Sound of hardened steel

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Gary W. Graley

Gary W. Graley

“Imagination is more important than knowledge"
Knifemaker / Craftsman / Service Provider
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Have you guys and gals noticed the sound of some blades have a more higher pitch that others? My take is that ring gives a little indication of how hard that metal might be. I may be way off point, but when a blade gives back a clean high pitch ring as you bring it in contact with a ceramic stone, it just seems that it is a bit harder and I've found those blades take an edge a little easier. Such as getting and removing the burr, they are not likely as much to have a burr that just hangs on and on, flopping back and forth as you try to get it removed. The harder blades the burr removal seems straight forward.

I recently got a very nice small fixed blade from navman navman in S90v steel, fairly thin behind the edge and hollow ground, so those three attributes probably aid in the higher ring sound when the blade contacts ceramic. Similar knives that are supposed to be heat treated as high or higher don't always give that audible feedback.

His blade also has a nice peaked spine, and a tapered tang, more work but all adds up to a nice knife.

Untitled by GaryWGraley, on Flickr

Untitled by GaryWGraley, on Flickr

Untitled by GaryWGraley, on Flickr

another knife that gives this type of feedback is a Civivi Trailblazer in damascus, an amazing edge on this one

Untitled by GaryWGraley, on Flickr

So, have any of you noticed this type of thing? Some that do not take a very good edge sounds dull which I figure means it's not hardened very much.
G2
 
I tend to have Peters' run the hardness a bit higher (61-62 RC) than what used to be conventionally accepted on these steels. Like it used to be thought that S90V/420V topped out at 59 RC, which led to it being a less favorable steel to some folks, although still an aggressive cutter. What I find is that with a smaller knife and the proper geometry these blades become laser beams that will cut for a long, long time.
 
I hear the effect during honing. The steel will, 'ring' as it's drawn across.

You can take a soft 440a and then...say, a Global knife. And the ring on the global is more bell like. The 440a sounds dull. Global runs their knives hard.
 
"Singing" razors are ground very thin. I suppose they need to be hard too, but does the hardness just let them be ground thin, or does the hardness itself make them ring as well? If the latter, and if my understanding is correct that the modulus of elasticity does not change to a large degree with hardening I think the ringing must be related to lower internal damping of the microstructure rather than being a property of the hardness itself. I hope Larrin Larrin will comment on this.
 
Mr.Wizard said:
"Singing" razors are ground very thin. I suppose they need to be hard too, but does the hardness just let them be ground thin, or does the hardness itself make them ring as well? If the latter, and if my understanding is correct that the modulus of elasticity does not change to a large degree with hardening I think the ringing must be related to lower internal damping of the microstructure rather than being a property of the hardness itself. I hope Larrin Larrin will comment on this.
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I don't remember learning about the sound of metals in metallurgy school.
 
Larrin said:
I don't remember learning about the sound of metals in metallurgy school.
Click to expand...


“The day science begins to study non-physical phenomena, it will make more progress in one decade than in all the previous centuries of its existence.”

“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
― Nikola Tesla


He knew..... He knew. ;)
 
If Larrin doesn't know we're really into the weeds, but here's a start.


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More for the truly curious. Apparently more martensite means less damping and therefore more ringing.


The diagram shows different microstructures produced during
different cooling processes, such as in the annealing process when the specimens cooled to
below 723 ̊C the microstructure changes from stable austenite to (Pearlite). Pearlite
combines ferrite and cementite, forming bands or layers, as shown in Fig. 9 (a), of
approximately 12% ferrite and 88% cementite. Annealing inside the furnace has a low
cooling rate, allowing grain growth during the phase transformation. Pearlite has excellent
ductility, leading to the increased area under the curve during the tensile test and getting a
higher value than other cooling processes. Also, for both processes of normalizing and
sanding, they have cooling rates faster than annealing. Thus, their microstructure shows a
Bainite, a mixture of carbides and ferrite, as shown in Fig. 9 (b).
Consequently, the Bainite is harder and has less ductility than pearlite, resulting in less
damping energy under the tensile test. The fourth cooling scheme is a quenching process
characterized by a very fast cooling rate, and the microstructure formed during this process
is (Martensite). In contrast to the disintegration of ferrite and pearlite, martensite transition
involves a sudden diffusion less shear process rather than atom diffusion.
When unstable austenite transfers to martensite at starting temperature (Ms) in the (TTT)
diagram, the martensitic begin forming. Fig. 9 (c) shows the microstructure of martensite,
which appears as a (lath) called lath martensite under an optical microscope. As a specimen
is quenched large percentage of unstable austenite turns to martensite until reaching to (M f)
line in the (TTT) diagram, at which point the transformation is completed. The martensite
phase has properties different than pearlite or Bainite. It is very hard with little ductility. For
that reason, the area under the curve of this process is very small, and its damping energy
less than the other three cooling schemes.
Click to expand...
 
I don't know nearly enough to even speculate about why some blades seem to 'sing' so loudly. I've noticed sometimes, that even some essentially unhardened table flatware really rings when its dropped on a hard surface, while others of the same type just land with a dull thud. I am inclined to think that very thin geometry contributes to it, but don't have any idea what other factors are involved.

I have one custom locking folder from Ray Cover with an ATS-34 blade, beautifully wide, thin and hollow-ground. Hardened up to maybe ~ 60 HRC or perhaps a bit higher I think. Even the burrs on this blade are impressively strong & tough when cleaning up the edge after sharpening. It had the coolest ring of any knife I've owned when the blade was allowed to snap shut. As beautiful as the sound was, I eventually realized that ring was the result of the blade's edge smacking the lock bar upon closing hard, which was leaving a dent in the edge. So, I don't allow this one to 'sing' anymore. But aesthetically, it's still one of the most attractive folders I own.
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Metalworkers will tap on a metal part with another piece of steel and listen to the sound for a preliminary assessment as to whether it's hardened. After that, you can take it to the grinding wheel and look at the spark. The sound especially is a quick and dirty assessment and you are only trying to find out if the part is hardened or not. The finer hardening and annealing levels of a knife blade would be harder to judge.

However, hardened and unhardened tool steel will definitely make a different sound if you tap on them.
 
I love playing with the sounds that a knife makes,
I balance the knife on my index finger, on its balance point or just behind, and then let the tip fall onto the worktop or whatever and mentally note its frequency. The sound profile reminds of spinning a coin and the tones changes as it slows down and eventually stops. It is also thought provoking that, as well as the sound, the number of reverberations can be quite different from one steel to another.
 
Thanks guys and that reminds me of when people check out an anvil that ringing resonance when drop a steel ball on the surface or strike with a hammer
Sound gives us feedback on some things that we might have taken for granted all along

on a different note, pun intended, I used to travel a great deal for work, training and installing glass container inspection equipment and will never forget my trip to a glass factory in Mexico. On one line they were making large water jugs the kind used for water coolers, big jugs. At the end of the annealing oven a worker would take each one and quickly look it over for any obvious defects and then he would swing it onto his shoulder, he had a pad of asbestos on his shoulder to protect him from the heat as well as any broken glass, while he would then take a large rubber mallet and strike the jug, if it gave a nice resounding tone it was placed on the pallet but if it went thunk, with no nice tone it meant that there was a fracture somewhere in the jug and he would toss it into the recycling hopper to be crushed and melted again. Sometimes when he would strike the jug it would shatter so it was a risky job!
I was amazed at the entire process on that line.
G2
 
Last edited:
Gary W. Graley said:
Thanks guys and that reminds me of when people check out an anvil that ringing resonance when drop a steel ball on the surface or strike with a hammer
Sound gives us feedback on some things that we might have taken for granted all along

on a different note, pun intended, I used to travel a great deal for work, training and installing glass container inspection equipment and will never forget my trip to a glass factory in Mexico. On one line they were making large water jugs the kind used for water coolers, big jugs. At the end of the anealing oven a worker would take each one and quickly look it over for any obvious defects and then he would swing it onto his shoulder, he had a pad of asbestos on his shoulder to protect him from the heat as well as any broken glass, while he would then take a large ru mallet and strike the jug, if it gave a nice resounding tone it was placed on the pallet but if it went thunk, with no nice ton it meant that there was a fracture somewhere in the jug and he would toss it into the recycling hopper to be crushed and melted again. Sometimes when he would strike the jug it would shatter so it was a risky job!
I was amazed at the entire process on that line.
G2
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There are other instances where sounds are indicative of quality or perfection,
In the casting of a brass Bell, its rung to check for cracks, on the service inspection of trucks the Hub would be struck with a hammer and technicians taught to listen for the correct ringing sound to check for cracks. A VOSA vehicle inspector would, on a roadside inspection, strike each wheel nut of a vehicle to check for tightness of the bolt or stud, thus ensuring the driver has carried out one of his daily vehicle checks.
Also,In England, we have a saying that a person of good character or good report is "Sound".
 
Expert flint knappers say they can tell where there are internal fissures/fractures/discontinuities in a big piece of chert by tapping on it and listening, too...

I also always check the integrity of grinding wheels before installing them by tapping on them and listening for resonance...the same goes for terra cotta flower pots before buying them...

This is also how I check for delamination in FRP boats: Bang on the hull with a screwdriver handle. If you get a sharp/solid bang, it's probably OK, but a "dead" or muffled sound is indicative of delamination (useful for hull repair when somebody hits something with their boat)...this method will reveal hidden problems that are undetectable to the eye.
 
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