Heat treat with soft soap?

shotgunner

shotgunner

Joined
May 19, 2010
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Below is a cut and past from another thread in, of all places, a microscopy email discussion list. Seems those guys like to make things too. Making the "perfect" microscope for themselves.

Here is the post:

The use of a burnt on layer of soft soap to protect the steel at red heat is standard horological practise, sometimes supplemented by a layer of iron binding wire. Slowly raise the temperature, so as to evenly burn the soap onto the part's surface. The soap will melt and the volatiles burn off leaving a black layer. Then raise up to a cherry red and quench. The black layer will fall off leaving a clean white surface with the minimum of damage, and that is easy to polish.The iron binding wire ensured that an even temperature gradient existed across more complex parts, and reduced the chanced of cracking and distortion when quenched.

end of post

I am a newbie. I was also part of a discussion regarding surface prep after heat treat. Seems like this could minimize after HT surface cleanup work. I thought I'd put it here and ask, "is anyone using similar technique on their carbon steel blades? I hope I did not ruin a secret!?!

What is "soft soap"? The kind my wife puts in a pump bottle in the guest bathroom?

Thanks!
 
I'm tempted to try that if no one chimes in saying it's dangerous. What's the worse that it does (assuming it doesn't create very toxic fumes), ruin a piece of steel through super fast corrosion? Seems like it would be a cheap version of the various steel coatings if it worked.
 
If the soap is a borax-based product then this is nothing new. Borax has been used for this basic purpose for many years. There are other modern products such as anti-scale compounds that do basically the same thing.
I have to wonder what this stuff does quench oil, though.
 
I doubt any 'soft soap' has borax in it. Most of these things are a mix of surfactants, glycols and water.

The theory as I understand it is this:

The organics in the soap are volatile and either boil off or break down until all that is left is a layer of carbon. The sacrificial carbon layer adheres and protects the metal surface from oxidation by oxidizing first. Sort of a defensive frontline. As a result, the carbon in the steel is left alone as well. If this is correct, then the carbon leftover will not harm the quench oil.

I have asked in the original thread what 'soft soap' is.
 
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I've used Ivory soap for this same purpose. Just heat the steel enough that the soap will melt onto it and go from there. Haven't done this in years, but I know it works. I just wish I knew WHY it works. I suppose the proposed theory is possible, but why can't you just use anything that would burn off and leave carbon? For example, I doubt it would work as well if you used pudding or something. :)

-d
 
Properly Soap is sodium stearate. But hard or soft 'soaps' may contain other things.
 
There is a difference between the HT for a small machine/watch part and something the mass of a knife blade.

I have heard of blacksmiths doing a similar coating by using beeswax/turpentine mix and slowly burning it off. Normally ,they use it to make the shiny "black" look of hand-wrought decorative items, but supposedly it works for a HT coating,too.

The problem I see is that the amount of heat applied and the time at soak on a knife blade would probably vaporize the carbon layer before the HT was done.
 
bladsmth said:
There is a difference between the HT for a small machine/watch part and something the mass of a knife blade.

I have heard of blacksmiths doing a similar coating by using beeswax/turpentine mix and slowly burning it off. Normally ,they use it to make the shiny "black" look of hand-wrought decorative items, but supposedly it works for a HT coating,too.

The problem I see is that the amount of heat applied and the time at soak on a knife blade would probably vaporize the carbon layer before the HT was done.
Click to expand...

Same issues I've had with it "in concept" Stacy. Thing is, I've seen it work on things with a good bit of mass (they were touchmark punches actually). I'll need to play with it again and see how it does for blades in a kiln rather than punches in a coal fire.

-d
 
deker said:
For example, I doubt it would work as well if you used pudding or something. :)

-d
Click to expand...

It seems the microscopy discussion is turning into a bit about files. Have a look:

The soft soap trick is to avoid decarbonising of the surface, and has been around since the 18th century. The Warrington file maker, Peter Stubbs, used beer barms - the leftovers from the brewing process, as part of a coating for files before they were hardened - his files were famed for lasting longer than his competitors.The reason why hardware store tools appear to be poor quality is more down to poorly controlled heat treatment than the starting material.


I wonder how well pudding would work! :cool:
 
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