Anti-scale coating/preventing decarburization

nine9jack9

nine9jack9

Active Member
Currently I use a product called ATP-641 that is marketed by Brownell's as a preventative for decarburization when heat treating carbon steels. I use it on O1 and have good results. Talking to an old machinist yesterday he mentioned that they would use to rub a bar of Ivory soap all over the piece to be heat treated to achieve the same results. Tried it yesterday on a scrap and had it tested for hardness and it Rockwelled at 58, post temper, which I didn't think was bad. Anyway, has anybody heard of this? How common a practice was this or is it still? Not that I'm leaving ATP-641 anytime soon but really wanted to know how this works, wouldn't think Soap was enough of a barrier especially at 1500F. I will say that compared to a blade coated with ATP; the soap coated blade came out black as opposed to the gray I'm used to in heat treated steel. Destroyed the piece that was soap coated too to see if there was crystallization and it seemed that it was just as difficult to break as the ATP coated stuff. Anybody out there with some useful info would be most welcome. Thank you.
 
Why would you even suspect that the soap coated piece would break any different than the ATP coated piece, or even a piece with no coating at all? What do you define "crystallization" as being? Any internal change in the steel is going to be dependent on the heat and cooling process, and not what is, or is not on the surface, unless you attempting to case harden. What you should be checking for is depth of decarb, and surface condition between the different coatings. I use 01 and coat with ATP. It is very good stuff, but I still get maybe .002 decarb, even if double coated. If you're heating your 01 blades at 1500°, you heating a tad bit higher than necessary, although I doubt any great harm is being done, 1475° is a very sufficient heat for 01.
 
Another old machinist trick was to coat parts in a thin flour paste, which I think would work even better than the soap. 58HRC post temper is nice for 1084 or larger choppers but for O-1 you want a slightly higher hardness. O-1 has a sweet spot in abrasion resistance vs. impact toughness that peaks in the 61-62 HRC range, I often advise people that if this is too high for their application they can save a little money and go with another alloy that will give them better toughness at a lower price. For short time heat exposure I also use soot. when I heat treat my fittings (guards, butt caps etc...) I preheat them with a oxy-acetylene torch with little to no oxygen on, this coats the piece in a heavy carbon soot layer, I then quickly high heat it and quench, this allows me to then etch the damascus fittings with no blotchy finish from decarb.
 
Soooo if I am reading these posts from Wick and Kevin correctly it is the coating of the piece that does the trick!

Not so much the medium that you coat with but the complete covering of the piece with a medium, that will withstand the heat for the allotted period of time needed to to HT, without degrading or contributing to the decarb on a blade, in that time period it takes to HT the piece!
Dang, say that real fast 10X!

Is that kind of a simple assessment Kevin or am I still missing something???
 
"IF" (and that's a BIG "if") I understand the process correctly, it's not the medium for the coating that counts. AS LONG as the medium will seal surface of metal from oxygen at the temperature of HT - AND is thin enough not to affect the quench process. The trick is getting a medium that won't burn off at HT temps to maintain sealing from oxygen causing scale build up.

Ken H>
 
I believe KenH is correct. Steels that require long soaks at austenitizing heat benefit greatly if you can seal them from oxygen. With air hardening steels, an air tight SS foil envelope is commonly used, but with most oil hardening steels, it takes too long to remove such an envelope for the quench, so direct coatings are an alternative for them.
 
I use the ATP on O1 and 1095. Works great, no reason to fool with anything else IMO. On O1 I don't think it has any noticeable effect on hardness or grain. On 1095, since its a shallow hardening steel, I do think it may have a very small impact on the thickest parts of your blade. I've noticed the cutting edge will fully harden and I get a mini-hamon towards the spine when using ATP. Disclaimer: I'm a newb and probably have no idea what I'm talking about. :biggrin:
 
Yeah I knew that was sort of a big "IF" when I spoke those words and I was not trying to influence anyone's opinion in any way! You see sometimes it just that light bulb lights up in your head and you have to say, there may be another way to look at this. I realized the "if" was the key word in that sentence when I wrote it but sometimes things are not always as cut and dried as they seem! Especially when you throw in all the variables. The variables are the one thing that can make you see it is not worth the effort to try a different approach, and your best choice may be something like the Brownell's as a preventative for decarburization!

I just found the statements by Kevin as an aw-ha moment as to their were other possibilities! Not advocating for a rewrite on how to when HTing!!! I have found over the years the best known way is often just that, because someone before me has tried it the other way and it was a complete disaster.

However that has not always kept me from exploring the why of things!! Often I find it leads back too the advice offered was the best. No one knew what was best for decarb without some experimenting on their part!!!

Nothing ventured nothing gained. A lesson learned the hard way is one you never forget! LOL
 
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There are two things we are fighting here, scale and decarb. Both are prevented by isolating the steel from the atmosphere. Scale is the result of oxygen, as nasty as iron oxide can be it is actually tamer than the oxides produced by other alloying metals, so the more alloying the less you want scale. Scale is simply a pain in the butt to clean up and makes the final polish much less than enjoyable.

Decarb is another matter. It can be a result of oxygen but other factors, like furnace atmosphere moisture content for example, actually play a more significant role. This is particularly true if you manage to remove the factors causing the scale but not those resulting in decarb since scale can actually balance out or alleviate decarb. The reason some things work well while others not so well is that some shield the steel from the atmosphere, others shield and also provide a carbon source to slow decarb.

I write all this to show, once again, how nothing with the treatment of steel is as simple as it seems or as we wish it could be, but the more we examine it the better we are equipped to handle all the curve balls that we can, and will, get when working it.
 
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Thanks Kevin! One thing I have learned that no matter how simple it may seem it is not! I love your knack of putting things into words that no matter at what level of expertise you have in knife making, the subject you speak of just became that much easier to understand.

I knew my statement was based in a lot of other variables but sometimes it is that ah ha moment that intrigues my brain and even though it is best not for me to try and express my understanding in simple terms,...............I just can't help myself! I guess I should have threw in those qualifiers I knew what they were but, it was the thought that intrigued me. I kind of figured the other went without saying but, guess not!
 
I found that soaking the blade with wd40 before ht gives the same results. I was taught to use wd40 by Jason Knight when making damascus as a flux and it hought I wonder if it will help with decarb. I sprayed it on until it was dripping and stuck it in the oven. It flared up a little but left a coating on it that allowed any decarb to simply flake off leaving the knife as it was when I put it in except for having a black color to it.
 
Decarb is a whole different thing than scale. Decarb does not flake off. It is carbon loss in the steel from high heat, and I assume oxygen contact, basically a burning out of the carbon. If you experience decarb, the only practical thing you can do is to remove steel from the surface until you get below the decarb layer. If your blades are flaring up in the oven, you are doing your oven no good.
 
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