Preventing Oxide layer during Heat Treating

[nate d.]

Folks,
First off i can't take credit for the trick that i just learned to do this weekend. PHil Wilson out in CA told me to do this but I didn't get it through my skull full of mush till this weekend. Grocery bag paper works great as a getter for oxygen in a stainless steel foil envelope. I was so impressed with the results that i had to share them with fellow knife makers. Here's the deal i took my double sided sticky tape applied a piece to the end of the blade. The blade material in this case is 440C. OK then i took the grocery bag piece i had laying around laid that on top of the knife and cut out a piece that matched just the blade portion not the handle. I repeated this for the remaining side covering only the blade portion. in my picture you can see the difference in surface colors. That is the difference between having a protective covering and not having a covering. In my experiment if i can call it that (more like being lazy truth be known) is a small piece of steel above the blade that was not protected at all but exposed to the furnace environment. metallurgically/chemically that last statement about the paper acting as a protective covering may be way off. I don't know concretely what it's doing. The part that i couldn't overcome was getting the paper to stick to both sides of the blade as i pushed it into the foil envelope. Well i finally came up with a solution. WooHoo I won't tell you how long it took me to come up with that fix. I guess i oughtta read the forum some and ask a question once in awhile. So in the picture the bright portion of the blade was protected with the grocery bag, the handle was not, all this was in a stainless steel foil envelope. the smaller steel piece above the knife was just placed in the furnace without any protective covering. (More in that piece later). Thanks for taking the time to read this long rambling.

[RJ Martin]

If you seal the foil packet properly (fold each seam twice and crimp formly), you have only a very small amount of air left in the packet. If you like the idea of burning off the air inside the packet, a small piece of brown paper will do it. It shouldn't matter if the paper covers the blade or not. In my experience, I have found that no paper is necessary.
That dark layer on the tang is so thin it will come right off when you re-grind the tang to make it flat anyway.

IMO, you are worrying about nothing here.

[gspam1]

I was taught to put a small piece of paper in the stainless foil to burn up any residual oxygen after double sealing the foil seams (like Mr. Martin recommends) on machine parts. I have never found a difference whether it was a small scrap or a large one, or even what kind of paper (grocery bag, typing paper), although brown paper is the kind I always see recommended from machinists.

From Mr. Martin's experience it seem obvious that the paper isn't needed at all so I'll omit that too on my next heat. I think the key is a form fitting foil pouch with airtight seams here.

George

[twistedneck]

Form fitting might stick to the blade at 2100F. Argon

[RJ Martin]

Pure Talcum Powder will solve the sticking issue.

The pouch only needs to be appropriately sized for the blade(s), and carefully sealed.

Too tight, and you'll get a hole somewhere.