Heat Treating Woes

S

Shotgunone

Joined
Oct 1, 2000
Messages
244
I was playing with my new heat treating oven and some 440C. It was thinned down like a blade edge, not a knife, but a test piece to check out warpage and hardening. Well anyway, I put it in the oven and heated it as prescribed in the instructions - to 1950 degrees and left it for 15 to 20 minutes. When I remove the piece from the oven it was naturally covered with scale. As it quenched in the air, the scale POPPED off everywhere.

Now the real concern. The steel didn’t harden. It might be a little harder but it still bends by hand. So can anybody tell me what happened?

Did I not leave it long enough or did I leave it too long? Can you cook the carbon out of the stainless steel so it won’t harden? Or is it possible the temperature is wrong. It would have to be on the high side because the steel was non-magnetic when I took it out of the oven. So what if you over heat the steel?

Any Ideas would be appreciated.




[This message has been edited by Shotgunone (edited 12-02-2000).]
 
First off, you need to wrap the steel in high temp stainless foil to eliminate the scale. Besides being hard to clean up the scale is mostly carbon burning out of the steel, not good. The bending you mention is normal with hardened but not tempered 440-C. Straighten if needed while still warm from hardening. After the first temper the steel will be springy. The steel may have been hard. If it wasnt you need to speed up the quench with a fan or use a press quench. If that dosent work cross check your pyrometer and make sure it is accurate. These high alloy steels are very temperature sensitive in the hardening cycle. Non magnetic dosent mean anything with 440-C as far as I know. And one thing that is very important to have if one is going to be heat treating the high alloy steels is a rockwell hardness tester. I cant imagine even trying to heat treat without mine!

Hopefully Paul Bos and others with step in with more info.

[This message has been edited by Rob Simonich (edited 12-02-2000).]
 
I have done some 440-c. I knew about the stainless foil but didnt know the bag plumps when you cook em like a ball park weiner. When it got fat the tip poked out though the foil and was exposed to the air. The tip was burnt to a frazzle and never did harden. The carbon was cooked out of it. After that one I fold the pouch tighter and put a piece of brown paper or cardboard in with the blade. The paper will burn the oxygen that has remained inside. I regrind my blades after heat-treating so I can leave them a bit thick in case it decarbs at the thin edge. Non-magnetic is about 400 degrees lower required temp for stainless steels. Forget the magnet and whatch your temp. Air quench with a fan blowing on the steel after taking out of pouch asap. straighten the blade when cooled enough to handle. I use liquid nitrogen (cryogenic treatment) after staightening and at room temp. leave it in the nitrogen for 6 hours. then temper according to the formula for that steel. I dont have a rockwell tester but the community college does. They are my buddies. I always check the hardness with it. Retemper if neccesary. Hope this helps. I respect others like Rob and Paul on this subject. Bruce
 
I had the same problem when I first got my furnace. 440C would harden (couldn't touch it with a file) but I could bend it pretty easily. It also would not respond to tempering temperatures.(It stayed hard) I found that if I shortened the amount of time that I used to harden it to about 13 minutes that I solved the problem. Most of the steel I use is less than 1/4" thick. I was told by another knifemaker who also heat treats that I was cooking the carbon out of the steel. It took alot of experimenting for me to arrive at 13 minutes. I assume that each furnace might be different ??? Hang in there, once you get it right it is pretty easy to duplicate.

------------------


[This message has been edited by Stickypoint (edited 12-03-2000).]
 
I should have mentioned, most of these test pieces were 3/32 inch 440C except for one end piece of 1/8 that was about 1 1/2 inches square. The 1/8 inch piece hardened so that a file won't touch it. But the 3/32 pieces are slightly bendable and the thin edge (like the cutting edge) will cut with a file. I even tempered them today just to see if that helped. 2 time for 1 hour each at 375 degrees. The 3/32 still bends but it is harder than the annealed stuff I start with. It seems like the thinner the piece the less hard it got while thicker sections fo 3/32 got hard enough not to bend.

Funny thing is I have been using a oxy /act torch to harden 440C for years with no problem. And it was hard. No file would touch it and no bend at all. I thought if I get an oven I would be able to do a much better job. But I am in worse shape now. I was really hoping to start using Ats34 like all the big boys do but now I DON'T KNOW.
confused.gif


I am getting some foil wrap and hope that helps. I know the instructions I got for this steel reads 1 hour soak time but I wonder if that is too long for 440C. Or will the wrap help that much.

Man is this funnnnnnnn or what
rolleyes.gif


I know I got to figure something out before I stick a real knife blade in to this thing and mess it up.
eek.gif
Any more Ideas?????

------------------
Tony Huffman
thuffman@texinet.net
Sporting Clays & Shotguns ... my other bad habit!

[This message has been edited by Shotgunone (edited 12-03-2000).]
 
I went through this and I know how frustrating it is. Generally when they talk about soak time they mean per inch of thickness. As an example if the instructions say to soak it for 1 hour and you have a 1/4" thick blade then you should soak it for approx. 15 minutes.
The stainless foil is meant to help eliminate surface scale, I don't think its going to help with the hardness problem. Try shortening the soak time.(I use 13 min. for 440C of that thickness) For 440C I keep the temp. between 1850 and 1900 deg.F. Hang in there, it's worth it.

[This message has been edited by Stickypoint (edited 12-04-2000).]
 
Ok. Here we go. I have cut ground and shaped some trapper blades and springs in 440c. Bought my heat treating foil. So if all goes well by Monday I will have heat treated these in my heat treating furnace and this time they will harden.
biggrin.gif


And if these works it times to break out the ats 34 for a test knife.
smile.gif


Any last thoughts or comments before I toast these blades.

------------------
Tony Huffman
thuffman@texinet.net
Sporting Clays & Shotguns ... my other bad habit!
 
:
Tony if it was me doing it and I wasn't real sure of my process I would try only one first and if it was successful then Go For It.
smile.gif
YMMV.


------------------
>>>>---¥vsa---->®

Each person's work is always a portrait of himself.

---- Samuel Butler.

Khukuri FAQ
Himalayan Imports Website
 
YES YES YES YES YES
biggrin.gif


Finally got some 440C hard in the furnace. Them Trapper blades and springs are hard as a ...........,
wink.gif
Well hard.

Thanks for the replys to this post and for the emails too!!!

Now Rob what was this about ats34

<font face="Verdana, Arial" size="2">...ATS-34 to have a snappier heat treat than 440-C... </font>
Click to expand...

Can you elaborate on that a little more. Advise is always welcome. I'm ready to try some ats just as soon as I get some blades ground.

------------------
Tony Huffman
thuffman@texinet.net
Sporting Clays & Shotguns ... my other bad habit!
 
Shotgunone, When I say snappier, I mean that it is more responsive than 440-C. I find 440-C rather sluggish in the hardening phase, ans see differences from batch to batch in how it hardens up. (Different mill runs of steel I suspect) Never had a sluggish batch of ATS-34 though....

Glad to hear your blades worked out this time.
 
Bob you asked if I put paper in with the blades and No I didn't. I know that is suppost to help with the decarb. I did my best to eliminate the amount of air in the foil pack to begin with, by starting with a tightly folded piece of foil and double folding the edges. After I got it figured out the wrapping went pretty fast and no cuts this time (knock on wood). I also wanted a little decarb for color as I do file work on the springs and blades so when I polish (grind) the blades off the cut areas will stay dark. This create some contrast.

So Rob your I think your saying that Ats will harden a little easier (not as critical on temperature). What about the cryo on ats. I have heard some that say it is better to cryo but not necessary and some that say you HAVE to cryo the ats or it won't work correctly. Any comments on that.

Thanks


------------------
Tony Huffman
thuffman@texinet.net
Sporting Clays & Shotguns ... my other bad habit!

[This message has been edited by Shotgunone (edited 12-13-2000).]
 
You must log in or register to reply here.
Back
Top