Thread: Trouble Heat Treating O1 at Home Consistently

Hi
Congratulations on a fine looking chip cutter.

I have a mate who does heat treating on a regular basis.He is a retired machinist and gunsmith. He is into making knives.
One of his toys is a little furnace made from several firebricks.

They are a white colour and the size of normal housebricks.

He has them loose stacked to form an aperture say 100 x 50 x 350 long. A brick on side has a hole bored in it which the LPG nozzle is inserted.

All he uses for the heat is an LPG torch on one of those slim cylinders you can hold in your hand -about 60mm in diameter.

The nozzle shank is cranked ( manufactured that way) so he has made a stand to support the cylinder which rests on an angle while working.

I have seen a piece of knife steel raised to red heat quench temperature in just over a minute. Because the heat is evenly distributed he has no trouble at all in heat treating is blades given they are all the size which fits in his little furnace.
Something like that on a smaller scale may work for you.

Grahame

I've got some fire bricks here you can borrow, to see if making an enclosure to heat them up makes a difference. I'll give them to Waldo today to pass on to you on Wednesday for you to give it a try

• I dim the lights, to see the red better (the room is a 3 x 2 meter square room with an open window (?maybe not enough air getting to point of combustion?)).

No this will not be a problem - but keep the window open or you will gas yourself!

• The O1 is sitting on a large round an powerful magnet, (Is it possible that the magnet is acting as a conduit for the heat drawing it away faster?)(see photo.)

Yep - this will be a problem. Leave the magnet aside while heating up, with an LPG flame you can't overheat O1.
Heat the thing up to cherry red hold for a while (2 minutes) - then test with a magnet. After a while you can gauge the colour and forget about the magnet altogether.

• Then as quickly as I can (1 - 2 seconds) move the cherry red blade into the oil. I dunk the O1 blade in veg oil, stirring it around (the oil is at room temperature).

- Get the oil as close as possible to the cherry red blade, the blade should not have a chance to cool down much when it is quenched, it should enter the oil as red as possible.
I would also apply heat (ie make cherry red as far up the blade shaft as the length of the blade itself otherwise heat will leak out up the blade shaft.
You should not stir but dunk up and down vertically, stirring is not as good at quenching as dunking and will allow one side to cool more slower than the other

• I am able to bring the temperature down to just above skin temperature in half a minute.
• Then I test with a metal file, on the first O1 blade the files just skids and makes a high pitch sound, if I run the file over the area heat treated. If I run the same file over an untreated area the file digs into the metal.
• Also, successfully heat treat O1 will form a bur when you are sharpening and will take an edge. However a failed heat heat the bur never form (breaks off to fast to form, maybe?) and the blade never develops a sharp edge.

How much oil are you using. For a tool that size I would use at least 500 mL.

I would definitely make up a little forge from some fire bricks - the O1 will heat and harder quicker but bear in mind the above factors like accessibility to the oil etc.

All these factors will add up and contribute to the problems you are having.

Cheers
Bob

Originally Posted by DJ's Timber

I've got some fire bricks here you can borrow

Dj that would be really great. I was planing to make a small brick forge, but had not gotten around to making one. It will be good to see what difference they make.

Thanks for the tips Bob. I will try them and see how I go. I am using over a liter of oil in a large tin.

I will report back tonight.

Originally Posted by DJ's Timber

I've got some fire bricks here you can borrow, to see if making an enclosure to heat them up makes a difference. I'll give them to Waldo today to pass on to you on Wednesday for you to give it a try

I knew I forgot something when I walked out the door this morning , should be in Melbourne on Tuesday I think, so I'll pass them on to him then or otherwise Wednesday morning as I am in town for sure then.

There is some good info on heat treating at this site.
A brine solution is better for quenching thin blades , oils are better for thick blades.
Also make sure you quench with the cutting edge entering the quench oil first.
If you have a partial ground edge that is thin ( nearly sharp) then it may be loosing its heat before you quench it or you are not quenching the edge first , giving same result.

http://www.evenheat-kiln.com/technic...at%20Procedure:

Just been doing a bit of reading on heat treatment of metals and as it says in the book, to get consistency you need to get the right heat for the right time and the right cooling to get it right every time..

In the book it has a table of heat treatment temperatures that contains the tool steel O2A..It says here you need to get above 730C which is the transformation temperature...A bit above this temperature is where you want to be as once you go hotter grain growth occurs which leads to a less tough final result.. Really I think you need a proper heat treatment oven to do a proper job every time...

Originally Posted by Retromilling

A brine solution is better for quenching thin blades , oils are better for thick blades.

O1 ,the steel being used in this case is an oil hardening steel and thick or thin is not really suitable at all for brine quenching. I agree with the rest of the statement but it must be a water quench steel.
The brine seems to give a better overall quench and does it quicker to boot.
If the 01 is not suitable, why not a steel in the .8 to 1% carbon range. Some thin warding files might do the trick , being from memory right on the edge of the 1% carbon content range.

Mind ,it something I have not tried as yet! but is on the gunnadoo list.

Tubal Cain wrote a good book on hardening tempering ^ heat treating aimed at model engineers.Its part of the workshop practical series. As soon as I remember where it is or whom I have lent it to I'll get some info from it to post ,other wise I have to depend on my dodgy memory.

If any one needs it I can post a table on using recycled steels for cutting tools.

Grahame

The best way to heat the blade/s is to make an "oven" as previously described using fire bricks. The style I used was simply three bricks laid down edge to edge and one brick on edge and seated on top of the brick at the rear. Lay another brick on edge again, along both sides and on top of the base bricks. Adjust the size of the oven with more bricks if needed. A coupe of bricks on top will keep the heat in. Get a bigger burner, one about 20mm dia would be the minimum size. It depends on how much volume of oven / blade you have to heat. Too big a burner is better than too small as you can turn the gas down. The bigger burner nozle wont give you a hotter flame but it will give you more volume of heat. Get rid of the magnet. The heat from the torch/oven will destroy it anyway. Buy some temperature crayons and use these by drawing lines on the blades. These crayons change colour when the temperature reaches a desired peak and are available for an extensive range of temps.
Soak the blades for at least two minutes but be very careful that you dont burn the thin cutting edges. For cooling, it is best to dip the blade verticaly from one end to the other. You dont really have to stir the blade around and never take it out as you dip it into the oil. I would use a twenty liter drum of oil for quenching. This may sound rather extravagant but the large volume of oil will do a quicker and better job than a small can full. I always dip blades verticaly as a sideways horizontal dipping/cooling can warp the blade as it cools. Never drop the blade in on its side as it will turn into a banana from uneven cooling. The blade should also be tempered.
The way I temper thin material or small parts is to get a slab of mild steel about 12 or 20 mm thick and at least 40mm wider and longer than the blade. Grind the scale off the face and edges then heat the steel until the desired colour is reached (or use a heat crayon to tell you the temp). Place the blade on the steel plate and let it cool. Temper in this manner at least three times and grind the steel face each time before heating. By using the steel plate a very uniform tempering of the part is obtained.

Kody

Kody
Good solid advice ,the steel plate for tempering is what I was going to suggest as we used this method when tempering metal punching tools .We also had an oven made from refractory bricks .

BTW,,, O1 tool steel for hardening in oil and W1 for water .Both of these steels are commonly known as "silver steel" or drill rod, if my memory serves me correctly.
Comes in flat , round and square section.

Kev.

This might be helpful -->> http://www.box.net/shared/bb9gmpra84 2Mb pdf file on heat treatment

Thank you for all your advice.

I got some bricks loaned to me by Dj, and this morning I made a small oven. I again tried heating the second chip knife to a sustained cherry red. I managed to get the color I needed however, I found that I was not able to maintain the color of a large enough area. I think Kody is on the money when he says to "Get a bigger burner". My little burner is no bigger then a 5 cent piece.

I decided to get a much thinner 2 mm piece of O1 I had. I got it to cheery red easily, and it demagnetized very easily, I soaked for two minutes. I was however unable to heat and maintain the heat an area bigger then 20 mm at one time. After that point it was impossible to keep more then this tiny area cheery red and demagnetized. I then dunked it into pre heated veg oil (Just a little above comfortable temp if I stuck my finger in). I was able to easily sharpen an edge after this point.

I therefore believe that the root problem is not having enough hot air to consistently heat the required area continually. I will find the largest head I can find for my burner, and I will get back to you.

Thanks again for all your help on this.

Originally Posted by Kody

Get a bigger burner, one about 20mm dia would be the minimum size.

Do you have heavy fire bricks or light? The light bricks heat up and cool down quite quickly, but to get a bit of thermal mass heavy bricks might be better, as heat will not be drained away by cold air and you might be able to get a larger area an even temp. What keeps heat is thermal mass. Air can't really keep the heat.