more questions about quenching and tempering.

[Coutel]

I have read so much on CKD about quenching and tempering techniques and learnt a great deal from various videos, plus experimenting with my own destructive testing (mostly edge quenching).

I usualy edge quench then triple temper in an oven (10xx series).
I have not yet attempted a full quench then drawing the spine back with heat....

Question...Comparing an edge quench with a full quench with draw back...is there a difference in the final performance? .....
ie ...would a draw back give more of a spring than an edge quench?

I have watched some interesting videos recently from Tim Lively and William White (I am bending more to forging techniques than to stock removal as time goes on).

Both Tim and William temper over a heat source (following full quenches)...... William White tempered over an electric oven hot plate and Tim Lively triple tempers in what seems the ashes of his forge.......paying close attention to the colors of the steel.

2nd question.......Apart from this method (tempering over a heat source) being more traditional and 'tribal' (and a lot quicker).......is there another advantage to tempering like this?........

I read somewhere that tempering was a combination of time x heat, however, tempering this way takes no account of actual time!

I guess the best way is to experiment myself with as many different techniques as I can (which I will), but I thought it would be interesting to hear from others as well.


I have searched CKD forums but unable to find these specific answers...if this has been posted before, then just point me towards the link.

Thanks
Kevin.

[Dan Graves]

These are some interesting questions. I cant answer them other than to tell you my experience. In a full quench and draw back of the spine I can get a hamon line closer to the edge as to an edge quench. Terry Primos and I have discussed the pros and cons of these methods. Hopefully he will chime in and give some thought on this subject. Bill Moran once told me that he wants the spine "dead soft". Somewhere in the middle the spring begins as you get closer to the edge. I will be watching this thread as I do a full quench on large knives and edge quench on hunters. Also, I was told that when a propane torch is used (for draw back) that you must make sure to apply enough heat to soak thru the blade while the edge is in water so as not to just soften the skin.

Dan
www.theknifemaker.com

[Coutel]

Dan..thanks for the input.
Rather than use a propane or other gas torch which probably has the tendancy to heat a bit to quickly (and not penetrate the thickness properly?), I like the idea of drawing back and tempering over an electric oven hot plate or similiar...it seems this process tempers as well as draws the hardness out of the spine, and there seems to be a bit more control than using a flame to draw.
I am currently in the process of forging a knife now and am keen to give this process a go...maybe in the next few days I will be able to give it a try.

Kevin.

[Josh Blount]

Hey Kevin,
Well, I'm certainly no expert here, but I've asked a lot of these questions before. I use mostly the same method you describe of edge quench followed by three tempering cycles. I use three cycles of at least two hours, allowing the blades to cool completely between cycles. The multiple heating and cooling cycles are crucial. I have the William White video and I've used that method. Aside from what I just mentioned, it's very hard to get even colors on the edge. When I tried it I got a blueish color on the tip since there's less blade for the heat to travel through. When I broke the blades done this way the grain was large and crystalline, so I switched to the method I learned from Ed. By the way, check out the article about JS testing on Ed's page Caffrey Knives I've learned a lot from reading and rereading that. Like I said, I'm not an expert Maybe somebody with more experience can chime in here and give you some more help.

Josh

[Tom Ferry]

Hi Kevin,
Well I will best describe the methods I have used and see if I can clear some of your questions up for you.

"Question...Comparing an edge quench with a full quench with draw back...is there a difference in the final performance? .....
ie ...would a draw back give more of a spring than an edge quench?"
In my shop using my techniques yes there can be alot of difference in performance. Your right in that usually a draw back of the spine is more of a spring. A properly done edge quench whether just the edge is heated or the whole blade but only the edge is quenched results in a soft spine. An example that may better describe this is if you look at your annealling chart on say 1080 its states to heat to 1450 degrees then drop 20 degrees per hour to 1200 degrees then air cool. Now obviously an edge quench with a fully heated blade is not going to be completly annealed but it will be normalized and not hardened. By comparing this to what a drawing back of a spine on a fully hardened blade this will give you an idea of the penetration of heat and time to obtain a dead soft spine. Both ways work but for me an edge quench is more predictable.

"2nd question.......Apart from this method (tempering over a heat source) being more traditional and 'tribal' (and a lot quicker).......is there another advantage to tempering like this?........"
Personally I dont like the idea of a quick temper. The multiple tempers and times are to complete the transformation all the way through the cross section of the steel. Quick colors or flash tempers are great for stress relieving such as with a water quench. Then the blade is cycled through all the tempers. I have started doing my final grind in between the first and second temper, now whether it makes a real difference or not I cant say but in theory on the second and third temper the heat has alot less cross section to penetrate so in my opinion its a more thorough tempering.


As you stated the best info and lessons you can get are through your own experimentation. Ask the steel suppliers for heat treat specs and learn how to read and understand them. They are not always geared towards knives but they are great guidelines to start with.
I too suggest reading Ed's article on JS testing. It is very in depth.

Josh,
The tempering colors can fool you pretty easy. If there is oil or whatever on the blade they will not color true. Also there is a time game with them also. A blade in the oven at 350 for 2 hrs should come out straw but leave it in for 4 hours and it can turn purple or blue. The colors are oxides so they continue to form. I never trust the colors and rely on accurate thermometers.
Also the large grain you spoke of can be eliminated through multiple normalizing cycles after forging and before heat treat.

Hope this helps

[Josh Blount]

Hey Tom,
That's a good point about the variations in tempering colors. I always rely on one, sometimes two, oven thermometers, with colors as a backup, but I hadn't thought about the other variables that could effect them. As for the large grain, it was that problem that first brought me to this forum. Now I triple normalize after forging and before h/treat which has made a big difference in my blades. Thanks for the response!

Josh

[Josh Blount]

Hey Tom,
I thought of another question about normalizing regarding how long to let the blade cool between cycles. I've heard that it's important to allow the blade to sit until it's cool to the touch. But I've also seen people wait just until the color is out of the blade, checking it in a dark corner of the shop or something. What's your personal preference? I haven't had a chance to experiment with both, and I'm curious to hear other's opinions on this. Thanks!

Josh

[Tom Ferry]

Josh,
With simple high carbons such as 10xx series I let the blade cool to 900 degrees which all the color is gone then normalize again. With 5160 and 52100 alot of guys let cool to room temp in between with great results, I personally havent seen a noticeable difference in letting it cool all the way down or re normalizing after it loses its color. This is one of those things where makers get the same results using different techniques, not saying one is better than the other and I may do something different along the line that some dont and it may be unknownly. Plus there is no standard equipment for doing this type of stuff so what applies in my shop may not in yours. I have very accurate controls on my forge and can run within 20 degrees of any temp so I dont rely on color as much as others. I also slide a steel tube in my forge to do all my normalizing and hardening in so as no hot spots or direct flame can touch the blade. The blades come up to temp very evenly and accurately.
Here is the method I have developed through trial and error and lots of destructive testing.
Forging: the first heat is up around 2100 degrees and I try to work down in heat as I am forging so my last heat is around 1650, I turn the forge down to that temp rather than try and bring the steel out sooner. I then normalize twice right away at around 1450 to 1500. After the blade has cooled I do all of my grinding and clean up. I then normalize three times at 1450 and hardening after the third. This normalizing after grinding helps eliminate any stresses from grinding to eliminate most warpage as well as set up your eyes to read the proper color for hardening.(I do use a magnet also) Then temper right away for 2 hrs. I finish grind the blade then temper two more times for 2 hrs each.
Even if your doing stock removal on carbon steels you can still reduce the grain about twice as fine than it comes from the mill through normalizing.
Have fun breaking blades!

[Josh Blount]

Thanks Tom,
That's sort of what I'd figured. I forge 5160, though right now I have only a coal forge. After doing the basic bladesmithing course in Larry Harley's shop using gas, I'm hooked, and hope to have my gas forge up within the next month or so. What kind of thermometer do you have in your forge? Larry had one and we used it to normalize and heat-treat, which I found very helpful. Also, out of curiosity, what is the purpose of finish grinding before the final two tempering cycles? Thanks!

Josh

[Coutel]

I had a bad day today......Yesterday, I completed forging my knife......going for maximum forging and no stock removal except for filling the edges smooth.
I have normalised this knife 4 times and annealed it twice.
Spent ages tidying up the tang (hidden tang) and made a good job of filling the shoulders before final heat treat.
Even forged the guard, drilled the handle and tested for fitting. Every thing was going great and I was pleased.
I went for the heat treatment.......bought it up to critical then edge quenched it in peanut oil...left it in there to cool down.
When it cooled I took it out to inspect it.........saw two hairline cracks running at 90 degrees to the edge!!!!!

I usualy use 1095 but this time I was using 5160.......I cant think what went wrong?....I did everything I could think of to reduce stresses and the profile looked even.

I am going to temper it next time I temper others then break it to look at the grain structure...shame, because it was going to be a great knife!

One of those days!!!!

[Tom Ferry]

Josh,
I am using an analog pyrometer, not sure of the brand but they sell them at pottery or ceramic shops. A friend of mine Bill Cottrell is now using a digital readout and I will be going that direction in the future.
My reasoning for finish grinding in between the first and second temper is so the following two tempering cycles have less cross section to penetrate in order get a thorough temper. In testing I cant say it makes a huge difference but in theory it should help.

Kevin,
Sometimes we can do everything right and still have failures in the quench. A quench creates mass stress on a blade. The only thing I can think of is what was your oil temp when you quenched I try and run mine at 120 degrees. Also you might want to grind the blade and see if they arent just surface cracks, I have had 5160 and 52100 do this in a water quench. Do you know exactly when it broke, was it during the intial quench or as it was cooling?

[Coutel]

Tom...re my failure...
The two cracks do go all the way through....I can clearly see them cross the edges at 90 degrees......permeate about 1/2 an inch.

I did pre heat the oil first by placing a heated piece of scrap metal in.....I dont have a thermometer in the oil, but would estimate it is near the 120 degree mark (too hot to put my fingers in!)...no different then I usualy do.

There are a couple things I did different here to what I have done numerous times before.

......Firstly, this is the first time I have used 5160 (usualy use 1095).....maybe its less forgiving?

Secondly.... when I usualy quench, I wait till it is just cool enough to handle (but still very warm) then immediately place it in the oven for tempering which has been pre warmed to the right temperature, so the steel never really has a chance to cool down to room temperature from the initial quench until after the first of three temperings.On this occasion, I left the knife in the oil till it was room temperature.

One other thing that could have been a problem is that the quenching oil is now old and well used and I wonder if it could be contaminated as the color has changed....I intend to change this oil before the next quenching.

The blade that failed was 2 inches in width, and so I am wondering if an edge quench where the blade was only immersed 1/2 way in may have caused a lot of stress in the other half that was cooling much slower?.........

Going back to my original posting which was asking questions about tempering in an oven (time x temperature) or tempering over a hot plate or charcoal and 'chasing ' the colors.

What if I were to fully quench the blade (no differential quenching and so no differential cooling) then triple temper in the oven to remove stresses THEN clean the metal to shiny again, and re temper over a hot plate (as in William Whites video etc) to draw the spine.......in effect, using two methods of tempering.

Thanks
Kevin.

[Josh Blount]

Hey Tom,
Thanks for the reply. I'd like to try to integrate the pyrometer with my gas forge.

Kevin,
In the bladesmithing course I mentioned Larry Harley showed me how to check oil temp w/out a thermometer. If the oil is too hot for your finger, then it's probably too hot. I don't think that would make it crack, though. Ideally, you should be able to put your finger in for a second before you have to take it out. It's kind of crude, but he swears by it, and it seemed to work very well. Just a thought . . . Usually the blades that crack on me are the one's I did everything right on until heat-treat

Josh

[polarbearforge]

Kevin, where it cracked, were there any notches, deep grooves, or 90 degree corners? All three of those can contribute to cracking. I was helping a friend make a knife, and checked it out before tempering and it had cracked where there was almost a 90 degree corner, just near the plunge. What finish was the knife taken to?

Jamie

[Coutel]

Josh......yes, I read that somewhere too (probably on ckd)...thats how I check the temperature of my oil.

Jamie.
One crack permeates from inside the cut I made with a chain saw file which marks the begining of the cuttiong edge...thats a strange plact for a crack to start as its rounded!
The other crack is about 2/3 of the way down, at 90 degrees to the edge...no sharp corners there either.

As to how far my blade was finished before HT. .....I am making a knife in the rustic (almost primitive) style...the only stock removal is some touching up with a file around the edges....so the profile/shape is forged to shape, 3 normalising and annealing then straight into HT.

It could be that I streesed the blade during profiling/forging. I was careful not to strike it out of color, but maybe I slipped up?.
I am currently forging another and am being ever so careful....will be interesting to see what happens.
Thanks for your interest.