Using Boric Acid and Iron wire to reduce scale when tempering/heat treating

dbb-the-bruce

Dave
H-M Lifetime Diamond Member
Joined
Feb 28, 2019
Messages
494
I'm very interested in being able to make my own high quality bits, cutters etc. I've got a couple of tasks that are well suited for making a custom D-bit, one I need to make a lot of precise diameter ~ 0.060 and ~0.03125 deep flat bottom holes. Another I need for a number of small pitch racks, and finally a broach type tool for inside splines that are ~0.060 sq. - spaced evenly on an inside hole. (I'll probably ask for tips on tool geometry, but that's not this question!)

I watched the ClickSpring video on making a simple D-Bit (the guy does awesome videos!).
In the video he uses soft iron wire and boric acid paste to reduce scale when tempering.

I've managed to find 99% pure boric acid power.

My question is about the "soft iron wire". I've found "black annealed wire" 16 gage for about $10 at Home Depot. It seems to be the right stuff. However it doesn't say if it's steel or iron. With a little more googling, I've found both "black iron wire" and "black steel wire".

My question is, for reducing scale, do I have to be absolutely certain that I'm using iron vs. steel? what's the chance that the wire I bought is iron or steel? Is there an easy way to tell?

I'm not up on the chemistry involved, but my understanding is that the wire and the boric acid are "greedy" rob any air that gets near the part being treated of either/or carbon & oxygen. Hence less scale because the elements to create the scale are less available.

A second question is: In the video he makes a paste and says he used denatured alcohol but his jar of paste has "mineral spirits". I'm guessing that the what liquid you use to make the paste probably makes very little difference as long as it doesn't react - it's all going to evaporate very quickly once you start heating it up.

I've got a muffle / oven for heat treating so this should be pretty easy to get done.
Thanks in advance for any help!

-Dave B
 
Hi dbb,
i'm sure there is little difference whether you used iron or steel wire, they both contain iron
the annealed wire you got at home depot is soft steel
correct, the boric acid is a flux.
impurities that melt at a lower temperature will float to the surface and not contaminate the substrate

i really don't think it matters too much what you use
denatured alcohol and mineral spirits will flash off at a relatively low temperature

i have mixed water with boric acid in a pinch, it works-
but, i often wonder what i created when i substituted water :chemist:, :grin:


have fun!
 
Pure iron wire is really soft,like lead wire......but I imagine also expensive.........much easier to get a tight wrap,I suppose.....a free source of this wire is/was motor car ignition coils....any coating is going to affect quenching.
 
Or, a person could use silver solder flux, essentially borax. I doubt that iron wire exists in the modern world, steel is what we have these days, such as baling wire and tire wire used for tying reinforcing rod. personally I use ground coke for protecting heat treating work in the furnace, it also prevents scaling and due to the relatively short time in the furnace, does not significantly increase carbon in the (very shallow) effected zone that is normally ground away in finishing the tool.
 
Dave, I've been using Boric acid and rebar tie wire for heat treating for about 25years now. I used to tightly wrap the item with wire and applied the BA before heat treating but I found that the wire does little, if anything, to alter the outcome. The BA does. Now I just use the wire to either tie on to the item or form a basket and pay attention to applying the BA.

I mix termite powder, which is 100% BA, with denatured alcohol until it forms a paste that sticks and doesn't run. Apply with an acid brush to entirely cover the item and heat it. This forms a dark gray layer after heating but that comes off readily with a Scotchbrite pad. Then I temper it.

Works good, no problems.
 
Dave, I've been using Boric acid and rebar tie wire for heat treating for about 25years now.

Works good, no problems.

Dang, I passed up on driving the extra 4 miles to Tractor supply for rebar wire..... Based on your comment though, the wire I have is probably fine. Any idea as to why the traditional approach calls for iron vs. steel?

The boric acid I ordered should be fine, probably sold for termite powder. Claims to be 99% boric acid. I looked for boric acid at the local HW store and all I could find was Borax products with all sorts of other crap in them.

Thanks.
 
Any idea as to why the traditional approach calls for iron vs. steel?

Sorry, no. This method of reducing surface oxidation has been around for a very long time but I have not read anything based on fact; just anecdotal stuff like I'm laying out here.

I tend not to believe everything I read so I tried it both ways - wrapping the item to be heat treated tightly with wire and without. In both cases, the results were the same every time. Seems to me that the wire thing is either overblown or perhaps I'm missing something but I can't see what it might be. Now I usually just tie a long piece of wire directly to the part so I can safely hold it while heating it and quenching it in oil. The BA goes on after the tie wire is in place. If I cannot tie on directly to the item (like round stuff) then I make a basket from the wire and drop the item in there after coating with BA. I like the rebar tie wire because it gets red hot but doesn't break in use. Plus, its easy to work with so good enough.

There is a significant difference between using the BA and not using it. Clean up of the item is much, much easier with the BA than without. Hardness is the same; just the amount of work afterwards differs.

Just so you know, it is recommended that you temper the part while it is still warm, like right out of the quench. I tried this and also tried tempering a cooled part and I cannot see any difference in the tempering results. However, I don't have a hardness tester so my claims are suspect, okay? Anyway, I raise this because I temper by color and I need to see the surface of the part. I do not trust the temper of the whole part if I only clean one small area so I clean the whole thing. I usually clean off the dark gray stuff left from the BA until the part is clean, with a nice smooth surface finish. I also clean all traces of oil off with Acetone or Lacquer Thinner and put it in the tempering oven with a nitrile gloved hand. I learned that oily fingerprints will stay on a part forever after if you don't clean them off; hence, the glove.

I also experimented with cleaning stuff to get the BA residue off. I use Scotchbrite most of the time because it does not change the dimensions of the part like sand paper does. Metal polishes also work but are slow. I even tried buffing it off with a wheel and rouge but it removes metal so I learned not to do that. The combination of Scotchbrite that works best for me is the green fine one, followed by the extra-fine gray one to smooth the finish. Works fast, works good, and works even better when you can chuck the part up and use power.

Much more than you asked for - sorry. I just wanted to tell you a few things that might make things easier for you. Heat treating is something we all have to do from time to time so I hope this helps.

Oh, one more thing. If you haven't bought a torch yet, have a look at the Bernzomatic TS8000T. Puts out a lot of BTU's and works well with Propane or Mapp. I don't bother with my OA anymore because of that torch.
 
I also clean all traces of oil off with Acetone or Lacquer Thinner and put it in the tempering oven with a nitrile gloved hand.

I learned the hard way that if there is oil on the piece being tempered it will turn yellow/amber then brown long before the steel does the same thing. You get a brittle piece if you go by the oil color.
 
Interesting, they call it, iron wire.
We’ve always called it bailing or mechanic’s wire.
I’ve been following along. I have considered a heat treating oven. The science of heat treatment is very interesting to me.
Great thread!
 
Back
Top