[JohnKSa]

I was poking around doing some odd reading today and happened upon the factoid that iron is not particularly impressive in terms of hardness as metals go.

I know that there are a few non-steel knives. I have absolutely zero interest in those specifically oriented toward defeating metal detectors, nor am I interested in ceramics due to the fragility. On the other hand, I would like to know more about those that use another material because it is superior to typical steel alloys.

It looks to me like a Cobalt would be a good starting point--just looking at its properties/place on the Periodic Table. I can find some references to Cobalt based knives, but they seem to be mostly oriented toward extreme corrosion resistance rather than improved toughness/hardness/edgeholding/etc.

So what's the deal with non-steel?

Is cost the main thing that's keeping it from becoming mainstream or is the performance lacking as well?

[hso]

Cost is the deciding factor along with properties like brittleness, lateral strength, shock resistance and toughness.

There are cobalt alloy knives out there (stellite, talonite (http://www.simonichknives.com/gallery.htm), Boye Dendritic (http://www.francineetchings.com/catalog/index.php?cPath=22_34&osCsid=9a2e519341bb17f81b8403581365a3a9)) that are readily available. There are also beta Ti knives available. Liquid Metal has been used for knives. The cobalt alloy and Liquid Metal knives all have superior knife properties, but they all have very very high prices.

http://www.geocities.com/mdpoff/talonite.html

[daniel (australia)]

Those cobalt and titanium alloys may have superior corrosion properties but don't seem to match good steels in other properties important in a knife, like edge retention. Useful for dive knives, yachtsmen's knives and so forth perhaps, but not otherwise IMHO. There was some useful and interesting information here (http://www.cutleryscience.com/reviews/blade_materials.html)

Thinking out loud for a momemt though, I wonder if you could form an edge from some harder material in the softer but tough and corrosion resistant beta Ti? A laminated structure or a composite involving hard crystals (or glass?) in a beta Ti matrix perhaps?

[redneck]

Its just as these guys said, cost is a big deciding factor. It also comes down to compromises. Other materials may offer higher hardness, but lack in other important areas.

Carbide has a much higher hardness and wear resistance than steel but it is fragile as glass. Drop a carbide router bit onto concrete and watch it snap.

Liquid metal is a neat material with a lot of neat properties but it lacks the overal strength to be good for most knives. It can be bent 180 degrees and springs back to shape but is not suitable for chopping. The edge will dent or roll easily. Knifemakers I talked to who worked with it said it was difficult to grind because you could "push it around" too much.

Cobalt alloys have great corrosion resistance, and other good properties but they don't hold a fine shaving edge very well. They tend to have a toothy edge that cuts agressively, but isn't suited to all types of cutting.

There have been attempts at Beta ti, and composite materials. I know Mission Knives made some titanium blades with carbide embedded in the edge somehow. They were popular with the EOD and metal detector crowds but still not really that good for a general use knife.
I'll have to look around a little bit but I know that there was one custom maker who actually was machining stuff to have a puzzle peice fit between two materials. He had blades made with carbon fiber and titanium, and other materials that were held together mechanically. Cool effect, but I don't know how well they worked in the long run, and once again very expensive.

[hso]

Daniel,

The Talonite and Stelite and Dendritic Cobalt blades are very good at edge retention. I've handled several and watched the cutting tests with them. Impressive. They are better at toothy instead of razor edges, but then so are some steels with some bevels.

Another problem with Liquid Metal is that it is a Be alloy. Chronic exposure to Be and Be alloys can result in berylliosis in those susceptible to it.

[daniel (australia)]

hso

I suppose when you think about it the dendritic cobalt and similar materials at least does have the right microstructure - hard carbide in a softer tougher matrix - for a "toothy" sort of edge, but at the expense of some toughness. From what I've read though the edge retention of these alloys depends quite heavily on how they are prepared and what is being cut: they don't stand up well to being reduced too fine and don't stand up well to cutting tougher stuff, as the edge breaks down or deforms as a result of the comparative softness and lack of toughness of the matrix.

I'll admit though that my direct experience of working with these classes of alloy is confined to applications for the chemical industry and the like, and even that a good while ago, so I rely on what I've read about their performance as knife blades.

[JohnKSa]

The Talonite and Stelite and Dendritic Cobalt blades are very good at edge retention.The hardness figures I see for the cobalt alloys don't seem to be all that impressive. Are you saying that they hold a good edge or that they hold an edge better than the best steel-based knives?

[hso]

Hardness is not a direct indicator of edge retention or cutting ability, especially in non-iron alloys. Resistance to abrasion, bevel, edge sharpening all are better indicators.

The ability to cut and keep cutting is dependent upon more than hardness.

[daniel (australia)]

While hardness may not be the be-all and end-all it must play a role. After all hardness is more or less the measure of resistance to deformation, and if your edge is lacking in resistance to deformation it will tend to, well, deform, ie dent, fold, curl or otherwise run from its responsibilities when faced with a cutting task - particularly if the workpiece resists the cutting.

Now of course you might ameliorate this with some smart thinking, perhaps by arranging the microstructure in such a way that the soft matrix runs away only to expose hard and perhaps angular secondary phases or inclusions, which seems to be the mechanism relied upon in the dendritic cobalt alloys, and perhaps also by tweaking the grind and bevel to give the edge more "meat" but this lack of hardness does seem to still be something of a bugbear from the tests I've read of these blades, especially on tougher tasks.

They do however certainly have some interesting properties and redeeming features - not least the corrosion resistance. I can see the value for dive knives and yachties knives for example, but I am less than persuaded for general hunting and EDC type applications.

[Corndogg]

Cold Steel "Nightshade" series
http://www.coldsteel.com/nise.html
:D

[auschip]

Cold Steel "Nightshade" series
http://www.coldsteel.com/nise.html


Something tells me these won't hold an edge very well.

[Corndogg]

nope, not at all. pretty much just a solid point for stabbing, so best to get the push knives or a solid stabbing only style... the skean dhu is really flat and low profile, and its light enough to tape to your leg. other than being able to take em on a plane, really no reason to get one of these.

[coelacanth]

and I can vouch for their aggressive cutting power. The combination of edge geometry and hardness makes them hard to beat as slicers and cutters but I would avoid chopping or prying with them as they are a bit brittle for such treatment. I've often wondered if anyone has tried making an edge of beryllium copper to see how it would perform. There was a company that produced .45 automatics using that alloy back in the 1980's but I don't know if the metal is suitable for an edged tool/weapon.

[Jack A. Sol]

there are soem titanium knoves out there made ofr EOD type work. I want to say that Mission knives made them. Brigade QM might still sell them