Electropolishing to remove burnt oil after HT?

[Dr Heelhook]

I like to do as much work on my blades as possible before HT, including a mirror polish. I was thinking, will it work well to use electropolishing to remove the burnt oil and get the polish back after HT?

 

[Stacy E. Apelt - Bladesmith]

I am sure someone will correct me if I am misinformed on this, but I have seen electropolishing used in the jewelry industry, and don't think it would translate to polishing a kanifr blade. The biggest reason is the needed surface flatness. A shiny knife blade that has microscopic ups and downs will look like a fun house mirror.

On knives, you need to remove the thin layer of decarb after HT no matter what. The smoother the finish pre-HT, the easier it is to finish up after HT, but taking to a mirror polish pre-HT is wasting time and supplies …. because you will have to do it again to get the flat and smooth surface desired for a mirror polish. Just get the blade to a 400+ grit finish pre=HT.

Electropolishing of knife steel would take off the discoloration and some of the decarb and oxides, but you would still have to sand and polish it if you wanted a mirror finish. It is used in the knife industry to deburr stampings and after some grinding applications to remove sharp corners and stress risers. I don't recall any industrial makers using it to clean up post-HT, because that is where they do most of the grinding. Many hobby and small shop knifemakers today are switching to doing the grinding after HT, too.

 

[Natlek]

I like to do as much work on my blades as possible before HT, including a mirror polish. I was thinking, will it work well to use electropolishing to remove the burnt oil and get the polish back after HT?

I found that this Correction fluid work if you like me don t want to mess with that burn oil after quench .Help with decarb. too .After quench you can wipe it down as it is grease and blade is clean in seconds
.....

After gently wipe ........

 

[Randydb]

Are you putting that correction fluid on prior to heat treating?

 

[Natlek]

Yes , before HT

 

[Stacy E. Apelt - Bladesmith]

What he is doing is basically the same as using Turco II (which I use on all carbon steel blades). It coats the blade and cuts down on decarb. It won't leave the surface shiny, however.

 

[Dr Heelhook]

Could you quickly explain what decarb is? I haven’t quite wrapped my head around it.

What he is doing is basically the same as using Turco II (which I use on all carbon steel blades). It coats the blade and cuts down on decarb. It won't leave the surface shiny, however.

 

[Natlek]

Could you quickly explain what decarb is? I haven’t quite wrapped my head around it.

What decarb is ? It is the nightmare of everyone ....probably worse part of knife making

https://en.wikipedia.org/wiki/Decarburization

 

[Michael.Drinkwine]

What he is doing is basically the same as using Turco II (which I use on all carbon steel blades). It coats the blade and cuts down on decarb. It won't leave the surface shiny, however.

Stacy, where are you sourcing Turco from?

Thanks,
Michael

 

[Stacy E. Apelt - Bladesmith]

My last can of Turco II came from K&G, IIRC.

Decarb is the layer of surface steel that has had the carbon depleted (DEpleted CARBon). The high temperature and exposure to oxygen causes this. In a HT in a forge, it is the worst. It can go a good .020" in the surface. In normal HT in a HT oven. it is more like .010" deep. Using things like Brownells PBC, Tuurco II, white titanium paints ( Natlek's correction fluid), etc. will greatly reduce decarb.

Just looked it up. Turco II at K&G - $60 :
https://www.knifeandgun.com/SearchResults.asp?Search=turco&Submit=
It goes a long way, so that isn't as much as it seems.

 

[Dr Heelhook]

My last can of Turco II came from K&G, IIRC.

Decarb is the layer of surface steel that has had the carbon depleted (DEpleted CARBon). The high temperature and exposure to oxygen causes this. In a HT in a forge, it is the worst. It can go a good .020" in the surface. In normal HT in a HT oven. it is more like .010" deep. Using things like Brownells PBC, Tuurco II, white titanium paints ( Natlek's correction fluid), etc. will greatly reduce decarb.

Just looked it up. Turco II at K&G - $60 :
https://www.knifeandgun.com/SearchResults.asp?Search=turco&Submit=
It goes a long way, so that isn't as much as it seems.

Very informative, thank you.

 

[Natlek]

My last can of Turco II came from K&G, IIRC.

Decarb is the layer of surface steel that has had the carbon depleted (DEpleted CARBon). The high temperature and exposure to oxygen causes this. In a HT in a forge, it is the worst. It can go a good .020" in the surface. In normal HT in a HT oven. it is more like .010" deep. Using things like Brownells PBC, Tuurco II, white titanium paints ( Natlek's correction fluid), etc. will greatly reduce decarb.

Just looked it up. Turco II at K&G - $60 :
https://www.knifeandgun.com/SearchResults.asp?Search=turco&Submit=
It goes a long way, so that isn't as much as it seems.

One quart is almost one litre so 60 bucks is not to much .Will last long time to me .Correction fluid works but it is pricey compared to this Turco II . Is it easy to clean after quench this Turco , Stacy ?

 

[Stacy E. Apelt - Bladesmith]

Natlek, try a can of plain white metal paint. It will be mostly titanium dioxide. Let it dry and it should work just like your correction fluid. Same for lining the tubes/box in making canister damascus … use white paint. Even a spray can of white metal paint should work. Test it out for me and see how it works.

I have experimented with making my own Turco II. The main ingredient is yellow ochre as far as I can tell. there is a binder, which I am using gum Arabic for, and then the solvent, which is where I am still experimenting. Water works, but denatured alcohol seems to dissipate and drive off faster. I think Turco has toluene in it, but am not sure.

 

[Ken H>]

Stacy, that's a neat idea using white paint - I wonder if it would wash off easy with a good solvent after? I'd always expected it to burn off at 1500°F, but since it's TiO2 it might well burn the binder but leave the TiO2 layer in place.

What is wrong with simple old cheap borax powder (roach powder)? I don't do much carbon steel, but when I do I sprinkle a layer of roach powder on top of blade, heat bottom with propane torch to melt powder forming a protective glass layer on both sides. That washes off easy with hot water after HT'ing and seems to work pretty good.

Ken H>

 

[Stacy E. Apelt - Bladesmith]

Borax will help, but it gets corrosive above 1600F. That is fine when welding damascus, but not so good on a blade sanded to 400 grit.

The TiO2 is easily sanded off after HT. It will survive on a stainless blade done at 1950F.

I use the white metal marker paint pens To mark all my blades when grinding and sending out for HT. The marks with any notes are still there when I get them back. The white color has turned a dark grey, but I will know which steel the blade was for and the customer. I put a mark like SA/FR/S35VN ( Stacy Apelt - Fred Rodgers - CPM-S35VN)

I also use the markers to mark all my steel bars ands sheets on both sides and both ends. You have no idea how many makers have a couple bars of steel they don't know what they are because they didn't mark them.

 

[daizee]

simple liquid paper, eh? Interesting.
How do these various products affect watching the steel change colors when heat-treating by magnet and eye in a simple propane forge?

 

[stezann]

I don't know if white spray paint could do the trick...never tryied myself, but if i think about those heat gun paint strippers i figure the forge can have the same behaviour, on that kind of paint.
Maybe high temp paint has got suitable carriers in its composition and if regular paint wouldn't work this might worth a try.