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Jonny C

Unquenchable leaf springs

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I believe similar threads have already been posted but I’m curious if someone out there is familiar with what kind of spring steel this could be and possibly how to harden it, I recently acquired a stack of thick leaf springs that look like they came off of a trailer, being a rookie I instantly went to work at forging some big bad blades and to my dismay I was unable to harden them in quench, neither in oil nor water, any insight or suggestions? Thanks

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Hmm, that isn't much info to go off of. 

What temperature did you have the steel at when you tried to quench?  Were you simply testing for hardness with a file?

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After failing to harden a blade I had forged I cut multiple test pieces and attempted to harden them, at different temperatures, in cold oil, hot oil, cold water, and hot water, all test pieces were above non magnetic, some well above non magnetic, even approaching forge welding tempratures, all with roughly the same result, I tested with files, ball bearing bounce, and hammer blows, the steel did not become brittle, though one test piece quenched in cold water seemed to harden superficially , but I may have been kidding myself 

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I’m fairly new to this and am working with very primitive equipment, but I have had great results quenching other steels, these leaf springs are making me scratch my head though, they were free so I’m not heartbroken if I can’t use them but if there was something fundamental that I’m missing I’d gratefully accept any advice 

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I attempted to quench this blade 4 times and was very careful with decarb and kept it to a minimum, also the blade was normalized between quenches and I observed recalescence and quenched at varying temperatures 

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I am told granger can test and tell ya what the steel is for about 100.00

Non magnetic is 1425 if I am not mistaken. your 10xx steels harden at 1475-1500*

1550 is more like 1550-1600...a magnet isnt much help there.

I have had decarb fool me more than once. Try and toss it on the grinder for a pass or 5 before the file test.

How does it spark test.?

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It sparked pretty good actually, and I was real careful about decarb, I have no accurate way of getting an actual temperature but most of my test pieces were well above non magnetic, I’ll try putting on the grinder like you said, is it possible for steel to deep harden but stay soft on the surface?

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If anything I’d expect the opposite, like a 1095 that would harden on the surface or in thin spots but not harden deep

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Yes, it's possible.  If you run an overly oxidizing OR overly reducing atmosphere in the forge (gas, solid fuel, or electric) the surface of the steel will lose carbon.  This is called decarburization, or decarb for short.  The amount and depth depends on the alloy and the time at heat, and also how hot.  With a long heat or a high heat or several heating cycles it's easy to get a soft skin of pure iron a few thousandth of an inch deep.  That's why people always tell you to leave the edge of a blade as thick as a dime when you heat-treat it.  Not only does this help with warping, it gives you enough room to grind off a layer of decarb.  

Of course, the steel may also be some kind of low carbon alloy.  If it were 5160 it should have cracked when quenched in cold water.

Forge out a long thin (say 1/4" square) rod of it, do all your normalizations, quench it,  and start breaking off pieces of it.  It should snap like glass.  If it bends, it's some strange alloy not suitable for blades.

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Thank you for the advice! I did heat this blade multiple times and I only ground the surface briefly before trying a file on it, I’ll try your advice, thanks everyone for taking the time to respond to a greenhorn 

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Well, I was looking to see if you got it hot enough, and if decarb was fooling you, but you seem to have covered those bases.  I'll be curious to hear how your other testing goes.

I'm a little shocked that a leaf spring is made out of something that doesn't harden at all.  With my limited knowledge, I would have expected at least a mid-level carbon content.

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Well I just managed to get a very thin piece of the steel to harden, I quenched it in cold water while the steel was yellow hot and there doesn’t appear to be any cracking 

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Break it and check the grain size.  Yellow is probably too hot be a few hundred degrees.  

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Yes it has large grain, and not as brittle as I would have expected, weird stuff, just crappy metal I guess? Old timers at the wrecking yard figure the springs were from a golf cart or something similar 

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Just returned from the wrecking yard with some good looking coil springs and a big old black diamond rasp....I should think I’ll have better luck with this steel lol thanks for everyone’s advice

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Have you ever given using a known alloy consideration?  You don't have to be guessing at things all the time and you can get consistent results batch to batch.  Just a thought.

Doug

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