Liquid coating for HT?

[G L Drew]

I just saw a small ad in Blade magazine for a liquid coating for steel to be heat treated in an electric furnace. The coating is supposed to replace foil packets to keep air away from the steel and cut down on scale. Has anyone had any experience with this? As a friend says "I am tired on cutting my fingers on the foil".

 

[deker]

I just saw a small ad in Blade magazine for a liquid coating for steel to be heat treated in an electric furnace. The coating is supposed to replace foil packets to keep air away from the steel and cut down on scale. Has anyone had any experience with this? I am tired on cutting my fingers on the foil.

It comes as a liquid? I've heard of the high-temp PBC powder that brownells, etc sell for use on stainless, but never a liquid. Who's the manufacturer?

-d

 

[LRB]

I have heard of the liquid, but also heard that PBC powder is much superior. I use the powder and cannot complain. It does a great job preventing decarb.

 

[mtnsct]

Could either of these products be used with oil quench steels to cut down on decarb? Be nice to grind O1 to near completion before heat treat in the oven.
Rod

 

[deker]

Could either of these products be used with oil quench steels to cut down on decarb? Be nice to grind O1 to near completion before heat treat in the oven.
Rod

Yup you can quench with PBC, etc.

I managed to get a very nice result this morning with no coating at all though. I have a piece of 316 stainless tubing with one end capped that's a little smaller than my forge opening. I cut and slotted some firebrick and slid it into the tube, then slid the tube into the forge once it was lit (gas forge BTW). Once I had the temp stabilized where I wanted it, I tossed a few small pieces of firewood into the tube to eat the oxygen. Once they burned off the volitles I had charcoal (yes, I could have started w/ charcoal, but what I had was wood...). Then set the blade into the slotted brick and waited for it to come to temp.

I ran 3 normalizing heats and a quench this way and only had VERY light scale/decarb when all was said and done.

Just another thought on how to avoid scale on a budget. I happened to have the 316 capped tube around, but mild steel would work just fine as well.

Oh yeah, it was 1084/15n20 damascus I was working with.

-d

 

[Phil Wilson]

Drew, I haven't seen the Blade add but I use a liquid called "Turco". It is a spray on coating that works excellent for me. I bought 5 gallons a few years ago from the manufacturer direct since that was the minimun they would ship. I have heard that Knife and Gun Supplies does carry it now. If you can't find it and want to persue it further shoot me an e mail. I also worked up application instructions for use. There is a learing curve to go through on this stuff but it is worth the effort.. Phil

 

[Rob!]

Both Vacuum furnace and inert gas are out of my range and I can't get performance this good out of anything but foil.

This is right out of the plate quench - before the cryo. This blade is CPM154 but the results are typical.

 

[Rob!]

I am curious about the PCB and liquid methods. Could someone post some "right out of the oven" pics of how they turn out?

 

[rlinger]

I have a gallon of liquid HT coating. I bought it off Ebay just to try. It works great except for one little draw back. It cures like concrete. On the label they say to wire grind it off (a jack-hammer would work better). Too much work and too much expense in grinding for me. Yours may be different though and I am not familiar with the spray on either but I have been using PBC for a couple years and am sticking with it (PBC).

Roger
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[Chris Meyer]

I haven't seen Blade either, but here's a link to the Turco Pre-heat Solution at K&G. Checking Google, it looks like the Turco stuff is made by a company called Elf Atochem North America Inc. I couldn't get their website to open, but that might be because of our evil IT guy here at work.

 

[rashid11]

To remind folx:

- there're 2 _different_ PBC powders. One for O1 and like "low-alloy, fast quench" steels with HT temp under 1500F, and the second one (I think it is called PBC-special) for air-hardening steels, it is rated for just under 2000F. Don't try using 1st type where 2nd type is required or you won't have much steel left after HT

- both require first warming up the blades to about 600F and then applying a nice even layer (put some into common kitchen sifter and shake it over the metal). This way the powder fuses to the metal

- I tried Turco a long while back. The results were a total disaster and I never had the heart to try it again. Really bad pitting and it was nearly impossible to take the darn coating off after HT. I know some people have a much better luck with it.

- Foil is the safest/easiest way to HT air-hardening steel in a home shop (for steel that is, not for the operator's fingers !). Make sure to get right type, it must be rated for at least 2000F . If you use foil, get $5 "welding plyers" @ nearby HF, to safely crease the edges. Still wear gloves, the 0.002 cuts just like a knife, only MUCH deeper

- "regular" PBC works great for low-alloys. Here's why: even if you miss a spot, decarb/pitting will be moderate and can be easily dealt with. If you don't protect air-hardening steel 100%, the carbon will be cooked out and the pitting might get really bad. Reason: about 500F of difference in required HT temps.

 

[G L Drew]

Sorry for no response guys, I have been out of town for a couple of days. The ad is from ATP supply in Cincinnati. They are sending me a brocure and told me that the stuff costs $12.50 per pint. will report back when more information is available.

 

[LRB]

ROB, with the PBC coating, the blades come out of the oven with full colors of heat. A lot of the coating comes off in the quench, and the remainder washes off easily with hot water, leaving a clean gray color to the steel. I prep my 01 blades right to the finished dimensions. I do make sure there is a good build up on the edge however. I heat the blade to 600o, then sprinkle the powder on. I then use a propane torch to keep the heat up and add more powder until I am confident that there is full and adequate coverage. The powder forms bubbles here and there, but the torch flame breaks them down. I always add a little more powder to these bubble areas and the edge. When in the oven, the powder remelts and forms a semi-liquid coating giving good coverage. It is a lot easier to do, than to explain. Great stuff!

 

[Rob!]

Thanks LRB. That's the kind of info I was looking for. Playing with a 600 degree blade for complete coat and the torch work sound like an extra step and I'm envisioning melted PBC all over the bottom of the oven. Of course, I could line the oven bottom with foil. I think I'll stick with foil for my air quench (plate quench) blades, but the PBC sounds superior to turco and might have application on oil quench applications. I'll give it a try.

Rob!

 

[Phil Wilson]

I get very good results with Turco, Here is a little write up on how to use it for those who want to try or have had trouble in the past.


Turco is a coating than can be used to protect custom knife blades from de-carbonization and oxidation during heat treating. I have been using it for about 15 years and have developed a method of application that gives consistent results. There is a learning curve associated with its use and am writing this to pass on what I have learned. Turco works ok up to 2040 degrees F. Above that the results are not consistent and pitting and scale can occur. It is also not useable with the high Vanadium alloy steels like CPM S-30V, CPM S90V or 10V. I have used it with success on the following steels. 440C, D2, CPM 154/ATS34, CPM 154, AEB-L, 12C27, AISI 420 (.5% C), RWL 34 and Damasteel.

The blade preparation prior to coating is important. If the finish is very rough or very smooth problems can occur. The finish has to have enough “tooth” for the coating to adhere. I have found best results with a 120/150 belt finish on the blade grind and either a 120 hand sanded finish or surface ground finish on the flats. The blade must be free of oil or dirt before application. The best method to clean the blade is to wash it with a paint brush and solvent. I like MEK or Zyol. Before the solvent evaporates blow it off with an air gun. If it doesn’t look shiny clean repeat the process.

The directions say that the coating can be applied with brushing, dipping or spray. Spraying is the only method I have had success with. A too thin coating will not provide adequate protection and too thick seems to cause problems also. I use a “top trigger” type touch up spray gun that is available from places like Harbor Freight for about $20. The guns hold about a cup of material which is enough for 5 or 6 blades.

It is important to use a paint filter to fill the gun. I like to thin it just a little, maybe a tablespoon of solvent in the spray gun. I try to spray it as thick as I can and still get good atomization out of the gun nozzle. Zyol or Zylene have worked best as thinners. 40 to 60 psi is the best pressure range at this viscosity.

Hang the blade on a board with either a hook or nail. The blade can be flat against the board for application on the first side. Spray the length of the blade with a tack coat to start with. Just enough so you see a little color. Wait until the first coat flashes off and apply a second fuller coat. Spray the edges all around at the same time you do the flats. The objective is to get a nice even medium dark golden color just like gold anodizing on aluminum. It may take 3 to 4 applications to get a nice even coat. Let it dry and turn over and do the other side. Spray the edges again from this side. You should not have any runs or sags or any bare spots. Dirt or dust embedded in the coating will cause a pit so be sure the surface looks even and clean. If not just wipe the blade down with solvent and start over.

I put my blades in inconel rack in the furnace. A hook made from inconel wire can be placed through a hole in the blade tang. Reach in the furnace with a rod and snag the hook and pull out the blade quickly. In one fluid motion get it in front of a fan or into the oil quenchent. The coating will flake off and leave a nice clean blade if every thing went right. Once you get the technique down it makes heat treating much easier since you don’t have to fumble with the foil pack. PHIL