Can we talk about warpage ?

S

skinny_dan

Joined
Dec 10, 2003
Messages
193
Hi guys.

I'm just about ready to send my first batch of knives off for heat treat. Steel is O1.

I'm really nervous because I have spent so much time grinding them and polishing them up.

From what I understand, warpage can occur during the HT for the following reasons

too thin (causes wavy edges)
uneven grinds (causes warped/curved blades)
uneven heating (as above)

Firstly, what is considered too thin ? Is there a minimum thickness which will guarantee no warpage ?

How can I test for an uneven grind ? I look down the blade, and across it from the edge, and to my eyes it is even. Is that a suitable method of checking for eveness ?

Uneven heating, well that will be left to the heat treaters.....

Also, what steels reduce the likelihood of warpage ? I hear the A series of steels are air hardening, and if I remember correctly, they are quenced in air (not sure how that works). Do they combat warping well ?

Thanks !
 
Any time you do things to one side of the blade differently from the other you invite warping. Including forging , all heat treating steps and grinding. The more severe the quench the more reason for warping , so water quench is the worst and air quench the best .Air quenching means you just take it out of the furnace and let it cool in still or moving air.
 
No , a torch increases the chance of warping because it is more difficult to uniformly heat the blade
 
Warpage is is just the reason that people need to bite the bullet and start heat treating their own blades. You can straighten most warpage shortly after you quench the blade.

For folder blades and small fixed blades I heat treat before I grind. This prevents edge warping. You have to be careful when you grind the bevels so as not to ruin your temper. This is not a problem if you use sharp new belts. I am not one of those guys that gets 20 or 30 blades from one belt. 3-5 knives is about all I get with the ceramic 3M belts I use and the flat ground blades. For larger fixed blades I grind the bevels about 2/3 to finished and then heat treat. I do the final grinding after heat treat.
 
I've oil quenched O1 with bevel edges as thin as about 10 thousanths inch with no edge rippling. Hollow ground bevels are more apt to edge ripple if too thin because of the width of continued thinness. If your edge is 15 to 20 mil thick, especially if flat ground, I doubt you should worry about edge warp.

RL
 
Mete, You mentioned different quenches. I know you know your steels. I've got some Quenchtek B from Texaco. Its very fast. A week or two ago I was wanting to get some type "A" that is slower but found out they no longer make it. If I got some more "B" what can I do to it to slow it down?
 
I understand exactly what folks are talking about when they say that "too thin" can cause distortion, but the way the concept is presented is misleading. It is not that the blade is too thin (fillet knives can be quenched without distortion) it is that the edge is ground too thin in relation to the thinker body of the blade. This causes uneven cooling regardless of the quality of most quenches. And will result in an expanding edge that is constrained by a thicker body or spin; all it can do to acommodate this is ribbon up :eek: Even this can be overcome by equalizing the temperature above before plunging into martensite. I think my friend Brian lyttle has virtually sharpened knives before heat treating them in salt baths just to prove a the point. I have seen and cut with some of the blades and they are as straight as I could want them.

mete you say that factors in distorion would also include forging, wouldn't you agree that if a person suspects forging as a major contributing factor in distortion in the later heat treatment, that re-examination of their normalizing or stress relieving practices would be the first order to alleviate this problem?
 
Raymond Richard,

Contact Shane Justice if you are interested in some Texaco type A oil. He has been buying and selling the stuff for some time now. I believe he sells it in whatever quantity that you need also. Shane's email address is:
justicecustomknives@yahoo.com
 
Just to point out, when hot, steel expands, and when it is cooled (slowly) it shrinks, when you quench hot steel, the more quikly it cools, the less it will shrink, This is why when heat treating a japanese blade, you start with a straight blade, and after the differential heat treat, the blade is curved. the edge froze in it's expanded state. while the spine cooled more slowly, shrinking as it did so.

If one side of a blade is thicker than the other, it will be the concave side. if you have a very thin edge, and a thick heavy spine, the spine won't curve, but the edge will ripple.
[Edit to add]: This is why salt baths work well, they keep the entire blade at the same temperature, without any differential heating
Make sense?

Tony
 
Kevin, We've been through this warping [and cracking ] question before , perhaps in bits and pieces. I think that if you have the problem , it's a good time to review the whole process.Forging- try to do the same thing on each side of the blade , that is equal number of blows on each side .The normalizing is done to refine grain and produce uniform structure throughout the piece. Normalizing as in all heat treating , the point is to uniformly heat the the metal [ especially important for those who use a torch].Normalize , check for straightness , if you have to straighten, normalize a second time .Harden ,and when quenching make sure you are inserting the blade point down or edge down.If moving the blade do it edge to spine not side to side .Even in cryo make sure what you do to one side of the blade you do to the other....I would repeat here that blades are a very simple shape and should have a lot less problem of warping than more complex shapes.
 
So if I have a blade of 3/16" ATS, and I ground a 1/2" flat grind to almost an edge, can I expect some bad warpage?? I can still run it on my hand and not get cut, but the edge is pretty fine...Thanks for the help.

~Brian
 
Skinny and Brian I will give you my input (for what it’s worth).
Awhile back I hollow ground 7 blades with a new Grizzly grinder that I bought. I started with 36 grit and by the time I got down to 600 grit the edges had all become very thin (about like you described). I grabbed up all 7 blades and headed out to harden with an A/O torch. I heated and quenched 3 blades before I really took a good look at them. All 3 had warped (wavy) edges and 1 cracked. :mad: The other 4 blades went back to the grinder and I ground them back to get more meat on the edge. I had no more trouble with those warping. As far as a measurement I’ve never measured I just eyeball it. After making a mistake like that the eyeball becomes educated. ;)
 
Thanks for the info guys.

What I plan to do is just thicken the edges where it is possible without ruining the look of the knife. I guess if I were to be more creative I could thicken the edge and still have something presentable.

Will also rub down with lower grit sandpaper to flatten the sides a bit more, make them more even.

And once that is done, cross my fingers and send them off.
 
I already sent mine off...I hope I didn't blow my money. :( I sent a second one with it that was ground a lot less...I learned AFTER I made the mistake on the first :( . Oh well...at least I learned :D

~Brian
 
Hey guys, update

I got my knives back last week, they turned out fine, all blackened from the HT but no warpage.

They are much harder, I have trouble filing them now, but that is probably a good thing :)

thanks
 
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