Vacuum heat treating O1?

[Danbo]

Ok, I noticed in a for sale thread, and the actual maker's website, that the blade was O1, vacuum heat treated. Sounds good, but how does one go about vacuum heat treating O1?

My understanding of O1 is this; it's an oil hardening steel and at some point, must be quenched into oil. Most folks simply heat the blade in their forge or oven at a certain temp, hold for a proper soak, and then quench into warmed oil. High tech dudes like Kevin Cashen and a few others use computer controlled salt pots to heat their blades to the proper temp and then quench. Where would "vacuum" enter this process?

BTW, this is just me wondering out loud.

 

[Hummeroid]

There are internal oil quench vacuum furnaces.

The vacuum is there for practically eliminating oxidation during heatup and soak time. Usually it has an internal gas quench though, and oil quench vacuum furnaces are rare. And a nightmare to maintain.

 

[james terrio]

The vacuum is there for practically eliminating oxidation during heatup and soak time.

BINGO. Scale doesn't come from the quench oil, unless maybe it's filthy. Decarb, scale and other unpleasant things come from HOT steel reacting with oxygen. No oxygen, no scale. That's why almost all stainless guys use a snug wrap of foil on their blades: to keep the evil oxygen away. That's part of the advantage of salt-pots, too... the molten salt simply doesn't leave any room for "air" to damage the steel.

My O1 and 1084 blades are indeed "vacuum heat-treated", by the fine folks at Peters HT. All this means really is that the furnace itself has almost no oxygen in it, so the steel can't decarb and develop scale. I think this is accomplished by filling the furnace with a different gas to displace the oxygen, so it's not truly a "vacuum", but I could be wrong. Anyway, the actual quenching method doesn't seem to make much difference.

The upshot is, I can grind my oil-quenched blades right to final dimension and finish, same as my air-quenched ones, without fear of scale. They both come back from HT with nothing more than a very thin layer of tempering color, which is easy to sand off.

 

[jdm61]

Wouldn't a vacuum furnace cause oil or any other liquid to boil away at temperatures much lower than anything you would need to austenize steel not to mention the oil being WAY too hot? Perhaps "inert gas furnace austenizing" would be a better description of what they are doing. They would still have to remove the blades to quench them, but there likely wouldn't be enough time for scale to form between the oven and quench tank.

 

[me2]

Industrial ovens have some pretty fancy set ups. They can inert atmosphere austenize, then drop the parts into a separate compartment for quenching. I don't see a huge barrier in doing the same thing from a vacuum.

 

[james terrio]

Perhaps "inert gas furnace austenizing" would be a better description of what they are doing.

Yes. It's a bit wordy for us knifemakers, but actually, that's how the folks who HT things like jet-turbines describe it.

They would still have to remove the blades to quench them, but there likely wouldn't be enough time for scale to form between the oven and quench tank.

I'm sure they do. Time between Aus temp and quench is not the issue in terms of decarb or scale. Scale does not form between the kiln and the quench, it forms IN the kiln if the steel isn't protected from oxygen. Hence, foil-wrap, anti-scale-coatings, inert atmosphere kilns etc.

 

[Error 404]

Correct Joe, there are no open liquids in the chamber itself. The pumps would never draw a vacuum. We have facilities in humid climates (e.g. Singapore) that have pump-down issues simply because of the moisture condensed on the vessel walls (due to double wall cooling). We typically argon gas quench, but I'm talkin nickel superalloys and titanium (aerospace applications), not steel.

 

[lazlo]

Wouldn't a vacuum furnace cause oil or any other liquid to boil away at temperatures much lower than anything you would need to austenize steel not to mention the oil being WAY too hot? Perhaps "inert gas furnace austenizing" would be a better description of what they are doing.

Most high-end heat treat shops, including Peter's, really do use vacuum heat treat furnaces. The material is austentized in a vacuum, and then pre-quenched with an inert gas to get the material below oxidizing temperature.

http://www.petersheattreat.com/cvt.html

Most tube furnaces I've run across at surplus have a gas port for (hopefully ) inert gas. Hmmm...


"An inert gas, such as Argon, is typically used to quickly cool the treated metal back to non-metallurgical levels (below 400 °F) after the desired process in the furnace. This inert gas can be pressurized to two times atmosphere or more, then circulated through the hot zone area to pick up heat before passing through a heat exchanger to remove heat. This process is repeated until the desired temperature is reached."

 

[jdm61]

Having the oil boil up when the pressure drops. Even seen a beaker of water in an evacuated bell jar? You would have to pressurize the oven first.

Industrial ovens have some pretty fancy set ups. They can inert atmosphere austenize, then drop the parts into a separate compartment for quenching. I don't see a huge barrier in doing the same thing from a vacuum.

 

[jdm61]

Most high-end heat treat shops, including Peter's, really do use vacuum heat treat furnaces. The material is austentized in a vacuum, and then pre-quenched with an inert gas to get the material below oxidizing temperature.

http://www.petersheattreat.com/cvt.html

Most tube furnaces I've run across at surplus have a gas port for (hopefully ) inert gas. Hmmm... .


"An inert gas, such as Argon, is typically used to quickly cool the treated metal back to non-metallurgical levels (below 400 °F) after the desired process in the furnace. This inert gas can be pressurized to two times atmosphere or more, then circulated through the hot zone area to pick up heat before passing through a heat exchanger to remove heat. This process is repeated until the desired temperature is reached."

Some of those furnaces have to be able to inject that gas at up to 12 bar with some metals from what I have seen. That might be enough for a deep hardening oil hardening steel. I was under the impression that Peters used "sand beds" for the stuff that needs to be quenched more rapidly

 

[lazlo]

Some of those furnaces have to be able to inject that gas at up to 12 bar with some metals from what I have seen. That might be enough for a deep hardening oil hardening steel. I was under the impression that Peters used "sand beds" for the stuff that needs to be quenched more rapidly

I was wondering that too -- if you can vacuum heat treat carbon steels. I wouldn't think argon, even at 12 atmospheres eek could quench carbon steel in under 4 seconds?

 

[shqxk]

If you open the vacuum furnace at high heat to quench, the coil inside would sure get damage from the atmosphere.

Vacuum furnace design to be heat treat with gas quench only.

 

[me2]

There is a local heat treating company that makes vacuum ovens the can nearly equal water quenching speeds with their pressurized nitrogen quenches. They'll cool as fast as you want basically.