Comparative edge durability--heat treatment vs. work hardening?

FortyTwoBlades

FortyTwoBlades

Baryonyx walkeri
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This is a question mostly pertaining to scythe blades. In continental Europe scythe blades are traditionally heat treated to the mid 40's and the edge beveled by peening it against a narrow anvil to draw it out thin and the hardness brought up for better edge retention. By contrast, blades in the English, Nordic, and American tradition are brought to high hardness through heat treatment, often in laminated construction to provide support for the hard core under accidental impacts.

My question is this--what is the difference in edge durability under impact between two blades, presuming 1080 for the steel, where one is heat treated softer and the edge hardened through peening vs. one that is simply heat treated to equal hardness?

From my understanding the peened blade would have less martensite as more would have been converted back to pearlite during tempering, and then the arrangement of the crystal structure at the edge rendered hard through being deformed by the blows of the hammer in cold state. That slipping of the structure would decrease the ductility of the steel at the edge, leading to higher strength but with an increased chance of brittle fracture under impact. The blade that was heat treated harder with the edge formed through grinding would have a larger ability to roll if impacting something like a stone rather than cracking as it would be taking its hardness through the greater presence of martensite with the lattice structure being left in the natural state.

Am I anywhere near the mark? :confused:
 
You're talking about two different things. The scythe blades are low carbon ,.40-.50 % C .They are sharpened by cold working as you say.Cold working has it's limits as they knew even in the bronze age ! About 10 %reduction in area is all you can get before cracking occurs. You can still buy scythes and anvils and hammers to harvest your wheat etc. It's an excellent system .Adjust the nibs for you ,take long sweeps ,let the tool do the work. For me and my scythe each swing cuts a swath 2' x 6' .
For high carbon it's all together different It's not appropriate for cold working and the worker can't do repair of damage , rolled edges , dings etc like he can with low carbon.
 
bladsmth said:
Not really.
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This is a minimally useful reply. Please explain. I want to learn, silly!

mete said:
You're talking about two different things. The scythe blades are low carbon ,.40-.50 % C .They are sharpened by cold working as you say.Cold working has it's limits as they knew even in the bronze age ! About 10 %reduction in area is all you can get before cracking occurs. You can still buy scythes and anvils and hammers to harvest your wheat etc. It's an excellent system .Adjust the nibs for you ,take long sweeps ,let the tool do the work. For me and my scythe each swing cuts a swath 2' x 6' .
For high carbon it's all together different It's not appropriate for cold working and the worker can't do repair of damage , rolled edges , dings etc like he can with low carbon.
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No I'm actually not--continental European scythe blades made by the largest producer in the business (Schroeckenfux) currently use a steel with .80% carbon, and they use this same steel but with a different heat treatment when making American pattern blades under contract for Seymour Mfg. Blades with even higher carbon content are reported to have been used for making continental blades back in the day. This is why I'm curious.

I already own and use scythes and have about 60 snaths and hundreds of blades out in the workshop awaiting restoration. I'm asking a question about quantifying the difference in performance for equal steel and hardness but different heat treatment and methodology to attain it.
 
You are talking baseball rules for a football game. You can't use RBIs to describe how well a quarterback completes passes.

Work hardening has almost nothing to do with changes in structure. It has to do with dislocations along grain boundaries causing the structure to be "Jumbled" and thus slightly more resistant to movement. Gain in hardness is small.

Hardening and tempering has to do with conversions of structure resulting first in a greatly harder structure followed by a greatly reduced brittleness in the tempering.

A hardened blade is many times harder, thus giving a much better edge, and the tempering yields a tough body. The edge life from full hardening and tempering to match the blade task will be much greater than any work hardened blade in durability.
 
Thanks for the response, though that's not quite what I was getting at. :)

The blade to be work-hardened isn't in a fully annealed state or anything, but is heat treated softer than an Anglo-American or Nordic blade and then the edge work-hardened through periodic hammering. So, for instance, if one were to heat treat a blade to 48RC and then work harden the edge, producing a gain in hardness of 5 for a resulting edge hardness of 53RC (Here's an example) then how would the mechanical properties of it differ from a blade that was simply heat treated to a hardness of 53RC in the first place? That's what I'm curious about. I want to know if there's any appreciable difference in a softer edge brought to a given RC by work hardening vs. a blade simply brought to equal hardness strictly through heat treatment.
 
As I said in the explanation - The hardened and tempered blade edge would be better.

A blade hardened to Rc48 would be largely pearlite. The edge work hardened to Rc54, will just be dislocated ( coarsened) pearlite.
A quenched and then tempered Rc54 blade will be largely martensite. The martensite will be stronger and more than tough enough.

Work hardening methods are normally used in taking a low carbon steel tool and gaining some edge hardness. I can see no possible advantage in taking a eutectoid steel and deliberately creating a lesser quality edge.

My only explanation for anyone doing it with a reliable 1080 steel would be tradition, not any gain in quality. Many old smithing procedures refuses to die away despite modern steel quality and metallurgy, because "we have done this for centuries" is the test, and proof, of quality to some people.
 
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Okidoki--that's pretty much what I suspected. Thanks very much!

Am I correct in my presumption that the work-hardened edge would be more susceptible to brittle failure?
 
Yes, the dislocated pieces would have no lattice or structure to try and help retain them. They would chip out easier.

I have added some more info to the last post.
 
Awesome. Now that's exactly what I was looking for! Thanks a million!
 
To be clear, I'm actually asking the question because I'm arguing AGAINST the practice of work hardening edges compared to hardening through proper heat treatment. Thanks guys!
 
FortyTwoBlades said:
To be clear, I'm actually asking the question because I'm arguing AGAINST the practice of work hardening edges compared to hardening through proper heat treatment. Thanks guys!
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Of course this means that you will be shunned. Sharpening the blade at the end of the day instead of every 15 minutes - :( .

Peening a martensitic blade could be advantageous to straighten a bent edge. And at these low hardness values many accidents (rock impacts) will result in a bent edge instead of a chipped one.

If anyone is interested there is a great thread on the scythe over in the ax and tomahawk subforum.
 
While I've come across many bent blades in my collection and restoration efforts I've yet to ever directly experience a wrinkled edge that would really benefit from peening to straighten it. I have done this on damaged edges during the restoration process, but never been able to reproduce such an effect in the field. I suspect that the fellows that induced such damage originally were a tad rough in their work! :D
 
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