Rockwell testing forged blades

If I'm not mistaken, a forged blade will be harder near the cutting edge than along the "main body" of the knife blade. So, if you Rockwell tested a forged blade, you would get different results depending on where along the blade you tested it. Is this correct or am I missing something?

If this is correct, where along a forged blade do you Rockwell test it or, is there no standard location?

Bernie

 
Cougar Allen

Cougar Allen

Buccaneer (ret.)
Joined
Oct 9, 1998
Messages
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A differentially tempered blade will have a harder edge than spine, whether it was forged or not.

You naturally have to test it in at least two places to see if it came out the way you intended it to. If you don't have Rockwell testing equipment available you can file or grind at it and get a pretty good idea of how hard it is.

-Cougar Allen :{)


[This message has been edited by Cougar Allen (edited 16 December 1998).]
 
I'm not trying to be master of the obvious but, anyone who knows this (that a given blade will test at different Rockwell readings) will not put too much importance at all on the numbers, right?

Bernie

 
Bernie, "differencial tempering" can be done to a forged OR "stock removal" blade.

"Stock removal" means you start with a solid chunk of steel and remove everything that isn't a knife/sword/whatever.

Differencial temper pieces list TWO Rockwell ratings. My Mad Dog WSP1 (ATAK variant) is Rockwell 62-63 at the edge, 50-54 at the spine through tang. It's 01 tool steel, stock removal ground, chrome plated and an absolute wonder. List me among the Mad Dog fanatics where it comes to toughness.

The old Japanese method of adjusting the hardness was to coat the blade in clay during the heat-treat, more clay at the spine and a thinner coat at the edge. The boundry can be seen and is known as a "hamon". Mad Dogs have a hamon too - until they come back from the chrome shop with it all covered up, something that would horrify a Japanese blade purist and is an example of Kevin's "tough at all cost, damn the cosmetics" tank-ugly philosophy of which I heartily approve. If his stuff looked as good as it performed I know *I* couldn't afford one.

Jim March
 
How expensive are Rockwell testers anyway, and how hard are they to use?

Jim, do you know how far Kevin's superhard edge extends into the blade?

-Cliff
 
Cliff...
My understanding is that the testers are relatively spendy (>1000).

They seem to be easy to use. Depending on the substrate tested, there are interchangable points and the tester calculates hardness (also 3 or 4 diff Rockwell scales) based upon the depth of 2 indentations made by the point.

Rob Simonich has a pic of his tester on his workshop section.
******************
addendum: check this site out...diagrams, theory and overview of Rockwell testing

http://www.ccsi-inc.com/p-rockwell1.htm

[This message has been edited by DC (edited 17 December 1998).]
 
Cliff, not only do I not know the exact hardness pattern of a Mad Dog, I suspect it might be *very* difficult to find out due to the chrome plating. Sure, the cutting edge is exposed but that's *it*.

I also don't know at what Rockwell the Panther/Cougar/Wild Thing false edges are at. I seem to recall the Shrikes are fully hardened on all cutting edges, I suspect the P/C/WT false edges are hard but I'm not certain.

Jim March
 
OK, maybe I'm missing something. As I understand it, even if you temper a forged blade non-differentially, the edge is going to be harder than the spine. This is because (I think) the steel molecules near the edge have been compressed by the forging process more than the molecules near the spine. That's the benefit of forging, right?

If you snap a forged blade (which has been tempered non-differentially) in half, the cross section will be rough at the spine and smooth near the edge because of the compressed molecules near the edge which is where it's harder. Is this correct?

I know one way to figure this out: somebody send me one of you non-differentially tempered forged blades so I can snap it in half
smile.gif
.

Bernie



[This message has been edited by Bernie (edited 17 December 1998).]
 
DC thanks for the pointer, I guess I will not be getting a RC tester for awhile.

Jim, yeah, you could however just scrape it off. There was a fair amount removed off of my TUSK from impacts on metal.

By the way it appears that Kevin really does not go that soft even at the spine. I have read on his forums how you can use one ATAK to drive another through a piece of wood by hitting them spine with no damage. I did this with my HI khukuris and saw slight impacting. Nothing functional now, just cosmetic stuff which I couldn't care less about.

-Cliff
 
Bernie --

I'm glad you brought this up, and I hope an experienced bladesmith responds.

There are various theories about what forging does to the steel, including "packing" the edge, which is usually described as refining the grain structure at the edge. However, no less an authority than Wayne Goddard says that whether or not packing actually happens, its effects are nullified during the remaining heat treat. Some other bladesmiths disagree, and say that packing does have an effect even after the heat treat.

Joe
jat@cup.hp.com
 
Cliff: quite true; many fairly functional knives have Rockwells in the low 50s which is where the Mad Dog spine/tang is tempered to. Cheap Pakistani crud runs down into the 40s, sometimes worse.

Chris Reeve only hardens his A2 fixed line in the 57 range, right? We should all remember though that this isn't totally "apples to apples", 01 and A2 are different critters; A2 is usually viewed as superior esp. when both are uniform temper. If Mad Dog gets ahold of *any* steel all bets are off
biggrin.gif
.

Jim March
 
Mad Dog tempers his spines springy; some other makers temper them softer than that. As is well known MD believes it should not be possible to bend a knife; it should break before it takes a permanent bend. Not everyone feels the same way about that.

The easiest way to find out how far the edge temper extends on his knives would be to ask him.

As far as I know it is not possible to differentially temper both edges of a double-edged knife -- if you figure out a way to do it please let us all know.
smile.gif
MD differentially tempers his knives with false edges the same as those without, so the false edge is not as hard as the other edge. Since the false edge would be used only for fighting it doesn't need to be very hard, and spring temper is quite adequate for it IMHO. If you make a habit of utility cutting with it, though, you'll notice you have to sharpen it often.

Except for David Boye's dendritic cast steel, all knife steel is rolled or forged before it's made into a blade, so even stock-removal blades have a dense and fine grain -- forging it again doesn't make it any denser or finer. There are some people who claim forging a blade can improve its strength by aligning the grain along the length of the knife, but that claim is controversial.

-Cougar Allen :{)

 
Cougar: re: differencial on both sides of a double-edge, the late great Bob Engnath had hand-drawn diagrams of where his temper lines ran, and per him he did indeed harden both edges of double-edge models. This was on his Japanese-pattern series which included a few double-edge pieces used as your choice spearhead or knife.

Info on Bob's methods is available here:
http://www.knives.com/engnath.html

and:
http://home.earthlink.net/~grind/BladesNStuff.html (look under "Japanese blades")

Jim March
 
Swordsmith, Mr. Randal Graham has also done differential heat-treating on his broadswords.

Joe Leung
 
After writing the above it occurred to me it ought to be possible to zone harden both edges of a double-edged blade. Now I'm stuck with either arguing that zone hardening is substantially different from differential tempering or admitting I was wrong. I think I'll just admit I was wrong.
smile.gif


-Cougar Allen :{)

 
Cougar,
Who says forging does't make a better blade. It does, you must not have ever used a good forged blade it is better. I never heard it was controversial on carbon blades the only ones I have heard that it is controversial on are stainless some say it helps some don't but on carbon there is no question that a forged blade is better then a stock removal
 
Greg,

I'm not sure it's as simple as "forging is better". Even most (all?) forgers will say up front that the heat treat is way more important than whether or not the piece was forged or done by stock removal. So forging is immediately moved into more of a supporting role, with heat treat being the star.

From there, we have differences of opinion in how much of a difference forging makes. It can make a noticeable (but not nearly as noticeable as a good heat treat) difference according to some people; according to others, the difference really is quite small. And of course there are mistakes that can be made during the forging process that stock removal makers don't often make, so when it comes to forged knives you have to be extra careful.

I love forged knives for the idea of someone putting so much sweat and work into the piece, it gives it soul. But whether a knife is forged or not isn't particularly high on my list of buying criteria. That's just me, of course. I just wanted to point out that I don't believe there's a *consensus* that forging makes a big difference in quality; small difference, maybe.


Joe
jat@cup.hp.com
 
Joe,
I don't agree. I have seen to many tests on some steel(5160, 52100, w2, 10xx)by Ed Fowler, Wayne Goddard, Tim Zowada and others that a forged blade is better I know that all thess guys are forger but I have saw the test they did. The stock removal guys say there way is better but have never saw a real test of theirs. They may test their knives but not against a forged knife.
 
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