Why my heat treatment sucks and how to improve it?

[DantheDJ]

Hello everyone,

I understand that using mystery steels such as old files and leaf springs and heat treating in a charcoal fire can never be a fully controlled process, especially for a newbie, but Im looking for any tips on how to improve my chances of a successful heat treatment with this method.

Dont get me wrong, I make decent looking knives that work fine, they are sharp and stay sharp decently long, but as soon as the edge smells something metalic, like a beer can or some stainless steel can, it gets destroyed.

I dont know how to explain it, I see people make and heat treat knives just the way I do and they can cut nails and mild steel bars with them.
I only managed to cut one nail without damage, and that was using a file that I tempered to straw and just put a crude edge on it.

Its like somewhere along the process, I make the steel too brittle or something. Im telling you, you can shave with those knives, I have, they eat any wood for breakfast, but the slightest touch on metal and its done for...

Maybe its the edge geometry, though I use flat grind with a convexed edge, which should be the strongest, maybe Im getting the steel too hot or too cold during forging, Im clueless...
I dont really know how how it gets while forging the knife out, but I have the same problems on both forged and stock removed pieces.

I normalize at least once before the quench.
For heat treatment, I heat to non magnetic, wait just a bit and then quench in oil.
The martensite can be clearly seen on the thinner parts of the blades, about 15mm from the edge, it skates a file like a breeze when I check it. Then I temper in the coals to straw a couple of times, quenching in water in between or just the edge if I overheat a bit. I even oven temper on top, from time to time, but tend to avoid it lately since it stinks up the house real bad.

My main suspect is large grain size, or too much oxygen in my fire that messes up my edge and I need to regrind it further, though I would prefer not, since I mostly use hand tools, and filing hardened steel is kind of a no go for me.
I mean, my fire really scales parts like crazy, its like Im forge welding all the time, just that the parts dont get that hot.
Maybe its my fire management?
Or maybe the fire pit altogether??

What do you guys think?

Whats causing my knives to fail when contacting metals?

I know I cant expect much when I hit a random rock in the ground, but I would very much like to at least be able to accidentally hit a nail and have my edge survive the encounter, I know its possible, Ive seen it, Ive done it, just not with steel that I heat treated...

If anybody can think of a reason, no matter how minute or irrelevant, please let me know, or ask me whatever you need to know, Ill try my best to answer.

Thank you for your help and time, cheers!

 

[Mecha]

Hello everyone,

I understand that using mystery steels such as old files and leaf springs and heat treating in a charcoal fire can never be a fully controlled process, especially for a newbie, but Im looking for any tips on how to improve my chances of a successful heat treatment with this method.

Dont get me wrong, I make decent looking knives that work fine, they are sharp and stay sharp decently long, but as soon as the edge smells something metalic, like a beer can or some stainless steel can, it gets destroyed.

I dont know how to explain it, I see people make and heat treat knives just the way I do and they can cut nails and mild steel bars with them.
I only managed to cut one nail without damage, and that was using a file that I tempered to straw and just put a crude edge on it.

Its like somewhere along the process, I make the steel too brittle or something. Im telling you, you can shave with those knives, I have, they eat any wood for breakfast, but the slightest touch on metal and its done for...

Maybe its the edge geometry, though I use flat grind with a convexed edge, which should be the strongest, maybe Im getting the steel too hot or too cold during forging, Im clueless...
I dont really know how how it gets while forging the knife out, but I have the same problems on both forged and stock removed pieces.

I normalize at least once before the quench.
For heat treatment, I heat to non magnetic, wait just a bit and then quench in oil.
The martensite can be clearly seen on the thinner parts of the blades, about 15mm from the edge, it skates a file like a breeze when I check it. Then I temper in the coals to straw a couple of times, quenching in water in between or just the edge if I overheat a bit. I even oven temper on top, from time to time, but tend to avoid it lately since it stinks up the house real bad.

My main suspect is large grain size, or too much oxygen in my fire that messes up my edge and I need to regrind it further, though I would prefer not, since I mostly use hand tools, and filing hardened steel is kind of a no go for me.
I mean, my fire really scales parts like crazy, its like Im forge welding all the time, just that the parts dont get that hot.
Maybe its my fire management?
Or maybe the fire pit altogether??

What do you guys think?

Whats causing my knives to fail when contacting metals?

I know I cant expect much when I hit a random rock in the ground, but I would very much like to at least be able to accidentally hit a nail and have my edge survive the encounter, I know its possible, Ive seen it, Ive done it, just not with steel that I heat treated...

If anybody can think of a reason, no matter how minute or irrelevant, please let me know, or ask me whatever you need to know, Ill try my best to answer.

Thank you for your help and time, cheers!

Best place around these parts to ask this type of question is Shop Talk:

https://bladeforums.com/forums/shop-talk-bladesmith-questions-and-answers.741/

A moderator should be able to move it there for you.

My answer to your problem, is that you'll need to test HT using bars of known, clean, annealed steel in order to zero in on the cause.

 

[Aidenag]

Can't really help much with so many unknowns. Could be overheating, could be not enough heat, could be your not getting an even enough heat, could be your forging too hot or too cold, could be your tempering is off, could be your unknown steel needs something different than what you are doing. It's almost endless here with so many unknowns.

I would suggest biting the bullet and buying $20 worth of 1080 or 1084, and seeing how it goes with your current method of heat treatment. If it still isn't performing well, then you know something needs to change and can start narrowing things down.

Also, i would strongly urge you to not use Forged In Fire levels of 'testing' as a metric for if the knife is good or not. The words "Knife", "cut" and "Steel bar" should never be in the same sentence

 

[DevinT]

Mayday.....mayday....

You are most likely over heating the blade during austenitizing.

Sounds like your equipment is inadequate and you lack experience.

You cannot see martensite with the naked eye.

Hoss

 

[Willie71]

I don’t mean to be rude, but any single one, combo of, or all of your variables could be the issue. Heat treat is a precise process. Without accounting for every variable, no one can pinpoint what went wrong.

 

[scott kozub]

Are you sharpening on the grinder? You may be burning your edge. Have you tried a brass rod test? Have you tried a hardness test? Have you snapped a blade to check the grain? All kinds of things you should look at to get an idea.

 

[A.McPherson]

If you are wanting to do home heat treat, with primitive methods, you need to do lots and lots of samples.

Take your steel that you are going to use for making your knife and make s bunch of 1" x 2" sections, as thick as you want your blade. Then wait till night time, turn off all the lights, then heat treat them.
On each one change one variable, and keep the rest the same. I.E. change how bright the steel is before you quench slightly with each one...
This way you can dial in on what is effecting your HT.
Really it's better with more high precision equipment and known steel, but if you're using unknown steel, you've just got to test, over and over and over!

 

[DantheDJ]

I would suggest biting the bullet and buying $20 worth of 1080 or 1084, and seeing how it goes with your current method of heat treatment. If it still isn't performing well, then you know something needs to change and can start narrowing things down.

Also, i would strongly urge you to not use Forged In Fire levels of 'testing' as a metric for if the knife is good or not. The words "Knife", "cut" and "Steel bar" should never be in the same sentence

I would like to be able to buy steel, but unfortunately in my country, I cant, there is no steel adequate for knife making at all...
I could order some, but I dont like having to pay 3x the price in shipping. Thats why Im stuck with junkyard steels.

For the second part, I dont even watch that show, I dont like it for some reason
Im just encountering random bits of iron in my daily tasks where I use my edged tools. I have a small hatchet that is made out of a leaf spring, but with its original HT, which might be a bit soft, but its doing a far better job hitting a wire or even a nail than the blades I HTed manually.

Mayday.....mayday....

You are most likely over heating the blade during austenitizing.

Sounds like your equipment is inadequate and you lack experience.

You cannot see martensite with the naked eye.

Hoss

I always thought I was under heating , because I count to about 10 after non magnetic and quench, but the whole puting the blade out and back in is sucking the heat away quickly. Maybe my steels have a shorter temp range for a good quench...

The second part couldnt be more spot on lol
I have a couple of metal files, one for wood, a cheap drill press, an even cheaper bench grinder that barely works, and my forge is a couple of fire bricks in a V shape, with a metal pipe with perforated holes at the bottom of the V. Dont even own a good set of tongs

I meant, in the quench, where martensite forms, the black oil residue gets peeled off of the steel surface, so it stays gray, which gives me a good indication that the quench worked.

I don’t mean to be rude, but any single one, combo of, or all of your variables could be the issue. Heat treat is a precise process. Without accounting for every variable, no one can pinpoint what went wrong.

I knew that much, no hard feelings. I was just hoping that somebody had a similar issue at least and could help me narrow things down a bit, because there is truly A LOT of things I need to check on my own in order to fix the problem

Are you sharpening on the grinder? You may be burning your edge. Have you tried a brass rod test? Have you tried a hardness test? Have you snapped a blade to check the grain? All kinds of things you should look at to get an idea.

I sometimes sharpen on my weak a$$ bench grinder, but mostly I do it with sand paper and coarser stones. I dont know what burning the edge means
but Im extra careful not to overheat the blade and Im constantly soaking in cold water and I grind with my bare hands to feel the heat.

I havent tried the brass rod test because I dont own one. I have some brass rods that are used in welding to my knowledge, they seem harder, could I use that?
Im not really sure how to hardness test my knives, I usually check with a file after quenching, and again after tempering where its a bit softer. After that, I do a scratch test on a piece of leaf spring, which should be softer given its a spring, but none can scratch each other...
The same happens when I try scratching an axe, or some other knives I made. I dont really know why that happens, harder steel should scratch softer steel as far as I know

 

[DantheDJ]

If you are wanting to do home heat treat, with primitive methods, you need to do lots and lots of samples.

Take your steel that you are going to use for making your knife and make s bunch of 1" x 2" sections, as thick as you want your blade. Then wait till night time, turn off all the lights, then heat treat them.
On each one change one variable, and keep the rest the same. I.E. change how bright the steel is before you quench slightly with each one...
This way you can dial in on what is effecting your HT.
Really it's better with more high precision equipment and known steel, but if you're using unknown steel, you've just got to test, over and over and over!

Im getting in touch with some people that are relatively close to me to supply me with some pieces of known steel, so I can try working with them first. Then Ill work from there as advised

 

[Aidenag]

What country you in? There should be a supplier in pretty much every nation at this point unless your in like Liberia or something. Let us know and i bet someone here can find you a in country source for at least some carbon steels.

 

[TheEdge01]

How thin is your edge when you heat treat your blade. Thinner steel heats up much faster and if your edge or tip is very thin it will reach critical temp while the rest of your blade is still heating up. Leave your edge and tip a little thicker, and move your blade around in the coals to keep your heat as even as you can. I heat treat with a coal forge too, it may not be a controlled furnace, but you can make a very good blade if you do your part.

 

[scott kozub]

Hardness testing would be using a machine that tells you the exact hardness of the blade. These machines are expensive but if you have a machine shop near by they may be able to help you. Heck if you have a machine shop near by you could get some tool steel off them. They're are also files you can by on ebay that will give you an approximation within 5 Hrc that are much cheaper.

Burning the edge simply mean that it is over heated when sharpening ruining the temper. This can easily happen if sharpened on a belt grinder. Bench grinder as well but less likely. If you using sandpaper you won't be over heating it.

Here's some videos on some simple testes you can do that are very effective in letting you know if have harnenable steel and if your heat treat is good or not. These are cheap free testes that you'll learn a lot from.

 

[DantheDJ]

What country you in? There should be a supplier in pretty much every nation at this point unless your in like Liberia or something. Let us know and i bet someone here can find you a in country source for at least some carbon steels.

I thought I put that in my info, guess not...
Im from Serbia, you can find some carbon steel here for sure, but its usually either not very cheap, in terms of how much you can buy or not in a state which is suitable for knife making. I will find some though, and Im gonna try making a couple of knifes from that, see how it fares compared to my current ones.

How thin is your edge when you heat treat your blade. Thinner steel heats up much faster and if your edge or tip is very thin it will reach critical temp while the rest of your blade is still heating up. Leave your edge and tip a little thicker, and move your blade around in the coals to keep your heat as even as you can. I heat treat with a coal forge too, it may not be a controlled furnace, but you can make a very good blade if you do your part.

I cant really tell you on the top of my head, but I know that in the beginning I went too high, something like 1mm, then I got a bit lower as my bench grinder slowly died on me, but I can be certain that I never overheated the steel during that part of the build.

Hardness testing would be using a machine that tells you the exact hardness of the blade. These machines are expensive but if you have a machine shop near by they may be able to help you. Heck if you have a machine shop near by you could get some tool steel off them. They're are also files you can by on ebay that will give you an approximation within 5 Hrc that are much cheaper.

Burning the edge simply mean that it is over heated when sharpening ruining the temper. This can easily happen if sharpened on a belt grinder. Bench grinder as well but less likely. If you using sandpaper you won't be over heating it.

Here's some videos on some simple testes you can do that are very effective in letting you know if have harnenable steel and if your heat treat is good or not. These are cheap free testes that you'll learn a lot from.

Ive been told those cheepo tester files are not that good, but I can try it, why not...

Yeah, belt grinders sure seem scary, but my old bench grinder needs a lot to overheat a blade sadly. And as Ive said, I feel the heat with my hands, and as soon as it gets warm, I quench. Im a bit paranoid after HT, so I take extra precaution

Thanks for the vids, Ive watched some of them already, the one with the spark test is actually one of the first videos I ever watched when I started this whole beautiful mess
I use spark testing regularly, especially when Im making steel. I dont like however, to break my pieces, as the third video suggests. I only broke a piece to see if I can through carburize mild steel stock for knife and spring making.

 

[noseoil]

I think the best steel you could get locally & easily would be the "leaf springs" from a light truck or a small car back axle. It should be about 0.6% carbon, perhaps with a pinch of other stuff in it (less than 1% chromium, a bit of manganese, etc.) but it is one of the best steels which is easy to work with, heat treat & keeps an edge. It's already flat, so you would need to straighten the stock & forge what you need to shape it. The only problem may be that it might have fine cracks, if it has seen too much life in a car or truck, but your forge should be OK to work with it & for heat treat. It should be available in a lot of places, salvage yards, car repair shops & people who work with cars & trucks. Find some & try a couple of different heat treats to see how it works. 200C will do the temper pretty well for a good knife with a good edge with this type of steel, once you have the right quench heat & sequence. An oven in the house will work well enough for the temper, if you check it with a simple oven thermometer.

You need a consistent type of steel first, then work out the heat treat process which works best for you for the edge, then make blades until you have the right edge geometry to withstand some harder use. It's possible, but it will mean a lot of testing, note taking, & evaluations to make it right. Start with a known steel you can get cheaply (& enough of the same type) to be sure you have plenty to learn with & test. Best of luck!

 

[Willie71]

E-mail me at wjkrywko at gmail dot com, and I’ll send you some steel to work with.

 

[DantheDJ]

I think the best steel you could get locally & easily would be the "leaf springs" from a light truck or a small car back axle. It should be about 0.6% carbon, perhaps with a pinch of other stuff in it (less than 1% chromium, a bit of manganese, etc.) but it is one of the best steels which is easy to work with, heat treat & keeps an edge. It's already flat, so you would need to straighten the stock & forge what you need to shape it. The only problem may be that it might have fine cracks, if it has seen too much life in a car or truck, but your forge should be OK to work with it & for heat treat. It should be available in a lot of places, salvage yards, car repair shops & people who work with cars & trucks. Find some & try a couple of different heat treats to see how it works. 200C will do the temper pretty well for a good knife with a good edge with this type of steel, once you have the right quench heat & sequence. An oven in the house will work well enough for the temper, if you check it with a simple oven thermometer.

You need a consistent type of steel first, then work out the heat treat process which works best for you for the edge, then make blades until you have the right edge geometry to withstand some harder use. It's possible, but it will mean a lot of testing, note taking, & evaluations to make it right. Start with a known steel you can get cheaply (& enough of the same type) to be sure you have plenty to learn with & test. Best of luck!

Im planning to do just that, thanks. However, each leaf spring I buy can not be regarded as the same steel, if its not from the same truck of course. Thats why Im gonna need to find a known steel, I should be able to procure some 1075 somewhere...

E-mail me at wjkrywko at gmail dot com, and I’ll send you some steel to work with.

I dont think thats a wise idea, shipping costs from Canada to Serbia would be abysmal. Thats the reason I dont order steel online
Thank you for the offer though

 

[noseoil]

If you can get a batch of old truck springs, that should keep you busy for a while. Spring steel from a truck or car should be fairly similar, at least for your needs. The chemical composition should be very close for heat treat, since it's the same type of material and in the same application. There's a lot of it out there for you to use & it should be pretty cheap once you find a good source.

I think the biggest problem you will have at first will be judging the heat in the steel prior to quenching. It's not easy to "see" the color, unless you're working in a mostly dark area or room. In bright sunlight it's really much more difficult. Once you can see the color each time, I think your heat treat will get better pretty fast. Just get a good color chart to judge by & have at it!

 

[DantheDJ]

If you can get a batch of old truck springs, that should keep you busy for a while. Spring steel from a truck or car should be fairly similar, at least for your needs. The chemical composition should be very close for heat treat, since it's the same type of material and in the same application. There's a lot of it out there for you to use & it should be pretty cheap once you find a good source.

I think the biggest problem you will have at first will be judging the heat in the steel prior to quenching. It's not easy to "see" the color, unless you're working in a mostly dark area or room. In bright sunlight it's really much more difficult. Once you can see the color each time, I think your heat treat will get better pretty fast. Just get a good color chart to judge by & have at it!

I dont quench by color, I check with a magnet and wait a few seconds after it gets non magnetic and then quench in cooking oil.
I get martensite every time, no warps, nothing. I think that after the tempering process do my knives start to suck. Maybe my oxygen rich fire decarbs a lot more that it should, so I get a weaker edge or something?