O-1 Blade warpped during heat treat! Dangit
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Hello.

I've been a machinist for 18+ years, and I'm new to knifemaking.

I have always wanted a Japanese Cleaver, so instead of springing the $150.00+, I thought "I'll just make one.. I am kinda handy".

Got the blade cut to shape, filed the tang, and made a start on the sharpening angle...

Into the electric heat treat oven goes the blade, and run the temp to 1475, test with a magnet. Grab the blade with a pair of pliers and go for the quench.

The pliers lost grip of the blade, and it dropped into the oil. "Not good", I thought to myself.

The blade warped .100"

So the question: What do I do now?

My thought is that I'll have to anneal the blade, but how do I straighten it?

Any thoughts are very welcomed at this time...

Thanks,
_kevin archibald

First, welcome to the CKD.

Now to business: This is "what I'd do" advice. Take it for what it's worth.

You have two choices: Anneal and straighten (hammer the bend out, use a vise, etc.) or bring back up to critical temp, and just before quench, straighten. Either way will be OK, but you'll get more time to eyeball it if you anneal. I know that most people have to straighten out a warp from time to time, and I have done it as soon as the blade comes out of the oven. I'm pretty sure others do it that way, too.

As with so much else in this art form (and yes, it is an art form), it's up to you. ;)

Hope you stay active on our forums. The more the merrier.

Kevin , welcome and I would agree with Jamey on the anneal and straighten.I use O-1 primarily and have for years.I use an oxy-acetylene torch for HT most of the time and applying heat at the warped part will pull the warp out and straighten it.Since you use an oven I would guess that might be where the warp occured not in the quench.Did you lay the blade flat in the oven or standing up? Laying the blade flat equals warp.Hope this helps and good luck.Dave:)

Thanks for all of the assistance. It is much appreciated.

When I hardened the O-1, I used an electric Heat Treat Oven. I layed the blade flat on the firebrick which lines the bottom of the oven. Why could this have warped the 1/8" thick blade?

Should I have stood the blade up in the oven? Lean it against the side of the oven's interior? What method do other maker's use for oven heat treating?

I've never hardened a piece of steel this thin before, so this is new territory for me. (I mostly do chamber reamers, custom cutters, etc.)

Dave mentioned that he uses an Oxy-Acetylene torch for the HT. Do you bring the entire blade to the critical temp, or just the cutting edge?

Again, thanks for all of the help.
_kevin "still learning" archibald

If you lay the blade down flat in the oven, it will flex when you pick it up to remove it from the oven. Most people place the blade edge down, spine up in a rack on the bottom of the oven. When the hot blades are picked up, there is less tendency to flex. My oven is incredibly small, so I have to place my blades as follows: Edge down, but the point wedged in the upper back corner, while the end of the tang is at the front bottom corner. Yep, diagonally top to bottom and front to back. It works, though, and I rarely have a warped blade. I think the important thing is to get the blade in there with the edge down and spine up.

I think laying the blade down in the oven can cause a difference in temp between the side which is down and that facing up. Just my thought on it without evidence to prove this. It is best to have the knife in a position where air can circulate around it for even heating.

My method for doing this is to slice a soft fire brick in half lengthwise on the bandsaw. Then I slot the brick lengthwise with a table saw blade 1/2 to 3/4 inch deep. I get about 4 slots per brick. You could get more. I place the blade with the tang toward the door and the cutting edge facing up into the slot. My reason for placing it cutting edge up is that I don't want the thinest part of the blade touching anything. I am not an expert but this method works for me.:smokin

That's a great method, Fred. I'd steal that from you and use it if my oven were bigger!:D

Your free to use it Jamey. Just make smaller knives:D

Kevin, I thought that might be where the problem was.Steel will react to uneven heating by deforming.To prevent warping or at least keep it to a minimum do like Jamey and Fred said, stand it up.
When doing HT with a torch, I heat all but the end of the tang that I am holding usually with Visegrips.I usually quench the whole blade then drawback the tang and spine with a propane torch till blue with a gold edge.I have also been trying just an edge quench and drawing back the edge.I haven't noticed much difference in the two methods concerning performance though.

I have been a welder for many years and see the effects of uneven heating alot.If you have access to a torch, try heating a small knife sized piece of 1/8" on one side only and watch it move.It will make a believer out of you.Good luck,Dave.:)

Kevin, after grinding and before heat-treating.... normalize, normalize, normalize.

Kevin,

Look at your blade to see if your grinds are the same on both sides of the blade. If they are then it's very possible that the warp may come out of the blade with another heat treat. After placing the blade edge up in the slot of the brick, normalize by soaking at 1100 for 10 minutes then raise to your critical temp and soak for 20 minutes. Check the blade, if it has straightened in the oven then you can quench normally. Otherwise you will have to straighten it by hand.

Gary

Gary:

You bring up a very interesting point about the grind.

Since this is a Japanese Cleaver it has chisel grind (one bevel). The blade warped to the left, and the grind was on the right side of the blade...

What does the normalizing do?

Thanks again,
_kevin

Kevin,

It's very possible that the asymetrical grind is the culpret in the warping. One way that you may try which could help is using a press quench on the blade. Since I am not an O1 user, I don't know what hardness this will give you but would be worth a try. It definately will help with the warping. I would use either aluminum or brass for the press quench if available.

Normalizing helps eliminate stress in the steel that is created by grinding or forging.

Good Luck

Gary

Kevin, I also use a lot of O-1 and do the edge quench, chisel grinds and all those nasty things you can do to steel. Had a very similar thread going some months ago - not sure how to access the "archives" though,

The chisel grind is NOT GOOD with oil-quenching steels - invariably warps towards the flat unground side. All the other feedback is also true, but I find that uneven heating is a major culprit. I have taken to accounting for the risk of warpage by HT after only a rough grind. At least 50% of grinding is done after HT on O-1, 1095/1084.

The summary of what I learnt when I posted my original thread was :-

1) Even grinds (chisel grinds makes it a different kettle of fish)
2) There will always be a certain percentage of warpage amongst your blades, work that into yout grinding time / arrangements.
3) Normalise before quench. I do a triple anneal by bringing it up to critical, then letting it cool to air temp, x2, on the third heat, take it past critical and quench.
4) When heating up, O-1 needs to be brouight up to critical quite slowly. What Gary Mulkey said about soaking is about making sure the process is slow. I'm not sure what forge / oven setup you have but I've changed my practise from placing the blade right in front of the burner as this tended to heat up one side to quickly. I now put the blade right in the middle of the forge and let the flames swirl around it evenly.
5) Learn some straightening techniques !
6) Thicker blades warp less provided you've made sure about even heating. Thus I do a lot of hardened grinding, especailly with a thinner blade.
7) Warpage can occur even at the tempering cycle (this is also when straightening techniques are done).

Hope this helps. Cheers.

What is a press quench?

The only thing that I can envision is a pair of cooled pieces of aluminum, brass, steel that the critically heated blade is pressed between...

_kevin

That's it. The aluminum/brass blocks pull the heat out of the blade the same as the oil does. You can also use steel blocks though they don't remove the heat as quickly do to steel being such a poor heat conductor. Some people use a vise for this but I place a heavy weight on top.

Gary

I don't use quench plates yet because I have evidently been lucky. But, when you say cooled be careful. Just like your quenching oil you want those plates warmed up so you don't shock your blade.:smokin :smokin

when quenching make sure the blade goes straight in or it will warp- made 10 chisel ground blades once and they all warped, it's the uneven shape. you want a chisel ground blade, harden it first, then grind. 01 has about 10 seconds to beat the h.t. curve; so i don't think using blocks to quench will work. if you remove the blade from quench around 400d. you'd still have time to straighten if you're quick [ it's not hard yet and can be bent- be quick]. never heard of anyone straightening during tempering- only after it's first pulled out of the quench. play around with just heating the edge and edge quenching- that may work. good luck, let us know. paul

I still believe the major cause of warping is due to uneven heating. As I said before,my primary steel is O-1 and I also do many chisel grinds.I have had very few warp and when it did is was minor and usually on blades 5" or more in length.But using a forge to HT, the type of grind may come into play more because of a lack of control of heat placement.Dave:)

I started with O-1 and still use alot of it. I agree with the uneven heat, that is where I have had most of my problems. I now bring my forge temp up in steps and turn the blade over often. Since I've started doing that and normalizing at least once after grinding I've not had any problems. One thing that hasn't been mentioned yet. If you edge quench your blade and end up with a warp that isn't too great ( probably 10 deg. or so) and that only moves in one direction, you can go ahead with the temper cycle. I triple temper at 375 ( in my house oven don't know how exact that is) for at least an hour each cycle. If your edge passes a brass rod test you can place the blade in a padded vice and gently straighten it. Just a thought.

Steve

Double S Custom (http://doublescustom.tripod.com)

Instead of doing one blade at a time, I did a whole batch, eg.- 15 small (less than 4inch blades) O-1 blades, did all the HT at once, changing the oil every 2 blades. I use a hand-built forging chamber, just a glorified one-brick forge and propane torch burner.

The uneven heating seems to be a HUGE factor. The no-warp technique (which I am getting just a bit better at) involves a slower heat than I'd previously used. I stick the blade near the back wall of the forge where it glows red hot, instead of in front of the flame. This seems to distribute the heat a bit better. I make sure to flip the blade around, passing the length of the blade in and out of the "hot zone." Even with the edge quenching technique, I got no warps at all in all 15 blades done this way. However, I suspect, uneven heating might still pose a problem for the larger blades unless I got a bigger forge with more heating points.

The other is overheating. I suspect that unless I am very careful about judging critical temperature, it is easy to take it too far beyond critical, instead of the momentary 25-50degrees above. I haven't used a magnet for a long time, because I thought I'd learnt to judge the colours correctly, but over time, its obvious that things like a change of workshop, rebuilt, new lighting, summer now, not winter, makes a world of difference when trying to judge colours. Going back to the magnet a few weeks ago, showed me that I was taking the colour too far into the bright orange before quenching. Everyone's eyes are different so I call it "the point between cherry red and tangerine orange." Taking it to bright glowing tangerine orange will get you a good quench, but its too hot. That's my judgement anyway.

Steve, I've never been able to straighten a blade with a vice, I had to bend the blade back PAST straight to get it to correct. Most of the time, I just regrind the blade a bit back to shape. I do a lot of hard grinding on O-1. The straightening techniques are one I have to get better at, esp when building bigger blades.

Cheers.

Kevin, I have experienced warping of blades during oil quenching both from dropping them and from laying one down in a pan of oil. I checked back into a textbook on deformation of material that I have. The author states that during the austenite/martensite transformation, steel will lose elastic strength and may deform as a ductile solid under its own weight.
I use a sotted fire brick to hold the blades edge up and start from room temperature to avoid temperature differentials on the blades.
The austenite/martensite transformation is also atotal temperature dependent system. It is accomplished by bond length changes, and is diffusionless, thus not being time dependent. I imagine this statement will be disputed, but I can supply references if anyone is interested.

I use an old pair of tongs with 2 pieces of 1"x4" welded to the ends,I heat that set up to red hot,then apply to the spine to draw it down,works well

I was finally able to straighten my blade. I had to anneal it, pound it flat on an anvil, and reharden (just the edge) with an A/O torch.

Now it has a very distinct temper line. It looks good. Now on to the Handle!

Just a quick question, what is the Brass Rod test?

Thanks for all of the fantastic input!
_kevin

from a previous thread, kevin:
Another test I perform is called the 'Brass Rod Test'. To perform this test, set some brass rod (I use 1/4") on a flat surface, press the knife's edge on the rod at approximately 25 degrees, and roll edge of the knife along the rod. This causes (or should cause) the edge to deflect. A properly tempered blade's edge will return to normal. If the edge is too hard, it will chip. Too soft, it will deflect and not return to normal.
thanx to brett