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Ken Burbank

tempering / heat treating ,

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I know look on the noobie page , but I haven't found what I am looking for . ( Maybe the oldtimers kicking in )

I'm just getting stuff together to start forging , thinking 5160 to start . It has a rep for forgiveness , so maybe a good starting steel . I also want to try old files , because I have a good swapmeet in the area , a good source .

What I need , if somebody doesn't mind giving up a couple minutes , is start-up advice on quench / temper / heat treat for these steels . If I missed something in the noobie section , let me know . Sorry to be a pain , but I like doing things right , thanks !

 

Ken Burbank

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Heat treatment is a huge subject, and I can't do more than scratch the surface here. First, check out the Metallurgy section of this forum for more depth, and waaaaay more informed people than me.

 

You can get as in-depth as you want to, with heat treatment, but here are a few basics. Lots of good knives have been made with no more than what I'm going to say here, but to really get the maximum performance, you have to learn a lot more..

 

Critical temperature. This is where the steel changes state. It's the temp. you need the steel to be at for normalizing, and quenching. Most simple steels do us a favor, by becoming non-magnetic at about this temp. Keep a magnet handy, and check it as the blade gets hotter. Once the magnet no longer sticks, "soak" the blade just a little longer, (15 seconds or so), then you're there.

 

Normalizing. Also called stress relief, this consists of bringing the blade to the critical temp. and then cooling it as slowly as you can. Burying it in ashes works, or you can use garden center vermiculite. Once it's room temp., you've normalized it. The stresses that remain from forging can cause a blade to warp when you quench it. Normalizing relieves some of these stresses, and lessens the chance of warping in the quench. Many smiths will normalize three times before quenching!

 

Quenching. Take the blade, once it's reached critical temp. and put it in oil, (most of us), or water, (the bravest only!), and it will fully harden. A fully hardened blade will laugh at a file or drill bit, but you can snap it with your bare hands. That's too hard, and the next step, tempering, is done to soften it somewhat, making a good, durable tool. The oil you use for quenching can range from used motor oil, (about the worst), through transmission fluid, (works OK), to purpose-made quenching oils (the best). Getting started, I used transmission fluid successfully for quite a while.. Methods differ, but I put the blade in edge-down, and gently swirled it about just a little.

 

 

Tempering. This is the process of softening the blade down just a bit from fully hardened. Once the blade has been quenched, it is put into an oven and left for an hour or two at a temperature much lower than forging temp. Typically, the tempering temperature is around 400 to 500 deg.F. A used toaster oven will generally be a good choice for this operation. Using the wife's cooking oven to raost a blade that has oil on it will get you scolded pretty hard!

 

As I said, I've only scratched the surface here. The critical and tempering temperatures vary with every alloy, and the details of the procedure very with every smith. That's a basic rundown of the process, though, and you can ask more questions from there. The people on this forum are a great bunch, and will be glad to help you along. Good luck, and have fun!

 

Luke

Edited by jlkilpatrick

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Hi Luke , thanks . As you said that was just scratching the surface , but it puts one foot in front of the other for me , and that is how a journey starts !

 

Ken Burbank

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Ken, that's how almost all of us got started, and one foot following the other has taken folks far, indeed!

 

Howard, coming from you, that makes me happy! Ken, pay particular attention to Howard's posts. He's forgotten more about heat treating than I've ever known!

 

Luke

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Ok, I think I just learned that I learned it wrong the first time. I thought Luke's description of normalizing (for plain carbon steels anyway) was actually annealing. I thought that you let the steel cool in still air to normalize and in a pot of vermiculite/pearlite/ashes/whatever to anneal. Have I really been normalizing incorrectly all this time? :huh:

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jkv,

 

Depends on the steel. For most all carbon-steel (10xx), you want to air-cool to normalize. You use a furnace-cool or vermiculite to anneal. 5160 has a helping of Chromium, so it tends to air-harden somewhat--which means that you want a slower cool to normalize it.

 

Thanks,

Brian K.

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I have gotten very good blades from 5160 tempering at 385 degrees twice. Your batch of steel may vary....

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I, too, learned that normalizing meant air cooling, and annealing meant slow cooling. The more I looked into it, though, the more I realized that true annealing has to go much slower than what we're going to get with burying a blade in ash or vermiculite. Many hours in some cases, as I recall. Around then I started calling the regular blacksmith's kind of slow cooling "super normalizing", and just took it for granted that I'd never get a true anneal, but rather a very good normalization with the procedure that it was practical for me to use. That's why I called it normalization, instead of annealing. Quite possibly a mistake based on my own made-up terminology.

 

I'm pretty sure that the slower the cooling rate, the better the stress relief, and in that regard, it makes sense to differentiate between air and an insulating medium. I'm certainly no authority, and I'll happily go along with the consensus on this. The last think I want is to be handing out wrong advice to the new guys.

 

Luke

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I have gotten very good blades from 5160 tempering at 385 degrees twice. Your batch of steel may vary....

 

I recall reading a metallugry text that made it clear that lower temperatures held for longer periods achieved exactly the same end results in the tempering process. I don't remember it quite as clearly, but I sort of recall the author making a case for more uniformity when the tempering was broken into more than one session. Sounds like your experience backs that up pretty well.

 

Luke

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As far as I can tell, they can't be tempered too many times as long as you don't overshoot the temperature. So, I figure a bit of overkill won't hurt and do it multiple times, just to be sure... ;)

 

I guess I do it because the guy that taught me heat-treating suggested multiple cycles. The higher alloy steels can be prone to retained austinite, so multiple cycles are absolutely necessary with those, but the steels we bladesmiths tend to use doesn't really have this problem. Industry standards don't really call for the longer, multiple cycles I think most of us use (2 hours minimum in my shop, at least twice). I do it because it eases my mind knowing I built it stronger than it needed to be...

Edited by GEzell

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I, too, learned that normalizing meant air cooling, and annealing meant slow cooling. The more I looked into it, though, the more I realized that true annealing has to go much slower than what we're going to get with burying a blade in ash or vermiculite. Many hours in some cases, as I recall. Around then I started calling the regular blacksmith's kind of slow cooling "super normalizing", and just took it for granted that I'd never get a true anneal, but rather a very good normalization with the procedure that it was practical for me to use. That's why I called it normalization, instead of annealing. Quite possibly a mistake based on my own made-up terminology.

 

I'm pretty sure that the slower the cooling rate, the better the stress relief, and in that regard, it makes sense to differentiate between air and an insulating medium. I'm certainly no authority, and I'll happily go along with the consensus on this. The last think I want is to be handing out wrong advice to the new guys.

 

Luke

 

Hi Luke,

 

I see what you're saying, it makes good sense. I was just regurgitating my knowledge (gained from here). It's a pretty safe bet many of us cannot do a 40F/hr cooling. I may have to experiment with furnace-cooling versus air-cooling to see if makes a difference in the end product (grain, strength, etc., now I have too many experiments, I'll never make a blade :lol: ).

 

Thanks,

Brian K.

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Hi Luke,

 

I see what you're saying, it makes good sense. I was just regurgitating my knowledge (gained from here). It's a pretty safe bet many of us cannot do a 40F/hr cooling. I may have to experiment with furnace-cooling versus air-cooling to see if makes a difference in the end product (grain, strength, etc., now I have too many experiments, I'll never make a blade :lol: ).

 

Thanks,

Brian K.

 

 

Man, tell me about it! :) My "Pending Experiments" file is so big, sometimes I just hide under the covers and refuse to get out of bed!

 

Luke

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My thanks Gentlemen , very helpful ! The better I can make something , the bigger the grin .

Edited by snuffymanson

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Sorry I'm a bit late to the dance but her is wjat I do.

 

Before heat treating you want to normalize your blade to remove any stresses that may have appeared in forging. You normalize your blade by brining it up to non-magnetic and letting it air cool. Some people do this 3 times just to be sure that all the crystals have become the same size and that the blade is fairly soft. I'm not sure I can tell the difference between one cycle and three so do what you are comfortable with.

 

Heat treating is a 2 step process. The first is hardening and the second is tempering. Start with a normalized blade (heated to non magnetic and air cooled.) Heat the blade until its non magnetic. Test with a telescopic pen magnet if it doesn't stick it's ready to go. Then quench it in motor oil, canola oil, olive oil whatever works which should been pre heated to about 125 degrees Fahrenheit. If it's single edged then quenching it in a pan edge first would be best if it's double edged or 2 long for a pan then quenching it tip first will be fine. (I usually just plunge it all the way into the oil tip first. Do not wave or stir the blade in the oil as this can cause warping. I let the blade air cool I have known others who will water quench it after the oil quench. After that clean the baked on oil off of the blade then you can draw temper. The use of the blade depends on how hard you want the edge. You can do a differential temper by feathering a torch along the back of the blade until the edge turns light straw colored this is the hardest an edge can be with out over stressing the steel. The colors are straw, light yellow, yellow, light brown, dark brown, red, purple, blue, gunmetal gray. Straw is the hardest and Gunmetal gray is the softest and ideal for the back of the blade. If this is going to be a chopping/camp knife I would use a light brown for the edge. If it's going to be doing a lot of slicing like a kitchen knife then straw is fine for the edge. You can also put it in the oven for about 2 hours at 425 to get a straw. The colors start changing about every 10 degrees if I recall. I have the temp to color list someplace and will look it up and post it if it is useful to anyone. You should use the oven draw for double edged blades.

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Try reading Wayne Goddards "Wonders of Knifemaking"..It's available at large chain bookstores,Amazon or Ebay....It'll answear many of your questions in a understandable fashion...Good Luck

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These are the recommended procedures from the Heat Treater's Guide:

Forging:
Heat to 2200° F maximum, and do not forge after forging stock has dropped below approximately 1600° F.

 

Normalizing:
Heat to 1600° F and cool in air.

 

Annealing:
For a predominately pearlitic structure, heat to 1525° F, then cool rapidly to 1300° F, then cool to 1250° F and hold for 6 hr.

For a predominately spheroidized structure, heat to 1380 F, cool rapidly to 1300 F, then cool to 1200 F at a rate not exceeding 10 F per hour; or heat to 1380 F, cool rapidly to 1250 F, and hold for 10 hr.

 

Hardening:
Austenitize at 1525° F and quench in oil. (As quenched hardness should be ~63 Rc.)

 

Tempering:
After quenching, reheat to the temperature required to provide the desired hardness. (On the graph, it looks like 400° F will yield about 60 Rc, 450° F about 58 Rc.)

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There's some more help , thanks much ! I will get a couple books , but I have more faith in things " tried by real people "

This all gives me some starting points .

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