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Flame Hardening O1

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ebolton

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#1
I understand the basics- use a carbeurizing flame, heat till non-magnetic, quench in oil.

Would it be smart to coat the piece in brazing flux to protect the surface? Or would that just add to the cleanup later?

I wish I paid attention better, or remembered better, when they showed us this in machine shop class 40 years ago.

-Ed
 

Dave Paine

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#2
I have hardened small pieces of O1 drill rod to make cutter for wood turning tools. I did not use anything to coat the metal. It did go black when quenched, but this was easily removed with light sanding using a worn out piece of 600 grit wet-dry paper and a little water.

I just heated to above critical temperature with a MAPP gas torch. I was trying to make the entire piece hard. Not sure about flame hardening.

For my small pieces, I tempered in the oven to about 330 deg F. Easier to control the temperature with the oven than the torch.
 

Silverbullet

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#5
Ive been doing it the same way for many years , only I draw it back to stray with the torch and let cool. Never had a problem with breakage or dulling of the tool. May not be right but it works for me. You can use a wrap to cut down on finish loss. Even to case harden put it in the wrap covering piece to be colored.
When I went to vokie we did our tools that way. We really had everything in our school. Separate rooms for heat treatment and grinding room. Besides the shop floor full of lathes mills and all sizes up to 20" turnado lathes. My favorite and the small south bends .
 

ebolton

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#6
Thanks. This is a small tool, about 5/16 diameter by 3-1/2 long. I only care about the business end for hardness, and don't care about color. I already turned a groove in it to hang it up by a wire hooked from above while I heat it. I'll then unhook the wire and use the wire to dangle it into the oil for quenching.

I've never been great about judging the colors, hence the fixation on the magnet.

-Ed
 

mikey

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#7
I understand the basics- use a carbeurizing flame, heat till non-magnetic, quench in oil.

Would it be smart to coat the piece in brazing flux to protect the surface? Or would that just add to the cleanup later?

I wish I paid attention better, or remembered better, when they showed us this in machine shop class 40 years ago.

-Ed
As discussed in another thread, coating with Boric Acid is a good idea because it comes off easily with a Scotchbrite pad. I haven't used brazing flux but it might be the same thing. The boric acid actually works well and I've been using it for 20 years.

Basically, you take some boric acid powder (termite killer) and make a thin paste using rubbing alcohol. You don't need denatured alcohol, although it won't hurt. You want the paste thin enough to spread but not so thin that it runs. Add alcohol sparingly as the powder will thin out fast; if too thin, add more powder.

Use some wire (I use rebar tying wire) and tie it to the part. Some folks tell you to make tight wraps to cover the part with wire; I see no reason for this and just tie the wire so it hangs on to the part well. Cover the entire part with your boric acid paste; I just use an acid brush for this. Then heat it to critical temp.

Using color to heat a part is reasonable but cherry red to me and cherry red to you may differ. Lighting conditions also make this a very subjective thing. I use a Mapp gas torch (or two if the part is big) to evenly heat the part until it looks cherry red, then start to introduce it to the magnet until it no longer attracts. Then I plunge and twirl it in ATF until it stops bubbling.

Once the part is cool enough to handle it is up to you how you want to temper it. I have been advised that the part should go into the tempering oven as soon as it comes out of the quenching oil. This is the way you should do it. However, I usually take the wire off and use Scotchbrite under running water to get the boric acid stuff off so the part is clean. Then I use lacquer thinner to completely clean the part before putting it in the oven. Oil from the quench or your hands can stain the part in the oven so I want it clean.

I normally use a toaster oven with a glass door so I can see colors easily. I normally preheat the oven to 350-375 degrees or so and put the part in, then watch for the color change. Naturally, thinner sections of your part will draw back faster than thicker parts so if you want a differential temper, where one part must be softer than another, then an oven is not the right tool. Use a torch and temper until your thin part (like a cutting edge) reaches your desired color (like amber), then heat the rest of the tool to purple or blue or whatever you need. Just stay away from the thinner part and it should work fine. This is not an exact thing but differential tempering this way does work.

Hope this helps.
 

ebolton

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#8
Mike, helps a lot!

I just changed the oil in my motorcycle, so the used MC oil was going to be my quenchant rather than ATF.

-Ed
 

mikey

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#9
Mike, helps a lot!

I just changed the oil in my motorcycle, so the used MC oil was going to be my quenchant rather than ATF.

-Ed
Good idea - your part will go faster!

Actually, the only reason I use ATF is because it smokes and flames less than motor oil. I also use old, used Vegetable oil as it also flames less but I have to pick off the crumbs from deep frying first before tempering ...
 

mikey

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#11
OK, now I know to keep the surrounding area clear and turn off the smoke detectors.

-Ed
Also stand clear of the can of oil unless you want to permanently live without eyelashes and eyebrows! You think I jest, eh?

Leather gloves to deal with the inevitable splashes and eye protection are a must. I don't normally use a mask because there isn't much smoke and I can hold my breath long enough to get clear but safety is a really big deal when doing this stuff so please be careful - hot, splashing oil is not that much fun.
 

Rockytime

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#12
Thanks Mikey for the post. That is exactly how I was taught in clock repair school 40 years ago. I still use boric acid when making small single point cutters.
 

Downunder Bob

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#13
If you are using a MAPP gas torch, you are indeed flame hardening (as opposed to using a controlled atmosphere heat treat oven).

Thanks,
-Ed
No, not exactly, you might be using a flame as your heat source, but that is not "Flame Hardneing". Flame hardening is defined process, I don't think MAPP gas has enough free carbon in it. You need to use oxy acetylene with the flame set to give a caburising flame, or even a blacksmiths forge, this adds carbon to the steel so when quenched it hardens it. Also flame hardening is not required to harden what is already tool steel, just heat and quench. Flame hardening is used to harden steels that are low in carbon, so the process is used to add extra carbon, it will result in a surface or case hardening only, for through hardening you need an alloy designed for this.
 

WoodBee

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#14
, this adds carbon to the steel so when quenched it hardens it.
Bob,
I have no clue about flame hardening, but reading this thread made me wonder.
I assume using flame hardening in combination with boric acid is a bad thing because it interferes with the carbon absorption into the steel?

Thanx,
Peter
 

WoodBee

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#15
, this adds carbon to the steel so when quenched it hardens it.
Bob,
I have no clue about flame hardening, but reading this thread made me wonder.
I assume using flame hardening in combination with boric acid is a bad thing because it interferes with the carbon absorption into the steel?

Thanx,
Peter
 

Downunder Bob

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#16
Bob,
I have no clue about flame hardening, but reading this thread made me wonder.
I assume using flame hardening in combination with boric acid is a bad thing because it interferes with the carbon absorption into the steel?

Thanx,
Peter
Yes Peter, I think it would interfere with the carburising effect of the flame. I have never heard of, or seen any flame hardening process where any coating was used. That doesn't mean it can't be done
Bob,
I have no clue about flame hardening, but reading this thread made me wonder.
I assume using flame hardening in combination with boric acid is a bad thing because it interferes with the carbon absorption into the steel?

Thanx,
Peter
Quite OK peter, we all have to learn somewhere, I have the benefit of having done a 5 year apprenticeship, and although a bit rusty in some areas, I think I've remembered most of it, and spent some 50+ years in the industry.

Of necessity I was rather brief in my description on flame hardening. and I really only mentioned the process where it is used to give a thin shell or case hardening effect to low carbon steel. In the case of higher carbon and other alloying ingredients the flame hardening process can also be used but it is not essential to provide the carburising effect of a reducing flame, as you are really only using a flame as a heat source. In this case I guess you could use MAPP gas on small parts.

As in almost all things, Google is your friend, look it up. Ignore the articles that go against the main stream. I'm sure you will even find links to books that you can buy if seriously interested.
 

EmilioG

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#17
What about using TempilSticks? Do they work and are they better than watching for color change? More accurate?
 

Bob Korves

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#19
Ignore the articles that go against the main stream.
Consider them with careful thought. We are only parrots if we just just regurgitate the party line. Read and listen to all ideas, take them under advisement, give them discriminating scrutiny, and then test for what works best for YOU. This is not a popularity contest...
 

Downunder Bob

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#20
What about using TempilSticks? Do they work and are they better than watching for color change? More accurate?
I haven't used them but I imagine they would be a help, depending what accuracy and at what temperature.
 

Downunder Bob

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#21
Bob,
I have no clue about flame hardening, but reading this thread made me wonder.
I assume using flame hardening in combination with boric acid is a bad thing because it interferes with the carbon absorption into the steel?

Thanx,
Peter
Our founder Nels has written a nice article on heat treatment. "Heat Treating (annealing/hardening/tempering) Metals". it's in the Beginners Forum.
 

WoodBee

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#22
Bob,
Thanks for your replies.
I have found the article you mentioned, an am reading it.
Peter.
 
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