Heat Treating 01 Tool steel

[Tony Shea]

I need a bit of help heat treating my O1 molding plane blades. I have a setup of just a Bernzomatic 8250 torch with a can of Mapp gas and a few blocks of fire brick to hold in some heat. I'm sure I;m able to get the heat high enough with this setup but due to the lack of control I am not able to get a sufficient soak time at the right temperature. I've heard that this should be fine with such small blades in a molding plane (#8 Hollow and Round--1/2" radius). I've made my planes per Larry Williams DVD, which is great.

Anyways, my question is about knowing when I'm at the right temp. Larry suggests not using the color of the steel but watching for bubbles (which he calls flux bubbles) coming to the surface of the steel. I personally never saw any of these bubbles on my first and only attempt but didn't dare go any further as the steel color was into the orange range. I also had a magnet nearby but couldn't get that setup so the magnet wouldn't stick to my red hot blade, just got too awkward. What are these bubbles Larry is talking about and is it something truely reliable in determining the proper temp?

My blade does seem a bit soft so I'm not sure I really did get up to temp. But seems to hold an edge well enough to make the plane useable. In fact I'm very happy with the plane so far. But I want a better result on the matching hollow.

Also, I'm stuck on the tempering side of things as well. I have a reliable oven that I use but am not confident on the time and temp to temper the blade at. Larry suggests 375 deg and Ron Hock 325deg. But the time is not clear to me. Ron says 325 for 20mins per inch of cross section. With my half inch by 1/8" blade what does that equal? Might be a dumb question by I just can't wrap my head around that.

Last question is about re-hardening 01. So if Im not happy with the hardness of the blade is it possible to re-harden it? I've seen where it has to be annealed first before this is possible and that seems like it would be beyond what I can do with my setup. And I've also heard where there may possibly not be enough carbon left to re harden this blade.

Sorry for being so long winded. There is a lot more to this heat treating than I thought.

[Adam Neat]

Ive heat treated a few items using O-1 but I always use a small lab oven that I have. The big test after you quench is run a file over the part, If its "hard" the file will just slide over the surface and not bite into the part.
If the file bites in and cuts, The part didint heat treat right.

On tempering, its not the time thats critical in as much as getting the part to the correct temp. So you want your part in the oven long enough to reach the desired temp, A little longer wont hurt as long as the temp is the same.

Im not sure about the re-heatreating a what steps are needed. If you do need to anneal its just a matter of getting to the critical temp (1400-1500 in this case) and cooling very slowly instead of quenching

[Mark Baldwin III]

Orange is the right color for O-1, so you did good there. Color vs bubbles is probably a matter of personal preference, I've gone by color with the couple of irons that I've made. You may want to try a dual torch set up to get a bit more heat. I've rehardened one iron, with no noticeable ill effects, though it probably lost some carbon.
Tempering takes a little more touch than hardening. You will want to verify the temp of the oven you are using. A kitchen oven can be off by 50 degrees in some cases. That's enough to change the level of temper you're shooting for. The advice given to me was to start at the lower end of the tempering scale, and if the blade was too hard, then to retemper at a slightly higher temp.
While reading "The Tool Steel Guide" (Jim Szumera), he says that you must let the iron cool back to the 150 degree range before tempering. The hardening process is still working as it cools, and that process must be allowed to work. Once you can hold the iron in your hand, it is ready for temper. If you go too soon, it's actually possible that you might not obtain full hardness.
No...not trying to sound like an expert, I'm still learning this too! But hey...my irons work pretty darned good ;)

[george wilson]

The Szumera book is an excellent book. I had one at work and need to buy one for home,though I memorized it pretty much. Just like to have one.

Orange is a good color for hardening. Use vegetable oil,automatic transmission fluid(we had a 5 gallon bucket at work),or any other CLEAN oil. Used motor oil is a big NO NO. It will coat your iron with a thick,black coating that is hard as blazes. The quench should be large enough that the quench is not noticeably heated by the blade being quenched.

If your steel "bubbles",you have burned it. Likely,you can't get a decent sized piece of steel that hot with a Mapp gas torch. Just heat to orange,no more.

Do not bevel the blades before hardening,or you run the LIKELY risk of the blade becoming cupped,as there is a different amount of surface area on either side of the blade. You could file the shape of the molding you want onto the blade before hardening,but leave the edge square from front to back,and grind the bevel later. If the blade is pretty narrow,like 1/2" wide,not much cupping will occur.

To temper,do like the above mentioned book says: Have a PRE HEATED toaster oven ready. As soon as you can BARELY hold the blade in your hand,put it into the hot toaster oven. I recommend about 400º. Too many people like to make their blades TOO HARD,and they don't hold a good edge because the thin cutting edge microscopically breaks off,and the blade seems dull. I KNOW THIS FROM LONG EXPERIENCE.

The toaster ovens and kitchen ovens do not have reliable temperature settings. The kitchen oven can really be off as much as 75º. I bought a long backed high temp.thermometer from Brownell's Gunsmith Supply,and inserted the long thermocouple into the toaster oven from the back.

If you want to keep things cheap and simple,for most of my life,I just tempered the blades to a medium brown(straw) color,varying as to the purpose of the steel. Blue for a spring. The FIRST thing you MUST do correctly,though,is get the steel so hard a NEW,fine toothed file,and NOT a Mexican Nicholson,will just skate across it. Use an older USA one,or buy a Grobet from LV. Polish off the crud from hardening the blade till clean steel is had. Heat the blade from the non cutting end,and let the colors SLOWLY creep to the cutting edge,then quench at once. You will make a perfectly satisfactory simple blade this way. The book(above) was really written concerning extremely expensive tool and die work,when you want to extract every bit of the performance from the tool steel that is possible. Your plane blade is not as critical as a $100,000 die.

I have used the more advanced methods for the last 20+ years,but in the 60's and 70's,things were done more simply with a torch OR 2,bricks,and a quench.

[Mel Fulks]

Thanks George. I have always been interested in this type of stuff,but no real expirence with it.Printing your info out as a permanent reference and I know many others will too.

[Trevor Walsh]

Tony,

I would agree with your assessment that the iron is not fully hard. I've done a lot of blades and cutters in 1095, W1 and some O1. I usually do this work in a dark room (not black but no overhead lights indoors around 6pm in the fall is good) or a basement with small ground level lights or a door open to the outside, heat to a medium/bright orange and quench. In the past I've tempered according to color in the straw to dark bronze range, but on the #6 round iron I made I used a toaster oven at 350F. The difference in temperature between Larry and Ron's suggestions is a few points on what's called the Rockwell Hardness Test scale C, It's like the Janka test but for hardened metals. The higher temperature of the temper means the metal is a little softer but a little tougher. Either would work fine.

As for re hardening, don't worry about burning out the carbon, you would have to hold it at very high heat for a while to burn the carbon out of it. Think of it like this, Steel is an alloy of Iron and Carbon, Iron makes neat organized lattice (cages) of atoms and the carbon sits around these, when you heat the metal to Critical (~1600F) the carbon atoms go inside the little iron cages, when cooled quickly the carbon doesn't have time to exit the cages and gets trapped inside, this makes the metal really hard but brittle, tempering takes some of the hardness out of the metal so it doesn't shatter when used.

To reharden the iron, just get your torch and a can of wood ash or sand or vermiculite, heat the iron up to critical (~1600F, med/bright orange in a dark room, until it's not magnetic) and bury in the can of material until cool. Then it's really soft again and you can try the hardening over again.

[Adam Neat]

Here is a good PDF with the basic parameters for heat treating O1

http://buffaloprecision.com/data_sheets/DSO1TSbpp.pdf

[David Posey]

Tony, to get the magnet to work, put it in a pair of vice grips. When you get ready to check the iron, pull it out of the fire and bring the magnet to it. When it's non-magnetic the iron is ready. I usually have to heat treat in full sunlight, so I tend to rely on this rather than color.

[george wilson]

Try to not get the magnet too hot,as that will demagnetize it. I'd prefer to take the Alnico V magnet out of an old speaker and use it. Alnico V looks like surface ground steel. Don't try using rubber based magnets. I guess ceramic based ones would be o.k.. I just prefer the old time Alnico V myself. I'm not sure how sensitive two heat the new "super magnets" like LV sells are. They aren't real large,so might heat up quicker when touching to red hot steel.

I don't use a magnet myself any more,as I've done hundreds of heat treatments,but if I did,the old Alnico V has some mass to it. One out of an old 4" radio speaker is fine.

[Ron Hock]

Hi Tony,

Sounds like you got pretty close. I find the magnet the most reliable temperature sign for the "shade tree" heat-treater. I use the magnetic end of a carbide scribe but any magnetic parts pick-up type tool will work. You can't just leave the magnet on the piece until if falls off, though. DAMHIKT. Kluge up a way to either stick the magnet into the "furnace" or remove the piece to test. I test when the steel makes a leap in color brightness. The time-temp curve flattens out while the steel is undergoing the transformation from ferrite to austenite, the high temp crystal structure. So the steel glows progressively brighter as it heats but the increase in brightness levels out for a while during the phase change then jumps to a brighter orange. That's when I test with the magnet to be sure. When you've done it a few times you'll start to trust your eyes and won't need the magnet except to show others the magic.

I like peanut oil to quench because of its high flash point and it smells way better than any petroleum oil in this app. It will still catch on fire though so use all safety gear and keep the extinguisher handy. And don't even think about doing this in the kitchen.

Temper as soon as you can handle the piece with your bare hands. For Rc62, shoot for 325F. This you can do in the kitchen, especially if you have an oven with a digital control. The rule is, as you mention, 20 minutes per inch of cross section but for things as thin as blades, you can pretty much just get it to temp and you're done. A short soak is recommended, however and if you trust your oven to not exceed the target temp, you can leave it in there while you have some lunch. And no need to quench from here, just let it cool and you're good to go.

There will be some degradation at the surface from carbon that was lost at the high hardening temp so plan on giving the cutting edge an aggressive, deep honing to expose the good metal that lurks below the soft surface. If you test with a file, it may bite that soft surface but if you cut a bit deeper you'll feel the hard steel beneath.

There's more here: http://www.hocktools.com/diyht.htm

Good luck. Be safe. Have fun!

[Jacob Reverb]

Tony, to get the magnet to work, put it in a pair of vice grips. When you get ready to check the iron, pull it out of the fire and bring the magnet to it.

Another trick is to hang a magnet from a wire or piece of string, and simply wave the hot steel past the magnet. When the magnet no longer moves when you wave the steel past it, you've hit the critical temperature.

[Tony Shea]

Thanks for all the advise. I've used the blade just a bit more without doing anything more to it and it seems to be working ok. I'm not 100% happy with it but haven't decided if it's the hardening or the temper. I'm leaning toward the temper as the edge of the blade is more chippy than folded over steel. Sharpening the blade also proves to act as though the steel is hard. Running a file over it is not really that convincing to me. The file marks it up but really doesn't remove much metal. The blade is small so I don't really want to file marks into it to test it out, more than I already have. But the file is certainly not biting into it like soft metal. I'm just going to use it a bit more, make my matched hollow and see how it performs.

I like the magnet hanging from a string idea so as not to have to put the steel on the magnet and struggle with getting it off. As long as I hang it close enough to my bricks.

Is there some kind of thermometer I can buy that I can throw inside my oven to show the accuracy for tempering?

So, not many responses on re-hardening the iron. If it does turn out the blade is actually soft what methods should I do to re-harden my blade. Trevor's advise does sound reasonable about annealing. I do understand that annealing is a very slow cool down time but there is no need to soak the steel at the proper temperature for an extended period of time?

Thanks again for all the help.

[Adam Neat]

Something that had slipped my mind that I used before I got my oven is temp-laq paint.

Its a temperature indicating paint, you put it on your part and when the specified temp is reached the paint melts away. Its pretty accurate stuff and available all the way from 175 to 1900 degrees.

I would say you could get by with using your torch and getting 1500 for the heat treat and 400 for the tempering.

McMaster sells the stuff http://www.mcmaster.com/#temperature-indicating-paint/=js2tcl
(http://www.mcmaster.com/#temperature-indicating-paint/=js2tcl)

[Adam Neat]

Oh and the re-hardening, I would just try re-heating and quenching, and not worry about annealing

[Larry Williams]

Tony,

First, I suggest you avoid using a MAPP torch. MAPP only burns a little hotter than propane, maybe 100º if I remember right, but all the MAPP torches I've seen generate a pencil-point flame. Your goal should be to uniformly bring the bit of the iron to critical temperature and the concentrated pencil-point flame makes this very difficult. You'll most likely overheat areas of the surface which will result in pitting.

I realize the torch I use is expensive and maybe hard to justify for a few planes. If that's the case, I think the one at this Harbor Freight link would work okay:
http://www.harborfreight.com/propane-torch-with-push-button-igniter-91037.html?ccdenc=eyJjb2RlIjoiNzk2OTM2NTIiLCJza3Ui OiI5MTAzNyIsImlzIjoiMjQuOTkiLCJwcm9kdWN0X2lk%0D%0A IjoiMjI3NyJ9%0D%0A&utm_medium=email&utm_campaign=4212b&utm_source=1002
I haven't used this torch and can't say for sure but I believe it would do the job. I can forward a coupon for this if you're interested.

Another thing is that I greatly appreciated Ron's information and help when I was trying to figure this all out. We still use peanut oil today because of his suggestion. When heat treating small things like what you're doing, though, I found the magnet unworkable. By the time I knew what the magnet was supposedly showing me, I'd lost a lot of heat in the small piece of steel.

With Ron's information and encouragement, I did learn to judge color with pretty good success. But I was heat treating outside in varying light conditions. The time I realized how unsuitable judging color was is when I taught a workshop and planed to heat treat at dusk on the loading dock of the school. It was about this time of the year and by the time we were set up the mercury vapor lamps had come on. The color shift of those lights made judging color impossible.

I knew I needed better consistency, the kind of consistency I found in old tools. 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. I set about finding a way to consistently get the steel to show when the phase change happens then wrote to everyone I knew who could help explain what was happening. I even wrote Ron and he didn't seem interested so I moved on. I had a lot of help from some pretty educated and experienced people and at one point a PhD metallurgist in Australia had the information run past some of the metallurgy faculty at Oxford University which is considered the World authority on the phases of carbon steel.

When heat treating steel going beyond critical temperature will increase grain size so will keeping at critical temperature or above for any length of time. If you look at the carbon content of O-1 steel you'll find a 15% variance in tolerances. Look at a phase chart and you'll see that 15% makes a difference as to what temperature the phase change to austenite happens. There are six or seven other alloys in O-1 that also have variable tolerances and these also impact critical temperature. If you want to work accurately, work to the visual signs of the phase change.

We've made a significant effort to make sure the work we do in our shop is the best we can and that the information in that DVD was the best we could provide. If you actually use that information, I believe you'll get very good consistent results.

[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.

http://www.inthewoodshop.com/ShopMadeTools/LowTechHeatTreating_html_2b9cae2e.jpg

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

http://www.inthewoodshop.com/ShopMadeTools/LowTechHeatTreating.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


(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.

[Tony Shea]

I am not against the cost of a torch< just couldn't find athe one i was looking for.

[george wilson]

Tony,a weed burner and a trailer bottle really puts out a huge flame. You can run the torch for about 8 hours on a trailer bottle. Refills are about $27.00 around here if you exchange bottles. But,there's a gas station down the road which will just refill your bottle for $10.00 less. You may need to buy a special part that screws into the bottle to use the burner. I don't know what it's called,but our weed burner would cut off after several minutes using the nozzle on the bottle because the valve would freeze shut. A guyat a welding supply helped me to get the part,which bypasses the safety valve. If too much gas escapes too rapidly,the bottle is designed to shut down as it thinks an out of control fire is going on.

[David Weaver]

I used a weed torch last year to do a plane iron. It was one that was specified as a 100K BTU torch, and even at that rate, it was difficult to use a large set of uncoated wireman's pliers I have to keep the iron in the heat - even with leather work gloves on. There was another torch branded as 500k btu. I don't know if it's really 5 times more heat than the one I have, but it would be very difficult to use if someone had one like that. I can't remember the brand of mine, but it's green. Something a quarter of the output would've been easier to use.

It did the job, though, and it's not something you'll be using 10 times a week.

[george wilson]

David,do you mean you hand held the iron in the flame with pliers? No need to do that! Just place the iron in your brick "corner",play the flame on it,and turn it over to heat both sides equally. Otherwise,go to a flea market and get a pair of long,old time blacksmith's tongs. Those weed burners do put out a LOT of heat in a wide spread area.

[David Weaver]

Yeah, I did. I threw down a couple of firebricks behind the house and tapped into the propane tank on the grill and went from there. I didn't have a good setup to elevate the iron on something so it could be heated from above and not be sitting on a fairly cold surface, but in hindsight there was so much heat that I could've just put down one firebrick and propped the business end of the iron across the edge of a brick to suspend it. I just didn't know beforehand that it was going to be so hot, and a foot long pair of wireman's pliers was not enough relief. I wish I had blacksmith tongs, but I hope to not be using that setup to do many irons. Most of the irons that I've made are 1.25" wide or less, and I've been just fine with one or two mapp torches - much rather do it that way. Faster to set everything up and take it down.

I can't imagine using those weed torches to burn weeds, what a waste of propane. They are energy pigs, even the smaller of the two.

[Adam Neat]

I love my weed burner, sounds like a jet engine.......... No I cant imagine burning weeds, I do use mine to start a fire (outside) and it will drain an LP tank fast enough to frost up the outside ;)

[David Weaver]

I love my weed burner, sounds like a jet engine..........

It was enough noise to get my neighbor out of his house 50 feet away, he and all of his buddies popped out of the house with beers in hand trying to figure out what I was doing squatting down at dusk. He has enough sense and real world exposure to know what I was doing when I told him I was heat treating steel, though.

[george wilson]

We use one on our gravel driveway.The tank will frost over if prolonged use,and it can freeze up if you don't let it rest for a while. But,this won't happen any time soon and won't affect using it on a blade. Small potatoes compared to burning weeds.

[Larry Williams]

I am not against the cost of a torch< just couldn't find the one i was looking for.

Tony,

A couple weeks ago this was the place with the best price I could find on the torch we use:

http://www.waresdirect.com/products/Commercial-Products/Goss/Kp-Series215952?trackUR

Part of the expense is that this torch comes with a regulator. If you get the proper gas line parts for connecting to the tank, the regulator probably isn't necessary. We always set the regulator as high as it will go. There may be some safety issues involved, though. Goss does sell their AP-1 torch and BP-5 tip separately but I've never tried to find them.

Just to make a point again--if your goal is to put steel in its austenitic phase in an oxygen atmosphere, its behavior like steel in its austenitic state in an oxygen atmosphere should be expected. This behavior tells you that you've been successful, not that you've overheated the steel.

[Ryan Baker]

I've got one of the cheap weed burners from Harbor Freight, and it works just fine for the occasional heat treating job. It throws out some serious heat and will frost up the bottle in a few minutes.

[Phillip West]

Hello, this is my first post here but I believe I can contribute to this thread..
First off there are two mindsets in heat treating in general..Basically it comes down to "The best way" and "Good enough"..O1 is a good example of this..First off the bladesmiths answer..O1 is a high carbon, high manganese tool steel..Which makes it deep hardening and requires a somewhat slow quench..To reach its full potential it also requires strict temperature control and a controlled soak..
O1 needs to be soaked at between 1475*-1525* for 15-20 minutes..That means it needs to stay at that temp for that ammount of time before its quenched in a medium/slow quench oil..Then tempered to desired hardness for two cycles at about two hours each..
What the soak does is let high alloy or hypereutectoid steel to come into full solution.(longer soak for higher alloy steels like O1 or shorter soaks for simpler steels like 1095,W1,W2)...It will get close to full hardness but not all the way there..Lots of people are shocked to learn that the 1095,W1,O1 etc,etc that they are using is only getting to RC60 out of the quench instead of RC 64-66 like it suppose to..They think its say for instance RC64 then they temper it for that they think will be RC59 which ends up being RC 54 because it never got fully hard..The file test is not a good test of hardness..A lot of files will stop cutting way short of full hardness for a hypereutectoid steel..Meaning you may be 5 full rockwell points shy of full hardness but your file is telling you uts dead hard..
Now most folks dont have temp controlled heat treat..We didnt starting out..So the pointers I can give for a homebrew heat treat on something like O1 is **Dont overheat it** Orange is several hundred degrees above critical for this steel..By my eye anyway..1500* is just about cherry red, I was supprised too but thats it..when you over heat steel your growing the grain and its not going to get full hardness either..Overheating is as bad as underheating, often worse..Steel looses its magnatism at about 1414* if Im not mistaken..So a bit above non-magnetic..A nice even heat is what your looking for..Temper in your oven that you know is correct..Start a bit low and then go up if you have too.
if you get O1 full hard at about RC65 then a temper of 400* will leave you at about RC61..
Now im not saying you cant make a good usable blade without temp controlled heat treat and metalurgical grade quench..You can make a perfectly serviceable blade by not overheating and tempering correctly.

[george wilson]

Good post,Phillip.I had a Versitron hardness tester at work,one of the finest made,and VERY expensive. I got it for $50.00 at Federal surplus because they didn't know what it was!! Could get stuff there being from a museum.

I don't have 1 at home,but plan to get one. I have heat treated so many years I don't really HAVE to have one by now,but it would be good to have. There IS a 25 degree window to get the most out of your steel. I observed that carefully when making punches and dies from A2 for our jewelry business to get the most cycles between grindings. Each grinding shortens the punch,and they can be a lot of work to make.

About the weed burner: They WILL freeze up soon UNLESS you get the brass valve that screws INTO the hole on a standard small trailer bottle. This bypasses the other valve that is normally used. If the normal valve thinks gas is escaping too rapidly,it will shut down the bottle as a safety precaution. I don't know what the extra valve is called. The guy at a local welding store solved the riddle of why the weed burner was shutting down for me. Go there,explain your problem,and a competent welder salesman can put you onto this needed extra valve.

[Phillip West]

Id also like to add that overheating grows the grain horribly..Its plain to see under a microscope.Honestly if you know what your looking for the naked eye can see bad grain growth.Grain growth is bad,very bad..
break a heat treated blade that has been overheated and it will look like gravel in the cross section..break one that has been heat treated correctly and the cross section will be silky smooth..

[george wilson]

Yes,large grain is VERY bad. I was brought a black powder pistol repro that had had the whole cylinder and barrel blown off 50 feet down the road. The poor guy had never even ever fired a gun!! NOT a good intro!! The cylinder pin ,which is pretty fat,is the only thing really holding open top Colt pistols together. The cylinder pin sheared off flush with the fire shield,sending everything flying. The cylinder pin looked like it was made of coarse grained brown sugar(except it was gray!) Must have been terribly overheated and not tempered. That was on a Uberti pistol,too,usually a fairly decently made Italian repro(they do have other problems,such as the cylinder holes being smaller than the rifled bore!!)

This was my ruling on what caused the gun to blow apart.