Mission knives

[Annie]

Is anyone using mission titanium knives?
They've got a fantastic reputation for being unbreakable within the dive community. Not that anyone would normally do anything so unthinkable to a knife but I've seen one thats been left standing in sea water for ages & not a mark on it.

 

[addyb]

I don't know a lot about titanium blades, but I have heard that they are generally very difficult to temper and usually end up on the low end of the Rockwell Hardness scale. (Not that that makes any difference in a dive knife)

Of course, I could be wrong.

Adam

 

[C_Claycomb]

Temper is not quite the right word. Temper is removing hardness, not adding it.

Titanium has advantages and disadvantages. For a dive knife the former, high strength, light weight and extreme corrosion resistance, outweigh the latter, mainly low hardness. The lower hadness means that they generally have thicker edge bevels and don't do well on push cutting, which is what wood carving is.

For bushcraft they don't really have a place. For survival knives they are only justified if you are in a situation where cutting ability can be sacrificed for corrosion resistance. For working around fresh water I would look at the H-1 and X15 steels (if I remember the names right ), they both get a bit harder and should cut better.

 

[Neiltoo]

Temper is not quite the right word. Temper is removing hardness, not adding it.

.

From wikipedia


"Tempering is a heat treatment technique for metals and alloys, most often the toughening of martensitic steel."

 

[C_Claycomb]

Neiltoo, um, thanks for the reference reitterating what I said.

Ok, so saying that tempering is softening is a bit of a simplification, but normally martensitic steel is both softened, and toughened, by tempering. Say for O-1, it starts after the quench at about 65Rc, tempering reduces the hardness to the well liked 57-59Rc region, which makes the steel less brittle/tougher.

The simplification is that some steels, notably the high speed steels, have a secondary hardening peak for tempering up around 540degC which can take them up to 65Rc, and titanium is not quench hardened and tempered in anything like the same way as steel. If I remember correctly it is age hardened, no tempering involved.

Looking at the Mission web site they actually have some pretty good info.
http://www.missionknives.com/articles/breakthrough.html see page 2 for info on hardness.
Being an engineer I like the idea of a titanium knife, and for what they are using it for it sounds a good thing, but I still don't think its a good choice for a general purpose knife, and cost aside, I reckon Talonite would make a better slicer.

 

[sargey]

in addition to chris' points above, one of the other issues driving the development of the titanium dive knife was the lack of magnetic properties, or it's magnetic "signature". this was significant for underwater special forces working around or near magnetically activated mines, or sneaking into enemy harbours...... obviously there's always marketing oppertunities with kit as used by special forces &c.

generally speaking titanium knives are not as good for general use as a steel knife. even stainless steel dive knives will rust horribly after exposure to sea water if they're not looked after, which effectively cancels out any edge retention advantage they may have had. so titanium knives are a great option for lazy divers near magnetic mines.

there is a school of thought that says that the edge on your knife is more likely to rust away than be worn away, so the marketing dept says that titanium knives are great for people who don't use their knives very often. some people would have us believe that Ti is the optimum choice for a neck knife too.

the other options for a rust free knife chris listed were those either in talonite, or H1. talonite doesn't rust because it's a non ferrous colbalt alloy. H1 doesn't rust because it has no carbon in it.

i haven't used talonite, but i can heartily recommend the spyderco knives in H1.

in the end, mission knives derived from a very specific application, as the knowledge on titanium alloys increases and how to best treat the material, i'm sure they'll close the gap.

cheers, and.

 

[TAHAWK]

What happened to the idea of putting very hard titanium oxide(?) coatings on steel knives to increase their resistance to wear? I always wondered if it made any sense when the cutting edge itself would be uncoated.

 

[C_Claycomb]

Titanium nitride on the edges of knives works okay for cheap kitchen cutlery. It is a boon for a company that wants to make its knives from soft, easy to work steel, and still have them capable of cutting something. It is possible to coat a knife with better steel, nothing comes to mind. Some knives have boron carbide and DLC coated blades for wear resistance (think folders around the pivot), lower friction and corrossion protection, but that is a different thing.

Back on the titanium nitride blades, only one side of the cutting edge bevel is left coated. The other side is ground back to bare metal. This leaves the last few thou of the cutting edge entirely made of the coating, which is very hard. Such knives can be sharpened, using diamond hones, by working the uncoated bevel, and contrary to popular belief/advertising, they do need sharpening every so often. Hard though it is, the coating does wear, more likely it takes micro-chips, and dulls that way.

 

[addyb]

Okay but theoretically lets imagine that you've got a blade that's hardened on the low end of the Rockwell scale, say a 55 or a 56. That's quite soft and while it'll be very easy to sharpen and it'll be very tough, the edge retention won't really be anything spectacular.

So to level out the low blade hardness, the knife manufacturer produces a blade with a thick spine and slightly obtuse geometry. Just as Chris said, that won't help push cutting. But isn't push cutting or wood carving a good field test of edge retention? Because if a knife won't push cut, other than slicing, what good is it as a blade if a person can only use it as a pry bar?

I know that stainless dive knives are a softer steel with much more chromium in them than a "general" blade to increase stain resistance and have very thick blades to compensate for that. But does it really compensate at all? Does a person with a soft blade really want to have to sharpen it every 10 minutes?

I'm curious!

Adam

 

[TAHAWK]

Okay but theoretically lets imagine that you've got a blade that's hardened on the low end of the Rockwell scale, say a 55 or a 56. That's quite soft and while it'll be very easy to sharpen and it'll be very tough, the edge retention won't really be anything spectacular.

So to level out the low blade hardness, the knife manufacturer produces a blade with a thick spine and slightly obtuse geometry.

A relatively soft blade made up in a relatively thin and acute edge describes the SAK. It cuts, to some extent, even when "dull" due to the geometry.

And I seem to recall that many steels are LESS tough below a certain hardness because they simply deform, rather than fracture, under given loads.

 

[addyb]

I never actually thought of that but it makes perfect sense; a SAK is still quite useful when it's dull because as you said Tahawk, the blade is very thin. I suppose that's one of the SAK's more redeeming qualities and why people keep coming back to use them year after year? Even if your SAK won't shave hairs off of your arm, you can still slice up feather sticks or cut that apple for your lunch.

Adam

 

[C_Claycomb]

The hardness of some alloys is not a good measure of their cutting ability. Alloys that add wear resistance, vanadium, tungsten, other carbides can be set within a softer alloy matrix. A hardness tester will easily dent the metal, pushing the carbides out of the way and only give a reading of the soft support matrix. Such a metal will make files skate, and drills scream, be a bear to sharpen and can slice through tough, fiberous material for an incredible length of time, but it won't push cut or shave well at all.

That does not mean it doesn't cut well. Just as a mirror polished edge that can push-cut really but slides off rope can't be said not to cut. Its just horses for courses. Dive knives, and skinning knives for that matter, tend to do more slicing than pushcutting, they have to cut fiberous material and live with corrosive environments. Just because those requirements aren't at the head of one person's priority list, does not mean that a knife made to meet them is a bad knife

Personally I think that pushcutting is a rather poor test of edge retention, any metal that is hard enough, and ground thin enough, will pushcut to some degree. I have had knives I have used for whittling, push cuts, surprise me when I find they won't slice cordage. I never noticed them getting dull as long as all I was doing was pushcutting. After sharpening they did whittle better, but the most obvious difference was in slicing ability.



I

 

[Brian]

The Mission knives multi purpose knife was tested for use by the US Navy SEALS and did quite well as I recall, not sure what the tests were though. They also tested the SOG Seal knife 2000 which I think was the one they chose.

Brian