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The old leaf spring debate

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The springs I have are hard a heck..bit I still don't know what kind of steel they are can anyone help...my quench is hit and miss for hardness and and I'm getting cracks on the backbone(2of 3)...my oil is hot and my steel is non magnetic at quench...and I annealed twice...

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"Generally", broadly, leaf springs are probably 5160 or something very close and can be treated as such.

About the cracking,

What type of oil are you using ?

What temperature are you tempering at ?

Are you sure you are not, (assuming you are forging and not stock removing) hitting the steel when it is too cold?

The reason I ask the last two questions are because ,

"Non-magnetic" is not the point at which you need to quench. You want to reach a higher point called "decalescence". If you aren't getting there then it's hard to think, that with any decent tempering temperature, the hardening and tempering could be the culprit.

Have you read the "So you want to make a knife" thread pinned at the top of this section yet ?

 

 

 

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One thing you have to know about leafsprings, particularly heavy loaded ones from cars/trucks, is that they suffer from metal fatigue. Metal fatigue is basically cracks forming, starting at the edges, holes etc. These start as tiny hairline cracks as soon as the springs start being used, and slowly grow throughout the use. Normally they should stay quite small, but there may be more significant cracks in there. Now if you forge, these can open up.

Also, how hot are you forging? If you forge too cold, then you can get cracks. The worst thing you can do is straighten a piece out just before putting it back in the forge. On the other hand, if you keep the steel very hot for a long time, you get grain growth. This makes the steel more prone to cracking during forging, in particular the if you do the former.

Annealing twice sounds insufficient. You need to go through at least 3 normalizing cycles. Break one of the cracked blades, and it can tell you a lot. What does the grain look like? And what does it look like at the crack? Is it significantly more coarse there, and/or oxidized? Then the crack was was in there before you annealed and quenched.

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It's hard to tell from what you've given us but I would guess  that  Jeroen is  correct and you've worked the steel at either too  high or too  low a temperature.  Take his advice and bend one of the blades until it breaks and show us a picture of the break.  We  will probably be able  to tell you more then. 

This is another good example for not using used, mystery steel as  well.   Another test that you might try doing is to  do exactly the same thing with a new piece of 5160 and see how  it  turns  out.  When you  use used steel,  you will never know 100% if it's you or if the problem was in the steel.

Do some reading on normalizing steel.  You don't need or want to  do any annealing but the normalizing is a must for anyone who forges their blades.

Don't let this frustrate you.  We've all been there.  It's just part of the  learning curve.

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What Gary said... did you anneal (reaching critical then slowly, as in hours, cooled down) or normalize (reaching critical then air cooling to black)? 

Annealing causes grain growth, so if you annealed twice before quenching, that grain is going to be way to big for optimal performance. 

I second micro cracks/ metal fatigue being the likely issue, or cold forging temps perhaps. But break one of those blades and let us see the grain. 

 

Edit : here is the annealing process for 5160 (assuming youre working with 5160) the source is the HTS Heat Treaters Guide. This type of accuracy requires a kiln or heat treating oven. I know i cant cool at 10°/hour in my charcoal forge! Lol! 

20180328_081921.png

 

Edited by Will W.
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My opinion on using "Found Steel", in this case leaf springs.  How much is your time and effort worth? 

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If you have nothing else, whether due to finances or location, it's worth every ounce of effort and every drop of sweat.

Thanks again for the info guys, I bought a small multi meter that can measure up to 1000C this week, and I hope to "play" around a bit with the leafspring I have to nail my process down.

 

Just another question, except for cracks, what would be the indications of a mediocre heat treat and maybe too large grain size on a leaf spring blade?

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It's not the cheap option. Steel is cheap, fuel isn't (unless you can make your own fuel, or use waste oil as fuel f.e.). So it will generally cost you more when using scrap metal, particularly if you have failures because of it. You should only use scrap if you like the challenge of making something out of scrap, and are willing to pay the price. Just like people who like making steel from ore. That's not the cheap option either, eventhough you don't have to buy any steel at all.

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6mmx40mm 5160 is relatively cheap in South Africa, if I import any I start by paying 31% tax $45-85 for transport.

I would really like some of that, and I could kill for some 108x or 80crv2....all extremely unlikely considering the cost.

That said, I do get a lot of satisfaction making a knife that will outlast me from discarded and unwanted "scrap".....

Just want to point out to the anti-mystery_steel_gang that while your advice is on point and correct, it might demotivate somebody just starting on this journey.

My DIY gas forge is running great, forged till I was tired on Saturday and the 9kg LPG bottle still had a lot left.  Same day I bought a 19Kg LPG bottle just in case, that was about $90.

So for me, gas for several days forging costs the same as just the transport to get steel in the country......not the tax, not the actual steel.......

For $4.20 I get a bag of hardwood charcoal that can last me a day.

So I guess, here at least, fuel is cheap and steel is expensive.

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6 hours ago, Gerhard said:

If you have nothing else, whether due to finances or location, it's worth every ounce of effort and every drop of sweat.

Thanks again for the info guys, I bought a small multi meter that can measure up to 1000C this week, and I hope to "play" around a bit with the leafspring I have to nail my process down.

 

Just another question, except for cracks, what would be the indications of a mediocre heat treat and maybe too large grain size on a leaf spring blade?

Yes, and had it been you asking the question, because of your location, I wouldn't have wrote that.  However, even thought the OP hasn't given his location, the chances are high that he is living in a industrial country.   Here in the US, I can buy a 4 foot length of 1 1/2 by 1/4 5160 for under $30.  

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3 hours ago, Gerhard said:

6mmx40mm 5160 is relatively cheap in South Africa, if I import any I start by paying 31% tax $45-85 for transport.

I would really like some of that, and I could kill for some 108x or 80crv2....all extremely unlikely considering the cost.

 

Quick question...is that just if you purchase it from a commercial source? I.e., would your fees be different if, say, a friend from the forum were able to chop some pieces of steel down and send them your way via international mail or DHL or something?

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9 hours ago, Gerhard said:

 

Just another question, except for cracks, what would be the indications of a mediocre heat treat and maybe too large grain size on a leaf spring blade?

About the only way to tell is by (potentially) destructive testing.  The brass rod test, which consists of pressing the very edge flat across a brass rod, will tell you a lot.  If the edge chips, it was too hard or the grain was too large.  If it flexes and returns to true you did a good job.  If it flexes and stays bent it was too soft.  Once you've done that, take the ones that chipped or stayed bent and break the blade in two to see the grain.

If you have a metallurgical microscope lying about the house, you can also polish a spot and etch with nital to see the actual grain boundaries, but I only know one guy (Kevin Cashen) who has that setup at home.  He also has an electron microscope...:ph34r:

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55 minutes ago, Alan Longmire said:

but I only know one guy (Kevin Cashen) who has that setup at home. 

Well, you know me too (at least via the forum)!  B)  Technically it is packed up until the new house/shop is built, but I have it!  

I don't have a SEM though, nor would I want one.  I've logged a couple hundred hours on one, that is some tedious stuff.  

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Cracks are fairly common (I had a big ol one that I had to chuck because of them), but easy to spot when you start working. 

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7 hours ago, Gerhard said:

 

Just want to point out to the anti-mystery_steel_gang that while your advice is on point and correct, it might demotivate somebody just starting on this journey.

...............

I agree with you about both the satisfaction from using discarded steel and your point about discouraging beginners. I am guilty of taking for granted the fact that we, in the U.S. have so many options. That and, where I live, it is actually easier and no more expensive for me to order new steel than to set out on a search for recyclable. That being said it is still, for someone who does have easy access to new steel, it is IMO much better to take advantage of it. Look at your own struggles with mystery steel. That too could be discouraging itself. Nonetheless it is a rather gauche faux pas on my part to automatically assume everyone has an Aldo Bruno and brown truck just a phone call away. 

I'd just kind of like to see our screen names include some clue as to our location so we don't have to go to the profile to discover/remind that we are talking to someone in different circumstances.

I remember the "pre internet" days when salvaged steel was my world. It wasn't just that it was harder to get new steel it was also a lot harder to find out what to do with ANY steel. At least now there is a forum where you can get advice about it. 

 

 

 

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18 minutes ago, Vern Wimmer said:

 

I'd just kind of like to see our screen names include some clue as to our location so we don't have to go to the profile to discover/remind that we are talking to someone in different circumstances.

 

If you had a laptop or desktop PC you could see that just under the avatar.  I too wish the mobile version showed more, but it's what we've got.  

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27 minutes ago, Vern Wimmer said:

I remember the "pre internet" days when salvaged steel was my world. It wasn't just that it was harder to get new steel it was also a lot harder to find out what to do with ANY steel. At least now there is a forum where you can get advice about it. 

 

Have to go here:  Library?

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I think the topic comes up so much because springs are the most exciting form of steel stock and we have to talk some sense into ourselves when springs are mentioned so that we dont go tresspassing to get a spring we saw on an abandonded train car 15 years ago even though it was about 1" diameter and nobody would waste their time on a piece of metal so its probably still there.....

If a simple heat treat doesnt work well enough then dont use that steel, but you can know what a steel is and still not be able to heat treat it correctly,  if my bar of wrought iron doesnt forge well do I just leave it in a drawer?  

I have used blades that werent totally hard and I never noticed until I chopped into a nail, even a low quality knife is an incredible tool if you make it yourself. My best hardest sharpest blade was a drill bit.

It may not be the "best" but it still can be desirable.

Like how bladeforums has more members and pictures but here you dont have any jerks calling everybodies knives paperweights just because they can make a distal taper with a grinder, not even a complex one, which you dont always need on anything shorter than 12" anyways (but it looks nice). Who knows what would happen to the world if you had to swing something balanced like a hammer. Naginata and seax can be thickest closer to the tip than the tang, and if you made a bowie knife that way it would be that way too.

So to sum it up, springs are wonderful, we all want to make better knives, and we want eachother to make better knives, but we all have our own ideas about what is best. as long as we dont just say "NO" we are on the right track.

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^^^^^^

We actually have a pretty definitive basic test for mystery steels if we can convince folks to take the time to hammer out a test, or a couple of test coupons, just quench and break them. Answers a lot of questions right there.

BTW almost every knife I have made has less than a 6" blade and are not "FIF Choppers" and I can't remember the last one that didn't have a distal taper. The distal taper combined with edge geometry is a key factor in how a hunting knife performs in use. 

 

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47 minutes ago, Alan Longmire said:

If you had a laptop or desktop PC you could see that just under the avatar.  I too wish the mobile version showed more, but it's what we've got.  

Ah well, and I thought I was being "state of the art" by breaking free of a laptop and relying on this communicator/tricorder thingie wingie.

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I have to add that I almost exclusively recycle steel myself. Most of the hardenable steel I've used are antique leaf springs from hand carts that were used in the early 20th century in my city. I got a whole pile of them for only a few euros. I also use wrought iron that comes from 17th, 18th century buildings from my city that have been renovated. I've even used some broken springs from an antique bicycle saddle that I've restored. I enjoy using materials with a history. Nice thing even that with the old leaf springs, occasionally one is shear steel too. Since these were not as highly loaded as car springs, I don't have any problems with cracks in them. A lot of rust pits though, so I have to flatten the surface before forging them, but after that, they are fine. Never had a problem quenching them either.

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P.s. I don't use most of the blades that I've forged from the leaf springs, except for a kitchen knife. That one is a lot better then the commercial ones that I use (stainless). It just stays sharp much much longer.

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I occasionally check my local spring shop. You will often find "off cuts" of new stock used in making up orders. Sometimes it's pretty heavy- that being said, I have a press and it's neat sometimes to see a 3-foot sword emerging from a one-foot bar of heavy stock.

This being said, I've used a lot of scrap spring. I can usually tell if it's going to be bad within a few minutes of forging- cracks will start showing up. This has been pretty rare, though. I've made a number of blades from this stuff and tested them pretty abusively and they've held up well. 

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When I first started out, I didn't have any money. I was in highschool. So, on the weekends I would search around Pawpaw's  (grandfather's) farm, the train tracks, garages for old junk. 

I have to say It was way more fun to go hunting for metal. Climbing over and digging through piles of rusty treasure just has a certain allure. You would be suprised how many cool pieces of firewood I found for handles, and shed antlers, even a turtle shell. 

Now that I buy my high carbon steel, I just hunt for wrought, and non ferrouse. But, if I wasn't after hamons and good welding steel; you can bet your buns I would be using springs, axles, and bearings for it all. 

Nevermind the anti scrap Nazis. Do what you love and make an adventure out of it. Just do as Vern suggests and learn the properties of the steel via tests before making a blade from it. 

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I got my start with Leaf Springs as I have access to a nearly limitless supply of them ( my dad and kid sister are big into drag racing so I get all their old springs, and their friends old springs as well. ) and even though I have moved on to known steel for anything I intend to sell, I still use leaf spring any time I attempt to forge something I have never tried before rather then waste my good steel. 



 

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