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Leaf Spring Thread?High Carbon Steel Thread (Beginner questions)


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Hey guys, I don't know whether this exists already but I figured I'd just go ahead and start one.

Anyways, I have a couple questions. Around 6ish years ago (I'm 18 now) when I first tried blacksmithing, my dad was running a "Build Camp" for kids. We have a large shop and almost all the tools you could ever need including many machines. For this camp, we decided to try blacksmithing, building a forge and trying to make something. My dad had done a little bit when he was a teen, but still, he didn't really know what he was doing, he just had a basic knowledge of it. It was still fun, everyone enjoyed it and we all learned something anyways which is the important part. 

So, in regards to this topic, when we hosted that build camp we tried making some small "Tomahawks" out of leaf spring. First off we never really got the stell that hot, maybe just barely an almost bright cherry. And we weren't making quality tomahawks, just a little thing the kids could take home. 

Needless to say they were all trash. Ugly, pine dowel handles, not flat at all and just... Bad. But for kids it was still freaking awesome. 

I remember some of them cracking. and breaking and such because we weren't heat treating the steel right I don't think. So I think my question is, do I need to handle leaf spring steel delicately? I have never really worked with high carbon steel, just mild steels so far. I might just need some overall tips on how to handle high carbon steel without cracking it, breaking it, making a situation that seems fit for a string of profanities, etc. 

I plan to try making a wrapped tomahawk head, a real one, from a leaf spring. After I read all the threads on here about forge welding first. And all the heat treating forums too.

 

I believe that is what I want to ask, I just need some advice on handling high carbon steels. (Also, a thought, if I ever have to leave a high carbon piece to finish later, it would be best to leave it in the coals wouldn't it? So it doesn't cool down so fast?... This is the kind of stuff I'm asking about. Thanks!)

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Lots to go through here:  may I point out that "bright cherry" is an ORANGE colour---they were referring to PIE cherries back then not Bing cherries.  Bright cherry would be a decent temp for 5160.  Red would be low.

Biggest issues in working with HC steel is forging temps: too hot it burns, too cold it cracks. Many people starting out will manage to do both on the same heat!

Heat treating: quench in warm vegetable oil and temper immediately---did you do so and if so what temperature did you temper too?  (Hawk for kids---I'd probably go with *blue*!)

Note that 5160 can be difficult to weld to itself.  Be good at welding before trying it.  Sometimes an intermediate layer of plain steel can do the trick.

I generally make small hawks from farrier's rasps using the fold and forge weld method.  Get friendly with a farrier and you may be deluged with worn out rasps. (At one Quad-State I saw used Farrier's rasps being sold anywhere from US$3 to 50 UScents apiece.  Guess where I bought 20 of them!)

I try not to teach things I'm not already skilled in.  I've had to "un-teach" a lot of stuff with students who have "learned" on the net.

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I'm looking through the heat treating stuff, just need to study it over and over now. When you say tempering to the color blue you are talking about to color/temperature spectrum right? I have a book... The Modern Blacksmith? I think? I can't remember the name but it is very informative. It talks about heat treating and tempering, but it really only mostly talks about the scratch/watch the color/quench method of tempering.

If I am thinking of this right, after I quench my piece I would stick it in the oven for an hour, And like Steve has said in one of his posts let it cool and sit for a day and then temper it for another hour. What should the oven temperature be? And do I just leave it in the oven until it turns the wanted color?  

Also is 5150 the steel number for most leaf springs? 

And yeah, definitely. It wasn't so much about learning blacksmithing then it was just introducing kids to building something, welding, grinding and building things.

Also, I don't want to try to be spoonfed, so if I'm asking too many redundant questions I apologize. I just like having conversations with people and learning from them.

Okay, I just went over Steve's heat treating post again. He says 320F-350F. I take it that just depending on the temperature and how long you leave it in, the softness/hardness will vary with it? Is this just something that you have to get a feel for and decide which "Recipe" you like best?

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The colour correlates to the temperature.  You choose tempering temps based on Alloy, intended use, design and personal preferences.  Temper 5160, a common automotive spring alloy, to 320 to 350F for a hawk and it will break in common use!  Making a pocket knife it would be fine; I'd go a bit hotter for a big  camp knife that sees a lot of abuse, etc.  Time once it reaches temp does not change it's hardness much in small amounts; I don't hold at temp long enough to make a difference myself.

Doing several tempering cycles is suggested; but after it has cooled to ambient is fine; *except* the first cycle should start ASAP after quenching!

AND BEWARE most ovens have fluctuating temps and may go higher in their cycle than you want!

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Okay. Me and my dad have plans to eventually build a heat treating oven. I just searched it up, and google says to temper 5160 at 375F-400F. 

So now I have another question, is that number found on google just what you would temper 5160 at? Or are there different temperatures that 5160 can be tempered at?  

Simplifying the question, is the tempering temperature that I'll find on google for whatever steel I may be using just the set temp for that steel? That's the temp for everything you might use the steel for?

Also you're saying that the time it is tempered doesn't really matter, as long as it is long enough the relieve the stress on the steel (1-3 hours?)

Also I'm adding this on, but I am currently at school (I'm enrolled in a technical college learning CNC machining) and my instructor just gave me a Metallurgy Fundamentals book. This ought to help a lot too, perfect timing. =D

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Different steels, different temperatures, different times, and different properties. Get to know that metallurgy book, it will all start to make sense... (I personally loved my materials classes back in college. It was one of the things that just came naturally to me.)

And, yes, the same steel can be tempered differently for different properties, but only within the range of that specific steel. Different leaf springs, can and are made out of different steel. Best thing to do is test any unknown steels.

David

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Basic old school testing would be to take a number of coupons of the same steel and test what to quench in, what temperature to quench at, what temperature to temper at.  The quench test is usually to break the test piece and examine the grain structure by eye, you want fine grain (and no cracking in the quench). You can then try what is the best starting temp for quenching and having determined the proper temp and quenchant try various tempering temps to see which one gives you the properties you want.

Note I've met a number of BNBs  (Big Name Bladesmiths) over the years and their heat treating guides are usually about 1/2 inserts of their notes on how to modify what the book says to use that alloy for blades.  Book recommendations are generally based on 1 inch cross sections.  If your blades have a 1" cross section when quenched; you are having more issues than just heat treat!

Sad to say there is no one answer to any of this.  Even for blades the temp you temper a razor to is NOT the temp you temper a hunting knife to is NOT the temperature you temper an axe to.  Even the same blade design in the same alloy may be tempered to different temps based on the preferences of the end user.

So to start out: know what alloy you are using; make notes on how you did things; test and draw conclusions!

This is why I suggest folks starting knifemaking take a low miles auto/truck coil spring and  cut it down the diameter getting a bunch of "(" pieces that they can then forge and test the same steel until they get it down pat.  Only then add in and learn a second steel and keeping notes progress along the darkling path...

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