# How to sharpen Titanium knives?



## Ruso (Jul 14, 2015)

My Dad has scuba knife made of titanium and he asked me if can sharpen it along with his kitchen knife. Since I am not sure about this material, can I use same water stones? Should I get some specific stones or just give to the the scuba shop? Any input welcome.


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## aboynamedsuita (Jul 14, 2015)

No experience with titanium knives, but I have a titanium Victorinox Dive Master 500 and after 7+ years it gotten some minor scratches on the clasp from everyday things, so presumably it isn't excessively harder than other materials. I know the finish was said to sandblasted so there is something out there that can abrade it. Do you know if it's all titanium or else PVD coated?


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## EdipisReks (Jul 14, 2015)

You can probably sharpen it with normal stones. It's likely not going to be very hard compared to good steel knives.


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## Ruso (Jul 14, 2015)

I will give it a try on the usual stones, see how it goes. It says 100% titanium, but who really knows :-/


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## Keith Sinclair (Jul 15, 2015)

Ruso let us know how it sharpens up


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## Adrian (Jul 15, 2015)

Titanium is quite soft. It will sharpen fine on a wet stone, but take it easy as you will remove material quite fast. Some people say that titanium can clog up the stone surface a bit.


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## Mangelwurzel (Jul 15, 2015)

According to the Mohs scale, Titanium is 3-4 times harder than steel (see https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness).

You might be ok on normal whetsones but it will just take a lot longer. Alternatively, Jon's new diamond stones might be a good bet...


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## WingKKF (Jul 15, 2015)

I think the mohs scale is used for minerals, not the refined forms of the metal as used in knives which is much softer. The titanium mentioned in the mohs scale is probably in the form of rutile or ilmenite, the ores. Titanium alloys can't be heat treated to the hardness of what is possible with steel. They can only go up to about mid 40s on the rockwell scale. This is probably why we don't have more titanium kitchen knives.


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## Pensacola Tiger (Jul 15, 2015)

Try it with your lower grit waterstones, but you may have to use a diamond plate if the stones load too much. Go slowly and don't use too much pressure.


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## Ruso (Jul 16, 2015)

Thanks guys.
I followed the advice and used very low pressure. Knife was dull dull, did not cut the paper at all.
Started on Shapton 320, raised the burr in no time. Had to spend some more time on the tip.
Followed by Chosera 800, few passes to flip the burr couple times.
Finished on King 1200, thought that muddier stone might help with burr abrasion. Removing the burr was somewhat tricky. 

I did not feel that stones were loading, seemed to be pretty normal. 
In conclusion, nothing special, hard burr removal time.


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## Culverin (Jul 19, 2015)

WingKKF said:


> Titanium alloys can't be heat treated to the hardness of what is possible with steel. They can only go up to about mid 40s on the rockwell scale. This is probably why we don't have more titanium kitchen knives.



Is this an innate material property?
Or something mankind has yet to devote time to discovering the process?


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## spoiledbroth (Jul 19, 2015)

didn't mac make a titanium knife? /offtopic


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## panda (Jul 19, 2015)

http://www.amazon.com/dp/B0038EG39C/?tag=skimlinks_replacement-20 what does titanium bonded mean?


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## WingKKF (Jul 19, 2015)

Culverin said:


> Is this an innate material property?
> Or something mankind has yet to devote time to discovering the process?



I'm pretty sure material engineers have tried and are still trying stuff with titanium. Whether or not the process exists to make titanium alloys as hard as steel can get without being really brittle, that's the million dollar question for which I have no answers to. 

Marketing loves to use titanium in naming their products as it is sexy. I'm guessing here "titanium bonded, 3 times harder than steel" is a thin coating of titanium nitride or equivalent somewhere for surface wear resistance, cosmetics and bragging rights. I'm sure someone could contact the manufacturer and ask them what titanium bonded means exactly. They might even tell the truth.


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## EdipisReks (Jul 19, 2015)

Mangelwurzel said:


> According to the Mohs scale, Titanium is 3-4 times harder than steel (see https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness).
> 
> You might be ok on normal whetsones but it will just take a lot longer. Alternatively, Jon's new diamond stones might be a good bet...



As was stated, that is a mineral scale, not really a refined metals scale. It's also very imprecise. If you really want to use it, check the hardness difference between hardened steel and titanium on this chart. The Mohs scale is more or less logarithmic. A 10 is much harder than a 9. In this case, the generic "hardened steel" is given a Moh's hardness of of 7.5-8, which is much harder than the generic score of 6 for titanium.


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## ThEoRy (Jul 19, 2015)

**** mohs.


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## Culverin (Jul 20, 2015)

There are more things that make a material suitable for a blade.

- *Shearing*
- *Ductility *= stress under tension (slinky)
- *Malleability *= stress under compression (truck suspension vs play doh)


Hardness is 1 thing. Concrete is hard.
But it's crap for tensile strength.


Unless I'm mistaken, too little of any of those 3, and a material would be prone to chip.
Isn't that why tungsten is often used in kitchen knives and tooling steels?


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## aboynamedsuita (Jul 20, 2015)

Culverin said:


> Concrete is hard.
> But it's crap for tensile strength.



Very true, it is does well in compression. A composite of concrete with steel reinforcement (or as emerging research is showing FRC) strategically placed can achieve an acceptable balance.

I don't have the background in blade-smithing, but it follows that there are parallels with the proportions of Fe, C Cr, W, etc.


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## rick alen (Jul 21, 2015)

Culverin, using titanium as an alloying agent is something else altogether. Titanium based alloys, rather than titanium alloyed steels, can be stronger than the strongest steels, and 3/5 the weight. But the modulus of titanium is as low as aluminum, ie, less resistance to bending, and here you get an idea why it does not perform well in knives.

Titanium coating puts a very thin layer of titanium nitride or carbide on the surface of steel, or titanium. This stuff is very hard, close to diamond, but of course can wear very fast at the edge, especially where there is brunelling, ie, shock stress damage. Nice for asthetics though, it's a bright gold color but you can make it black also, and maybe some shades in between.

Titanium nitriding, gas or ion driven (ion being much superior), is a diffusion process that actually converts the surface of ferrous alloys to titanium iron nitride, and to a depth of up to .030"/.75mm. Hardness up to rc70. relatively tuff also. You can even nitide a sharpened knife without dulling the edge. It also removes surface imperfections. It is of little value to do this with a titanium knife though, because with titanium you can only get about .0001" penetration.

There process works wonders for saw blades, so much so that makers will not use it because it makes there blades last 3-10X longer, and that seriously impacts replacement sales.

Saw blades have a rather obtuse angle of course, and I really don't know what sort of edge stability the stuff has, but if any of you knife makers want to try this there was a shop in MA called Nitron that specialized in small batches, the original owners would be about 80 now, but the place might still be around.


Rick


Rick


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## rick alen (Jul 21, 2015)

Excuse me but I got a little mixed up there. The latter process is simply ion/gas nitriding, which converts steel surfaces to iron nitride, and Titanium surfaces to titanium nitride, and some other hard substances depending on how you mix the chamber gas.

In addition an alloy called nitralloy is used where optimum surface condition is the primary consideration, and most knives would fall into this category. And of course where blade thickness was less than .06" you could get full penetration and conversion of that steel to all iron nitride.


Rick


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## rick alen (Jul 21, 2015)

oops ingnore last post.


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## rick alen (Aug 3, 2015)

You don't have to ignore it, it's just that I thought I was answering a question that actually didn't exist, please don't ask me to explain how that happened.


Rick


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## merge03 (Aug 3, 2015)

Various alloys of Ti have properties in a wide mechanical range. Some are so hard as to be unmachinable by conventional methods. Others are so soft. Purity and contamination also play roles. The softer alloys are very susceptible to gaulling.


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## rick alen (Aug 4, 2015)

merge03 said:


> Various alloys of Ti have properties in a wide mechanical range. Some are so hard as to be unmachinable by conventional methods. Others are so soft. Purity and contamination also play roles. The softer alloys are very susceptible to gaulling.



Doing a search the highest figure I can find for Ti alloys is RC55, not exactly super hard stuff. Ti alloys in the upper range of tensile strength do have and edge on chrome moly steels, being about 60% the weight and about 85% the strength. They however do have a much lower modulus which affects their stiffness. They are tougher to machine for, what I think, is their tenacious molecular bond. But don't quote me their, my googling time for this evening is all used up.


Rick


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