Keeping 01 free of carbon buildup while hardening.

[Iampappabear]

Is there any way of preventing the back carbon coating ones gets on steel (01) when heat treating it? pretty sure I saw something about a coating you could apply but cannot find anything about it or if it even exists. McMaster Carr has a product but it appears to be more for case hardening. my main concern is build up in internal 2-56 threads as it won't take much to stop the screw going in and trying to clean it out will destroy a tap.

Thanks in advance

Colin

 

[rklopp]

You wish it was carbon. It is iron oxide "scale", and actually depletes the carbon from the surface, causing it to be soft. it is less of a problem with O-1 than other alloys, but still a risk. You want something like PBC anti-scaling compound. PBC Anti-Scale Compound - Rose Mill Co

 

[SmithDoor]

Use stainless steel fold

Dave

Is there any way of preventing the back carbon coating ones gets on steel (01) when heat treating it? pretty sure I saw something about a coating you could apply but cannot find anything about it or if it even exists. McMaster Carr has a product but it appears to be more for case hardening. my main concern is build up in internal 2-56 threads as it won't take much to stop the screw going in and trying to clean it out will destroy a tap.

Thanks in advance

Colin

 

[Tim Wescott]

Youch! I just priced that! $30 for 10 square feet of the cheap stuff!

Granted, that much would last me until I die, but still.

Can you re-use pieces, or is it wise to use once & toss?

 

[Tim Wescott]

I've been thinking of making little boxes to hold tool bits, that I can pack with charcoal then put into an oven or forge. Is that a good idea or stupid?

 

[rklopp]

You cannot reuse the foil. It is trashed by the heat treat process.

 

[Tim Wescott]

Man, I'm much too much of a cheapskate. My next thought was "old tin cans?"

 

[SmithDoor]

It is oxidation of steel not carbon.

I do use charcoal fill steel box for most heat treatmenting. This helps to keep oxide down.

The other way is use box and argon gas.
On O1 tool steel I just use torch and a bucket of oil as soon the steel gets hot I drop in oil and that helps to keep oxidation down.

Dave

Is there any way of preventing the back carbon coating ones gets on steel (01) when heat treating it? pretty sure I saw something about a coating you could apply but cannot find anything about it or if it even exists. McMaster Carr has a product but it appears to be more for case hardening. my main concern is build up in internal 2-56 threads as it won't take much to stop the screw going in and trying to clean it out will destroy a tap.

Thanks in advance

Colin

 

[clockworkcheval]

Clickspring in his YouTube videos shows how to package the part in Boric Acid, e.g. in his video 'How to make a square broach'. You wind the part with light iron wire, make a paste of the boric acid with white spirit, apply it and put the whole thing in a piece of steel tube so you will not directly torch it while heating.

 

[tornitore45]

Internal 2-56 thread! Screw in, for a few threads, a #2 screw. You can remove after heat treating leaving a clean hole. This case is special since needs to protect a small hole.
For other jobs I use liquid soap. I have the anti-scale powder but do not like the way it works. Once the part is cover is near impossible to see the color. For me is the only way to judge temperature since I have no oven.

 

[SmithDoor]

I use charcoal as easy to come by.
But the companies that make Anti-scale Compound use Borate Salts and Natural Carbon Powders aka charcoal or coal.
Below is the SDS from company.
https://rosemill.com/data-sheets/
Inorganic Borate Salts (1330434 n/a%) MASS, OSHAWAC, PA, TSCA, TXAIR *Natural Carbon Powders (7440440 n/a%)
Note you can use Borax most have this for washing clothes

Dave

Clickspring in his YouTube videos shows how to package the part in Boric Acid, e.g. in his video 'How to make a square broach'. You wind the part with light iron wire, make a paste of the boric acid with white spirit, apply it and put the whole thing in a piece of steel tube so you will not directly torch it while heating.

 

[HennieL]

The only way to prevent the black iron oxide from forming is to prevent oxygen from contacting the steel. This can be done by

• painting on of certain "mixes" such as those mentioned above (results are very variable)
• wrapping the steel airtight in stainless steel foil (my preferred method that works with 99% reliability)
• removing the oxygen from the kiln or oven where the steel is heated - this can be as simple as dropping a piece of wood into the kiln/oven a second or three before the part is placed inside this kiln/oven. The wood will then ignite, and burn up most of the oxygen in this oven (obviously the oven should be rather well sealing to prevent fresh air from moving in and replacing the O2...)
• if using a forge, one can place the part just inside the top layer of coal/coke/charcoal that is used to make the fire (in the region where the flames have used up most of the O2) - this sounds crude, but is how most tools were hardened in the years before electricity...
• using a reducing flame on a cutting torch and holding the part " just right" where the oxygen in the flame had been depleted, but not so far away that it is exposed to air - very difficult to get right...
• or by placing some inert gas (CO2 works well) inside a metal tube that is closed off air tight on it's bottom, and then heating this tube in a furnace/kiln/forge with the part hanging some way down inside this pipe. The heavier than air CO2 will stay inside the pipe even when heated, and this process works well if one uses a pipe that is (say) 200mm taller than the top of the part hanging in it, as this slows down the process of air diffusing down into the pipe, but one does have a practical time limit of only about 10 - 15 minutes to heat the part.

Apart from the wrapping in foil and the painting on of a protective coating processes, all of the other processes mentioned above will still result in some de-carbonation/forming of iron oxide when the part is removed from the heating container prior to quenching, and it then makes contact with oxygen in the air - but this process should only take a second or two before the part is quenched into water or oil, and the de-carbonation is usually not very severe.

Colin, if you don't want to use the foil method, I suggest you follow Tornitore45's advice and just block up the screw holes to prevent O2 from entering the holes. Also, keep in mind that any sharp corned (and threads...) could lead to cracking of the part when quenched, so use a slow oil for quenching, and don't be tempted to quench in water.

Good luck.
Hennie

 

[HennieL]

On O1 tool steel I just use torch and a bucket of oil as soon the steel gets hot I drop in oil and that helps to keep oxidation down.

Sorry to disagree with you Dave, but ideally O1 should be "soaked" for a period of 10 - 15 minutes to achieve it's full hardening potential. It contains smallish amounts of chromium (0.55%), tungsten (0.55%) and vanadium (0.1%), and these alloys take time to fully "dissolve". One would obviously still get the hardening provided by the carbon if quenched immediately, but then why use a higher alloy steel like O1 - rather use 1085 or 1095 steel if you don't want the get the benefit of the other alloying elements that you're paying for when buying O1?

Colin, there is also another way that I did not mention earlier, and I will mention it now just for completeness - that is to heat your part in a molten salt. Unless you have experience with this, and the right equipment and safety gear, I would not recommend it - the process is quite hazardous, but the outcome is usually perfect.

Regards,
Hennie

 

[SmithDoor]

It simple with torch and fast.
I have in past use a oven.
If you do not have oven a torch does job. I have not noticed any difference. I use a toaster oven for temper.

Dave

Sorry to disagree with you Dave, but ideally O1 should be "soaked" for a period of 10 - 15 minutes to achieve it's full hardening potential. It contains smallish amounts of chromium (0.55%), tungsten (0.55%) and vanadium (0.1%), and these alloys take time to fully "dissolve". One would obviously still get the hardening provided by the carbon if quenched immediately, but then why use a higher alloy steel like O1 - rather use 1085 or 1095 steel if you don't want the get the benefit of the other alloying elements that you're paying for when buying O1?

Colin, there is also another way that I did not mention earlier, and I will mention it now just for completeness - that is to heat your part in a molten salt. Unless you have experience with this, and the right equipment and safety gear, I would not recommend it - the process is quite hazardous, but the outcome is usually perfect.

Regards,
Hennie

 

[mfrick]

So when I was teaching I had students making hammer heads cold chisels 1,2,3 blocks all heat treated in an eclectic oven we used stainless foil wrapped part then we put some folded up paper in and sealed up the foil package put in oven cooked or soaked for 1hr per inch of thickness worked great and we did reuse the foil just need to take care when opening to get part out for quenching.

Mike

 

[stanstocker]

Jantz Knife Supply has 25 foot rolls of 309 heat treat foil listed at $77 USD.

https://knifemaking.com/products/kf321-1900-type-321-heat-treating-foil?variant=28297054748772
They also offer 321 foil rated for 1900F for $57 if you are OK with a bit lower temp capability. Both options are on the page given, click the option buttons to select which foil you want.

It's sort of interesting, in the clock restoration trade and for some HSMs how a $3000 machine and $1500 in tooling is OK, but suggest a solid carbide straight flute drill at $20 or stainless foil for heat treat and some folks will find that too expensive.

I still just wire wrap and coat with borax/alcohol, but intend to make or buy a nice heat treating oven this year. Figuring the oven will cost anywhere from $500 to $1000, $77 for a likely life time supply of heat treat foil seems a pretty low cost add on to improve results.

I'm not sure that foil is much use if you don't have an oven. HennieL pointed out quite correctly that if you can't soak at the specified hardening temperature long enough to get all the components distributed throughout the workpiece you aren't getting the full benefit of the material.

Cheers,
Stan

 

[HennieL]

Jantz Knife Supply has 25 foot rolls of 309 heat treat foil listed at $77 USD.
https://knifemaking.com/products/kf321-1900-type-321-heat-treating-foil?variant=28297054748772They also offer 321 foil rated for 1900F for $57 if you are OK with a bit lower temp capability. Both options are on the page given, click the option buttons to select which foil you want.

The high-temperature foil can be re-used a few times when heating high carbon and some higher alloy non-stainless steels (such as 1085, O1, 5160, etc) that are only heated to around 820°C / 1510°F. Heating high-alloy martensitic stainless steels require around 1060°C / 1940°F, and hardening of HSS and "super" steels such as stainless mold steel (e.g. Bohler M390) require temperatures in the order of 1150°C / 2100°F, and no foil lasts more than one heat - I often have to literally grind off the foil that becomes welded to the steel it is protecting.

Something else that might be of interest/use - one can just quench most stainless and high-alloy steels whilst still wrapped in the foil, but the required cooling rate of lower alloyed and plain carbon steels is so high that the part will not harden properly unless removed from the foil.

 

[tornitore45]

Can anyone explain how all this bright idea are going to help the original post trying to protect a #2-56 threaded hole?

 

[Tim Wescott]

Can anyone explain how all this bright idea are going to help the original post trying to protect a #2-56 threaded hole?

Wait -- you expect us to read past the first line?

One of the suggestions is to block the holes with screws and then heat treat -- that seemed pretty direct.

 

[stanstocker]

Can anyone explain how all this bright idea are going to help the original post trying to protect a #2-56 threaded hole?

Well, as the original post started with avoiding scale during heat treat, then extended to mention the current workpiece with a threaded hole. It seems every post has offered one or more approaches that would apply. Your specific suggestion of threading in a screw is good, although I'd be inclined to also add a layer of the borax/iron wire to reduce the chance of the screw seizing in the hole. All of the general suggestions regarding protecting a work piece in heat treat posted will also apply to the threaded hole while also covering the general avoiding scale question included in the original post.