Quench(cale?) question - does it protect blade ?

A

Angus McGunnigl

Joined
May 22, 2002
Messages
1,485
I've made a few knives now and have polished/sanded them to a final finish with 600 grit by hand.
All 3 knives have been made of old US made Nicholson files. They turned out fine, each one a tiny bit better than the last.
I do have some new O-1 that will be used after my skill improves a bit. For now I use these old files as a extremely inexpensive medium to learn with.

Upon quenching, the blade comes out of the oil(1 part hyd canola,1 part 10-30, 1 part ATF preheated to 130 deg), with alot of crusty black stuff. I let it cool enough to handle, sand off the black crusty stuff, polish again and then to the toaster oven for tempering.

My question is about the crusty black stuff left on the blade after the quench.
I see a cool looking finish/patina? on so many blades, is that from leaving some of the crusty black stuff on during tempering ? In particular Rick Marchand(sp) has a cool finish on his blades.

Does the baked on quench fluid add some protection to the steel ? How tough is this stuff if left on during temper ?
I suppose it depends in what fluid is used for the quench. SO MUCH TO LEARN !!!!

I admire the work of so many people here and am slowly learning.

Thanks for any input.
 
The finish you see folks use is added afterward in most cases. The easiest economical way to remove the scale is vinegar, it can be very hard and the vinegar breaks it down pretty well. There's not really any need to remove it before tempering, in fact, you risk other problems by delaying the temper. I don't recall exactly what steel those files are, but some steels can develop micro cracks if not tempered in a timely fashion. Then there's the risk of breaking the blade due to the highly brittle nature of untempered steel.
 
It is best to run a temper cycle, even just 350F for a 1/2 hour or so, to relieve stress from the quench. Then you can shine it up to see the tempering colours in the cycles to follow. I used to leave my blades "forge" finished prior to HT but found that the surface pitting was working against me in the form of stress risers. During tests, blades where breaking where the pitts were prominent. So in order to keep the style I wanted, I had to impart the aged/weathered look AFTER the HT was done. I do this with various chemical etches and sanding techniques. I still do rough forge finishes when the piece just screams for it. I sand the bevels to where they need to be and after my last temper, rub a beeswax/linseed mix on the hot blade. That darkens the scaled areas and seals the finish.

Thank you for the compliment, sir.

Rick
 
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