Straighten During The Temper

Thanks for the clarification, Stacy. So do I understand you correctly in that the steel could even be straightened at room temperature, but that's it's just easier and a little safer at elevated temperature? Or is the actual temperature critical, along the lines of Rick's theory that perhaps the straightening needs to be done at a higher temperature than the blades were previously tempered? How about time at temp?

Rick, and most others it seems, are doing their straightening during the course of tempering. My blades were already tempered twice, and I was going back after the fact and trying to straighten them. I had tempered at 400, and was trying to straighten at 400, trying it both after just a few minutes to heat them back up, and for as long as an hour. I also tried 'quenching' under the faucet and slow cooling, neither of which seemed to make any difference.

Karl, when you say you do a third temper at 350, where is that temp in relation to your 'normal' tempering temperature (ie, higher, lower, same?)

I had decided to start over with these, doing the anneal/straighten/normalize/quench/temper thing, but if I could still make this method work it would save me a lot of time.

Thanks guys!

Edit to add: Specific blades in question are: 3/16" thick 1080, flat grinds/hollow ground tangs/stock removal, heat treated in digitally controlled kiln and quenched in oil, tempered at 400
 
Last edited:
Okay, I've been doing this since rick first chatted about it, and I've had possibly a few varying experiences. (not ten years, of course!)

It seems to me to depend somewhat on steel type and thickness. I get better results running one hour at 385 with 1/8 inch 15N20 or 1080- while with 3/16 to 1/4 inch 5160 is teems to like one hour twenty minutes at 395 a lot better.

I'm not sure 300 degrees (depending on alloy) is enough to get the steel to "take a set" to straight.

The 2 issues I've had learning to make this work are:

1: shims. It's hard to say how much shim where and how tight, you have to learn that.

2: rigid enough, thick enough clamping bar. Turns out farrier's rasps are all over the place out here (former owner was a farrier and had kids. I rake one a week up) and they work pretty well on 1/8 stock. I'll double up for 3/16 or 1/4. I tried to get away with clamping 2 or 3 blades together in a batch without a backing plate and it doesn't work as well.



For the earlier post on interrupted quenching. clamping between large aluminum bars is going to cause some issues, I expect, as the aluminum is going to pull the heat out and take you out of the malleable stage very quickly. The only way I can see that being workable is mounted to a press or woodworker's vise where you can get the plates on the entire blade quickly. (and even then, since you've already quenched.... dunno)

I do a lot of interrupted quenching and I have wood jaws in a post vise arrangement that I use to help me tweak blades. Go through the wood jaws pretty quickly, but it gives me a solid hold to work on tweaking with gloves and tong handles.
 
Ok details...

It worked! I took a piece of 5160 from quench and noticed it had a slight bow. You could probably almost slip a credit card in the gap between the bow and file.

I took one clamp (all my others are painted I guess) and clamped the bow down to a big file with no shims and tempered for about 2 hours and 15 minutes at 400F. I water cooled it under the sink and when it was cool I unclamped it and it was straight as could be!

I'm doing temper #2 right now for another 2+ hours at 400 again... report back when done.
 
Thanks Rick! After seeing you in your shop clothes I can see why you are so helpful.


Rick Marchand said:
superman-returns.jpg
Click to expand...
 
koyote said:
For the earlier post on interrupted quenching. clamping between large aluminum bars is going to cause some issues, I expect, as the aluminum is going to pull the heat out and take you out of the malleable stage very quickly. The only way I can see that being workable is mounted to a press or woodworker's vise where you can get the plates on the entire blade quickly. (and even then, since you've already quenched.... dunno)
Click to expand...

My plates are on a vise as you say. After quench, I cool to room temp between the plates. Almost never have warp anymore. Double temper after that.
 
P J 234 said:
Karl, when you say you do a third temper at 350, where is that temp in relation to your 'normal' tempering temperature (ie, higher, lower, same?)
Click to expand...

Depending on steel type and use, most of the stuff I do is in the 415-430 range.
350 will work to continue correcting post-quenching warps without advrsely effecting temper.
And I cut the time down to about 45 minutes.
It's enough to tweak a point one way or the other.
 
Guys... this thread is totally fascinating to me. I'm not near as experienced as most of the folks here, so I have a couple of questions:
  • How often (what percentage) of your blades are coming out of quench with a noticeable warp?
  • What kind of stress-relief cycles are you running before the quench?

The reason I ask is because I haven't had a noticeable warp in a long while. When I first started, I would occasionally get warps after quench, but then somewhere (probably in one of Kevin's threads) I read about pre-quench stress-relief cycles. Now, I'll run a few 1200F stress-relief cycles... soak for ~10 min and air cool. Any warps usually show up here. I straighten them in a 3-point jig then run another stress relief. When the stress-relief cycles no longer produce a warp, then I go to quench. I haven't had a post-quench warp since. Now I only work with 1080, 1095 & W-2... so I can't say that this works in all cases, but it has been working for me so far. Maybe I've just been lucky. :confused:
 
I'd say 1 out of every 10 blades has a warp... usually only a slight "wow" at the tip. I have a lot less warpage now that I use a controlled kiln. The last few blades have been in the 20-24" range and they warp a lot more. An interpted quench fix and maybe a temper tweak takes care of the problem.
 
Rick Marchand said:
I'd say 1 out of every 10 blades has a warp... usually only a slight "wow" at the tip. I have a lot less warpage now that I use a controlled kiln. The last few blades have been in the 20-24" range and they warp a lot more. An interpted quench fix and maybe a temper tweak takes care of the problem.
Click to expand...

Cool Rick. I'm not making anything that long right now... probably one of the reasons I'm not getting much warping. Plus - at the rate that I finish them - the 1 in 10 could take years to appear. ;)
 
Will be trying out a straighten temper tonight. Will report back what I get. *Crosses Fingers*

It got better. Will try again.
 
Last edited:
Rick Marchand said:
I'd say 1 out of every 10 blades has a warp... usually only a slight "wow" at the tip. I have a lot less warpage now that I use a controlled kiln. The last few blades have been in the 20-24" range and they warp a lot more. An interpted quench fix and maybe a temper tweak takes care of the problem.
Click to expand...

This was the first warp I have had that I could see, I've HT'd about 15 knives so far. Mine had a slight bend towards the tip. (I warped a 1095 brine quench knife but that's a different story :D )

It was an odd chisel grind with a swedge so I guess that contributed, maybe the differential quench could have too. Just guessing.

By the way, I just finished the third 2 hour temper and it looks great! Warpage gone! Thanks!


Have you done this with a sword? I'm trying to figure out what would work as far as something to clamp the sword to, lol.
 
I want to say thanks for this awesome thread! I just heat treated my mini for the mini kith...had a .125 tip to butt bow...clamped it between 2 pieces of 3/4 x 1 inch pieces of 1018 and tossed it in the oven at 400 degrees for 2 1/2 hours....came out straight as an arrow! Awesome tips Super Rick! By the way...the spandex suit makes you a touch more irresistable!
 
Just wanted to report back on this. Yesterday, I spent more time trying to get my blades straight by clamping them in the oven. I was able to improve them, but still not able to get them straight enough.

Today, I went to a friends shop where he has a 3 point jig for his vise, and we heated them back up to 400 and then were able to get them nice and straight in his vise jig. I think the problem I was having here was that the blades were significantly warped, and I was unable to get enough counter bend by clamping to correct it. I believe had the warping been more minor, clamping probably would have worked for me.

Thanks again, Rick, for passing along this tip!
 
Yes, Thanks again Rick. This was a major breakthrough for me. I was very intimidated by the idea of straightening a blade and this was easy and worked great!
 
Rick - thanks a LOT. I have been doing LONG blades (short swords, really) and I have taken to clay heat treating because you can always straighten them since the spine is soft. But, if they TWIST, well, that is another kettle of fish. I will definitely use this next twist.

Of course, I interupt before fully cool and tweak, too.

I have been putting between pins in a vise and then heating the blade with a small torch while tweaking in vise. It is basically the same idea but I can't hold at temp for any length of time (accurately) with a hand propane torch.

the oven with clamps will give more time and control. I hope I never need it, but I am not able to remember any blade longer than 12" that did not warp a little. Most swords just bend a little under their own weight when heating before quench in my horizontal venturri forge.

thanks a million.
kc
 
The easiest way to straighten a warped blade is to prevent it in the first place. Years ago we did many experiments trying to find the cause of blade warp. We developed many cures that contribute to eliminating blade warp, but the most significant method of eliminating blade warp is that after the last forging cycle, before the normalizing cycles is to quench the blade from over critical temp. in room temp Texaco type A oil, hold for 35 seconds re heat in the forge to over critical temp and quench again for 35 seconds, then a third similar cycle, then your two flash normalizes and a full normalize cycle. Then grind to the shape you want and harden and temper. Never had a blade warp since using the thee post forging quenches.
 
Ed, don't you torch heat the edge only? You are probably not getting as much internal stresses as someone who fully hardens their blade.


Guys... you'll have to excuse my recent "registered user" glitch.... they are working on it... lol.
Rick
 
A blade warps due to stress, most likely because of something you did or did not do. I believe that the challenge to the blade smith is to eliminate the source of stress rather than add more stress to the blade by straightening the it. It only took us over 20 years to figure this out. Test a few blades to destruction by evaluating lateral stress failure and this phenomenon will become obvious.
 
Rick Marchand said:
Ed, don't you torch heat the edge only? You are probably not getting as much internal stresses as someone who fully hardens their blade...
Click to expand...
Really good observation Rick. For what it is worth I think you are doing fine, steel is not a perfect substance and when introducing the stresses involved in full and proper hardening things are going to happen that we cannot be in total control of. I think a post about destruction testing may have gotten accidentally pasted together with this concept because I cannot readily see any connection between the two topics.
 
You must log in or register to reply here.
Back
Top