Controlling Blades in the Quench Tank...

[ErnieB]

Good Sunday Morning Ed,

We may have been through this issue before and if we have, I appologize. I have accumulated a library of folders full of notes from stuff I've gotten from here, various other forums, websites, etc., and as usual, I've gotten so much stuff that I can't find a thing! I am making a commitment here this morning before the whole knife making world to get that stuff in order pronto!!

The question this morning is related to the bending/warping problems I'm having, all which seem to occur in or around the quenching process. FYI, my normal procedure is to clamp the tang of the knife to be quenched w/vice grips to hold it for the torch heating, dipping the blade into the tank, and finally, as a "rest" of sorts to keep the knife sitting on its edge, nice and straight, in the tank while the oil cools to room temp. It seems no matter how hard I try, usually on the 2nd quench, I'll get the warp and/or bend. Should I be using soming lighter than vise grips to hold the knife with? I though perhaps I'd use a piece of coat hanger thru a hole in the tang and then, for the purposes of the rocking motion on the limiter plate, using something light such as a small pair of pliers. a long pair of needle-nose I have, etc., to grasp the spine to help control the knife thru this part of the process. But if I do that, it will be difficult to heat the blade evenlywith the torch and I would not have any way to get the knife to stand on its spine on the bottom of the tank while everything cools down? I am assuming the knife should not be left laying on one side or the other while cooling down - am I correct on that? This is an issue I'd really like to get figured out so I can do it correctly.

The final matter, how quickly should I get the tempering done after quenching? Sometimes due to my medical problems / Dr's appointments, etc, I may not get to it for a day or two after I'm finished quenching. If this occurs, should I just leave the knife in the oil? Once in the oven, should the 3 cyles be done back to back to back with no down time (other than oven cool down) in between cycles - or does this matter? Again, what is the best way to keep the knife in a standing position in the oven? If I'm not mistaken, if laid on its side, it would warp...

In addition to the above, how important is it, once the knife is forged and ground to shape, to go from process to process in the least amount of time possible, time for the various required cool-down periods not withstanding....

I appologize for asking so many questions of you and the others on here but I want to learn to do this thing right and you all are basically the only support I got at this point.

Thanks in advance for your help...

[B.Finnigan]

"usually on the 2nd quench"

Are you quenching the same blade more then once?

[AwP]

The most common cause of warping is unevenness somewhere. It could be forged unevenly, ground unevenly, heated unevenly, or quenched unevenly. Normalizing before quenching definately helps, especially when all the other factors seem to be good. I can't see how what you hold the blade with matters unless it somehow puts weight onto the blade. You're correct that you don't want it laying on it's side. It's a very good idea to do a first temper immediately after it cools from the quench, after the first it doesn't matter so much how long between any others. What I do sometimes is do a snap temper at a lower temp right after quench so I don't have to mess with getting the temper just right until I have more time. About 350F or so will relieve the stress from quenching (on occasion a blade can crack just sitting there from the strain in it) but have little to no effect on the hardness.

[Ed Caffrey]

Warpage can come from many sources. As Andrew mentioned, warpage usually indicates that something, somewhere in the process is "uneven". To minimize the potential for warpage, normalize after you've completed forging, then again after you have rough ground the blade (just prior to hardening). Thickness in conjunction with the way you apply the torch to heat the blade when quenching can also play a vital role in whether or not warpage occurs. Thin cross sections will heat up very rapidly, and since that area is hot, and the surrounding areas are not, the steel will warp from the heat alone. It often appears that it has happened when quenching, but that's because you cannot visually see it when it actually occurs (while applying the heat).
If I'm hardening with the torch, I always hold blades with a small pair of "needle nose" vise grips. That shouldn't be an issue for you. As far as placement of the blade for cooling in/with the oil, your doing it in the same manner I do. Your 100% correct in assuming NOT to lay a blade on the bottom of the tank....the mass of the tank will suck heat out quickly enough to cause the blade to warp.

On to tempering........ The sooner you do at least a "snap temper" after hardening, the safer you'll be. I have goofed up in the past and left 52100 blades sitting on the bench for a couple of days before tempering......and found that I often ran into micro cracking when hand finishing those blades. That's VERY frustrating.....I went through all that work, and just before the blade was completed, it had to be trashed.

One thing that I didn't see in our initial post was anything about pre-heating the quenchant. If your quenching in room temp oil, I would be surprised if anything DIDN'T come out warped. Pre-heat the oil to 130-160F, then quench. Warm oil will cool the steel more rapidly than cold oil. I know that might sound strange, but here's why..... cold oil will cause a vapor pocket to form around the hot steel, which holds in the heat, rather than letting it disapate. If the blade your working on varies in thickness (such as radical distal tapers) the effects are compounded. So, pre-heated oil is a very important ingredient to achieve a fully harded blade that doesn't warp.

If you still can't get past the warpage probelm, I would suggest leaving your blades a little thicker prior to hardening.
Remember that each step in the knifemaking process should be setting you up for a successful next step. From beginning to end, keep each step/process in mind, and be mindful of how each step/process effects the next. If you use that philosophy, it makes it pretty easy to spot your problems in technique.

[ErnieB]

Thanks for the help guys... As for the normalizing, I normalize after I'm done forging and them again after grinding, as you've told me to do before, Ed. In fact, I have been triple normalizing before the quenching. As for the oil temp, I heat the vet. grade mineral oil to approx. 145 deg. before quenching. I also make sure its the same temp for each of the three times I guench (I'm using 5160, remember?). Just know thinking about it, the warping is happening when I am edge queching, as I have been doing on the longer blades. Come to think of it, when I have done smaller blades using full-submerge quenches, I can't remember any of those being bent or warped. I'm guessing I'm trying to figure it all out too quickly and not giving myself enough time to make the mistakes I'm sure most of us make when we are just starting in this business...

With regards to "snap tempering", thats the first I'd heard of that but I'll have to remember it. I'm assuming thats done as soon as the oil & knife cools back down to room temp??

As far as my tempering process goes, I temper my 5160 3 time @ 400 degrees for 1 hr. each time.

Thanks,

[Ron Hicks]

Ed
You do your harding with a torch - how thick are you leaving the edge of the blade to harden? I have tried it a few times and get a tiny bit of a warp from the heating with the torch? The edge on the blades were maybe 1/16 thick and only heated about the bottom 3rd.

ErnieB
Ed Fowlers book tells about Allotropic Phase Change - heat to no magnetic hold in a dark place ( I use a section of stove pipe ) and watch the color change. It will darken then brighten back up and darken again. I do this 3 times normalize then aneal. I use a roasting pan with a limting plate and veg. oil heated to about 150 and stir it up good before harding
I have had good luck on my past 6 blades but I have been heating the whole blade in my forge. I am trying to learn how to heat treat with a torch so I dont need to run my forge.
Ron

[Ed Caffrey]

Hi Ron!

More often than not now a days I use the salt tank for heat treating. But, in order to get a good temper line, the torch is still my favored method. I feel that 1/16" isn't thick enough, especially if your trying to harden a fully flat ground blade.......warpage from the intense heat will almost be certain. I never really measure how thick the edges are, but if I had to guess, I'd say they're closer to 3/32" or 1/8" in a lot of cases. The other problem that many have with the torch method is that they want to run the flame too "hard". In other words they have the torch cranked way up, with sometimes a too large tip. Using a "soft" flame, with a #3 or #4 tip (one that isn't roaring) will take longer to heat the blade, but on the other hand it will not produce near as much warpage. If you ever have a blade where the edge gets slightly wavy, then that's a sure sign that the heat was too intense and the edge was too thin. Hardening with the torch method should take a little time......at least 5-10 mins with an average sized hunter of 3-5". Long blades can be a real challenge with the torch method. What I do is to preheat the blade in the forge (to a dull red) then use the torch. Again, this takes some time and effort.


Erinie,

The "snap" temper is done as soon as the blade is cool enough to handle. Basically this is a quck tempering cycle, often done below whatever temp you intend to finish at. This should be done on ANY blade that you anticipate might lay around for any time before you can finish the heat treatment. It prevents any of those micro cracks that I previously mentioned.

[Ron Hicks]

Thanks Ed
I was heating to fast and blade to thin for sure.
I have another ?
With like old old leaf springs ( 1095?) is 1 harding all I need or should I do it 3 times ?
I allways check the blades after each harding with a file , My last blade I only harden 1 time, now that I almost have it finished I am having second thoughts about it.

Can you explain the benfits of 3 harding cycles and do all steels need it?
Ron

[Ed Caffrey]

I personally have found that multiple hardening to only be benificial to those steels that contain small amounts of chromium, such as 5160 and 52100. In the tests that I've done on plain carbon steels, I, nor the individual who does spectrographing for me, can find any positive differences in plain carbon steels that have been multiple quenched. Based on the evidence I've gathered, I would surmise that it's a waste of time to multiple quench plain carbon, or any other steel that doesn't contain those small amounts of chromium such as 5160 and 52100 do. There's even controversy over using multiple quench on those two steels, but for me the evidence is there, so I continue to do it.

What the spectrograph shows is that with each sucessive hardening/cooling in the oil cycle, up to three times, the grain structure is reduced, and the amount of retained austinite is lessened. (with the methods I use) Both are good things. I've had pieces tested that have been quenched from 1 to 6 times, and once you get past 3, the benifits either level out or degrade. So for the way I'm accomplishing the task, 3 seems to be the magic number.

[ErnieB]

Thanks Ed & Ron,
Sorry for the delayed response - I'm fighting a kidney stone!

Ron: Bill Moran told about heating in a dark place so you can watch the colors - I think he said he made a special box of some sort to do this in. Anyways, it must be a good thing to do - he really pushes the idea, especially for greenhorns such as myself...

Ed: Much appreciate the info on the snap temper. This is very helpful as I often have to stop during various stages of the process for Dr.'s appnt's, etc. RE: the time reguired to harden a blade w/a torch, I was in the ball park. My 6" camp knife took be 10 mins. (I timed myself) exactly to heat it to where it "felt" right & was non-magnetic.

As far as multiple heats on other steels, when I use O-1 for a stock removal knife, I only harden it once. I made a small squirrel skinner for a friend a couple months back and he says it holds the best edge he's seen on a knife. He's really pleased with it (and so am I - the boy complains about everything!!).