I just bought my first bar of 440V to use on folder blades.

To what degree do I need to finish the blade before heat treat?

What should I know about heat treating the steel? What is the optimal Rc? Does it require cryo?

What is the best finish for the blade? I typically satin finish to 400 or 600, is that still OK?

Do I need to sharpen it in any special way to take advantage of its properties?

I've made several folders with 440V and absolutely love it. I've done everything from a fairly rough 220 grit before heat treat up to a 1200 grit (essentially finished). I send out for heat treat (Texas Knifemaker's Supply) and have them cryo-quench. I'm not sure how hard they take it, but they claim to try for 58 to 59, and this seems reasonable (they do Rockwell test, but curiously don't include the report). It grinds pretty easy after heat treat, and can still be worked with stones or silicon carbide paper - just don't expect paper to last very long - but it isn't too difficult to finish or even shape the hardened blade. It's tough on belts even annealed - ceramic works best, but I also like 3M Micron belts on it. Use carbide to drills if at all possible - it will chew up HSS drills quickly even annealed, but carbide will still work even after hardening (I drill for the detent after hardening to get a crisp sharp detent).

Finishing is a little trickier, although a 400 - 600 grit satin seems pretty easy to obtain. I try for a finer finish (1500 grit) as I want a blade that's as stain / rust resistant as possible (I have LOT'S of pitted ATS-34 knives - my skin must be like acid) and 440V seems just about perfect in this regard. 440V does have a graininess when finished, so a real mirror polish might not work too well, but it's real consistent (at least on the blades from the bar I have) and not objectionable.

I sharpen with diamond stones, and finish with an arkansas or ceramic - nothing special. I've sharpened to either 25 or 30 degree angles, and either seems to work well. It takes an edge that's scary-sharp - can't comment on how long it will hold it because I have yet to have to resharpen one and the knives still shave - this is better than ATS-34, 154CM, or anything else I've encountered.

Good question... :)

I did a couple blades in 440V a long time ago. These were heavy hunters and not likely a good test of the steel's performance. Lately I've been hearing that 440V (aka S60V) is a bit brittle. I'm usually a little skeptical when I hear that, especially of a stainless alloy, because these steels tend to be very picky in their heat treating needs. A very rapid quench is needed to keep the Chromium Carbides under control (meaning small), and hence keep the steel from being brittle. Getting a rapid quench is VERY difficult using tool wrap and air cooling. The Crucible Steel book recommends a salt quench or interrupted oil quench, to get the temp down to about 1000F VERY quickly.

It's my guess that the main reason Crucible had for introducing CPM-420V (aka S90V) with 9% Vanadium instead of the 5.5% in 440V was so the increased Vanadium would take up the excess Carbon that would otherwise bind to the Chromium and create that quenching/brittleness problem.

Tempering at 300-500F is recommended to achieve Rc56-58 if air quenched. Oil or salt quenching achieves a little more hardness, a couple points.

Cryo-quenching should be done between the first and second temper.

Just for your reference, impact toughness when 440V is properly tempered is only about 60% that of 440C so this is not a sword steel by any means.

As for your other questions, I can only go by my experience with 3V. I usually finish to a quick 400 grit (meaning some scratches are still there) before tempering. I finish my blades to a worn 600 grit belt (after having started back at 220 grit after tempering) then brush with 400 grit Matchless Greaseless Compound (Koval) on a loose buff at 1800RPM, with the buff running the length of the blade. This erases the last few light scratches and leaves a finish that is a little finer than 600 grit hand sanding.

That's all I know, and then some...

Good luck with it.

Seems like 440V would be a prime candidate for heat treating in high temp salt pots. That way it would not require the foil wrap and you could take it directly from the high temp pot to the quench with very little time for the metal to cool off any prior to quench.
Comments?
Mike

I think any kind of atmospheric control, being it an argon flushed oven or a salt pot makes a whole lot of sense. The bigger issue I think is getting the quench going and the temp down to 1000F or below as quickly as possible. The problem is also a little aggrevated with CPM's because they usually benefit from hardening at 2050F, which stresses anything short of commercial level HT systems.

The same arguments, BTW, can be applied to 154CM, ATS-34, 440C, or any other stainless.

That's why I decided to go with salt pot for my heat treating. I am building a vertical forge with a forced air burner. The 316 stainless salt pots will be placed in the top of the forge supported by stainless brackets and a stainless plate covering the top of the forge which is vented at the back.
I may be wrong because I don't have much forge experience, but I believe it won't be much problem to attain 2000+ temps with the set up. I am building a control system to maintain the heat at a programmed temp. I have a pyrometer that will read temps up to 2500 F so we'll see when I get it finished.
Mike

Mike, you might want to communicate with Don Fogg about salt pots and forge design. He has lots of experience with both, but not with high alloy steels maybe. Here's his website:

www.dfoggknives.com (http://www.dfoggknives.com)

What size pots are you thinking of?

Don's site is where I got most of my ideas. I already have the pots made, they are 3 inches in diameter and around 18 inches deep. I went with 316 stainless pipe and plate because it is very corrosion resistant and should last a long time. I plan to use the high temp salts in one for heat treating and the low temp salts in the other for tempering. I have been told, you very seldom get any blade warpage when using the salt pots. We'll see.
Mike