Heat treating 440C ?'s

L

LCoop

Joined
May 5, 2007
Messages
629
First I'd like to say thanks for all you folks who regularly share their knowledge on here. I've been a member for a couple years and mostly just read and learn. I've been dappling making knives out of files and 1095 with a two brick forge and been pretty pleased with my stock removal knives.

Just recently I made my own electric heat treat oven 240v with a PID controller and K theromcoupler and I gotta say it's been working great using the auto tune feature and holds temps really close.

So I've been wanting to make some SS knives and purchased 440C used the foil wrap with some brown paper inside and heated to 1900 held 15 minutes and plate quenched between two alum plates. I don't have a RH tester but man they seem incredibly hard and a file "skates" across them.They came out great but while warm gave them a quick buff to shinny again. Then I tempered one cycle at 375 for 2hrs turned a golden straw color and tested again. File still skated across. So I then tempered two hours at 415. Again still a golden color and a file skates across them. Everything I've researched and read says they should be in the 57 - 58RH scale.

I just purchased some new Nickolson files but haven't gotten a chance to test again. But does my method seem on target. Are there better receipes? After I temper a cycle for 2hrs should I slowly let it cool down in my oven or pull it out in room temp to cool? My homemade oven has the usual fire brick inside but also used 1 1/2" insulating material on all outside surfaces(it came with the burned out ceramic kiln that I salvaged the fire brick from) and it takes a LONG time to cool down! Would appreciate any and all advice on HT on 440C. Thanks in advance.
 
Your method is alot like what I do, but I heat to 1880 and hold for 15 min. and plate quench. then temper at 375 for 2 hrs then again at 375 for 2 hrs. I use a toaster oven to temper in, so it cools faster than my kiln would, but that should'nt matter, and I do try to remove them from the oven to cool at room temp air. My blades from 440C also skate a file after temper, really sounds like you are ok to me. I don't know if it matters how slow or fast the cool down is in the temper cycle. Some use a cryo treatment, but I don't, but it would probably improve the hardness a point or so.
 
Your methods seem right on target.After the 415 temper you should be getting 58 or so.
Letting them cool in the oven won't hurt anything but I usually pull mine out and let them air cool to room temp.
Stan
 
The cooling rate from temper is not of consequence. If you have time, let it cool in the air. If in a hurry, quench in water and put back in the oven for the second temper. There will be no damage from the quench.
There is no need to oven cool the blade.
 
Looks good up until your 415 temper. The Crucible datasheet shows 400F temper giving RHC56. I'd stick with the 375 for both tempers. Should give you about RHC 57-58.

Rob!
 
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