heat-treat foil sticking

D

Donald Bell

Joined
Dec 9, 2003
Messages
57
I've got a new (for me) problem!!
I just did a heat treat of stainless damascus using HT foil, at 1925 deg for 30 min, then plate quench for about 5 min. When i opened the packet the foil was stuck to the steel in several places. most of it scrapes off, but there are still many spots where the foil seems to be welded to the steel.
Questions;-
1) what caused this , and how do I avoid it happening again?
2) how do i get the bits of foil off without resorting to grinding,which would wreck the tolerances?
Any and all help would be greatly appreciated.
thanks, Don

www.Bellknives.com
 
This has never happened to me. I think your blade and the foil were too clean, it must have welded to blade during the plate quench. I always put a piece of paper or a piece of charcoal in the envelope, I guess it does have a buffer effect between the blade and foil.

Here is my thoughts, even if it didn't stick to blade you would have a thin layer of decarb you need to grind to reach the good hardened steel. So you better grind lightly the balde same way, the welded foil should go away... Good luck with it....
 
I've had the same thing happen to me on occasion, though I'm not sure why.

I always take my blades back to the grinder at a high grit after heat treat, so it hasn't been an issue for me. The only time it really stinks is if I am trying to pull the blade from the foil to check for warps (after the pearlite nose and befoe martensite start).

--nathan
 
A few suggestions to examine;

  • Always use 309SS foil. The 321 will sometimes let you down
  • Quit peekiing! When the envelope heats up, it expands away from the metal - when you peek, the air inside contracts like a vacuum seal for freezer bags. When the door is opened, the pack comes out and goes to plate quench.
  • Use a home-made brass chisel to get stuck foil off the blade
  • There should be no decarb on a well protected and properly plate quenched blade. Hopefully you don't need to grind after HT unless you are doing very thin blades and trying to avoid warping.
Hope that helps in some way.

Rob!
 
check the max temp that your foil is rated for, some is 2100 degrees, and I have seen some rated for a max of 1900 degrees. Just a thought.
 
My reason for going back to the grinder after heat treating isn't for decarb; I haven't had any decarb on foil packed blades. I just find it faster to use a high grit belt to remove the rainbow coloration I get from heat treating than to use sand paper. After that, it just takes a few minutes to re-sand to a final finish.

--nathan
 
we ha that problem at work and found that we where getting hotter then we thought and so we where exceeding the foils rating. we now onley use the high temp foil.
 
Thanks for the quick responses guys.
I got the foil from a supplier at the Blade Show a few years ago, but there is no marking to indicate type or temp rating.
I put in a snip of paper, as usual, however I did rinse the steel in acetone before wrapping-(first time I tried this)
Some of the foil actually did weld to the steel, because the brass chisel,and then a mild steel chisel, could not get it all off- so back to the grinder!
I am also using a different kiln this time, so I will have to check the accuracy of the temp indicator.
Regards, Don

WWW.Bellknives.com
 
Donald: You can eliminate sticking by dusting your blade with pure talcum powder before you wrap it. No snip of paper is necessary in the packet.

RJ Martin
 
I have done the foil HT with and without the small piece of paper and I can't tell any difference. I now use only the 309 foil as I had a welded on piece of 321 foil that became a real hassle. Unless the foil is advertised as 309 it is probably 321. I do mostly D2 at 1850.
 
I've had the problem at 1950 degrees F., but not consistently. I can't figure out which variables might cause the difference.
 
This has happened to me, and usually ocurrs when I put too many knives in the oven at once. I work with 440C and put a small wood chip in each pouch to elliminate O2 and reduce the chances of scale.

I was thinking that perhaps my oven was hotter than it should be.
 
Wouldn't hurt to check oven temp but sounds like the foil is 321, the 309 foil isn't that much more expensive and it good for a higher temp, its all I have used at home or at work at the shop never an issue. Its a good idea to use a piece of paper, less chance of scale and it burns up the oxegen so the bag is not as puffed up
 
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