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5160 leaf springs quenching and tempering


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I'm new to metal working and recently acquired leaf springs from my old truck. I'm pretty sure that they are 5160 spring steel. And I was wondering what temperature would be ideal for working a tough steel like this. I plan on making knifes and swords( at least I'm going to try). I would also be grateful if someone could tell me what temperature is best to temper them at. Thanks!

Also is it better to quench in oil or water for 5160?

Edited by Phillip Gentry
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I would always recommend to quench in oil with regular carbon steels.  The old Japanese swordsmiths considered a 25% failure rate with quenching in water to be normal.  If you are using a steel that will not quench in a fast oil I'd recommend that you get another steel.

As far as the steel in the springs go there is a fair chance that it's 5160.  There's also not a bad chance that it's 1095.  It could be something else too.  If you want to assume that it is 5160 then slowly heat the blade until it just becomes non-magnetic and then heat it just a little more then quench.  Temper for two one hour cycles at 375°.

Doug

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The springs are most likely 5160 if the truck is less than 30 years old, but even then they may be something else.  The key here is that whatever it is it has to respond to the same heat treatment recipe as 5160 in such a way as to make a functional leaf spring.  This means no matter if they are 5160, 9260, 6150, or 1075 they'll work if you follow the same steps and temperatures.  

So: forge between around 1900 degrees F down to around 1700 degrees F, or a bright yellow down to medium orange in dim light.  This helps prevent cracks. Normalize after forging by bringing it to around 1550 degrees F (a low red in dim light) and letting it air cool to totally black in the dark.  Do this three times.  This refines the grain you allowed to grow while forging at higher temperatures.

If you can watch the blade, you'll know it has achieved the phase transformation necessary by observing the swirling shadows in the steel as it comes up to heat.  The phase change takes energy, which means the bright blade will darken a bit.  This is the shadows.  As soon as they are gone, you know the transpormation is complete and you are ready to either air cool to normalize or quench to harden.  Note that the phase change happens at 1525-1550 degrees F in 5160, while all steels go nonmagnetic at 1425 F.  So a magnet can get you close, but you need about a hundred degrees hotter. Don't try to hold it at heat, it does not benefit from soaking.

Always quench 5160 in oil.  It will crack in water, period.  Mineral oil, canola oil, peanut oil, actual quenching oils, but never motor oil, especially used motor oil. It has stuff added that can ruin a quench, especially used motor oil which almost always has water in it.  Heat your oil to around 130 degrees F, just hot enough you don't want to leave your finger in it more than a second or so.  You can do this by repeatedly quenching a big chunk of scrap mild steel. This speeds up the quench, oddly enough.

Always quench blades edge first or point first, and do not swirl it around or it will warp.

Now then, tempering: this depends on what the blade needs to be able to do.  Small knives are fine baked at 350-375 degrees for two cycles of an hour each. This gives great edge holding ability at the expense of flexibilty and impact resistance. 400 is good for bigger knives, 450 for small axes and really big knives for greater impact resistance at the expense of a little edge-holding ability. Swords need flexibility and impact resistance more than anything else, so they need a full spring temper of anywhere from 575 to 700 degrees, depending on the type of sword.

Temper as soon as possible after quenching in a preheated oven using a good oven thermometer (your oven itself will cycle lower and higher than the set temperature by up to 75 degrees either way, with potentially poor results). A pan of dry sand or a couple of bricks in the oven will add thermal mass and help minimize the temperature swings.  Be sure to clean the oil off the blade and wrap the bricks in foil if you're using your kitchen oven so you can be allowed to do so again if you're married.

That's the basics.  There are loads of variations for different purposes.  Look around the site, you'll find a lot of info on this.

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