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9:31 pm
NWBA Member
February 21, 2019
Offline
I attempted to heat treat a chisel (9" long, 5/8" round, 4140). I did... something... to it, and I would appreciate a suggestion on what I should have done, and also, what to do now.
What I did: After forging, I heated the tool to orange and left it in the (propane) forge, turning the forge off. The tool remained there overnight as the forge cooled to room temperature. Next day, I fired up the forge, putting the tool half-way inside, so the cutting end glowed dark orange, and was nonmagnetic; the hammering end remained gray-black. I quenched the cutting end in oil. Not for long, maybe 5 seconds, swirling around. Result: the chisel showed colors bunched up in the middle, not at the end. I watched it cool and the colors remain in a band about one inch wide, more or less in the middle, not running up.
What I think I should have done: Quenched the entire tool (probably for longer, 10-20 seconds). Then reheated, slowly, from the struck end, watching for running colors. When the right color reaches the edge, quench just the cutting end. Done.
What I think I should do now: Start fresh by reheating the tool in the forge and letting it cool slowly back to room temp, and trying again.
Any thoughts, corrections or insights?
8:08 am
NWBA Member
March 22, 2011
Offline
Good morning, Dan.
First question I have is: why do you think you messed up? Have you checked the tip to see if it hardened?
Second (or 3rd as the case may be) question is: What kind of chisel are we talking about? a wood chisel? a hot cut for forging?
as always
peace and love
billyO
9:25 pm
NWBA Member
Board Member
April 26, 2010
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Colors are the result of different thicknesses of oxides. Since the tip was hot enough to form a thick layer of oxide, it stands to reason that there would be a color bunch-up.
Most folk will quickly polish after quenching and watch the colors run on the bright metal.
Page six of this resource explains how Rashelle Hams does it: https://blacksmith.org/2015-2-hot-iron-news/
No matter where you go... there you are.
9:11 pm
NWBA Member
February 21, 2019
Offline
Lee, thanks for the link: that's a helpful description of the process.
BillyO, I haven't checked the hardness. I'll do that when I get back to the shop. I think I may have hardened it -- but not tempered it properly (or at all). Seemed to have missed a step. The chisel is a going to be a hot cut for forging.
Thanks, both of you.
11:38 pm
July 2, 2022
Offline
Your detailed description indicates a thoughtful approach, but for precise guidance, I would recommend consulting with a emergency heating engineer . They are such experienced professional in heat treatment. They can provide insights into the specific characteristics of 4140 steel and guide you on the appropriate heating, quenching, and tempering processes.
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