Hi All,

This is my first post on this Forum.

I'm from south Africa, and am an absolute beginner as far as heat treating & forging goes - given that my electric kiln is only to be delivered tomorrow

Having read up on the subject of heat treating for some time now, I understand the process and metallurgy involved, to some extent, but will only be gaining first-hand experience over the next few weeks...

My current concern, is that my first heat treatment project will be to harden a knife that I have just completed. Now, according to many sources on the 'Net, any steel will be degraded if heated in the presence of oxygen, and I have read that one should wrap the knife in newspaper, and then in foil, before heat treating. The foil is supposed to prevent the stainless steel from discoloring, and the wrapped newspaper is supposed to combust, and in the process remove all the O2 from around the knife within the confines of the foil.

Is this true?

Is it worth doing, if true.

Thanks

Hennie

It will help, yes. It usually isn't a perfect solution. It is worthwhile if you will be soaking the blade at high temps for extended times, which is common in heat treating stainless and high alloy tool steels.

Note that this is stainless steel foil; not aluminum foil.

If you have left a proper amount of thickness to be removed after heat treat you will grind off any decarb layer---and it will be less likely to warp or crack in heat treatment. If you have ground it down to finished size then the paper and foil will help.

Thanks for the info so far

If you have left a proper amount of thickness to be removed after heat treat you will grind off any decarb layer---and it will be less likely to warp or crack in heat treatment. If you have ground it down to finished size then the paper and foil will help

The blade is 3mm thick, with the cutting edge ground down to approximately 0.5mm (0.2") thickness. I've been toying with the idea to cut this back a bit to around 0.75mm (0.3") - will this be enough?

The steel is a German made steel, sold in South Africa as "Pantzer 36" - I could not find much info on it on the 'Net, but here is the analyses, if that can help:

Carbon: 1.00 - 1.10 %
Silicon: 1.00% max
Manganese: 1.00% max
Cobalt: 1.30 - 1.80%
Chromium: 16.50 - 18.50%
Molybdenum: 1.00 - 1.50%
Vanadium: 0.07 - 1.12%

Thanks
Hennie

Oops... I think that should be 0.02" and 0.03"

Not used to working in the archaic imperial system

Hennie

Go ahead and use metric. We have google to do the conversions.

Your steel is very close to N690. Very unusual stuff. It should make a very good blade. You're not exactly starting slow. ;)

You're not exactly starting slow.

Oh, I did start slow... first knife was ground and filed by hand (took one week to do the shaping). Once the bug bit, though, I've gone into overdrive and have since bought a very nice belt grinder and electric kiln... so now I'm probably hooked for life

Hennie

Seems a bit thin for so high a carbon steel; but a lot of heat treating of blades is learning how a particular steel actually works compared to the book values that are designed from 2.5 cm cross sections.

Never bet you will have a successful blade the first time you try a new alloy or heat treat regime!

The big thing is you need to know if the steel is air hardening or needs to be quenched in a liquid and if so wot liquid? I have used foil on air hardening steel blades. When you take it from the oven you need to rip that foil off really fast so it can quench in still or moving air depending on the steel. I practiced doing that a few times before I heated a blade. If you have to remove the foil and dip to quench you may lose enough time taking the foil off that the temp drops below that desired level to quench. That may be a bit wordy but I think you can see wot I mean.

The big thing is you need to know if the steel is air hardening or needs to be quenched in a liquid and if so wot liquid?

It's an oil quench steel.

According to the data sheet, the hardening should be done at 1030 ³C to 1080 ³C for a period of 1 hour per 30mm of thickness, then double tempered at 100 °C to 200 °C, again for 1 hour per 30mm thickness, with a freezing cycle thrown in for good measure...

If you have to remove the foil and dip to quench you may lose enough time taking the foil off that the temp drops below that desired level to quench.

Could one not oil quench with the foil still wrapped around the blade? seems to me that a thin piece of foil would not be much of an insulation to keep the steel from rapidly cooling, but of course I've never done it before, hence the question

That may be a bit wordy but I think you can see wot I mean

Thanks, I appreciate all the input and advice. It's quite frightening to venture into the world of high heat

Hennie

You could try quenching with the foil on. LEt us know how that works out. A quick check after quenching is with a file, it should not be able to cut an edge of the steel. It should just slide along. If your steel does that, then its time to temper...have fun and post pics when you can.

For what you're doing, the real right answer is a high temperature salt pot.

For what you're doing, the real right answer is a high temperature salt pot.

would you care to elaborate on this please... remember, I'm a complete newbie when it comes to heat treating.

Hennie

You heat the blade for quenching in a bath of molten salts. Rapid, more uniform heat transfer, which minimizes warping, and no oxidation problems because the salt protects the steel. But there is also some real danger involved.

You heat the blade for quenching in a bath of molten salts. Rapid, more uniform heat transfer, which minimizes warping, and no oxidation problems because the salt protects the steel. But there is also some real danger involved.

Mind if I parse your sentence a little differently? "You heat the blade.............. for quenching in a bath of molten salts". even confused me the first time I read it. If there is any confusion, Matt meant "You heat the blade in a bath of molten salts, for quenching" .

Could one not oil quench with the foil still wrapped around the blade? seems to me that a thin piece of foil would not be much of an insulation to keep the steel from rapidly cooling, but of course I've never done it before, hence the question

Unless you want to take the chance of an uneven quench, the foil should be quickly shucked off. Wrap it for easy removal and plan ahead on how you're going to snatch if off, practice before heat treat if necessary.

Thanks, Grant. You're right. That wasn't as clear as it should've been.

Matt meant "You heat the blade in a bath of molten salts, for quenching" .

Thanks, Grant - It did take me a few reads, but I did suspect that is what Matt meant.

From the little that I've since read about this subject, the molten salts are electrically conductive, and will speed up corrosion of the heating element - I will rather give it a miss at this point in time.

OK, then - if the consensus is to first remove the foil, then that is what I will have to do. I will wrap it so that the blade is covered, but the tang is sticking out - I don't mind removing some scale from the tang, but would prefer to keep the blade as clean as possible.

Will be practising on a mild steel clone of the knife a few times before attempting the real one.

Hennie

Yes, they're very conductive. I would think that serious electrical grounding would be essential if you were heating a salt pot with something like an electric kiln. As to corroding the heating elements, I think that's only if you let the salts out of the pot -- which you're not supposed to do. (That "wink" there is because keeping the salts in the pot apparently isn't always as easy as it sounds.)

Salt pots, like stainless, are not for beginners, Slow down start with carbon steel, and oil quench then move up.