Vibe?

[Dan Zawacki]

I have searched both here (with the google thingy) and on SFI and come up pretty dry, so I figure I'd actually start a thread.

In some racing circles (yes, I know that racing has little to nothing to do with knifemaking) the frame welds are conditioned with vibratory stress relief, resulting in significantly lower incidence of breakage and cracking along weld lines. I have read lots of very generic descriptions about the impact of the process, and tried to do some real research, but there's scant little information available, unless I'm missing the boat.

Has anyone tried applying vibratory stress relief to tool steels and / or high carbon steels? The 4340 they're using for their frames isn't exactly knife material (for most of us anyway) but if it is actually a stress relief then the mechanics of it should translate pretty directly.

The most technically capable description I found was in an article written by an obviously biased source (a company that produces the equipment) but that invoked methodology and descriptrs that I could at least relate to. The article was on the relative merits of a sub harmonic system vs a harmonic system, but the results they claimed were of significantly increased toughness with no loss of strength. This result was contrasted with torch stress relief, which resulted in a similar (slightly superior) increase in toughness, but with a significant loss of strength.

In another technical article, there was a lot of description, but with no numbers contrasting thermal stress relief against vibratory. Again, the sonic side came out on top, but for reasons that were likely suspect, as it was again from a biased source. However, the descriptions of the mechanisms and results were familiar and comfortable.

I do know that the equipment is rediculously expensive to purchase, but having the service done is not, and there are a number of shops in the US that will do it. Apparently in order to do something knife sized, is just has to be clamped to a larger plate of similar material.

I would try this out myself, but I figured it would likely be a heck of a lot simpler to ask if anyone here had actually done so before I go to the expense and effort of testing. If this has already been explored, why spend the time, effort, and money?

 

[sharpeknives]

AAAAAAAAAAAAHHHHHHHHHH, Yea! I agree. I think I do anyway. Way over my head.
Just thought a well searched out thread like this deserves a reply

 

[michdad]

I wish I could give a better reply, sorry I can't, but I can contribute this much. There is a big difference between the types of failures with differing stresses. Be it a thermal, harmonic, or mechanical stress, they each have characteristic failure results. The quicker learned, the quicker prevented.

 

[Dan Zawacki]

I guess I can see the point, however, it seemed to me the description of the problem that was plaguing racing chassis was one of embrittlement of the steel near the weld lines causing subsequent cracking and breaking under even nominal stress, which could be quite catastrophic if a driver's life ever depended on that roll cage.

It seemed to me (and I could be way off base, just trying to apply the bits I have been able to figure out) that when welding up the frame, the steel along the weld line would possibly be heated above the austenite transformation temp, but being in a thin cross section (walled tube, not solid bar) and being attached to more steel that can quickly draw away that heat, some of that area is self quenching and going martensitic. However, without some manner of stress relief, the new martensite is full of internal stress and quite brittle, causing the problem.

As I understand it (and I could be wrong on this) hardness as we typically apply it is an indirect measurement of the strength of the steel. Thus, when they reference increase in toughness at no expense of strength vs thermal stress relief, which is supposed to be nominally more effective at increasing toughness with a significant strength sacrifice, I am seeing the potential for using a lower tempering temperature to keep hardness (strength) higher, whilst reducing internal stresses and increasing toughness to levels normally reserved for higher temperature tempers and thus softer steel.

Maybe 1084 at 61 HRC as tough as it would be at 59???
Maybe W2 at 63 HRC as tough as it would be at 60???

I'm not looking for a miracle, but rather wondering if a measurable and not insignificant gain could be had this way. I would be quite happy with 1 or 2 points HRC with no loss of toughness, or, alternatively, a bit tougher at the same level of hardness.

 

[Dan Zawacki]

Anybody???

 

[mete]

In the welds there are thermal [expansion and contraction] stresses and transformation stresses .It can be complicated .Anything involving higher carbon and alloying elements has to be pre and post heated ! Though I've read about vibration I don't remember any details.

 

[Dan Zawacki]

That's what I thought too, with the pre and post heating, but apparently the teams that are using sonic stress relief don't do a post weld heat for stress relief (I'm pretty sure they still do some manner of preheat, but whether or not it's hot enough to prevent autoquenching, I have no idea) but just do the sonic instead.

I have sent out a few email inquiries, but have not yet gotten any answers back. I'll keep everyone posted if I find or do anything interesting!

 

[Mo2]

This post was from 2008, but its 2016 now and i have not found any more information about VSR and knife making. i have found this google books page to a book called Modern Engine Blueprinting Techniques (which is a great book if you're into automobiles) that goes into details of Cryo and VSR (vibratory stress relief).

https://books.google.co.id/books?id...X&redir_esc=y#v=onepage&q=vsr vs cryo&f=false

ive run past my viewing time so i cannot copy paste the text anymore, but you should be able to read the two pages it provides.

It seems like it would benifit the knife business in general, but there is no data in the knife world that i can find that would solidify this publication. since 2008 someones had to run some tests?

 

[lukus]

Wouldn't this be similar or the same as shot peening steel? I seem to remember a fairly small air-powered hand tool that has a bunch of steel pins that vibrate back and forth very fast. It descales the weld and reduces the metal stress at the same time. I think you also get a cool looking peened finish.

 

[Mo2]

Wouldn't this be similar or the same as shot peening steel? I seem to remember a fairly small air-powered hand tool that has a bunch of steel pins that vibrate back and forth very fast. It descales the weld and reduces the metal stress at the same time. I think you also get a cool looking peened finish.

No.

from the same book linked in my above post, starting on page 57

Shot peening is a material compression process. Shot peening hardens the surface while compressing the steel under the surface. This increases below surface density, which makes the part stronger and less prone to distortion or cracking.

Shot peening compresses the metal and reduces the chance for surface galling, cracking or corrosion fatigue. possibly reducing a stress crack.

The purpose of any stress-relieving process is to eliminate internal metallurgical stresses in the steel, which reduces the chance for fracturing by allowing the molecules to align more uniformly. Shot peening is not really a stress-relief process. because it compacts the surface of the metal, it can actually induce additional stress inside the part. true stress relief should treat the entire part all the way through, not only the surface.

Both cryrogenics and vibratory stress relief are treatments that can improve the molecular structure and can improve durability and reduced harmonics.

i really dont care about welds like the original poster. i care more about using vibratory stress relief for the blades, instead of using cryro. but alas there is no information on the topic in knife making. Hence why i am calling for help on the very topic. would anyone be interested in testing VSR on your custom knives and test the different factors?

 

[Stacy E. Apelt - Bladesmith]

This is an old thread because the topic doesn't apply to knives. In the thickness of a knife blade, the amount of flex-stress crystallization that could forming the martensitic structure of a blade ( racing cars are most likely pearlite, not martensite)is probably near zero. Vibrating a blade to reduce zero is a waste of time, as it would gain nothing. Cars, bridges, airplane wings and frames - all good subjects ... but they are not knives.


I'll leave the thread open for anyone who wants to offer any other opinions, but can't see the likelihood of new info from eight years ago.