Warping after temper?

T

tr3yanderson

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Mar 6, 2017
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Hey ya'll, still new to the craft and had a question. So I recently heat treated two knives (1084 in canola) I left the edge about thickness of a dime. they were heat treated about a month ago then tempered once the same day and then a second temper I did a couple days later. I have a piece of quarts I use to check flatness and I'm pretty sure after I quenched I checked both knives for flatness and i'm 99% sure I remember them being flat. but its been a few weeks now and I've just started hand standing the bevels further and just yesterday I noticed that both were bowed slightly. I don't think I checked after tempering, but is it possible to get a warped knife after tempering? or could there be issues because I had done the tempers several days apart?

They aren't too bad that I won't finish them but its enough to frustrate me and where I wouldn't want to give to someone.
 
First, you can heat them back up to temper temp and straighten them. Small warps can be straightened cold, but it's far safer to heat to around 400F and straighten.

Warp most often occurs from uneven cooling. If you temper a blade and set it down on a cold anvil, the bottom will cool faster than the top. This may cause a slight warp.
In some cases, the warp can come from uneven heating. If the oven is hotter on one side, or a blade is laid flat on the oven floor, then one side may heat up faster than the other ... causing a slight warp. Using a HT rack that stands the blade on the spine or edge is how to avoid most of this problem.

To avoid these problems in the future, check for warp when you take the blade out of the oven. If it is good, either hang in the air to cool, or cool in running cold water. If there is a slight warp, you can bend it out easily by hand while the blade is hot.
 
Stacy E. Apelt - Bladesmith said:
First, you can heat them back up to temper temp and straighten them. Small warps can be straightened cold, but it's far safer to heat to around 400F and straighten.

Warp most often occurs from uneven cooling. If you temper a blade and set it down on a cold anvil, the bottom will cool faster than the top. This may cause a slight warp.
In some cases, the warp can come from uneven heating. If the oven is hotter on one side, or a blade is laid flat on the oven floor, then one side may heat up faster than the other ... causing a slight warp. Using a HT rack that stands the blade on the spine or edge is how to avoid most of this problem.

To avoid these problems in the future, check for warp when you take the blade out of the oven. If it is good, either hang in the air to cool, or cool in running cold water. If there is a slight warp, you can bend it out easily by hand while the blade is hot.
Click to expand...

Thanks Stacy, This is really good to know. Previously I thought you would only get warping during quenching. When I temper, I have been just placing them flat on the rack in my kitchen oven; and now that I think about it, after a temper, I took one out while still hot and placed it on the stove top to cool. Now I know to change my methods.

Best way to Straighten? Do another temper and and while hot stick it in bench vice and and tighten till straight and let it cool?

Thanks
 
I also had this same issue and raised the flag about it. Folks chimed in saying how I tempered them, I layed them in the toaster oven on their side and the bottom was getting hotter than the top (not evenly per sides) and was causing my warps. Ive since been placing my blades spine down and have yet to have an issue! maybe give that a try. I would straighten yours by the tip above, giving it another quick temper at 400 and pull it out, straighten by hand if you can. then stand it on its spine to cool. If you cant straighten by hand, find 3 small sturdy objects and the vise and place two of them on the outer edges of the blade and the 3rd on the raised (humped up) part of the warp and gently clamp down the vise and checking for straightness. once straight take it out and lay spine up.
 
You can use a three point jig in a vise. You can make a dedicated one up from a HF 4" drill press vise ($15). Cut two 2" dowel pieces in half and epoxy one piece in the center of one jaw and two pieces 1" each side of center on the other. ( you will have an extra piece)
I usually just bend it by hand over my knee or the edge of the bench.
 
This is great. Thanks for the replies, I'm glad there is still hope for this knife. I was tempted to just throw it on the shelf, being the perfectionist that I am.
 
' quick temper " don't be so quick , The 400F heating is a must if you are trying to correct hardened steel if the original HT as 500 F use that but give it a bit of time . And bring it to temperature , hold to equalize .then slowly apply force . Then hold another bit.
 
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