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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 01-26-2019, 03:17 PM
Rasmus Kristens Rasmus Kristens is offline
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gassforge for ht help!

I just build a small propane "forge" with 5 insulating firebricks and a propane torch.
The forge is just for HT instead of using charcoal.

I just did my first knife, and im not sure if it went well.
Therefore i have a few questions:

1. I'w read about gas forge reslting in more decarb than charcoal, but i'm not quite sure i understand why or how it happens? And surely not how to avoid it.. Does the amount of oxygen have something to do with it?

1.1 I did 3 normalization cycles, is that necessary for stock removal? In case of decarb, i expect that the normalizitaion can make it worse?

2. The forge is build with bircks in the botton, sides and top, and then a brick closing the back. Is it best to have the back closed or open? The front i kept close till the forge was hot.

3. Is there anything specific i need to take care of when i use a gasforge?

4. I tried making a hamone with furnace cement. Should i be able to see the hamone right after HT or do i need to etch before it appears?

5. Should i expect to get a hamone on carbonsteel like 80crv2?

Wow that was a lot.. Looking forward to hear your wise words :-)
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  #2  
Old 01-26-2019, 05:32 PM
jimmontg jimmontg is offline
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For a simple ht don't think complicated

Decarb isn't a problem if doing a 5 minute heat treat Rasmus. You're going to get the blade just up past nonmagnetic for a couple of minutes with 80crv2, which has a small amount of vanadium in it which will prohibit excessive grain growth from overheating past 1550 to 1650, but with a 2 minute soak past nonmagnetic at 1420F, unless your forge is hotter than I think it would be given your setup, you shouldn't exceed 1600F in 2 minutes and what little decarb that would occur will grind off with the scale.

If your knife jumps up in color quickly don't wait two minutes. Also if your forge heats unevenly you need to make sure you don't get hotspots on your blade, move it around until it heats evenly, you don't want dark areas near the edge area. Be sure to have your quenching oil close enough that from forge to oil it takes less than one second, half second is best and what you should aim for.

A normalization is not necessary for stock material it's only for if you forged the steel and forging is where decarb can become an issue because you forge at high temps in the 1800+ range.

Yes keep the back of the forge closed if the knife takes a while to reach HT temperature which I bet it does. Wear sunglasses the light is harmful to your eyes, especially if you have blue eyes. They don't have to be dark, yellow is fine.

Keep your forge area dark if possible, but if you have to setup outside, oh well no big deal.
Here's a link to heat treating colors that may help as a guideline.
http://www.westyorkssteel.com/techni...-temperatures/

I can't help you with a hamon as I always used W2 or a Nicholson Black Diamond file and never did hamons very much anyway, so you don't want my advice on your hamon. But I will add get a good ht first before fooling around with hamons which I don't know if your alloy does hamons well or not, some don't hamon well like O1 steel.

Last edited by jimmontg; 01-26-2019 at 08:19 PM.
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  #3  
Old 01-27-2019, 01:07 AM
Doug Lester Doug Lester is offline
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I would not expect an hamon on 80CrV2 or if you get one it would probably be very faint. It will show up after tempering and sanding out to a high grit followed by an etching.

Doug


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  #4  
Old 01-27-2019, 02:57 AM
Rasmus Kristens Rasmus Kristens is offline
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Thank you very much for the detailed explenation! I think the reason My knife didnt harden properly was to low heat.
The hardening for the steel i have is 1550 to 1615.

I realise that i used a bad magnet.. I used s welders magnet which has steelplates that extend from the magnet. Mayve that gave me fake results. I Will use a small suspended magnet next time.

Can i just redo the ht of the blade? Og do I need to do something before?

Thank you for the safty warning, i didnt know about the sunglasses.
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  #5  
Old 01-27-2019, 03:18 PM
jimmontg jimmontg is offline
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The vanadium is your friend with this steel as it really does restrict grain growth even if you get too hot in spots. Getting too hot not only causes excessive grain growth it is counter productive because the blade won't harden up like its supposed to and will be softer with brittleness. At least if you don't get hot enough it's softer, but not brittle.

I know you don't have much experience with colors, but you said you normalized the blades, how? It takes a temp of 1600+ degrees to normalize with a long, slow cool down, how do you know you achieved normalizing temperature? I ask because if the blade doesn't harden again you may need to normalize it again. Actually if you did achieve 1600 degrees you should have quenched it. lol

Seriously if you overheated the blade you could have seriously caused it to decarb. My apologies for not seeing it before, did you just heat the blade until it was yellow hot and then let it slow cool and how did you cool it? Plus you did it three times? I should have paid more attention. If a second ht doesn't harden the blade I'd toss it and try again with a new blade because the decarburization may be too deep to just grind off, start fresh. I hope you didn't use up all your stock.

This is a simple steel to ht and you should have achieved some hardening, the welding magnets are powerful enough that they still would have grabbed hold if it was below 1420 degrees. Note if you achieve nonmagnetic, but drop below that temp the steel remains nonmagnetic down to a lower temp, I'm not sure what that is exactly, but I've noticed it in my forge before. Anyone know exactly what it is?
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  #6  
Old 01-27-2019, 04:19 PM
Rasmus Kristens Rasmus Kristens is offline
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I only have a slight clue if i hit the temperature during the normalization ;-)
I used the magnet to hit the ca. 1450 deg and then looked at the colour. I have a small colour chart i try to use as reference.

First cycle i try to hit about 1600 to 1650 and then slow cooldown in still air till i hit room temperature. 2nd cycle was just above nonmagnet to make grain smaller and then slow cooldown. 3rd cycle was to about 500 deg and then slow cooldown.
Thats just what i read at some point :-) Trying my best to recreate it.

I thought normalization did have a positive effect, but since the steel comes annealed and isn't forged, i see why its not necessary. Saves me a lot of time :-)
The blade did harden some and its much harder than the not heat treated areas, but with preassure i could still scratch the edge with a file.

I didn't know the steel stays nonmagnetic! Thanks for the heads up.
Time to do another HT, and if it doesnt work, break the blade to have a look. Luckily I'm not sure i like the design anyway, so this will be another test blade ;-)
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  #7  
Old 01-27-2019, 05:32 PM
jimmontg jimmontg is offline
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Shouldn't be any serious decarb then if you only hit a guessed at 1600 degrees and a simple air cool is what is called for. Try this Rasmus, grind off about 0.1 mm and see how much a file digs in then. If there was some decarb it probably wouldn't be deeper than 0.1 mm or .004" deep. The blade might be hardened under a layer of decarb. It's worth a try.

By the way as to guessing forge temps you can take a lot of the guesswork out by using Tempil Markers, they're not listed on their website, but they have markers that go up to 1800 in jumps of 50 degrees. My brother bought 1450, 1500, 1550 and 1600. If the temp is below 1450 the stick tip doesn't melt. So you can figure out your temperatures pretty closely. Also since they are the size of a marking pen shipping from the USA shouldn't be prohibitive and they last a long time too. You will find as your eye gets better you will need them less and less. I am surprised more knife makers don't know about them or use them.

http://http://www.markingpendepot.co...ikmarkers.aspx
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  #8  
Old 01-28-2019, 03:20 AM
Rasmus Kristens Rasmus Kristens is offline
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I still think i will try another HT. I have been looking at the tempilsticks but was put off by the price in Denmark, about 50 USD per piece and minimum bulge of 12 pieces... No thanks :-)

I just ordered 2 sticks from Amazon at the total price of 50 USD incl. shipping. Don't know why i didn't look in to that before.

I think i decided to skip going for a hamon at this point. Get the HT on point first.

Last edited by Rasmus Kristens; 01-28-2019 at 05:34 AM.
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  #9  
Old 01-28-2019, 11:17 AM
Doug Lester Doug Lester is offline
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Smart move.

Doug


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  #10  
Old 01-28-2019, 02:26 PM
Rasmus Kristens Rasmus Kristens is offline
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Just did the 2nd HT of the blade with much better results!

I dont know if its true or not, but the steel looks much more yellow at the nonmagnetic temperature than it did when i did the HT outside with the charcoal.
I guess i just have to get used to that.

Thanks a lot for the help, the blade is tempering right now, and i'm exited to see the final results :-)
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  #11  
Old 01-29-2019, 02:35 AM
Doug Lester Doug Lester is offline
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Watch the ambient light. It can really change the color of the steel at a given temperature. I would recommend that you learn to go by decalesence when heat treating and go by that. You will have to learn to do you heat treating after dark though.

Doug


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  #12  
Old 01-29-2019, 07:57 AM
Rasmus Kristens Rasmus Kristens is offline
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I only do the HT after dark with a small lamp on so i can find my way around.
If i lear to look for the decalesence iot only tells me the nonmagnetic temperature right? Or is the the point wherer you quench your bladE?
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  #13  
Old 01-29-2019, 12:44 PM
Doug Lester Doug Lester is offline
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No, decalesence occurs after the non-magnetic point is reached. It is possible to reach the non-magnetic point and not achieve phase change.

Doug


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  #14  
Old 01-29-2019, 01:59 PM
Rasmus Kristens Rasmus Kristens is offline
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So when the phase changes at the critical temperature and then you quench right away?
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  #15  
Old 01-29-2019, 07:52 PM
Doug Lester Doug Lester is offline
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That's the idea. If you are talking about heat cycling, however, you will want to heat to a bit above decalesence then air cool. Heat to decalesence and air cool. Then to heat to just below decalesence then heat cool.

Doug


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