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  #1  
Old 12-21-2003, 10:11 AM
Bearman Knives Bearman Knives is offline
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Fixing stress fractures in leaf spring steel

Hi guys,
Since realising that stress fractures might be a real problem in the leaf spring steel I want to use (some of this spring steel could be quite old. The stuff I'm thinking of using goes back to 1948) I've found a thread that suggests heating to welding temp. followed by light hammering and then allowing the steel to cool to room temp. This proccess to be repeated three times he claims will eliminate any potential problems and also get rid of the 'memory'.
I've heard of steel memory but I'm not sure what it means.

Can I throw this out to you guys - what do you think? When I eventually start forging this stuff is there any way I could test this?
If I could cause stress fractures in the spring steel, see how it breaks and then cause more fractures in another piece of steel, do the welding heat thing and then see how that breaks it should prove/disprove - yes? But then how do I cause stress fractures? Do you think this would work?

Bear


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  #2  
Old 12-21-2003, 11:31 AM
cactusforge cactusforge is offline
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First of all stress fractures are one of the reasons I use virgin steel, I got tired of finding the cracks after working on a blade for quite a while then finding the crack and junking the piece.
I don't think that the welding trick will work. Memory is when a spring remembers it's curve and goes back to it when cold and some times it won't EVER straighten out. I have had this happen
and nothing I did to straighten it out worked and I did every thing I could think of, Forging won't, annealing won't, normalizing won't. Another reason to use virgin steel. The only suggestion in using old leaf springs and yes I will use them sometimes is to tell the customer what you used. And never even try to use a spring that has been broken or came from a spring pack that has been broken or over stressed and straightened out. Be very picky. Gib


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  #3  
Old 12-22-2003, 12:23 AM
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Sweany Sweany is offline
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Ya fix the cracks by cutting em out.

Cracks in the old leaf springs will show up as a little dark crack line at a red heat.


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Old 12-22-2003, 08:04 AM
Bearman Knives Bearman Knives is offline
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Thanks for your thoughts guys,

Sweany, will fractures always show on the surface?

Thanks,

Bear


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Old 12-22-2003, 09:11 AM
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MaxTheKnife MaxTheKnife is offline
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It works just like Sweany said Bear. The cracks will show up as a thin, dark line on a spring that's heated up to a bright red and viewed in a dark place like under the forge. Think of it like this and it might help. The crack wants to cool faster than the solid steel so the edges of the crack, as small as they are, will get dark shortly after taking the spring out of the fire because of the faster cooling. You have to do this in a fairly dark place. That's me, a crack inspector. 5160 spring steel is all I've been using lately besides the odd file here and there. When you find a crack, do like Sweany says and just cut that section out of the spring. Mark it with a file or chalk marker before all the color goes out of the steel. Sometimes you get lucky and it's right in the middle of the spring going lengthwise. That's good because you can split the spring in half and have two slabs of steel to make knives from. I stopped buying knife steel a couple of years ago because I've had such good luck with leaf springs. Like Gib said, you need to avoid the 'sprung' leaf springs because cracks are usually what cause them to spring in the first place. Trying to weld the stress cracks back together sounds like an excercise in futility to me. Who knows how long the cracks have been there? And besides, 5160 just doesn't want to weld to itself in my experience. And believe me, I've tried many times. It must take a special flux or something. Or maybe a blacksmith's incantation at the right phase of the moon. Good luck with your leaf spring project and don't automatically assume that those old springs are going to be full of stress cracks. Do your homework and inspect for cracks as you use it. Some of that old steel is the closest we're likely to come to 'virgin' steel these days. There's alot of truth in that statement if you look at it close.

Last edited by MaxTheKnife; 12-22-2003 at 09:14 AM.
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  #6  
Old 12-22-2003, 10:21 AM
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Jeff Higgins Jeff Higgins is offline
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I'll have to say I'm with Gib on this one. New steel eliminates that stress situation, but then again, may have more inclusions (?). Another subject entirely, I guess. I like to use new steel when I can, but lucking out on an old truck or tractor in the woods and cutting out the springs is priceless, and I won't pass up on them. My expectations for a successful forging just can't be as high.

I don't subscribe to the "thrice this" and "triple-that" methodology, but I do take some precautions when preparing spring steel for forging.


1) Heat the spring to non-magnetic and then anneal it. I use a 50-50 mix of poplar ash and vermiculite. I always keep a steel tub of this close to my heat source, just so it stays dry. I try to do this before I cut it to size. Some folks will heat a spring up, hot-cut it to size, and THEN anneal. I think this starts the spring out with some stress, and I believe any stresses in the steel will cause a crack right then and there because the steel hasn't had any "relief" before it gets slammed with the hammer and chisel!

2) Normalize BEFORE forging.

I don't get too many cracks doing this, and the outcome is almost predictable.


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Old 12-22-2003, 11:19 AM
Bearman Knives Bearman Knives is offline
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Thanks guys.

Max,
When you say 'sprung' do you mean when the leaf spring has failed and lost it's 'springyness'?

Changing the subject a little guys, I've had a short leaf in a camp fire in my garden several times now. We build a fire and sit around with a beer - you know, I've been just throwing it in and leaving it there ( it's the shortest leaf from a heavy duty spring, it's about 9 inches long 2 inches wide and a 1/4 thick). It gets to a dull yellow heat and eventually disappears into the base of the fire.
Anyway, I must have done this a dozen times by now, do you think it would be okay to forge this leaf or would it have lost too much carbon as a result of multiple heatings?

Thanks,

Bear


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Old 12-23-2003, 08:24 AM
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Yes Bear. What I meant by sprung is just that. When the spring has been overflexed and didn't go back to it's original shape. That will most likely result in stress cracks, usually near the mount hole in the center of the spring. As long as they're lengthwise it's no big deal. If they go across the width of the spring I'd cut out the whole center or not even use that spring at all.

As to the leaf you've had in the fire a dozen times..... I would say that you now have a mostly iron leaf spring. At the very least, it's probably one of the most relaxed pieces of steel I've heard of. All you can do is get it to non magnetic and quench it in warm oil to see if it still has any carbon left in it. It's likely to be a spongy mass of iron though in my opinion. The grain may have grown to the point of no return. Give it a quench test and see if it gets hard. Or just leave it right there in the fire and see how long it takes to burn completely up. It will probably be a waste of time to fool with it. But you'll never know unless you try.
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Old 12-23-2003, 09:07 AM
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Jeff Higgins Jeff Higgins is offline
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Hey Bear, that leaf spring you've heated so much would make wonderful furniture for any knife. Don't throw it out!


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Old 12-23-2003, 10:32 AM
BDK BDK is offline
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i learn something every time i get on here, aint this place great.

thanks for the great tip max. i never thought of heating the spring to a red heat and then looking for the cracks. ive never had a problem using leaf springs myself. ionly use springs that look in good shape and from older cars and trucks.

ive also had a problem welding 5160 so id say fixxing the stess cracks would be hard . boo


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Old 12-24-2003, 07:55 AM
Bearman Knives Bearman Knives is offline
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Thanks guys,
I'll do that quench test - you never know...

Jeff,
What did you mean when you say the steel would make 'wonderful furniture for any knife.'

Merry Christmas to you all!

Bear


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  #12  
Old 12-24-2003, 08:54 AM
paul harm paul harm is offline
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guards, pommels- if you're makin old style knives- it looks great. paul
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  #13  
Old 12-24-2003, 11:08 AM
Bearman Knives Bearman Knives is offline
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Oh yes...I should have known that - thanks.

Bear


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  #14  
Old 12-29-2003, 01:25 PM
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Jeff Higgins Jeff Higgins is offline
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Yeah, what Paul said!


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  #15  
Old 11-29-2017, 09:48 AM
Benjimon Benjimon is offline
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Do you have a link to the thread about heating to welding temp to fix stress fractures? Also did you ever try to harden the campfire leafspring? How did it turn out?
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