be immediately obvious to the ELU w/o a lot of experimenting.

[MacLaren]

Nice vid. That was cool.

[Cliff Stamp]

What I meant with my question regarding the ingot process, was not whether it allows high hardness, but (sufficiently) high nitrogen to be infused to the steel; hence the comparison to Vanax 75 (a particle process steel).

I don't believe that would be the limitation as much as trying to find the balance of properties. For some information on Vanax vs Elmax vs O1 in regards to use in corrosive environments :

"Effects of tempering on corrosion properties of high nitrogen alloyed tooling steels in pyrolysis oil - Ashkan Reza Gholi"

-www.diva-portal.org/smash/get/diva2:441 ... TEXT01.pdf

There is a lot of information there, the critical part being how the processing is critical and that by choosing a tempering temperating alone incorrectly you could make a stainless high nitrogen steel have similar corrosion resistance to O1.

This paper also discusses the many reasons why nitrogen is beneficial and how niobium can be an improvement over vanadium for both enhancing wear and corrosion resistance.

[Cliff Stamp]

To anyone with a newer Nilakka - how thick is the secondary edge bevel?