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I REALLY Need Help With 5160 Steel Heat Treating and Tempering


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Hi!

 

I have some questions and I really need some help. I did a bunch of searches, spent countless hours researching on the internet and I keep hearing different things. My brain and my eyes hurt. Can someone be so kind to answer some of my questions that have been driving me insane? You probably get these questions often but I cant find answers and I really need help.

 

5160 Spring Steel Heating and Tempering Process

 

Normalizing

What heat and for how long? I hear people do this multiple times and others just once.

 

Annealing

What heat, how long and how? I’ve heard some say air cool and others in vermiculite. Is this a critical step or can it be skipped?

 

Harden

I heard 1650F. But for how long, how long do I quench it for?)

 

Temper

I heard between 375-400, but for how long? Do I let it air cool after?

 

What kind of oil do I quench it in?

 

Thanks!

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That is one of the two main steels I have used over the years. My process is a bit different then what is "forum correct" and posting it would just start a debate. Check PM's.

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To start off with, let me recommend The Complete Bladesmith by Jim Hrisoulas. It has the answeres to the question that you've asked and more. As you are finding out, the web has it's limits.

 

1. To normalize, heat the blade to non-magnetic and then get it a little brighter. Hold for a half minute to make sure that the steel is heated all the way through and then remove from the heat and air cool to at least a dark heat. I know that there are those who like to let the blade cool with the blade pointing north but all you will be doing is pointing the blade north. Multiple normalizations are done, usuall three, to correct grain growth that can occure while forging. It will also relieve any stress that has built up during forging or grinding by allowing the crystals to reform. Be careful not to get the steel too hot or you will grow the size of the grain.

 

2. Annealing is like normalizations except that the steel is cooled more slowly in an insulating material, such as vermiculite, or cooled by leaving it in a hot oven/forge as it cools down. The most techinically correct way is to heat it in a heat treating oven and then ramping it down at a given rate to a given temperature and then air cooling. This will disperce the carbide crystals and maximize the softeness of the steel. I don't bother with it. Normalization leave the steel that I use soft enough to grind.

 

3. 1650 seems a little hot for austinizing the steel for hardening. 5160 is a hypoeutectic steel (the carbon is below the saturation point in the austinetic [hot] phase) so it's not as subject to grain growth but why push it. Again, I would take it up to non-magnetic, then a little hotter (brighter) and hold for a minute to make sure the steel is heated throughout. With the lower carbon content there is no reason for a long soak, 5-10 minutes, to disolve carbides.

 

I would quench in vegetable oil that has been pre-heated to around 130 degrees. Plunge the blade in, most do point first, and hold in the quenchant until it's down to where you can hold it for a bit without it becoming too uncomfortable. I do not agitate the blade in the quencchant to avoid warping as much as possible. If you do agitate the blade it is up and down or spine to edge; never side to side. If you are edge quenching, you can put the blade at least 1/3 of the way up the blade into the quenchant and rock it a bit to cool the tip until the color in the spine goes away. Then put the entire blade into the quenchant until cool enough to hold.

 

4. Those temperatures for tempering sound about right but it is something that you will have to test. Do at least two two hour cycles, allowing the blade to return to room temperature between cycles, and a third cycle wouldn't hurt. The repeat cycles causes the retained austinite to convert to martensite and then temper the martenite. Always go by a themometer in your oven, not by the setting on the dial. Tempering with a torch by eye is tricky and often causes a partial temperature. I can't recommend it, especially for a beginner.

 

Test all the blades that you make for proper hardness before putting a handle one the knife, unless you like to remove handles to re-heat treat if it didn't work the first time. Put a rough edge on the blade and see if you can cut into soft iron wire, like bailing wire, or a thin brass rod. There should be no more than a very slight dulling of the edge. If it endents then someting is wrong. If the endentation looks chipped then the temper is too hard and you will need to grind the chip out and then retemper at about 25 degrees higher. If is looks torn or rolled over the it's too soft and it will need to be rehardened and tempered at about 25 degrees lower.

 

One last note of the book that I recommended. It is writen with the blade smith in mind but the grinding, steel selection, heat treatment, and finishing the knife are the same.

 

Doug

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Doug's description is close to what I do with it. I like to harden from around 1550 rather than 1650 for the reasons mentioned. This is about 125 degrees hotter than non-magnetic. My shop space is usually dark enough that I can watch for the appearance of the swirling shadows in the steel that shows the phase change is happening (decalescence/recalescence, look it up!). As soon as the shadows go away I know I'm at the right temperature, so then I quench into warm mineral oil if I'm hardening it, or allow to air cool if I'm normalizing. 5160 in thin sections will air-harden a bit, so if you're going to be drilling holes in the tang you may need to spot-temper the tang with a torch before drilling.

 

You'll have to play with the tempering temperatures until you get the hardness/toughness blend you want. I like 375 for an hour or so followed by an air cool, repeated two or three times for good measure.

 

As brent pointed out, there are many way to get a decent result with 5160, it's fairly forgiving stuff. Just make sure it's 5160. If it's a spring you may have 9260, 6150, 1075, or something similar if it's a leaf, or any number of odd alloys if it's a coil. You can get away with this process on any leaf spring steel (that's why they're sort of interchangeable) but to get the utmost you need to know the specific alloy. Old coil springs are usually 9260, new ones are sometimes a high-strength low carbon pulse-hardening alloy that isn't good for blades. And they don't mark 'em for you from the factory, the inconsiderate so-and-so's... :lol:

 

Oh, and welcome aboard.

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3. 1650 seems a little hot for austinizing the steel for hardening. 5160 is a hypoeutectic steel (the carbon is below the saturation point in the austinetic [hot] phase) so it's not as subject to grain growth but why push it. Again, I would take it up to non-magnetic, then a little hotter (brighter) and hold for a minute to make sure the steel is heated throughout. With the lower carbon content there is no reason for a long soak, 5-10 minutes, to disolve carbides.

 

 

 

Doug, I cannot thank you enough for taking the time to write such a detailed response. I REALLY appreciate it!

 

I just bought that book this morning and I'll be reading it asap.

 

I'm not quite sure what you mean "With the lower carbon content there is no reason for a long soak, 5-10 minutes, to disolve carbides".

 

Thanks again,

 

Steve

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Doug's description is close to what I do with it. I like to harden from around 1550 rather than 1650 for the reasons mentioned. This is about 125 degrees hotter than non-magnetic. My shop space is usually dark enough that I can watch for the appearance of the swirling shadows in the steel that shows the phase change is happening (decalescence/recalescence, look it up!). As soon as the shadows go away I know I'm at the right temperature, so then I quench into warm mineral oil if I'm hardening it, or allow to air cool if I'm normalizing. 5160 in thin sections will air-harden a bit, so if you're going to be drilling holes in the tang you may need to spot-temper the tang with a torch before drilling.

 

You'll have to play with the tempering temperatures until you get the hardness/toughness blend you want. I like 375 for an hour or so followed by an air cool, repeated two or three times for good measure.

 

As brent pointed out, there are many way to get a decent result with 5160, it's fairly forgiving stuff. Just make sure it's 5160. If it's a spring you may have 9260, 6150, 1075, or something similar if it's a leaf, or any number of odd alloys if it's a coil. You can get away with this process on any leaf spring steel (that's why they're sort of interchangeable) but to get the utmost you need to know the specific alloy. Old coil springs are usually 9260, new ones are sometimes a high-strength low carbon pulse-hardening alloy that isn't good for blades. And they don't mark 'em for you from the factory, the inconsiderate so-and-so's... :lol:

 

Oh, and welcome aboard.

 

 

Thank you Alan for your help! Everyone has their little differences with heat treating I see. I'll give these methods a go on some test pieces before I do it on my actual blade.

 

I love this board already!

 

Thanks again!

 

Steve

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If you are using leaf spring 5160 try hard to get the new drops and not used ones. The used ones can have micro cracks which you would not want in your blades. Automotive spring shops will have a lot of new drop pieces that are usually in the 10-14 inch range in length. And they make more money selling it cheap to you then the recyclers.

 

Initially I was buying new leaf spring for 20 cents a Lbs. from a spring shop about 5 mins from where I work. Then the manager found out he knew my dad and never has charged me since then. My dad worked at an automotive spring and custom suspension shop for 27 years. That's how I got into this madness. At a very early age I would go to work with my dad about once a week and watch the whole forging and heat treating process.

 

The smoke from the huge quench tank must have had some form of virus in it and I was exposed and then stricken with forge fever.

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I really don't want to hit you with too much metallurgy to start with but steels with less than 77 points of carbon don't form much in the way of carbides and the carbon goes back into solution more easily. They also tend to not grow grain as quickly so you can go a little higher on austinizing temperature. In general steels with over 77 points of carbon in them will form more carbides and need a longer time for them to disolve and release the carbon into solution but they grow grain more quickly at lower temperatures. By the way, a point of carbon is 0.01% by weight and with the SAE number codes is represented by the last two or three numbers in the code. That way 1095 has approximately 95 points of carbon, 52100 has about 100 points of carbon, and 5160 contains about 60 points of carbon. The first two numbers has to do with the other alloying elements. In the case of 5160 the 5 is for chromium and the 1 is for 1% or less concentration. That will all be explained in Hrisoulas's book as well as the AISI codes, which is like A-2, L-6, etc.

 

Unless you are using a regulated heat treating oven or molten salt pots learning to spot the decalescence and recalescence in the steel as it changes phases is a big help. However, it took me over a year to finally spot it-and did I ever feel accomplished when I finally did. It's basically the change in light in the steel as it changes phases. Right now, go by what a magnet tells you and pick up on the finer points later. After you get the basics down you may want to get a book or two on metallurgy and really make you head spin. There are a few good ones out there. I managed to score one from Abe Books for $4.95, shipping included. It was an old beat up, marked up text book but it was complete and accurate.

 

Doug

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Not much to add, except to say I agree, 1650 is too hot. 1500-1550 works fine, and you don't need a long soak. In my salt pot I go 1 minute or so.

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Steve - great responses above!

 

For my own reminders, I've bookmarked Kevin Cashen's heat treat page:

http://www.cashenblades.com/heattreatment.html

and at the bottom he's got links for a few specific steels - including 5160:

http://www.cashenblades.com/steel/5160.html

 

I've interpreted the time/temp/transformation chart at the bottom of that 2nd link that you must get the blade from forge into quench in 2 seconds in order to miss the "nose" of the chart... which means the quench tank shouldn't be more than a step away from the forge. And I've seen notes that you should get 5160 fully quenched w/in 7 seconds to achieve full hardness.

 

I don't have the control of heat treat that I /want/ to have... still working on it.

 

Michael Kemp

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I was confused by that 5160 TTT chart till I found, I believe, the same chart but with the time hacks annotated. Between the 1 & 10, the hacks were noted as 2 and 5 seconds. Therefore between 10 & 20 it would be 12 & 15 seconds, etc.. So, if the chart I saw was correct, one has just under 5 seconds to get under the nose. Still not a lot of time to dally...

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Steve - great responses above!

 

For my own reminders, I've bookmarked Kevin Cashen's heat treat page:

http://www.cashenblades.com/heattreatment.html

and at the bottom he's got links for a few specific steels - including 5160:

http://www.cashenblades.com/steel/5160.html

 

I've interpreted the time/temp/transformation chart at the bottom of that 2nd link that you must get the blade from forge into quench in 2 seconds in order to miss the "nose" of the chart... which means the quench tank shouldn't be more than a step away from the forge. And I've seen notes that you should get 5160 fully quenched w/in 7 seconds to achieve full hardness.

 

I don't have the control of heat treat that I /want/ to have... still working on it.

 

Michael Kemp

 

Thank you so much Michael!! I cant get over how helpful everyone has been on this forum!

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