One-piece line hardness questions and concerns

Warriorsociologist

Warriorsociologist

Joined
Dec 12, 2001
Messages
1,670
This post has been troubling me ever since I have read it:

Originally posted by rdangerer


Most steels tend to get tougher as you lower the hardness, as a general rule, but there are distinct exceptions, like A2 and D2.

I just thought I'd point out that A2 is a bit weird... it has a toughness "hump"... data from a Crucible Handbook on A2:

Temper@....Hardness Rc...Toughness Charpy C (ft-lbs)
400F............61................31
500F............60................41
600F............59................37
700F............58................33
800F............58................31
900F............58................29
1000F...........57................41

I.e., if CRK takes A2 down to Rc55-57, they do make the knife somewhat easier to sharpen in the field (overrated benefit IMHO), they give up some edge holding/abrasion resistance for sure, but probably get back to a localized toughness peak at Rc57 or less.



To Cliff's point, a selected few steels at their toughness peaks vs. HRC (at least per the data set in Crucible's handbook in a hardness range that might be used for knife blades). Order is in relative terms of "wear resistance, adhesive", highest wear at top:

Steel....Tufness(ft-lb).....HRC......Adhesive Wear Resistance
============================================
M4...........32.................62.........20-25
M2...........20.................62.........8-10
3V...........40.................62.........8
3V...........50.................60.........7
3V...........85.................58.........6

D2...........23.................60.........3-4
A2...........41.................60.........2-3
A6...........67.................55

L6...........68.................56-58
O1...........32.................55-57

S5...........138.................58-60
S5...........156.................56-57
S7........... 85.................59
S7...........125.................57.........1
S7...........190.................47


Hardness helps with edge retention, prevents "rolling" of an edge, but abrasive and adhesive wear resistance is only fairly correlated with hardness.

Nothing turns out to be terribly simple in terms of relationships between hardness, wear resistance, and toughness.
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This post awoke in me the need to find out once and for all: Why (really) does CRK harden their 1-piece line (A2 steel) to 55-57 RC?

I have heard that this is to allow them to be "field sharpenable" in a pinch (an overrated option IMHO). I own a project II. I like it…no love it…but I would like it to hold an edge longer (who wouldn’t want this from any knife?). Lately, I have been seriously considering sending it someplace to have it custom hardened to RC-60. The thread I have quoted above, along with several others, is what led me to this idea. If I decide to do this, I will then send my knife back to CRK to be re-coated (and yes, I know that a custom heat treat will void my warranty). I would obviously love to just have CRK do the heat-treat, but the last time I contacted them to ask if they would do such a thing, I was told that they would not harden the knives any more than RC55-57 because it would make them too brittle... Unfortunately, I have to admit; that I just don't agree such is the case. Bear in mind however, I only believe this (perhaps) out of ignorance – all my heat-treating knowledge is based on what I have read…AND the reason I have not yet sent my P2 anywhere is because I have a nagging worry that hardening it to RC-60 may in fact not be a good idea afterall (It’s hard to not heed the wisdom of the CRK staff). Yet…the more I think about this...I think that even a slightly more brittle, but harder 5/16"(?) thick blade of A2 might fit my needs better that the alternative...

Comments??? I would especially like to get some “hard & fast” comments from some of the CRK folks… J Thanks in advance to all…
 
Is there anybody that hardens A-2 to Rc60? Maybe you should ask them about it. If not maybe there is a reason. I cant imagine any edge holding gain would be worth the cost. What would be the edge holding gain. 5-10-15 percent? What about the fact the knife has been hardened twice? I think you are on the bad end of a losing deal. If its such a big deal switch steels and have a custom made for you that way you want. It wont be a Reeve knife, but neither is what your making going to be one. Good luck.
 
Originally posted by Mike990
Is there anybody that hardens A-2 to Rc60? Maybe you should ask them about it. If not maybe there is a reason.
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Hi Mike. Thanks for your reply.

"The reason" is exactly what I am hoping to find out by posting this thread. If the reasons for the current hardness are not such that they affect the tasks I use my knife regularly for, I for one, would be willing to incur the costs of a new heat-treat.

We may have to just “agree to disagree” on this one… While I very well could be wrong (and probably am)...I don't think that re-heat treating a blade constitutes as major a change as you make it sound... Further, I think it will still be a "Reeve knife' even if I choose to heat it up once or twice.:rolleyes: ;) :) I think that a gain from, say, 56 to 60 will be noticeable...and I already like everything else about this knife. So, in sum, I don't want another knife. What I want is to know once and for all if I can get my P2 to hold an edge even better without suffering any undue consequences. If A2 is truly at its peak toughness at RC 57 and RC 60, why not make it RC60???

BTW, this same logic applies to the new sebbies coming out in S30V. It appears that they will be hardened at a lower RC than the previous BG-42 knives. Given the characteristics of S30V, this seems strange.

My hope is that someone from CRK will post a reply here and clue me in to something I may have overlooked...because from where I am standing, the 1-piecers could & perhaps should be hardened to RC60, and the S30V sebbies to +RC60. If there is some reason that CRK has decided not to do this....I am just dying to know it!!! ;) :D :cool:
 
WS, you posted my same thoughts, I have a few smaller CRK fixed blades. I too have thought about having them heat treated to a higher RC. The smaller blades especially would benifit from better edge retention, I dont think toughness is as big an issue in a smaller knife. Look forward to a reply from an expert on the heat treat issue.
 
I believe the One Piece line was designed with hard use in mind, hence the lower hardness. This may be even more important in the smaller blades. There are times when a smaller blade is called upon to perform tasks better suited to a larger blade. The extra toughness would be very welcome.

Paul
 
Retreating the A2 blade will not change the steel in any way.

First remove the black coating, fine grit in air blast would be the fastest.

The heat treater should have an atmosphere furnace to prevent scale forming on the surface. Harden and temper to temperature recommended for A2 at Rc 60. Most heat treat companies will hold to +/- one point on Rc scale.

Recoat the blade as desired.

I agree with comments on low hardness of A2. Years ago Bob Loveless commented on his preference for A2 blade steel but could not offer it due to poor corrosion resistance. Have you considered hard chrome base with BC1 coating?

Regards,
FK
 
I'm no metalugist, but my thoughts are that you may well get the desired result. However, I think there would be a downside in that the edge may become prone to chipping out. My PII has shrugged off a fair few direct hits on stone, iron and bone. For the Projects are on the keen side, read thin, along the edge for a survival blade. This is one of the things that I like about them. You may well be pushing your luck. I haven't broken mine in nine years hacking about, so I woundn't change a thing.

Good luck though.
 
I am reviving this thread again.

I have contacted one particular well-respected individual who would be willing to do such a heat-treat (his initials = PB ;))...but at the same time, I feel a bit like a child who is about to be scolded for doing something his wise elders know to be foolish... I realize that CRK has been doing their thing for many years now....and with very good results too. While I was leaning ever-so-slightly in the direction of sending off my knife to make it RC60-61, Greenjacket's comment about the fine edge profile got me thinking......and as such...I am hesitating. The Project series has a very fine bevel angle (about 13 degrees near the edge I believe). I am a bit worried that while I may not have anything to loose in hardening an A2 blade with a less extreme grind (20-22 degrees or so), the Projects, at RC60, may be prone to the kind of edge-chipping I am worried about. Of course at RC55-57, this is not a problem...and the knife does hold a wicked edge...

Arrrgh... I wish I could leave things alone without endlessly trying to improve that which seems to work well already...perhaps this time, I will.

Anyway, I just thought I stir the pot again....
 
When it comes to the in-depth technical stuff, I need to get Chris' input - he is in Chicago this week so I'll run it all by him on Monday!

Anne
 
Thanks Anne.

BTW, for the record, I want to make clear that I think that your knives function great and that I know that there is a REASON why they are "the way that they are..."

I wanted to revisit this question so that we could hopefully (once and for all) put and end to the circular debate that has been popping up here and there, about why Chris has decided to go with a slightly lower hardness relative to other makers. I suspect it has to do with the edge geometry he uses... That being said, since nothing else cuts quite like a CRK knife, I would definitely prefer that the geometry and hardness stay as it is rather than changing the geometry to accommodate any (hypothetical) increase in the hardness of his chosen materials.
 
Send it to Paul Bos and have him heat treat it to 59 Rockwell. You will gain in all areas except ease of sharpening(I agree, an overrated quality, especially with diamond stones). A2 at 59 would be very tough and hold an extremely fine edge. I dont think you would have any brittleness problems.
 
Originally posted by Warriorsociologist
Yet…the more I think about this...I think that even a slightly more brittle, but harder 5/16"(?) thick blade of A2 might fit my needs better that the alternative...
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I blieve it is 1/4" but either way, it is plenty thick at the spine, that is no concern. As greenjacket pointed out, main issue is edge durability. Why don't you just have it heat treated to 59-60, try it out and let us know how it work? If you experience slight chipping or "micro chipping" doing what you normally do, increase the angle slightly until you find optimal angle balance for your cutting/durability needs. In any event somethng like 30 degree included angle should be more than adequate for A2 59-60 rc.
Martin
 
I wouldn't dare to re heat-treat a one piece knife. Odds are it will crack where the thin blade meets the thick handle. Metals of different thicknesses expand and contract at different rates and will cause microscopic fissures which will lead to failure. Reeve has been doing this since what 1984? And for good reason. I'd rather have to sharpen my knife a little more often than void my warranty and end up with a warped or broken knife.
 
Originally posted by extremesurvival
I wouldn't dare to re heat-treat a one piece knife. Odds are it will crack where the thin blade meets the thick handle. Metals of different thicknesses expand and contract at different rates and will cause microscopic fissures which will lead to failure. Reeve has been doing this since what 1984? And for good reason. I'd rather have to sharpen my knife a little more often than void my warranty and end up with a warped or broken knife.
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While I thank you for your comments, it doesn't sound like you've ever seen a Chris Reeve 1-piece knife in person. Also, metals of different types, not thicknesses, expand & contract differently - like steel pistons in an aluminum engine block. Finally, the Project II's bade is hardly "thin"...it is a full 1/4" inch thick and the entire knife is milled from 1-piece of steel...I hardly think it will warp.
onepiece.jpg

There are other reasons (like warranty issues) not to re-heat treat my knife...but warping is not one of them.
 
I have a Chris Reeve Knives Shadow 4. Heat treating a blade (which is thin in comparison to the handle) and a handle of such different thickness and size, I don't believe can be done very hard or it will crack. I have heard of other makers trying to it years ago and they could't get it to work. I know for a fact that it cannot be done with stainless steel, but with A2, you never know. I've always thought that was the reason for his low Rockwell, (the knife would bend rather than break), but I don't know. I'd like to hear what Mr. Reeve has to say, it'd be interesting to find out.
 
Originally posted by Warriorsociologist
While I thank you for your comments, it doesn't sound like you've ever seen a Chris Reeve 1-piece knife in person.
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Sorry, I was a little quick to assume (and you know what happens to people who assume...). Anyway...

Yep, I am looking forward to Chris's comments as well.
 
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