Paint can forge frustration - can't reach normalizing temps

Sean Jones

Sean Jones

Well-Known Member
I have a small paint can forge that I've been attempting to get some 1084 to harden correctly without success. Here's my procedure so far.

First forge attempt.
1. Brought the forge up to about 1450 (I do have a temperature probe, though I don't know how accurate it is in such a primitive forge)
2. I took a piece of mild steel and heated cherry red and dropped in the canola oil to bring the oil temperature up.
3. After that the forge would only come back up to about 1350 or so. Perhaps I should have waited longer to see if it would come up higher?
4. I decided to go ahead and heat treat with a magnet and color. When the blade was about red-orange I checked for non-magnetic, which it was.
5. I then returned the blade to the forge for about five minutes and then put in the canola oil tip down for roughly a minute.
6. After heat treating 3 1084 blades this way I put them in our kitchen oven for tempering. Set the oven to 425 degrees for the first two hours, and 390 for the second two hours. They didn't change color coming out of the oven.

7. I then ground any possible surface junk off and tested the blade surfaces with a file. All three showed scratches from the file.

So I heat treated all three blades again. The only difference the second time was I tempered the blades in my toaster oven. I tested the toaster oven with my temperature probe and it seemed pretty accurate. I threw in two fire bricks and set my blades on the fire bricks. Then I set the oven for 400 degrees for two hours, let them cool to room temperature and then another two hours at 400 degrees. The blades had a nice wheat color and some purple when I took them out.

Same result. All three show scratches from my file. I tested a piece of AEB-L heat treated to RC of 62 with the file to make sure I was doing the file test correctly and it didn't scratch at all.

Any ideas on what I'm doing wrong? I know I need a better forge and it's in the works. Do I need to normalize? Two of the blades are from the New Jersey Baron and the third is from Alpha Knife supply. I don't see any differences between them.
 
It sounds like you are doing everything right to me.
Prior to my oven I HT all my 1084 in the propane forge. I would watch the blade until the shadow passed through it and checked for non-magnetic and then soaked the blade for about a minute before quenching in canola oil. I now use parks but back then I used canola oil. If you didn't clean the blades good after the first heat treat, most likely tempering wouldn't change the color of the blades. Also is there a reason you do two hour tempering cycles? I only use two - one hour tempering cycles.
My question would be is a scratch test really a test of hardness? I test the edges of my blade to make sure the file skates. Are you saying the file digs in the edge or are you saying that you run the file on the flats and the file leaves marks? It's my uneducated opinion that a file would scratch any blade to some extent.
Maybe Ed can add more experience and knowledge to your question.
 
opaul said:
It sounds like you are doing everything right to me.
Prior to my oven I HT all my 1084 in the propane forge. I would watch the blade until the shadow passed through it and checked for non-magnetic and then soaked the blade for about a minute before quenching in canola oil. I now use parks but back then I used canola oil. If you didn't clean the blades good after the first heat treat, most likely tempering wouldn't change the color of the blades. Also is there a reason you do two hour tempering cycles? I only use two - one hour tempering cycles.
My question would be is a scratch test really a test of hardness? I test the edges of my blade to make sure the file skates. Are you saying the file digs in the edge or are you saying that you run the file on the flats and the file leaves marks? It's my uneducated opinion that a file would scratch any blade to some extent.
Maybe Ed can add more experience and knowledge to your question.
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Two one hour cycles would make a difference. If that's the case I've read Kevin's heat treat wrong. I'll double check that.

I'm also running the file on the flats not the edge.
 
I just ran a file over the edge of the blade and I'd say it skates. I'd really like a more definitive way of determining whether these turned out correctly but I can't afford a hardness tester right now.
 
After heat treat you may have light forge scale and baked on oil. It will scratch off with a file and is not an indication of blade hardness. If you run a file across the edge and it’s skates then the blade has hardened.
 
You need to go to at least 1400°F to get any appreciable hardening, and at least 1425°F to get uniform properties. With such basic equipment, I would not hold for any amount of time, I would get it to temp and quench it. Four hours total is a bit much in tempering, a total of 2 hours at temperature is about right. I am not sure about the lower temperature on the second cycle, it is usually more efficient to start lower and bump the temperature up. For 1084, heat to 1450°F-1475°F and, when evenly heated, immediately quench. This should result in an easy 65HRC. Then temper starting at 375°F for at least two hours for a final hardness of HRC 60-62.
 
Kevin R. Cashen said:
You need to go to at least 1400°F to get any appreciable hardening, and at least 1425°F to get uniform properties. With such basic equipment, I would not hold for any amount of time, I would get it to temp and quench it. Four hours total is a bit much in tempering, a total of 2 hours at temperature is about right. I am not sure about the lower temperature on the second cycle, it is usually more efficient to start lower and bump the temperature up. For 1084, heat to 1450°F-1475°F and, when evenly heated, immediately quench. This should result in an easy 65HRC. Then temper starting at 375°F for at least two hours for a final hardness of HRC 60-62.
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Thanks Kevin. I don't know where I came up with two-two hour sequences. I misread something somewhere.

I do need a better forge. In the mean time I've coated the inside of this forge with 3000 degree refractory cement. I'll let it dry over night and hopefully that will work until I get my two burner forge built.

Thanks again for the reply
 
Great responses and support!
I mentioned the passing shadow in my post - does anyone else look for it or know exactly what’s the shadow is. I’m sure there is another technical word for shadow but it sounds cool.
 
opaul said:
Great responses and support!
I mentioned the passing shadow in my post - does anyone else look for it or know exactly what’s the shadow is. I’m sure there is another technical word for shadow but it sounds cool.
Click to expand...

I do the the same though I will have to go back and read one of Kevin’s post to remember what it’s called.
 
opaul said:
Great responses and support!
I mentioned the passing shadow in my post - does anyone else look for it or know exactly what’s the shadow is. I’m sure there is another technical word for shadow but it sounds cool.
Click to expand...

I believe it is called decalescence.
 
The crystalline shift from one atomic stacking to another requires extra energy to complete, this is what would be called an “endothermic” transformation in that it pulls heat in. The actual process is indeed known as decalescence. I teach this method of watching the shadows to all of my students that are heat treating in a forge, it is much more versatile and can even be more accurate than the magnet. The magnet merely measures the Currie point of iron, which is around 1414°F, but steel isn’t all iron, the bits that make alloys behave so differently do not care as much about the Currie point, but the shadow of decalescence allows you to actually see the beginning, middle and end of the austenization process. All of my students are well versed in how to gently heat to the beginning of decalescence, in a forge that is dialed back, working all the shadow out of the blade without overheating any thinner sections, and then applying high heat after the shadow is gone. They are often amazed at how evenly the steel will heat after decalescence regardless of how fast it is done. Steel is actually a very good conductor and the body of the blade wants to pull the heat out of edges and tips in order to equalize, but decalescence won’t allow it.

If you want to practice it, do it in a darkened room and wait to see what happens on the way back down. The reverse process, on cooling, is called recalescence, and it is very cool to watch because it is exothermic instead. At round 1100°F there will be a bright wave of energy that will start at the edges and move to the center of the steel as pearlite is formed.

You can temper for longer than 2 hours if you like, but nothing more will really happen until you get out to a few more hours. In watching the chatter on the internet in the last 5 years I have seen this two hour standard grow to two, or even three, 2 hour cycles, taking tempering out to 4, 6 or even more hours. I hope it wasn't a misunderstanding of anything that I wrote that has people doing these crazy long tempers, there is no real benefit in intentionally going this long, and there can even be some bad effects after a certain point. If one is not doing HRC testing and walking in the numbers, a two hour cycle, at your chosen temperature, is more than good enough.
 
Thank you and very well explained. I always watch for the decalescence shadow when I use my forge.
 
I guess third time is a charm. After painting the inside of the can forge with refractory cement and a new torch, I reached 1525 without a problem.
With some waiting I would imagine it will reach 1600. But I doubt it will go beyond that.
So I heat treated and tempered for a third time. Last temper is running now but I already feel this is right this time. Everything just seems more consistent. Or maybe I just feel more comfortable after a third redo.

Thanks for everyone's help.
 
Sean Jones said:
I guess third time is a charm. After painting the inside of the can forge with refractory cement and a new torch, I reached 1525 without a problem.
With some waiting I would imagine it will reach 1600. But I doubt it will go beyond that.
So I heat treated and tempered for a third time. Last temper is running now but I already feel this is right this time. Everything just seems more consistent. Or maybe I just feel more comfortable after a third redo.

Thanks for everyone's help.
Click to expand...
Did you normalize before you tried round three? Seems to me that maybe that would be important
 
Jon Buescher said:
Did you normalize before you tried round three? Seems to me that maybe that would be important
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Oops. I was pretty frustrated by round three and didn't even think about it. I tested the knives with a file last night and so far they appear to be fine. I'll test again with a brass rod after I've sharpened them.

I need to write up my procedure so I don't forget a step; There was a thread on that a while back.
 
Sean Jones said:
Oops. I was pretty frustrated by round three and didn't even think about it. I tested the knives with a file last night and so far they appear to be fine. I'll test again with a brass rod after I've sharpened them.

I need to write up my procedure so I don't forget a step; There was a thread on that a while back.
Click to expand...
don't take my word for it. I am far from being the one to talk to about this. I just seem to think that heating that many times that hot would increase the grain size.
 
Kevin R. Cashen said:
Normalizing would be an extreme pre-measure just to re-harden. If one had serious concerns about grain size they could do a simple cycle to 1400°F-1475°F range and air cool. if you had concerns about distortion, you could do a stress relieve at 1200°F and the get right to re-hardening.
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You rule Kevin, as always thank you.
 
Kevin R. Cashen said:
Normalizing would be an extreme pre-measure just to re-harden. If one had serious concerns about grain size they could do a simple cycle to 1400°F-1475°F range and air cool. if you had concerns about distortion, you could do a stress relieve at 1200°F and the get right to re-hardening.
Click to expand...
thank you!
 
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