Home Forums Gear Knives and Blades Cryo, Salt Bath Nitriding and other steel treatments

Relatively new to custom knives. User not a collector. I see that some bladesmiths will Cryo Treat their steel. I am familiar with the purported benefits in barrels. What would be the benefits in knives? Also, I haven't seen any mention of Salt Bath Nitriding, which in many applications provide wear resistance and other benefits. Is there no benefit in knives? Is the use of PVD (ie Black Ti) purely cosmetic in knives?

My apologies for the newbie questions.
Chris.

Cryo helps the final transformation of austenite to martensite which in turn improves toughness, normalizes and stress relieves the blade and also typically increases rockwell hardness slightly

Not totally necessary, but if you want stainless to reach
anywhere near it's potential, you need to cryo.
Some use dry ice/acetone, and that's not quite truly cryo.
But it is really cold.
Like freeze the "Witches tit solid as her brass bra" cold.
So I consider cryo. Almost.


Very limited knowledge here. So bear with me.

I had a suspicion about nitriding, Google fu confirmed.

Knife steel is hardened at 1400-1500F, plus.

Much of the tempering process is in the 300-450F range.

Salt Bath Nitriding is done around 1000F.

So, you couldn't use the process to harden, or temper.
Used after heat treat, it would probably anneal your steel,
making it very soft.

And doing it before heat treat would either cause it to be ruined
by the hardening temps, (2000F plus for stainless) or
it would make it too hard to do any finish work after heat treat.

Before is an interesting thought.
It might prevent decarb if it made it throufgh the quench.
If so, you might not need to do any finish grinding.

Thank you very much for the explanations. I'm leery of some of the benefits attributed to Cryo in rifle barrels because they just haven't borne out in the real world. In fact, 300 Below was one of the big purveyors in the early days, advertising in Precision Shooting etc. Many of Kathy Fisher's claims remain on the current 300 Below webpage. Has anyone quantified the benefits in knife steel?

Thank you for the explanation of SBN as well. I was happy to accept that and go on my merry way, then I ran across this video which left me with more questions than answers;
https://www.youtube.com/watch?v=n1RUX2vj-dY

Supposedly this guy is using table salt (NaCl or Sodium Chloride) in his home process and getting to 1600+! My understanding is that Meloniting or the MMI Trutec barrel process uses some sort of Cyanide bearing salts! Not something I'll ever be playing with (even without the risk of exploding molten salt). Is the benefits they're talking about for real?...this is youtube after all! (although I swapped my toilet tank recently guided by youtube). The comments below the video created even more questions in my mind.
Thank you again for sharing the knowledge!
Chris.

My apologies...I think I missed the distinction between "Salt Bath Nitriding" and "Salt Bath Heat Treatment". The videos appear to depict Salt Bath Heat Treatment. I found this video more helpful understanding the Heat Treat application;
https://www.youtube.com/watch?v=9uPzc31bTD0
No nitrogen...no nitro carburizing.

Dont know much about salt heat treat.
Other than,
It's very specialized. No shade tree stuff.
It should be very precise.
The heats should be dead nuts on. 10 minutes at 1600F should be exact.
It is oxygen free. (You knew that)
And it could be dangerous. (Knife making is about flame, hot steel, grinding... danger is what it's about)

Just...wow...

You have something to add,
Add it.

As an amateur bladesmith I read all the pertinent posts on here and do a fair bit of poking around on other more specific sites. Then either store it away in the memory banks for later or try it out myself. Is any of this first hand?

Nope.

I am more amateur than you.

Been researching the heck out of things, trying to learn
and determine a direction in pursuits.

Interested in trying some stainless, but the cryo seems to be
required for best performance, and possibly rust resistance.
AEBL will be the first tried, but not equipped to do that yet.

Stuck with carbon steel for now.

My determination on the effects of nitriding were simply
based on the temperatures involved, and the temps involved
for quenching and tempering. They clash.

Pluck it...”deleted”

Some barrel makers Cryo the blanks before drilling. It improves machining properties and uniformity. Not sure if any are still doing this. The effect on knives is noticeable especially with the lessor stainless steels.

Thank you for the response.
Can you expand on "noticeable"? Do you mean noticeable in the grinding and creating of the knife? ...or noticeable in the use of the knife (durability of the edge, ease of sharpening etc)?

Krieger would cryo his blanks before rifling. He said it allowed him to make a better product. I'm not sure if they've continued with that. Second cryo after the rifling process was available but it was on you. . The purported increased accurate life claims have pretty much been refuted (at least in 416R).