Heat treating

[SDheavymetal]

I found this on an search on this forum from JeepinDoug

Oil quench is great to work with.
When you're done with the part, heat to cherry red then quench in oil.
Keep moving the part until it's cold.
That's full hard.
Polish it clean, then heat it again until a light purple.
This will draw the temper down to around the hardness of a band saw edge, rugged without being brittle.
-
I might try to heat treat my bully 2 cvd's. I get the part to about heat to cherry red and quench in oil.

BUT When you heat it again to "light purple" do you quench it in oil again or just let it air cool?

[sickcivic95]

You'll let it air cool because you are "tempering" the part at that point. Basically relieving the stresses from hardening and rapid cooling. So heat and let cool at room temp

Here's a quick blurb about the processes that explains a bit more in detail

http://www.metlabheattreat.com/metal...tempering.html

-Dan

[DrewHammer]

I have air cooled when tempering and also submerged the part in sand to retain heat and cool slower. I personally have never been able to tell the difference as most of this has been on custom tooling that hasn't broken.

Also, remember that if the part is welded to normalize it first to reduce any internal stresses. This will reduce warping when heat treating.

For heat treating/carburizing I use ND30 motor oil filled loaded up with "carbon black" to aid in the precipitation of carbides. Don't panic when the oil catches on fire, just make sure it's in a metal container and you have a lid you can use to snuff the flames.

Rather than utilizing color of the steel to determine when it's ready to drop in the oil I keep a magnet handy. If you're inexperienced with the color temps of black bodies a magnet is a sure way to tell when it's ready to drop. Ideally the crystal structure will be austenite, meaning the magnet will not stick to it when it's ready to drop.


Edit - Basic article on Austenite

http://www.threeplanes.net/austenite.html