work hardening

[Ken S]

Mike's latest Sharp Pad videos are fascinating. Especially interesting was his discussion of work hardening when removing the burr with the Sharp Pad. I would like to learn more about this.

Ken

[EOU]

Ken, thank you for opening this topic up.

From a physics and metallurgical standpoint we know that work hardening should benefit edge longevity. From an empirical  standpoint we can see its benefits although most of this work has been limited to stainless steel knives to date. What we have not been able to do yet is actually "measure" how much it benefits us.  While we certainly have the means to measure the level of edge degradation suffered during any one event we lack the instrument to degrade the edge in a standardized and regulated fashion. This is something that is in the works and of course will have applicability beyond just measuring the benefits of work hardening. 

The boss is driving the bus on this development project but I will be reporting on the progress from time to time. Thank you Ken very much for posting on the BESS Exchange

[Jan]

Mike's latest Sharp Pad videos are fascinating. Especially interesting was his discussion of work hardening when removing the burr with the Sharp Pad. I would like to learn more about this.

Ken, work hardening which is also known as strain hardening or cold working is a metallurgical process of metal strengthening by means of its plastic deformation. Plastic deformation occurs when energy is quickly added to the metal. The work hardening of a metal increases its hardness and yield strength. The reason for metal strengthening is movement and generation of many new dislocations within the metal atomic lattice.   

Here is a classical text book example: "Strain hardening can be easily demonstrated with piece of wire or a paper clip. Bend a straight section back and forth several times. Notice that it is more difficult to bend the metal at the same place. In the strain hardened area dislocations have formed and become tangled, increasing the strength of the material. Continued bending will eventually cause the wire to break at the bend due to fatigue cracking."

https://www.nde-ed.org/EducationResource...hening.htm

Jan

[grepper]

"One can actually remove the burr by cutting into hard plastic and or hardwood"

Interesting that you should say that.  I have done that when I have a feeling that there is remaining burr.  I've found it works but have always wondered how effective it is.  Could it be used instead of stropping?  Is there a risk of just smashing the burr against the edge?  Can you dull the edge with hardwood?

It's on my list of stuff to try and figure out.  If you have experience with that, I'd love to hear it!

[Ankerson]

"One can actually remove the burr by cutting into hard plastic and or hardwood"

Interesting that you should say that.  I have done that when I have a feeling that there is remaining burr.  I've found it works but have always wondered how effective it is.  Could it be used instead of stropping?  Is there a risk of just smashing the burr against the edge?  Can you dull the edge with hardwood?

It's on my list of stuff to try and figure out.  If you have experience with that, I'd love to hear it!

It will break off the burr.

Yes hardwood can dull an edge, but it takes a very long time.

I do either or both, I don't normally strop at all, I remove the burr with the stones.

[grepper]

You remove burrs with stones? Please explain.
Wouldn't that create a burr?
What grit compared to the grit you sharpened with?
At the same angle the blade was sharpened at?

To me that sounds fundamentally different than burr removal by breaking or tearing it off.

I'm in a serious search for a better way to remove burrs, so this sounds very interesting. Thanks for post that!

---

That only pertains to steel that isn't already heat treated and tempered.
For example use 2 nails.
A common nail and a concrete nail.
A common nail is mild steel normally around 30 Rockwell Hardness and not tempered.
A concrete or cutting nail is very hard, fully heat treated and tempered.
Try and bend both.
The common nail will be easy to bend and will eventually break.
The concrete nail will snap right away.
A knife blade is more like the concrete nail as they are fully heat treated and tempered.
As it pertains to knife blades and the burr:
The burr is hardened steel already, the reason why it cracks off, it's already very thin, hard and brittle.
...
Not sure how the confusion started with this or even were it came from pertaining to knife blades.

Hmmm.... Great post there Jim.  That actually makes a lot of sense.  

We need a metallurgist in this forum.  Nonetheless, that makes sense.

[Ankerson]

Well, with the sharpening system I use it's easy to remove the burr with the stone, I use the Edge Pro, like shaving off the burr so to speak.

Yes, same angle and stone I use to sharpen.

Yeah, you can't work harden a steel that has already been heat treated and tempered etc. That was making my head hurt just thinking about it. LOL

But you can damage the tempering with power equipment.

Figured I would clear up the confusion before others saw it.

[grepper]

That's interesting.  You remove the burr by using a very light touch?

I'm guessing that you are saying the power equipment could overheat the edge, thus damaging the temper?

Thanks for taking the time to explain.  A lot of the stuff you post is very interesting, and I want to make sure I understand what you are talking about.  Your input is really appreciated!

[Jan]

Ankerson and Grepper, the intention of my post was to explain to Ken the term work hardening in an understandable but physically correct way.  It explains the processes in steel wire Mike is bending in one of his videos.

Hopefully everybody here knows that a paper clip is made of low carbon steel and so could not be confused by the quoted classical experiment. 

I am aware that the work hardening is applied to non-brittle metals and for this reason I have not mentioned knife blade or burr in my post. 

I am afraid that our understanding of burr forming processes is still not complete. I am wondering if the microscopic structure and properties of a sub-micron burr are the same as those of the bulk blade material’s.


Jan

[Ken S]

It seems logical to me that as we approach a zero radius between the two planes that eventually the radius would become so small that it could not support the burr. Such a small radius would appear to be very smooth sharp.

After I was given a ceramic steel, I removed my traditional filelike steel from service. The more I use the ceramic steel, the lighter the touch I use. I have no supporting research, however, the gently used steel seems to be more effective.

Most of my knife sharpening transplanted from woodworking. For many years my burr experience was carefully raising burrs on hand scrapers with a burnisher. Maybe I should try using my burnisher as a knife steel.

Ken