Dear Tim,
Thanks for the great information. I'm
writing to get more information and the address of Park Metalurgical.
To clay temper 1084 steel do I use a fast quench oil or a meduim oil?
Sometimes when I etch my blades they
come out with light and dark blotches. Is there a reason?
Dennis P. Tingle
Dennis,
The address for Park Metallurgical is:
Park Metallurgical
8074 Military Ave.
Detroit, MI 48204
800-521-8562
They are an excellent source for heat treating salts and oils.
To completely harden 1084 steel you have to cool it from the critical
temperature to below 1000F in less than one second. That takes a pretty
fast oil as it is. When you add clay to the back of the blade it acts
as a heat sink and further slows the cooling of the edge. So just about
the only way to go is water or a very fast oil.
The water, although it will work, can be quite severe and lead to edge
cracking and warpage. The boiling water forms a vapor jacket around the
blade. This vapor jacket contributes to uneven cooling which, in turn,
can cause cracking of the edge and warpage.
The very fast oils are usually a better alternative. They will cool the
blade quickly enough to get full hardness, without the problems
mentioned above. My favorite fast oil is Park Metallurgical #50. It is
very fast and approaches water in speed.
The reason for the light and dark blotches is usually
decarberization of the steel at the surface. These blotches are
usually seen at the ricasso and along the spine of the knife. This is
where the least amount of grinding is done after forging. If you pay
attention you will notice that the blotches usually occur where the
last few forging pits disappeared while you were grinding.
It is good practice to leave all surfaces at least 0.010" oversize
after forging. This means that a blade you want to finish at Œ"
(0.250") thick should be forged to a minimum of 0.270". Forging in a
slightly oxidizing atmosphere will also help cut down on the
decarberization.
Blotches can also be caused by poor etching technique. Most commonly it
is oily fingerprints on the blade. Be sure to clean your blades with
acetone or laquer thinner before putting them in your etching solution.
Changing your etching solution once and a while doesn't hurt either.
I'm setting up a high temperature salt
bath system for hardening my blades and have a few questions.
How big a container do I need for the
salts?
Does it only have to be big enough to accept
the steel I am heating? Or should it be slightly larger?
Should it be made from stainless steel?
Is there a cheap way to make a heater
for the quenching salts? (I can't afford another kiln right now.)
Since I have to quench in oil, is
there any advantage to heating the oil to 300+ as opposed to 150
degrees?
Thanks for all the help. As you
can tell, I need all the help I can get.
Thanks,
Richard Rogers
Richard,
In setting up a high temperature salt bath your salt container can be
fairly simple. Schedule 60 or 80 steel pipe is all that is needed. Have
a thick bottom welded on by an expert welder. BE SURE IT DOESN'T LEAK!
The salts will destroy the elements and brick in your kiln.
The container for high temperature use only needs to be big enough to
get your blade in. But, a bigger pot doesn't hurt as it and the salts
will have more thermal mass and get your blades up to temperature
faster.
A container for quenching, low temperature, salts should be larger to
allow for agitating the blade as it cools. I use 6 inch diameter pipe
in both my salt pots.
Stainless pipe is not necessary, as the high temperature salt, Nu-Sal,
is not corrosive to steel. The outside of the pot will oxidize whether
it is stainless or not. In very high temperature applications (1900F)
inconel or ceramic salt pots are recommended.
Some knife makers have made low temperature, quenching, systems using
old electric water heaters, I have only seen one. It was slow in
melting the salts, but it worked. This might be a better question to
ask Al Pendray.
When you quench in oil use the temperature recommended by the oil
manufacturer. Different oils cool best at different temperatures. If
you are using waste or mystery oil a good guess is to keep it in the
150F to 200F range.
Some makers are trying to martemper using oils instead of salts for the
quench medium. While this works ok for air hardening steels, it is
simply to slow of quench to work well with oil and water
hardening steels. Also, sticking a hot blade in 300 � 400F oil is only
asking for problems. You are dangerously close to the flash point of
the oil and are very likely to have a fire on your hands � literally!
The salts aren't expensive, about $00.60 per pound for Thermo
Quench. Try to use the real thing if you can.
If you want to approximate martempering using oil, try interrupting the
quench. Use the best and fastest oil you can get. Pre-heat it to the
temperature recommended by the manufacturer. Then, as you quench the
blade try to give it your best guess of when the blade has cooled to
400F. This is usually only a few seconds. Pull the blade out of the
quench oil. It should be smoking lightly but not flash. Let the blade
cool to room temperature in still air and temper as usual. It isn't
quite martempering, but it works pretty good.
Please feel free to send questions and comments to:
Tim Zowada
4509 E. Bear River Rd.
Boyne Falls, MI 49713
E-mail: tim@tzknives.com