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chucktilbury
12-06-2010, 12:08 PM
I have heat treated 4 blades now. I have a couple of questions. I am working mostly with O1 steel and doing material removal.

Some people seem to recommend higher hardening temps than others, but I am seeing that the higher temps tend to give me warping problems. I found that a magnet stops sticking at around 1000F - 1100F, but the steel does not really get that hard. If I heat it to around 1400F - 1500F (I am going by color only, see here http://www.threeplanes.net/toolsteel.html) it gets hard but it warps really bad. What I am wondering is, if I heat it and quench it several times at the lower temp, will that get the steel hard? Maybe warp it less? How about several tempering cycles? I have seen some people recommend that as well. Thoughts?

Thanks everyone!
Chuck Tilbury

Doug Lester
12-06-2010, 02:04 PM
The short anyswere is no. To harden steel in the quenchant it must be at a stable austinized state throughout the steel that you want to harden when it enters the quenchant. The temperature where the austinite becomes stable, the A1 point, is usually, depending on the alloy, just under 1400 degrees. Then you add about 100 degrees to keep the steel from cooling too much between the forge and the quench tank and allow it to soak for a few minutes, again the time depends on the alloy, to disolve the carbon back into solution and to allow the undisolved carbides, if pressent, to distribute evenly. Don't forget the soak, it's important.

The difference in times recommended can vary according to different things. One is the alloy of the steel. Another is how the temperature is judged or measured. Judging by the color of the steel depends on ambient lighting. On a dark day the steel will appear a brighter color than it will under bright light. If pyrometers are used, it is easy for them to differ by 25-50 degrees. When you are dealing with austinizing temperatures, that's not much of a difference but it can be signifficant. Another thing is how the heat treater works. One person may not quite move as quickly between the forge and the quenchant. Then there is the difference in the quenchat itself. And, of course, there can be a difference in the precieved hardness. What it boils down to is that you will have to develope a process that works for you

Doug Lester

Kevin R. Cashen
12-06-2010, 05:10 PM
...Some people seem to recommend higher hardening temps than others, but I am seeing that the higher temps tend to give me warping problems.

This is very common in the knifemaking community, everybody seems to have their own specs and temps but few reasons or sources for the information. Fortunately we always have the recomendations of the people who really count, those who made or designed O1, and those guys say 1475F to a maximum of 1500F for what we are doing.



...I found that a magnet stops sticking at around 1000F - 1100F, but the steel does not really get that hard. If I heat it to around 1400F - 1500F (I am going by color only, see here http://www.threeplanes.net/toolsteel.html) it gets hard but it warps really bad.
The magnet actually stops sticking around 1414F. Colors are a very unreliable measure of heat until one has a lot of experience in it. All one has to do is open a door or pull a window shade to entirely change your color appearance, and there is no standard reference from shop to shop. A piece of steel that is clearly 1500F in a dark room will look like it is 1100F in sunlight. What is your quenchant? It could be the cause of your distortion, perhaps overheating, but most often it is the result of previous shaping operations not followed up with stress relieving.


...
What I am wondering is, if I heat it and quench it several times at the lower temp, will that get the steel hard? Maybe warp it less? How about several tempering cycles? I have seen some people recommend that as well. Thoughts?


So very much of what has been put out there about multiple heat and quenches is flim flammery at best, but it makes for great attention getting P.R. unfortunately the steel doesn't much care about sensational magazine articles. After your grinding and shaping heat the steel to 1200F and allow to air cool, then heat to 1475F for 5-10 minutes and quench in a good, clean and consistent oil. Temper as soon as possible.

Multiple tempering can help even things out in the conversion to hardened phases inside the steel but will do nothing for the warping since it is most likely happening before the temper. After the temper you can take a wet rag or wet ceramic wool and keep the edge cool while you heat the spine with a torch and pull the kink out when the steel is blue. (just never let the edge turn blue).

Doug Lester
12-06-2010, 05:26 PM
To piggy back on what Kevin has said. There are more than one thing that can contribute to warping. One is not normalizing the blade before quenching. That is done by heating the steel to above critical temperature, soaking for a few minutes, and then allowing to air cool to at least a black heat before repeating the cycle. Three cycles will relieve as much of the stresses built up during forging as possible and, if done right, refine the grain size. Over heating the steel before quench will also contribute to warping. Not plunging the blade into the quenchant straight can also cause warping. Some feel that grinding the edge too fine prior to the quench can contribute to warping but I have not found that to be a problem if I watch overheating the blade. Also, some minor warping is hard to avoid. If you are going to be making blades you will have to learn how to straighten them.

Doug Lester

chucktilbury
12-06-2010, 05:27 PM
Multiple tempering can help even things out in the conversion to hardened phases inside the steel but will do nothing for the warping since it is most likely happening before the temper. After the temper you can take a wet rag or wet ceramic wool and keep the edge cool while you heat the spine with a torch and pull the kink out when the steel is blue. (just never let the edge turn blue).

Do I use the wet rag instead of tempering? Or after it? I have seen where some people actually call this tempering.

Fred Rowe
12-06-2010, 05:52 PM
you can straighten the blade after you quench it, as long as you do it before transformation at 400fh. Use a good heat resistant glove to hold the hot blade in your hand.

How thin are you grinding the blades before they are hardened?
Too thin and you invite warping. Grinding after hardening is sometimes the trade off.
Personally I like to grind after hardening; its a "cleaner" grind.

Changing to a 1075 or 1084 steel will make for much easier heat treating; especially if you are judging temps using an eye and magnet.

Good luck in future heat treating ventures, Fred

Kevin R. Cashen
12-07-2010, 07:43 AM
Chuck, you can give a go at what Fred is describing, it is called marquenching and is the technique I use all the time, I didn't go into it much for you because you seem to have some little areas to work our in your basic hardening operation before throwing in the variables that interrupted quenching would add. The torching of the spine is done for tempering and the edge is held in water to turn the entire spine blue but leave the edge untouched, this is what is often used for the ABS bend test, but even with this a proper full temper is done beforehand. What I described is a method of clamping the tip of the blade is a padded vice jaw and heating just the are of the warp while keeping the edge cool with something wet. When the area you want to move is blue quickly set the torch down and push the blade straight while continuing to keep the edge cold. I have also kept the heat on and used my hip to push on the tang for straightening.

Normalizing is a process that would be more often used if you were forging to shape, since you are stock removing I would opt for the less extreme yet quite effective stress relieving operations. Normalizing redistributes carbides and affects grain condition and can lead to scaling and decarb while stress relieving only deals with the stress that could be causing the warpage.

Doug Lester
12-07-2010, 10:46 AM
If your blade is not too badly warped you might even be able to straighten the blade while cold. It is safer to do this before the blade is hardened but it can be done after hardening and tempering, though I do have to admit it is rather nerve racking. You can try to beat the curve out with a heavy wooden mallet or a cut down wood baseball bat. It is usually done over a slightly dished surface, which can be a large block of wood. Another way is using three brass rods in a vice. One of the brass rods goes over the peak of the curve on the convex side. The other two go to either side of that rod on the concave side. The vise is then tightened slowly to counter bend the blade. Remember a tempered blade has some spring to it and you may have to counter bend the blade farther than if the steel was in the normalized and unhardened condition. Under no circumstances try to cold straighten a blade that has been hardened but not tempered. The reason that "cold" tempering works with marquenching, if it's done immediately after removal from the quenchant, is that the straightening is done before the blade cools enough to fully harden.

If the warping is too bad then there is no way around heating the blade again to straighten the blade. It can be done with light blow with a hammer over the face of the anvil or the mallet and block that I described for cold straightening. It will get a little smokey but you shouldn't have contact with the wood long enough to cause a real fire. Of course you could lay a slighly dished flat plate of steel over your anvil instead of using the wood block. I often use a turning fork in the hardy hole of my anvil to do straightening with. Of course, after straightening you will have to repeat the hardening and tempering.

Doug Lester

chucktilbury
12-07-2010, 11:04 AM
I am using new (or almost new) 10w-40 motor oil for quenching. I have seen where some people use vegetable or another kind of oil for that. Does that really make a difference? Thinner oil transfer heat faster?

chucktilbury
12-07-2010, 11:06 AM
Changing to a 1075 or 1084 steel will make for much easier heat treating; especially if you are judging temps using an eye and magnet.

I searched around a little and I did not really find a local source for 1075 or 1084 bar stock. Is there a mail order house that is reliable and reasonably priced?

Michael Kemp
12-07-2010, 12:10 PM
And speaking as a newbie, 5160 seems pretty forgiving (can't do a temper line on it though)...
I have not used Aldo (I'm on the other side of the U.S.) but have seed great feedback for his NJ Steel Baron business:
http://njsteelbaron.com/shop
I'll have to check shipping costs next time I need to order steel...

I've gotten simple carbon steel from Texas Knifemakers:
http://www.texasknife.com/vcom/index.php?cPath=87_924_73
looks like they've got 1080 & 1095 anyway (a little spendy compared to Aldo)
and I've bought some steel from Pacific Machinery out here in Oregon - but I don't see 1075/1084 on their lists:
http://www.pmtsco.com

Leatherface
12-07-2010, 04:48 PM
I searched around a little and I did not really find a local source for 1075 or 1084 bar stock. Is there a mail order house that is reliable and reasonably priced?

hey bro

Give aldo a buzz...he has 1084 on da cheap and is awesome to deal with

njsteelbaron@gmail.com

You need good quality quench oil to get the most out of your steel...I use vet grade mineral oil right now but I do plan on upgrading VERY soon

If your using a forge as your HT method, I do almost all of my heating at night now...it is very difficult to judge color during the day

BUT

go outside and crank up with forge and kill the lights

gets kinda surreal IMHO and you can learn to judge the temps alot easier to assist your use of the magnet