How to straighten a warped blade??

Status
Not open for further replies.
jacqueeagonsr

jacqueeagonsr

Joined
Apr 24, 2008
Messages
203
I was heat treating some forged 5160 blades yesterday and 2 of them came out slightly warped. I must honestly admit that, if they came out of the quench warped, I didn't notice it. Being new to forging, these are my first warped blades. I thought I remembered a Blade article on how to fix this problem after it occurs, but, cannot locate that article in my 'how to' folder of articles from past issues. It seems to me that I recall it suggested to re-temper the blade and to gently straighten the blade after the tempering cycle while the blade is still hot (about 350 degrees).

Any comments or suggestions??

Regards,
Jacque
 
First prevent it .Always stress relieve after forging, you might also stress relieve after initial grinding . After the fact - never try to straighten the blade below 400 F, the higher the better.
 
I always normalize (stress relieve) three times after forging and anneal after the third time. Then, after grinding, I do the same - again, three times. On the third heat, I quench. Your comments are appreciated.
Regards,
Jacque
 
Yeah, like Mete said, the standard advice given is to do it hot. However, in my experience, that only helps so much.

If these are blade you're really attached to, you should normalize them again and re-heat treat. And this time, pull them out of the oil while still very hot, but under the pearlite nose, and let them finish cooling in the air. Aim for 500F - the oil will be "steaming", not smoking. This alone can reduce warping because martensite will form more evenly. But it also gives you the chance to correct any bends with gloved hands while the blade is still mostly soft austenite. Once it starts to set up you need to leave it alone.
 
There's no need to re-heat treat.
I see that so often and it's a waste of time.
Do your initial temper.
Then, with a C-clamp, clamp the blade to a bar of steel with the apex of the warp AWAY from the bar. Use a metal shim under the blade tip to create a space between the knife and the bar. Place the C-clamp on the apex of the warp, and clamp it until you actually push the apex PAST the point where the blade would be straight. So, in essence, you are pushing the warp to the OTHER side of being straight.
Give it the second temper and let it cool completely back to room temp. Make it a full two hour temper.
You may be surprsed how straight it is.
If you need to do it again, you are only doing the blade good.
I have saved MANY blades this way without going through a full re-heat treatment.
 
I use the same exact method as Karl does with great success. I have had other makers bring blades to me that warp during heat treat, usually due to stresses induced during grinding or just uneven grinding. I use old peices of heat treat foil as shims to put under the apex of the bend. Sure has done a number on the galvanized or cad plating on some of the small c-clamps I use, just have to wire brush them once in a while.
 
Karl, Jim -
Thanks - I knew I had read somewhere about how to 'fix it' during a subsequent tempering cycle - just couldn't remember the details. I'll give it a try this afternoon (I hope).

Regards,
Jacque
 
Nathan the Machinist said:
Yeah, like Mete said, the standard advice given is to do it hot. However, in my experience, that only helps so much.

If these are blade you're really attached to, you should normalize them again and re-heat treat. And this time, pull them out of the oil while still very hot, but under the pearlite nose, and let them finish cooling in the air. Aim for 500F - the oil will be "steaming", not smoking. This alone can reduce warping because martensite will form more evenly. But it also gives you the chance to correct any bends with gloved hands while the blade is still mostly soft austenite. Once it starts to set up you need to leave it alone.
Click to expand...

This is part of the real life magic of working with steel. Using your hands to move the metal while you know there is a massive reaction on a molecular level in the material. :D
 
The best way to fix a warped blade is to prevent it from happening in the first place. We have not had a warped blade in over 5 years in either 5160 or 52100.

After forging heat the blade to above critical, quench in room temperature quenching oil (we use Texaco type A) hold the blade in the oil for a minimum of 35 seconds, then re-heat the blade above critical and quench again for a total of 3 quenches.

Then do your normalizing, then a low temp anneal - I use 988 f. for two hours and let it cool down slow, naturally I do this three times.

Rex reports a steady increase in uniformity in blades quenched this way, he examined blades that had up to seven post forging quenches, it was a uniform progression, three quenches provided the best bang for our buck.
 
That sounds cool Ed!

I've been toying with the idea of post forging mild quenching (or "thermal packing"), then normalizing... There might really be something to that. :)
 
For us it works like a dream give it a try and let us know your thoghts.
Thanks for the kind words my friend.
 
ED... I think one could skip the annealing with your fast “10” and “W” series steels, and go straight into the quenching cycle/cycles from the normalizing cycle/cycles.

There might be a lot of advantages to all this other than just preventing warpage.

Keep up the great work partner! :)

(I first heard the term "Thermal packing" from Wayne Goddard.)
 
Hats off to Karl and Jim on how to 'fix it' during a re-temper. That worked for both blades. On the 'prevent it' suggestions, first let me say that the method I'm using was taught to me by ABS/MS Mike Williams of Arkansas. And, until now, has been successful. However, Ed swings a lot of weight in the world of knives and I'll certainly print off and try his method next time. It never ceases to amaze me how this community is always ready to lend a helping hand.

Many thanks,
Jacque
 
Last edited:
Tai:
Your mention of thermal 'packing' really brought back a lot of memories!
There was a time when 'packing' was an esoteric art known by only a few blade smiths who never submitted a blade for microscopic examination or any empirical testing for that matter. The issue was greatly debated and when Wayne mentioned thermal 'packing' it was heresy.

Naturally there is a whole lot more to it than what some will read, but it was a turbulent and fun time in the knife community.
 
I am working on a big bowie made of 5160. I am very new to bladesmithing and was crushed when it came out of the quench warped. It was probably due to uneven heat since I use a stack of firebricks and a propane weedburner to get the steel to temp. After calming down a little and reading Karl's advice I gave his method of bending during re-tempuring a try. The original temper was around 450 F. When laid flat on a level surface, the bow was about 5-6 mm at its worst spot. On my first try I pushed the blade about 2mm past true in the opposite direction of the original warp with some 1/2" aluminum rod sections on either end as spacers. I put it in the oven at 440 F for two hours. After a slow air cooling, I had about 3mm less bend in it over all. The next night I did the same thing, but doubled the amount of warp left in the opposite direction... so about 5mm past true (the blade is over 16 inches long so this isn't as crazy as it sounds... but still a good bend) and held it at 450 F for two hours. This time it came out completely straight and now lays flat on a level surface from the tip to the tail. I did mess around with it during the day while it was cold and no matter what force I put on it in the straightening jig, it always came back warped... so getting it to tempering temperature is necessary to see results. As for the jig, I had a section of "C" shaped aluminum channel made of pretty thick stuff that was more than strong enough to handle the force of the large c clamp I used. As mentioned before, I used sections of 1/2" aluminum rod a little taller than the blade as my spacers... mostly because I needed a lot of separation to get the amount of opposing bend I needed.

Thanks Mr. Andersen!

PS If any other forum members have a spare belt grinder and are in the DC/NOVA area let me know LOL! This stuff gets in your blood fast!
 
You are welcome.
I learned this from one who was making knives 40 years ago - and still does.
Keep in mind, irregular forging, irregular grinding, uneven heating, improper heat treating practices, scrwed up post-forging regimen, etc, are where crooked blades come from.
Keeping all those things in place will virtually eliminate warps in the first place.
Of course, only austenizing blade edges and edge quenches are often mentioned when folks say they don't get any warps, :cool: but when doing that, it would be almost impossible to get a warp in the first place.
Don't confuse the two.


Keeper556 said:
This time it came out completely straight and now lays flat on a level surface from the tip to the tail.

Thanks Mr. Andersen!
Click to expand...
 
Status
Not open for further replies.
Back
Top