Sharpening Nitrided Metals

[RichColvin]

Nitride treatment of steel has been around for 100+ years, and is often used for gun barrels.  There are great articles about it at these links: 

• https://www.asminternational.org/documents/10192/1849770/06950G_Chapter_1.pdf
• https://www.paulo.com/nitriding-steel-growing-popularity/

The picture above shows how the nitride treatment moves slightly into the base metal.  The Compound Zone has full treatment, and the Diffusion Zone shows how that is getting less and less so.  If I understand this correctly, the outer edge (the Compound Zone) gets treated to become quite hard, but that hardness only goes 0.002" or so into the metal.  Thusly, the underlying metal is softer, making it less brittle.  So, it seems much like the bonded metal process used by craftsmen to make Japanese chisels.

It is emerging onto the wood turning community, and has peaked my interest.  Robust recently introduced a line of turning tools they call "Turner's Edge" (http://www.turnrobust.com/product/turners-edge/ ), and these tools are nitrided M2 HSS.  Robust claims that their treatment hardens the edge to a 75+ Rockwell hardness.

So, what intrigues me from a sharpening standpoint is this question :  should nitrided metal be treated as if it were a Japanese chisel? 

I'd like to hear others' opinions.

Kind regards,
Rich

[Twisted Trees]

As it is bonded say to a bowl gouge, the bevel itself has no coating after the coating is ground through so the only piece of interest is the top coating which will form the cutting edge this as you say is a very thin layer and will probably sharpen very well on a standard wheel. The advantage comes in longevity of the edge created due to the coat being the actual cutting edge. (though as in other thread in wood turning the longevity of a woodturners edge is never long, miles of shavings can be cut in minuets of time) 

I don't have any nitride but do have some titanium coated spindle gouges, and anecdotal evidence is that I get about 50% longer on an edge than I do with HSS, they sharpen just fine on a standard wheel.

[Jan]

Rich, I am impressed to read about 75+ Rockwell C hardness. It is something hardly imaginable for me.

Jan

[Twisted Trees]

Rich, I am impressed to read about 75+ Rockwell C hardness. It is something hardly imaginable for me.


Jan

I don't use the honing wheel to grind my flutes, I just touch them enough to tidy up any burr I may have created.

[Jan]

Twisted Trees, I have deleted the end of my previous post because I have realised, that the abrasive grains of the Tormek honing compound are not hard enough to cut 75+ HRC material.

Jan

[Twisted Trees]

Jan, also deleted it from my quote of your post :-) It may be an issue for some using diamond paste, though as I said it's a light touch needed on the flute so even then it shouldn't be an issue.

[RichColvin]

These tools may well necessitate diamond wheels.

[Jan]

Twisted Trees, yes, the diamond paste should work for the nitrided steel zone also. In high concentration and with large grains (15 to 30 microns) the diamond paste is very aggressive and can potentially grind off the whole nitrided zone.

Rich, when you have a diamond wheel you can simply grind everything. Silicon carbides wheel cuts up to hardness of some 67 HRC.

Jan