question for the steel experts...

M

markmarkmark

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Jan 26, 2002
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we know that something like a spring has a limited life...it can only cycle through being "sprung and unsprung" so many times before it finally gives out and breaks...

my question is, does the process of forging (heating, annealing, tempering and especially NORMALIZING) eliminate that stress and "recondition" the steel? i mean, say for example you had a really old set of leaf springs on your truck that has seen so much wear that it would crack in a few more weeks of use...if you heated those springs, normalized, etc. would that stress be eliminated?

more importantly, if you were using old leaf springs for a knife would the knife have a more "limited" life? i would think that the process of forging and heat treating the blade would eliminate the stress that was there since it's actually changing the structure of the steel and moving it around...by the time you pounded out the blade, wherever that stress line was, it would have moved all over the place...

i'm not talking about the situation where you use old leaf springs and find out too late that they had little cracks in them...i'm talking more in theoretical terms where you have springs that were getting ready to crack, but didn't yet...and then you forge it into a blade...is the stress eliminated by the forging/heat treating, etc. process?

by the way, i realize that in practical terms this probably isn't much of a concern...leaf springs have A LOT of life in them and it takes a heck of a lot to break them...i'm just curious about what happens to the steel during the forging and heat treating process...
 
Originally posted by markmarkmark

i'm not talking about the situation where you use old leaf springs and find out too late that they had little cracks in them...i'm talking more in theoretical terms where you have springs that were getting ready to crack, but didn't yet...and then you forge it into a blade...is the stress eliminated by the forging/heat treating, etc. process?
Click to expand...

Yes. But I'm no expert.
 
Yet it may not be readily available in all places.
Here in Italy all carbon I can find right now is C70, and only in 3mm thick slabs.
I found some shear blades from which I plan to grind or forge some knives, but they'll have to wait till I have the way to cut them (heat treated hard steel, not good to cut by hand :D)
So salvage from scrap may be a good (cheap) way to get nice steel.
The question is quite interesting.
 
While you guys are playing with old car springs, have a look at the end that goes around the mounting bolt. Some are made so that the eye is central. Cut that a few inches along the flat forge to a blade and you have a very good little axe with the handle hole made for you.

Back to your question I don't know but thought this may intrest you while collecting the spring steel.
 
3M
That is a very intriguing question. I don't have enough experience to say if the steel gets "tired" forever or if it can be reannealed,normalized and hardened and perform like it did the day it was first made. I hope that someone more knowledgable comments on this. My guess is that an old "tired" piece of leaf spring with inner stresses about ready to bust is going not going to perform as well(in the long run) as new steel. I know fine knives are made from old leaf spring(I have made many from it)but there is no way of knowing if the blade has built up internal cracks that can't be removed through thermal processes. For me, if the knife is intended to be used in a casual and low stress environment, then leaf spring would be an excellent choice. However, if it were going to a tough environment for me and the knife, I spend and buy some new steel.
Just my $.02
 
just to clarify my question, this isn't a matter of which steel is better or safer to use...i have brand new 5160, 1084 and 1095 and i have old leaf spring, coil springs, etc. no shortage of steel...

i'm just curious about the structure and properties of steel here...when forging, we talk about normalizing steel to "take out the stress" accumulated in the forging process...i'm just wondering how far this "taking out the stress" goes...will it take out the stress of riding on leaf springs for 30 years?
 
stress to the point of cracking will not be taken out by thermal treatments.

But the stress that is induced during forgeing can be removed/reprogrammed by these treatments.

Some old leaf spring will actually have a memory of it's original shape (banana)and return to that shape after forgeing, normalize, anneal, harden and temp. Why? I dunno.

Stress cracks in old leaf springs can be seen as you bring the steel up to temp, a series of blue lines will appear if the stuff is heated slowly.

REG is right the less stressed part of the spring is the best. I always grind off the outside of the steel spring, that's where the rust and crud is anyway and the cracks will show up there from the heat of the grinding wheel.

So the answer to your question is yes/no and maybe.

There are a bunch of variables in the old springs, like was it driven by the Dukes of Hazard or Aunt Janice, Northern or Southern climate. Salt has a lot to do with stres cracking also.
 
i'm just curious about the structure and properties of steel here...when forging, we talk about normalizing steel to "take out the stress" accumulated in the forging process...i'm just wondering how far this "taking out the stress" goes
Click to expand...

You have a good question. There are limits. But it will depend on a specific scenario. I'll try and point out some things, but it actually can get REALLY complicated because of so many variables.

"Stress" can mean a few things. If you mean an actual fracture, forget it. You need to do some drastic work. I.e. re-smelting, MAYBE you can get away with some serious forge welding. If you mean random grain sizes from hot working or strained grains from cold work, those grains can be re-homogenized through most processes that surpasse Ac1 and held until equilibrium, then cooled.

In the case of a spring, you will see stress do to both stretching and compression. These stresses, over time will cause deformation of the grains. If that is all that ever happens to the spring, you must use the aforementioned method to recrystallize the grains and return them to an unstressed or considerably less stressed state. In many cases, this could be as simple as heat, quench (oil or water for example) and temper. However, if you are working the steel a hell of a lot, with many, many heats, it wouldn't hurt to give it a good, full anneal prior to hardening.

-Jason
 
Wow... Good thread. Thanks all for the contributions, this is mighty interesting. Steel is weird stuff...

For 5160 (and probably for most other steels), I'd think that it would be a good idea to first cycle the bar at least 3 times. It cannot hurt, and it will refine grains, reduce stresses, etc.

Folding & forge welding, followed by a good cycling (always necessary after forging anyway), should take care of the banana effect, I would think?

JD
 
Originally posted by Alarion
I found some shear blades from which I plan to grind or forge some knives, but they'll have to wait till I have the way to cut them (heat treated hard steel, not good to cut by hand :D)
Click to expand...

Sounds like you need someone with a cutting torch...
 
I don't think it would do any good to cyle the steel before forgeing.

The forgeing temp should wipe that out. Of course now that I think about it. With the memory phenomenon maybe it would be a good thing to try.



Talking *RTS here

* Rusty Truck Springs (may or may not be 5160)

I talked to spring shop once,asking for some 5160. He said we got it but it's mixed with the 1095. When they get a shipment in they take the cert papers and file 13, then stick it all in one stack..


*Life is like a box of chocolates you never know what you are going to get.

* same for junkyard steel

I'm not opposed to using it for somethings coil springs make great tooling, tongs etc.
 
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