a few 3v questions

crimsonfalcon07

crimsonfalcon07

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Dec 27, 2010
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I have a design drawn up for a short sword in CPM 3V, and would like to request some advice on hardness and grind strategies. Assume an 18" blade... what hardness is best for 3V? Still around 57-59? Or is it better to go higher or lower for a blade that long?

Second, I have taken to doing minimal grinding prior to HT to avoid warping. Is that unadviseable for 3V for any reason?

Anything else I should know?

Hoping for Mr Terrio to chime in. Thanks in advance!
 
Uh-oh, I've been paged. This feels like getting called to the principal's office :eek:

There's a lot going on with a blade that large, but I feel confident addressing the basics. First of all, I have yet to make a blade longer than 12" out of anything, so take all this with a grain of salt. Secondly, who's doing the HT? 3V requires pro-level attention.

crimsonfalcon07 said:
Assume an 18" blade... what hardness is best for 3V?
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By all accounts, 3V's best-balanced toughness is highest right at 58Rc. It still has very good edge-retention. (see the mechanical properties/impact toughness chart in the datasheet) If you really need it to be tougher than that, you probably need an S-series steel.

crimsonfalcon07 said:
Second, I have taken to doing minimal grinding prior to HT to avoid warping. Is that unadviseable for 3V for any reason?
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Yeah, it's going to take a while. Hardened 3V is pretty wear-resistant. Grinding it hard can certainly be done... but it's not going to be done by me... definitely not on an 18" blade. If you have a really odd shape with lots of stress risers or something, consult an HT pro. But except for really thin stuff (.050" paring/boning blades) I grind 'em right down to finished dimensions pre-HT.

crimsonfalcon07 said:
Anything else I should know?
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The finish you have on the blade pre-HT is pretty much what you're stuck with, unless you have a heckuva lot of time on your hands to sand and polish it. If you want a belt-finish or you're going to bead-blast it or something, you're good to go at 360 or 400 grit.

Hope this helps.
 
Peters rocks. If you have questions, call and ask for Brad Stallsmith. :thumbup: Tell him I sent ya, I said thanks for everything, and he can expect another batch from me in a week. :)
 
Thanks to both of you.

I have a large-ish blade in 3V I am working on right now. 10 inch blade and about 15 inches overall. Thickness is around 0.188" I think. The basic shape is quite basic--think typical ABS-style cutting bowie.

I am going to send this to Peters as well. Am I reading you correctly? Can I essentially finish this thing down to a sharp edge and all pre-HT? If so, great. If not, how thick are you leaving the edge pre-HT?

Thanks again.
 
i dont go to 100% cause of HT finish to remove and 3v is not as bad as some steels to grind post HT (but compared to 1084 its a monster )
dont hand sand the thing (i woudl got 10v but not 3v ) use a belt or 2 to get it cleaned up post HT and youll be fine
BTW ht hardness for 3v i woudl go 58-59 for long thin profiles and 60 for choppers and max it out on anything smaller or light duty (that stuff is tuff)
 
This is what I'm working on. Took your advice, and ground it down pretty close to shape. Need to touch it up a bit, because I REALLY don't want this to warp. 3V is a lot more expensive than 5160. Don't mind the incredibly ghetto cord + tape wrap. I just needed to guesstimate balance...

20130228_205157_zps8467ab3b.jpg
 
crimsonfalcon07 said:
This is what I'm working on. Took your advice, and ground it down pretty close to shape.
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I like it! As long as it's ground evenly, I don't see any problem. Unless you really really ground it aggressively/hot, I think any residual stresses will be taken care of as it comes up to austenizing temp and soaks. You might call Brad and ask if he would recommend a stress-relief cycle before hardening, just in case. From time to time there will be minor warping ("It just happens sometimes, mainly because you guys can only grind one side at a time" is what he's told me), but they can straighten that while the blade is still hot from tempering.

John Frankl said:
Can I essentially finish this thing down to a sharp edge and all pre-HT? If so, great. If not, how thick are you leaving the edge pre-HT?
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Definitely not a sharp edge. The edge should be flat and clean, with no scratches or grooves in it. I clean mine up with 400-grit paper before sending them in and try to keep them as consistent thickness as possible. I've had Peters' do blades with edge thickness ranging from .030" down to .010" (that's pushing it, and not needed for blades that large) without warping. Because they're hardened in vacuum furnaces (no oxygen to cause decarb), the blades come back very clean, with just tempering colors/oxides to sand off. That's why I go ahead and hand-sand to desired finish before sending them in. Again, if you want a machine finish, that's not necessary.
 
Very much appreciated, again. I'm definitely in favor of doing as much work pre-HT as possible; I just really don't want warpage, since 3V is so much more expensive than 5160...
 
"Definitely not a sharp edge. The edge should be flat and clean, with no scratches or grooves in it. I clean mine up with 400-grit paper before sending them in and try to keep them as consistent thickness as possible. ... That's why I go ahead and hand-sand to desired finish before sending them in. Again, if you want a machine finish, that's not necessary."

Thank you very much. On your hand sanded finishes, do you grind a noticable secondary bevel post heat treat, or are you blending everything in by hand sanding down nearly to a zero bevel?
 
John Frankl said:
Thank you very much. On your hand sanded finishes, do you grind a noticable secondary bevel post heat treat, or are you blending everything in by hand sanding down nearly to a zero bevel?
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It depends on the knife, and how thin the edge needs to be. On almost everything I sharpen them with a "normal" V-edge - mainly because that seems to be the easiest for most customers to touch up. I'll convex pretty much any edge down to zero on request - but I can't recall the last time that was requested.
 
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