View Full Version : When to heat treat and not?

Mark AJ Allen
11-16-2016, 7:23 PM
I was given a piece of O1 steel, so I fashioned a striking knife from it. I noticed that it was pretty easy to file, sand, grind, etc... so I suspected it was not hardened, which was confirmed by the donor. He asked if I was going to heat treat it. I have been using this knife for a few weeks, it's rather easy to refresh the edge and stays very sharp; sharp enough to score across white pine grain without tearing.

So obviously I'm not hacking away or hitting this knife with a mallet, so impact resistance isn't really important. Would I be improving anything on this tool if I were to go through the experience of heat treating it and annealing it? Seems to me that I'm doing OK as it is ...

Dan Hulbert
11-17-2016, 10:55 AM
If it ain't broke, don't fix it. That being said, heat treating and annealing will cut down on sharpening and, if you haven't done it before, could be a learning experience.

Mark AJ Allen
11-18-2016, 10:24 AM
Well, I answered my own question last night ... While I had been using this knife for a few weeks, I had not used it with a metal edge yet. It dulled on the first use.

I'm definitely going to need to heat treat. I've been told MAPP gas is a good bet.

Lee Schierer
11-22-2016, 9:20 AM
Unless you have experience with heat treatment. I would suggest you find a company that does heat treating so you get good results without making it brittle.

michael langman
11-22-2016, 12:39 PM
O1 tool steel will deform the piece being heat treated especially if the piece is long and slender like a knife blade.

How the piece is put into the quenching oil will help to lessen the bow and twist in the piece being hardened.

Heating the piece up uniformly with the torch will also help to lessen the deforming.
That being said, it is not too difficult to harden and temper a piece of O1.

Have a container of motor oil tall enough to accept the blade you want to harden.
Hold the blade in a pair of vice grips by the handle end.

Heaten the blade up with the map torch to a dull orange, along its length by moving the torch from the handle end to the point end, stopping an inch or so before the end of the point end of the blade.
When the entire piece is a uniform color, put the blade into the oil point first and as straight down as possible.

When the piece cools to about 200 degrees remove it and clean off the oil and scaleing to clean steel so you can determine the steels color when you temper it.
Now you want to heat up the steel, slowly, to a light straw color, which is a light golden yellowish brown.
Again quench the blade in the oil.

You can check the hardness of the steel with a good sharp file before tempering. It should be about glass hard. The file will skate over the steel without cutting it.

Tony Pisano
02-10-2017, 5:47 PM
As mentioned, be sure the oil container is tall enough. You want the entire blade to be quenched quickly and completely. Also, have a lid handy. Sometimes the surface of the oil will ignite. Just cover it and it will go right out. Also, again, when you heat to temper, play the flame on the thickest parts of the blade. Avoid the edge and watch very closely. Things can change very quickly and its okay if the back edge gets darker than the cutting edge.

Brad Harding
02-15-2017, 1:25 PM
O1 grade of steel is made to allow easy machining and then heat treating. Harder steels need sharpening less often so I do recommend heat treating. Micheal has given excellent instructions above on how to heat treat O1.
Allan Lancer has instructions on making and heat-treating a hook tool from O1 steel on his website:

Mason Truelove
03-28-2017, 11:14 AM
you can also try to sharpen it with a wet stone...

Anthony Albano
03-31-2017, 11:05 PM
Get this book; it will explain the whole process. I really enjoy making knives now.
Far easier than
you would think

Harry Hagan
04-03-2017, 11:17 PM
I like to watch Forged in Fire on the History Channel.

Paul K. Johnson
04-04-2017, 6:32 AM
Usually when you buy tool steel it is not hardened. It is made and meant to be hardened but you make the tool first while the steel is softer. Then you either send it off to pros to make sure it's done right or you attempt it yourself. There are a ton of videos on youtube explaining how to do it and O1 is probably the best one to start with.

Walter Sorrells does very good videos and he doesn't talk about nothing for ten minutes before getting down to it like most folks:


John C Cox
04-04-2017, 11:48 AM
Go for it. O1 is pretty forgiving stuff.

Expectation wise... Be careful here. Its going to warp. Dont get greedy and try to harden the whole thing... That just means more warp. Only harden the cutting edge - maybe 1/2".

Process wise - there is a lot of stuff written by knife guys.

You want to start by normalizing your steel. You heat it to cherry red and hold it there about 5 minutes, then let it cool in air. It generally ends up about half hard doing this. Check for warp and straighten as necessary. For wood use - you could probably stop here if you want to...

Then - harden. Heat to cherry red. Check for nonmagnetic with a magnet. Quench in lukewarm cooking oil. Check with a file - if you did it right, it will skate. Its now super hard but really brittle.

One trick for home use is to chuck it into your freezer over night after it has completely cooled. This can help finish the metal conversion if you overheat it a little during hardening. Its usually not needed... Wont hurt anything though.

Use a toaster oven to temper. I would start with 2 hours at 450F and see how that does.

Then - clean it up, grind out the warp, sharpen it up, and off you go..