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  • Dealing with heat treat scale

    I started to ask this on the Heat Treat oven thread (excellent thread BTW!) when scaling control was discussed a bit but I didn't want to pollute the topic with an almost unrelated question.

    Scaling is a problem and I have been somewhat successful using gas (C25 MIG welding gas) by flooding a small stainless steel box I built to place the parts in while heating. This has worked ok for really small parts but what I have has been a PITA to use at best and is worthless for all but really small stuff. I know little about stainless foil having only seen it mentioned and while I just recently bought some anti-scaling compound I have yet to use it so I know little about it too, the stainless foil appears to be the simplest to use but what is involved in properly doing so? Can the anti-scaling compound be used just as effectively? The gas seems to work ok but with my set-up it sure got spendy when I tried flooding the entire oven for a larger part but then maybe I could better control that? I am a complete novice with this oven so I am just learning these things.

  • #2
    One data point to consider is that the anti-scaling compounds off-gas nasty fumes that corrode electric heating elements and steel furnace casings. DAMHIKT.

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    • #3
      AFAIK, the stainless steel foil is to be used *with* some kind of anti-scaling compound.. Or at the very least, something that will burn and consume all the oxygen (Wood chips, charcoal, whatever)

      Idea is the foil keeps in whatever fumes where created by the anti-scaling compound.
      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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      • #4
        Radkins: I haven't done a lot of heat treating, but some people will put a small piece of paper in the foil pack to burn up the oxygen.

        Sarge

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        • #5
          Foil should be sealed carefully around the part with a small wood match stick or such inside to consume any oxygen.

          The anti-scaling compound (Staybright) I used worked okay as long as there aren't threaded holes it has to be dug out of. Don't know about off-gassing that might corrode heating elements, don't recall any mention of that on the can.

          When my parts have significant value they're sent to the heat treater (minimum charge around $150).

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          • #6
            I didn't know about the corrosion problem with the anti-scaling compound, that would be a concern, but then as the old saying goes I could probably write a book about what I don't know yet! I will soon have some small gun parts I need to HT and this time I REALLY would like to avoid the scale which in the past has been enough of a problem to cause me to trash the parts and start over!

            So simply wrapping in foil by itself is not sufficient? I suppose adding an oxygen consumer of some type would be simple enough but how about quenching when using foil?

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            • #7
              Originally posted by sarge41 View Post
              Radkins: I haven't done a lot of heat treating, but some people will put a small piece of paper in the foil pack to burn up the oxygen.

              Sarge
              Yes, this works perfectly. I had zero scale and minimal discoloration on O6. There's two (or more) grades of stainless foil - which one you can get away with depends on your temperatures etc.


              You keep the foil "loose" but with crimped over (couple of folds) edges to seal. To get the parts out hold the PACKAGE end by tongs and snip the bottom of the package over your quench. Practice this a couple of times before trying it HOT. If your foil is too tight (especially if the parts have sharp corners) they will not fall out!
              Last edited by lakeside53; 01-11-2016, 12:21 PM.

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              • #8
                Very good point. The stainless steel envelopes work perfectly, but the trickiest part is to get the content out and into the quenching solution VERY QUICKLY. Otherwise, the heat treatment result will be impaired.

                In this respect, stainless steel wrapping is especially full-proof for air hardening steels like A2.
                Mike
                WI/IL border, USA

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                • #9
                  This stuff is supposed to work well, but I have not tried it. http://www.brownells.com/gunsmith-to...prod23076.aspx

                  It is rated for temps above 1500F which is helpful for some tool steels. PBC doesn't take such high temps very well.

                  RWO

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                  • #10
                    If you put a bit of steel wool in the packet and seal it tight you'll eliminate the scale. If you don't have sstl foil then the
                    anti-scale materials work well. One in particular, taught to me by a clock maker, is to loosely wind the part with soft
                    iron wire and then gloop it all over with a boric acid paste made by adding just enough denatured alcohol to boric acid
                    powder to get a 'just wet' paste. Parts come out just about as clean as when they started. You need to boil the part
                    in water to get the last of the residue off (kinda like silver brazing flux) but it comes off in the boiling water quickly with
                    no scrubbing.

                    Pete
                    1973 SB 10K .
                    BenchMaster mill.

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                    • #11
                      We used the stainless foil and added a 2 inch square piece of a heavy duty brown paper grocery bag. We put a few drops of water on the paper to just barely dampen it and then folded it over a couple times to a 1/2 inch square and placed it in the SS envelope with the workpiece. All seams on the envelope were double folded and sinched in a BP mill vice.
                      As the oven heats up, the water flashes off as steam and adds some positive pressure to the envelope.
                      The heavy brown paper then burns and removes any oxygen from the enclosure. You now have a pretty much inert atmosphere to prevent formation of scale.

                      For air type steels we just let it cool as required. For oil hard we had a set of long snips to quickly slit the bag twice before dipping. Believe me, the oil gets in there just fine.

                      Air hard comes out super clean and oil just need a little Scotch Brite to take of the residue.

                      This was the method my mentor, Oscar Wilde Lyons, taught me back in '76 when I was just an apprentice and it has always worked for me.

                      Enco sells the foil for about $95. With a good % off sale code and free shipping it's worth having a roll in the shop.
                      Illigitimi non Carborundum 😎
                      9X49 Birmingham Mill, Reid Model 2C Grinder, 13x40 ENCO GH Lathe, 6X18 Craftsman lathe, Sherline CNC mill, Eastwood TIG200 AC/DC and lots of stuff from 30+ years in the trade and 15.5 in refinery unit operations. Now retired. El Paso, TX

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                      • #12
                        Radkins,

                        Some of my oil hardening parts I do not want to just drop in and hope they come out straight with a even hardness On these I use anti scale. They come out clean and the anti scale washes off with hot water.

                        As it has been said S S foil is double folded and squashed so the folds are air tight. I use a strip of brown paper bag to use up any oxygen in the bag.

                        Some of the knifes I have made require hardening at 2150 deg. These I have cooled by placing them between Two 1 inch thick aluminum plates and applying pressure. These are then tempered at 1000 deg. And I use anti scale to keep them clean. Results in a blade of Rockwell 62 and they do hold a edge. CPM 3V http://www.crucible.com/Products.aspx?c=DoList

                        Bob

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                        • #13
                          The Brownells compound is the one I have but as of yet I have not tried it, considering the simplicity and economy of use even if it does create fumes that attack the heating elements ad temperature probe it may still be a good choice because these are not expensive nor difficult to replace so I suppose the anti-scale compound is what I will try.

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                          • #14
                            I have used both the casehardening compound and the anti scale. The case hardening compound does have fumes, but have not noticed any with the anti scale. I use a Evenheat furnace for most of my heat treating and have not seen damage. I did buy a spare heating element, so if it fails I can fix imeadiately.

                            Link to both. http://www.use-enco.com/CGI/INPDFF?P...MITEM=328-1122

                            Bob

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                            • #15
                              Originally posted by Bob Ford View Post
                              Some of my oil hardening parts I do not want to just drop in and hope they come out straight with a even hardness On these I use anti scale. They come out clean and the anti scale washes off with hot water.
                              i'm not getting it....how does the anti-scale change the need for hoping and finger crossing that they come out straight?

                              Other that quickly straight in for even cooling and swishing about....I don't have a lot of techniques to avoid trouble. Oh, another is a long cycle stress relieve before heat treating.
                              in Toronto Ontario - where are you?

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