Straighten During The Temper

Great info Rick! I'll be keeping this in mind for the next time we get a warped knife out of the quench. Thanks!
 
I seem to warp O-1 on a regular basis. [usually 1/8" stock] So, I'v been going from quench to clamping between a pair of 2" x 2" x12" aluminum bars, slightly warm. Then to temper. I interupt my quench at a 4-5 count [Parks AAA], and then clamp. This works well on full tang, ground knives with a lot of 'flat', but a little tricky on forged stuff with a lot of distal taper. [but, I have fewer problems with forged stuff].

This has worked well so far. But, it's always nice to have another card up your sleeve....

Thanks for sharing Rick!
 
I'm not sure if I'm doing something wrong, but I'm not having much success with this unfortunately. I've tried shimming, longer times at temp, cooling while clamped under the faucet, cooling slowly while clamped in air, etc. I'm keeping my fingers crossed and trying one last time by clamping 3 of them together...
 
Not sure what to tell you man... I have never had an issue. The only thing I can imagine is that perhaps the warped blade needs to be a "tempering virgin" so to speak. To paraphrase Kevin Cashen.. In the tempering process, the martensitic steel is heated just enough to release some of the carbon atoms that were trapped in the interstitial spaces by the rapid cooling of the quench.. perhaps it is the release of these carbon atoms while in the clamped position that "sets" the straightening process. Maybe the fact that you have already tempered it prevents the technique from working. I'm reaching, here.... sorry, bud.

Rick
 
This is another reach......... perhaps try uping your temperature by 15degs to draw the blade back a bit further. What are you tempering in and what temperatures are you currently at?

Rick
 
I'll be watching this to see if Paul can make it work. I have to try it myself. I currently use the same 3 points setup in a vise as Salem does and it doesn't work that well and stresses the crap out of me every time I use it. :(

Thanks for sharing Rick.
 
Delbert, it wasn't so much the temperature I was refering to but the drawing up to that temp (if that makes sense).

For example... I do my initial temper at 400F. If there is a warp out of the quench I'll clamp it during this initial cycle. If it comes out of the 1st temper still warped, I will put it back in for the 425F temper. (which is were I usually end up) Most of the time the warp is fixed after the second cycle. I am wondering if the second climb from 400F to 425F triggers the additional release of carbon molecules and sets the blade true. If I just put it in at 400F again, I suspect that there would not be enough happenning within the structure to set the shape.

If there is any validity to my theory, then trying to straighten a blade (using the clamp method) is even more futile at a temperature lower than what the blade has already cycled through.

Okay.... I hope this makes even a tad of sense to you guys. Could someone with more metallurgical smarts than me chime in?


Rick
 
I think you have nailed the problem Rick. What you are pondering sounds very reasonable and valid. That's why the torch and water trick always works.
 
Richard,
The release of carbon molecules is a first for me, however I have done this at 300F after a 350f temper and it still works.
Its funny I had only one warped blade prior to kitchen knives.
I will say that since I am using O-1 and L-6 I do an interrupted quench in parks AAA and straighten that way too, but sometimes they move a bit even after I have straightened them. I have found its works best if you leave the blades in the clamps until they are cool.
Del
 
I kinda wondered about that Rick, but in my other thread Stacy indicates (if I understood him correctly) that the steel should be bendable about 300F, which I'm well above. I initially tempered these in my kitchen oven at 400, and that's the same temp I've been working with on these.

Excerpt from that post by Stacy:

"When the steel is quenched it is austenite , because it was heated above the critical or As point and held at the target or Af point.
It becomes super-cooled austenite in about one second if you did the quench right. Now, austenite is a real soft structure. It can easily be bent and twisted. It does not get hard until it reaches the martensite start point (Ms)...about 400F. Even then the steel has some percentage of austenite in it. The level drops until it is all martensite at the martensite finish point (Mf).....on most simple carbon steels ,that is around 200F. Thus, any straightening above 300F will be safe and easy to do. Once the steel starts to stiffen up, it becomes brittle martensite, and will snap like glass with any twist or flex. At this point stop all attempts to straighten the blade. It will need to be tempered to make the brittle martensite into tempered martensite before any more straightening can be done. The ability to be bent without breaking is greater at the temper point than room temperature, so doing the straightening right out of the oven is when the remaining bends/twists should be removed. If the blade cools down, just stick it back in for five or ten minutes to heat it up again and continue straightening until satisfied. You can do this as many times as needed and it will not affect the temper at all. Once done, dunk in water and check one final time."
 
P J 234 said:
I kinda wondered about that Rick, but in my other thread Stacy indicates (if I understood him correctly) that the steel should be bendable about 300F, which I'm well above. I initially tempered these in my kitchen oven at 400, and that's the same temp I've been working with on these.
Click to expand...

That only applies as it cools down from the quench, Paul. Once you drop below 300F and reach the Ms point, there is no going back. Raising the temperature back up past 300F won't give you the same effect as an interupted quench. It is better than room temperature, though... and I think that is what Stacy is saying.

Rick
 
Chris G said:
good info, but i wonder if it'd work in a propane forge
Click to expand...

it will work in an oven. I use a large convection oven and have been doing this as needed (I most often use interrupted quenching except on 5160)
 
Rick Marchand said:
That only applies as it cools down from the quench, Paul. Once you drop below 300F and reach the Ms point, there is no going back. Raising the temperature back up past 300F won't give you the same effect as an interrupted quench. It is better than room temperature, though... and I think that is what Stacy is saying.

Rick
Click to expand...

Yes, that is what I was saying. That discussion was about the changes happening as the steel quenches and cools. To straighten after it has cooled down , you have to bring it back up to tempering temperature. I use 400-425 for most tempers, and straighten at the same temps.

Paul,
It still will take a lot of pressure to straighten the steel once it has cooled off. The bending just happens a bit safer and easier at 400F than at 75F. A three point jig works fine in most cases, or a wood slotted board to bend/twist with. I attached a drawing of how to make a pair of straightening tools.
 

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Rick Marchand said:
I am wondering if the second climb from 400F to 425F triggers the additional release of carbon molecules and sets the blade true. If I just put it in at 400F again, I suspect that there would not be enough happenning within the structure to set the shape.
Rick
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Rick, I've been clamping to straighten warps for 10 years, and have done it successfully countless times.
I use a simple 1/4" piece of bar stock, a small C-clamp and a thin shim.
I don't even worry about the warp during the first temper. I do not want to risk any type of breakage, so I just temper as normal.
On the second temper, I just clamp as much warp to the opposite side as it is askew.
Temper as normal and let cool in the oven.
My success percentage on being straight after the second temper is probably 95%+.
If it needs to be tweaked, I'll do a third temper at 350 and fix it.
Don't over-think it.
 
Thats a neat tip Rick. Thanks.

I had tons of warp problems until I started cooling blades after initial quench between aluminum plates. Now, I'm using 01, so its a very forgiving steel. AND, I really don't do a lot of big knives either. And, the blades usually have nice flats to sit against the plates. But the plates basically solved the warp problem for me. Thank God.

Still, I hate breaking out my vise inserted 3 point bending jig, and its great to have another option to try.
 
Karl B. Andersen said:
Rick, I've been clamping to straighten warps for 10 years, and have done it successfully countless times..../snip/...Don't over-think it.
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I was just brainstorming to figure out why it works for some people and not others. Like you, I swear by this process and have a 98% success rate. I really don't see why I would go back to straightening jigs. That's why I'm kinda stumped that Paul is experiencing difficulties.

Rick
 
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