Heat treating a 4140 axe head

N

navasky

Joined
Dec 7, 2009
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I've got a few camp axe heads ready to go into the oven. Does anyone have a good recipe for heat treating 4140 edged tools? Will canola oil (which I've read is comparable to 10 second oil) be fast enough to be optimal? Thanks.
 
The book says 1575 and 450-500 temper. Hopefully some of the hammer makers will chime in.

Hoss
 
I do axes with just the bit hardened. Many have welded high-carbon bits, but some are mono steel blades from a tough steel like 4140 and its cousins.
I think canola is too slow. I use brine for 4140.
In a steel like 4140, IIRC, I go 1550-1575 and then quench all the way in, pull out after 5 seconds, count to five, and put it back most of the way up the cheek. I hold it there for a good 30 seconds and then set it on the anvil to cool. I temper at 500°F.
 
I was curious so poked around for a TTT curve, the top one here relates to 4140. This suggests that canola won't be fast enough here to be a good choice. You might get the edge hard enough to work, but buying a fast oil or doing something water based would likely be better and give you more room for error


(If you want optimal then spend the next 5 years defining the problem, building high precision tools, and testing every variable. Then expect someone to argue because they have a slightly different definition of the problem)
TTT-curves-for-A-UNS-G41400-SAE-AISI-4140-steel-037-wt-C-077-wt-Mn-098-wt.jpg
 
Thank you everyone for your replies! I couldn't find a TTT diagram anywhere so that was helpful Alex. A couple more questions: is a soak time likely to be useful in the case of small axe heads? And, one of the heads was made from 4142 prehard. I don't think I should have to do any extra steps because of this right? Just heat treat it the same as the annealed ones?
 
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