Heat Treating 01 Tool steel

[Derek Cohen]

My own needs are met by a simple process. Keep in mind that I do not have the demands of a producer such as Larry. Mine is suitable for one-offs. If I screw up it is only my time I waste ... and then I do it again.

I use two propane torches for greater heat and a wider flame arc. I do this in a gloomy shop so as to better see the colours. I like peanut oil for quenching.



The article was originally posted on a forum and then saved on my website. There are comments from Ron Hock ...

http://www.inthewoodshop.com/ShopMad...tTreating.html

Regards from Perth

Derek

[Jacob Reverb]

I started reading all the old texts containing heat treating information I could get my hands on. When they did mention judging the phase change to austenite it was always cryptic. I found descriptions like, "when the steel opens", "when it sweats", "when the flux rises." Never any mention of color or magnets. Then I found a better description in a 1938 Machinery's Handbook in a section on heat treating high speed steel. I knew I'd seen what was described as soon as I read it.

... and that description is ... ???

(Or do we have to buy your DVD to find out?)

[Trevor Walsh]

I believe he's referring to his video, the one the OP has seen if I recall correctly.

[Larry Williams]

... and that description is ... ???

(Or do we have to buy your DVD to find out?)

How about I show you what you need to look for? Clean, well prepared steel is uniformly preheated then brought up to temperature. I did say clean didn't I? When the phase change takes place the steel forms a carbon iron crystalline matrix and shrinks in volume. But the carbon will begin to burn off which leaves behind iron that is no longer in this shrunken state and the iron flows to the surface forming small pools. You can actually walk the phase change along a piece of steel as is done in this very short video. I think you'll find your forge to be an environment that's too dirty for this. It takes little to no surface contamination to change the way the iron vents from the steel. This iron for a hollow plane had already been preheated.

http://youtu.be/JMLJeBhyTis

[george wilson]

That is overheating the steel. I do not want the carbon to burn off of the surface. It is not necessary,nor desirable. The 01 steel will reach full hardening heat before it begins to "pool" and lose carbon. I have hardened many,many blades without loss of carbon on the surface.Heat treating HSS is entirely different from treating 01 and the simpler steels.

Like Derek,I have often used 2 torches before I got heat treating furnaces,one with proper thermocouple control. Those,and a "corner" made from bricks to set your blade in,will provide sufficient heat trapping for the home shop person to make a plane blade.

The largest plane blades we had to make in the toolmaker's shop were 6" wide crown molding blades,but those were done with the electric furnace. We also made large A2 blades,heat treating them with the furnace and wrapping them with high temp. stainless steel wrap to avoid decarbing. You MUST avoid decarbing on A2 and D2 steels,but these are beyond the scope of most home shop projects. It wasn't 18th.C.,but I felt sorry for the coopers trying to plane hard white oak staves.They work out of doors all year with just an open sided shelter. Since visitors couldn't tell the difference anyway from looking at the irons,they found the A2 blades very helpful. When asked to help,I could not refuse to try to make things better.

The Housewrights said they were able to plane 130 feet of crown molding in yellow pine before resharpening the 01 irons we made for them. We made other wide irons for them as well as the crown molding iron.

The Mapp gas may be only about 100º hotter than propane,but I always found it very useful to have that extra hundred degrees when using simple torches for hardening. It helps when working in less than ideal conditions with heat leaking away.

Peanut oil is better about not catching fire. Since we worked under a hood with 2 powerful exhaust fans,against a cinder block wall,away from all combustibles (where we also did welding),we didn't worry too much about a little fire( like you might have to in your garage!!) Grape seed oil is another high heat durable oil,if you want to pay for it.

[Larry Williams]

That is overheating the steel. I do not want the carbon to burn off of the surface. It is not necessary,nor desirable. The 01 steel will reach full hardening heat before it begins to "pool" and lose carbon. I have hardened many,many blades without loss of carbon on the surface....

George, you've advocated using a magnet to determine the Curie point of carbon steel. The problem is that the Curie point doesn't indicate phase change from ferrite to austenite. Steel will lose its magnetism before the transition from body-centered cubic to face-centered (austenite) configurations of carbon steel. They're different phenomena. Anyone interested in doing a little reading can verify this.

What I'm showing here, as best I can determine from a lot of reading, was professional trade practice in places like Sheffield. In Sheffield multiple companies were producing virtually identical products at the same price, all they had to compete with was their reputations. If one reads Memories of a Sheffield Tool Maker by Ashley Iles they'll learn a single bad batch of heat treating could and did put companies out of business.

We also use a furnace for bigger irons and its computer control does an amazing job of holding temperature to within a very few degrees. The problem I have with it is that I have to assume a carbon content at the high end of specification tolerance. This means I am probably getting much of the steel hotter than necessary. I prefer the torch where I'm working with the actual carbon and alloy content of each piece individually. When I was working to color, I always felt I was guessing to a degree and wasn't comfortable with just guessing.

[jamie shard]

George, is the goal to anticipate and stop right before the pooling? Or, at a minimum, quench when the first pool appears?

[Tony Shea]

interesting that there are two very different opinions on this from two very reputable sources. I did not expect to actually get this many responses from some of the industries top names.

So assume that the bubble do indicate overheating. In actual use of the blade what is the downside of overheating?

[george wilson]

If the steel is overheated,it loses surface carbon. Then,you have to grind away the surface to get to the good steel beneath. I can tell you that in heat treating A2 and D2 steels,if the surface isn't fully protected,they will have a soft layer that is pretty deep.

I haven't had a problem with unprotected 01 becoming decarbed at the correct hardening temp. It isn't hardened at as high a temp. as the more advanced steels. HSS is hardened at a VERY high temperature. I don't harden it(HSS) myself IN THE PROPER WAY,but IIRC,the hardening temp. is about 2300º F. I have made some extremely hard and TOUGH engraving chisels from M33 by just heating to a red(worm red) color,forging the 3/8" square steel bar down to 1/8" square at the cutting edge,and just leaving it to cool.

It does decarb some,even at that very low temp.,however,the chisels are ground to final size afterwards anyway. I am not letting the carbides get hot enough to go into solution,so I'm breaking them down into tiny carbides in a softer matrix by forging at low temp.. I began to do this back in the early 70's. I cannot recall what my line of reasoning was at that time,but a few years later,scientists discovered that the true Wootz steel was made the same way: By only heating to a red color,not white hot like European blacksmiths did. They started out with a very high carbon steel "hockey puck" melted in the bottom of a crucible. The high carbon steel they used is very hard to forge at that low a heat,but it made a remarkable sword. HSS is very hard to forge at that low heat,too,though,of course,it also contains additional alloys from the plain carbon Wootz steel.

I know Larry will argue about this "puddling" point,but I make perfectly good blades,and have been doing so since the 60's. I'm not sure what a description of hardening HSS has to do with hardening 01. Plus,I work with a much wider range of steels than are used on relatively simple wooden plane blades. One of my engraving chisels was tested by the gunsmith's shop by chiseling a groove up the tang of a file. It chiseled the groove into the hardened area of the file 1/8" before the tip broke off!

Having been around a number of blacksmiths and knife makers for decades,I can say that heat treating steel is an often debated area.

I am often,and am presently working on a job from a highly degreed conservationist. Why? Because they give me jobs that they cannot do themselves. Experience and developed skill account for something. I have seen people with degrees above Master's who could not correctly use a table saw,or stay within 1/4" of a line with a bandsaw. I have a degree myself,but it has little to do with nearly 60 years of working wood and metal,39 of them in a museum environment where I had ready access to other excellent craftsmen,conservators,etc..This has been what my life experience is.

[george wilson]

Larry,I have a very extensive library of my own,which I have read and re read over for many years.There is a 25 degree window to get the maximum out of hardening steels,generally speaking. How much are you overheating your steel? I advocated using the magnet for beginners. As stated above,I don't need to use it myself from years of experience.

My own electric furnace is also computer controlled. For smaller things,I don't bother with it.

The little Szumera book mentioned above is a very good book. I also have "Tool Steel Simplified" by Carpenter steel,which is a much more complete book,but I do like the Szumera book very much. Then,I have the Sheffield books,and others.

I think that getting overly complicated is beyond the requirements of the needs of the home shop person who wants to harden a simple plane iron. Use of the magnet is o.k. for them.

There have been projects where I had to be very careful,like hardening amputation knives,where there was a lot of freehand grinding and hand polishing before risking cracking and warping in heat treatment.

The curved amputation knife is ground as thin as a straight razor,VERY easy to break the edge off when heat treating,and quenching. The Bowie is D2,The pocket knife is W1. The beak iron is 01. They have all done their work well(except the amputation knife,which was for the museum!!,but needed to be fully authentic and high quality as were the originals.

[Adam Neat]

I think this illustrates why O-1 is easier to work with. Its more fogiving.. In the end when you get close to 1500 and quench, its hard. You can have different ways of doing it, torch, oven, coals.... dunk it in whatever oil, heck Ive even seen guys water quench it because they didnt like the smoke from the oil.... and still get acceptable results.

[george wilson]

You CAN get away with water,IF the shape of the part permits it. Otherwise,you can crack it severely. I have used WARM water upon occasion for rather large wire drawing dies,when I needed a bit more uumph from the quench than oil would give. But,a drilled hole on a part,a sharp inside corner,or any of a myriad of other factors can crack an 01 part quenched in water.

Another thing: Just because you "got away" with quenching in water,does not mean that the given tool will have the longevity or performance that it would have when properly quenched. Depends upon the future use you want from the tool. Sometimes I make "1 time use" tools. Most times I intend long term use. Just yesterday,I used a "1 time" use cutter that I made 30 years ago! Now it's had 2 uses!! (But,it WAS properly quenched.) It is a metal cutting tool.

You are correct: 01 IS more forgiving than W1. W1 is the most treacherous steel there is. BUT,it will also take a keener edge than A2 or 01,which is why the pocket knife was made from it as a retirement gift for Jon,my journeyman. D2 is a wear resistant tool steel,really intended for metal cutting shear blades. Sometimes knife makers will use it to get the benefits of that alloy.

My favorite steel for both longevity AND safety in not changing shape within a few ten thousanths for punch and dies that must mate perfectly,is A2. I have made dozens of these die sets for our jewelry business. They stand many thousands of cycles before they need re grinding. Some of these die sets take a LOT of work to make,and I want them to last as long as possible. You have to have the right equipment to use the steel,though: An accurately temperature controlled furnace,and either an inert gas atmosphere,or high temperature stainless steel heat treating wrap(with a little piece of brown paper bag inside it to burn out any oxygen).

I think my NEW,most favorite steel is the powdered metal that LV is starting to use!! Plus,they cyro treat it.

[Paul Saffold]

Larry, thanks for taking the time to make the video for us. Even if there is a difference of opinion between experienced craftsmen it is nice for those of us with little or no knowledge in the techniques involved.

[Larry Williams]

interesting that there are two very different opinions on this from two very reputable sources. I did not expect to actually get this many responses from some of the industries top names.

So assume that the bubble do indicate overheating. In actual use of the blade what is the downside of overheating?

I wouldn't call this overheating. If you were to graph the actual temperature of the steel, as you contently add heat during heat treating, the temperature would hit a plateau when the transition to austenite begins. Ron mentioned this in his post. Even though you're still adding heat the temperature of the steel won't rise until the phase change is complete. The additional energy is consumed changing the structure of the steel. You don't want to stop the process until the phase change is complete. If you're working in an oxygen atmosphere you'll lose a small amount of carbon, it's just the nature of austenite, the carbon is doing its best to oxidize while it's free to flow through the steel. The goal is to get the steel quickly, accurately, and completely through the phase change with a minimum loss of carbon and not raising the temperature more than necessary. I don't see anything else being offered here that accomplishes this and it has the advantage of being incredibly easy and direct.

The iron pools are about a molecule thick. They're so easy to remove during initial sharpening they're insignificant. The only way I know of to get as close without the iron on the surface is to work with an inert atmosphere furnace. If you don't like the cost of a good propane torch, I know you won't like the cost of an inert atmosphere furnace.

[george wilson]

Stainless envelopes work fine with a little piece of brown paper to burn up any air inside,but you do need a controlled temperature furnace if the steel is hidden in an envelope.