David
I am a woodworker interested in making chisels and other woodworking tools. I’ve got a little experience stick and gas welding and I’ve done a little heat work with tool steel. What I want to learn is the process for forming O1 steel in a new shape.  Say I heat up O1 steel to a forgeable temperature so it can be hammered into a shape while red hot. Two questions: 1) how do I prevent carbon loss in this process? 2) how to I prepare this forged piece prior to hardening quenching and tempering? Do I need to anneal it before starting this process? What is the best method for annealing for a DIY limited tools setup?
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jmccustomknives
Forging tool steels like O-1 can be tricky, but if you follow its rules it's not that difficult.  Start by heating a test piece.  As the heat comes up touch it with a magnet.  When the magnet stops sticking, that is the austinization temperature and also your bottom heat for forging.  It's really hard to describe colors since ambient light has a lot to do with how it appears but in my shop the steel is an orange/red (called cherry red by the old timers).  The upper end temp is going to be where it's transitioning from orange to yellow.  Do your forging in between those colors.  As the piece forms and gets close to being finished lower that starting heat temperature.  You'll finish the forging by working out the high spots right at the bottom end temperature into red.  At this point you're not trying to move metal, just work the high spots out.  Light hammer strikes are used here.

After forging take the piece, place it in the forge and evenly heat it just past that non magnetic temperature.  Take it out and let it cool to black in the air.  Repeat the heat again, this time pull it out at non magnetic and let it cool.  The third heat is taken just below non magnetic, let it cool.  This is called normlization and along with the forge procedure will leave the internal grain structure small and ready for the heat treat.

Before the heat treat clean up your piece to about 90% finished.  Don't have and sharp angles, these cause stress risers that will focus the stresses that occur during the quench causing it to crack.  Bring the piece up to non magnetic.  The hard part is to hold that temp as long as you can in a forge or with a torch as this steel require being held at austinization temp for a period of time for the carbon to go fully into solution.  However, I'd rather you quench to soon than overheat.  When it's ready, quench in canola oil.  For chisels you can just quench an inch or so of the cutting edge.  This is a differential quench and leaves the edge hard and the rest soft enough not to break.  

Tempering should be in the 400F-450F depending on the type of tool and should be done twice in at least 1 hour increments.  

Rule #10;  "I can make that" translates to; "I'm to cheap to buy it new."

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David
Thanks so much. These are the details I was looking for. I will give this a try in the next couple of months.
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anvil
O1 is a great steel for wood working tools. I've made many hand and lathe tools for wood with O1. It's relatively a very forgiving steel.

Here's some suggestions. Download this color chart. It is a PDF from Uddeholm steel. It shows forging colors and tempering colors.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.uddeholm.com/files/Temperature_guide.pdf&ved=2ahUKEwjXgNGF34TpAhUZHs0KHbKLDjwQFjAMegQIAxAI&usg=AOvVaw06rXRXuqoTvjlOyQwRMEQb

Next download "the heat treaters guide companion. It's a downloadable app for Android. This lists forging and heat treating specs for many steels. A great free source.

O1 is listed. Follow their guide for forging and heat treating. The Uddeholm chart shows colors/temps so between the two you have good specs and a great visual guide to aid you.
Like Jim said, make sure to read your colors in a constant light, not outside. The sun will fool you and the relation between temp and color will change by time of day, and cloud cover.

You will find that the steps for forging and heat treating  nearly all steels is as follows:

1)Forge
2)Normalize
3)Anneal
4)Cold work
5)Harden
6)Temper
7)Finish.

You will notice a difference between Jim and me. I always Anneal. I believe it's a critical step. I have never seen a spec sheet from the manufacturer ( ie Uddeholm Steel) or the HTG that doesn't list annealing in the process. There are a few common steels that do specifically say not to Normalize. O1 is not in this catagory. I believe It's a contemporary knife making thang. I also believe it's an unwise short cut as it takes more time to Anneal because it must cool slowly in lime, not air cool. Even Cashen, an excellent contemporary knifemaker, lists how to work 6 or 8 common knife making steels and follows the steps I listed to forge and heat treat all of them. It's a good site to check out.
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David
I have a really simple set up, an acetylene torch and a two burner majestic forge. No oven. So how would I anneal? I am working with metal that is 1/8” to 1/4” thick. Can I get away with much shorter annealing times?

Thanks for the good information.
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anvil
As a general rule, bring it up to just above critical temp(cherry red or what is recommended by specs) , then bury it in lime until cool. Lime is very dense and very fine. It will allow slow cooling. Wood ash works as well if you remove the big pieces of charcoal. I prefer lime due to its fine grain and being so sense. You can get lime at most feed stores.

I put the lime in an old rectangular baking pan. It just needs to be deep enough to cover your Work and not touch metal. A few inches top and bottom is all you need for small things. 

For our needs, generally I let my tools anneal til completely cool. This is usually pretty close to the time stated in the specs. 

I rarely use the stepped down cooling. When I have done this, I have not seen a difference in hardness of edge holding ability. I suspect that it would be critical if I were heat treating springs for the space shuttle, but I believe it's not critical for hand tools. 

There have been times when I've made quickie tools for me due to need. I then have not annealed, just normalized, hardened, and tempered. They work for a short while but do not hold up with daily use. Think of a cold chisel or a center punch. I've either thrown them in the scrap pile, or reheat treated and followed the steps above. 

This works very well for me with O1 steel.
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David
What do you mean by “sense”?

Would leaving the steel in the forge as the forge cools down to room temperature anneal it?
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anvil
I don't see "sense". Did you mean "dense"? Lime is more dense than wood ash. This means a cup of lime weighs more than a cup of wood ash. This denseness settles tightly around your tool and holds the temp in for a longer time. Meaning it cools much slower.

You have a gas forge, I believe. I don't know, how long does it take for your forge to cool down? Depending on the specs of your steel, you might need to slow cool for 4 or 5 hours or more depending on thickness of your tool.. This slow cool is critical

If you have a android phone, download the app I suggested and look up O1. Then I'll give you more help understanding the specs.
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David
To anneal the App says to bring the temperature up to 1400 F before starting the cooling process in lime. My forge is outside and so the color chart may be difficult to use. Would it work to bring it up to just before the non-magnetic austeniite temperature instead?.

Also, for my next project I will not be hot forging. The pieces of O1 steel come from the factory annealed. I am hack sawing and filing to shape. Can I simply go directly to the H&T phase without annealing or normalizing?

Thanks again for your help.
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jmccustomknives
I would normalize once.

Rule #10;  "I can make that" translates to; "I'm to cheap to buy it new."

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anvil
You can heat treat outside if you use a "dark box". A 5 gal bucket works. Keep it by your forge and put your iron inside. Don't drop it in, keep holding it with your tongs and look at the colors. Then you can see the colors properly. Just make sure it keeps the light out. When you do this, do it with a piece of mild steel. Heat it up to "just AFTER it loses its magnetism". Then stick it in the dark box. Just watch it and watch the colors as it cools. You could even get it real hot and bring it to a sparking heat. Then watch the colors in the box. box

As I understand it, heavy machining puts stress back into the iron. Big shops often do a complete new heat treat cycle after heavy cold work. Think large die blocks. However, I don't think the hacksaw and filework we do create much stress.  Unless you have a lot of money invested in quality ht ovens and tooling, you can only be close enough. You are at the bottom of the learning curve. The only way to not be there is to go out there and get her hot. Besides, what ya got to lose. Bottom of the line is it's just a piece of steel and steel is cheap.  Learning is the expensive part.  😉
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