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Thread: Why is DIY stainless steel so hard ?

  1. #1

    Why is DIY stainless steel so hard ?

    Recently I made small SS castings from ANSI 420 (Fe + 14% Cr) which worked very good. I melted mild steel and some chrome (total ca. 70 grams / 2.5 oz) in a graphite crucible connected to the anode of a a DC welder and held the cathode connected to a carbon rod on top of it. Using slag (lime + silica sand) the arc was remarkable sustainable and melted easily and quickly in three minutes at 140 Amps, and was easy to cast and the castings turned out very detailed like tin castings (I used Delft clay which is actually tin / pewter casting sand).

    After wirebrushing, I tried to saw off the sprue but to no avail. Only a Dremel with a grinding disk (same material as an angle grinder disk) could cut this. I found on the internet that ANSI 402 is indeed very hard.

    I melted the sprue again, adding proper amounts of elemental Cr and Ni to make 'standard' 304 (18/8) SS. When it was molten I stirred it a little by dipping the carbon rod in the liquid (which makes short circuit, but a welder can withstand this) and then arced again until some more sparks appeared (but far less than at melting plain steel) and poured it out. Again, excellent casting in the pewter molding sand.
    But, unlike commercial 304 SS, it was again very hard, a hacksaw gets blunt and used the Dremel.

    Is there a heat treating method for 304 SS ? Commercial SS can be cut with a hacksaw, albeit harder than plain steel.

  2. #2
    are you sure you arent adding far too much carbon to the steel due to the carbon arc rods and graphite crucible that your melting it in? With the temperature that it would have to be poured at, it would absorb carbon like crazy into the steel and turn it into a higher carbon steel, which could explain why it's so hard.

  3. #3
    Can be a possibility.
    Add some oxidizing stuff into it, just like a Basic Oxygen Furnace squirts O2 on the steel in commercial steelmaking ?

    EDIT: I realized that commercial EAFs for any kind of steel (including stainless) also use carbon rods (three ones because of three phase power) hovering over a steel bath of 1600 C, just like I did on a (million times smaller: 70g vs 70tons) scale with one rod, but the chemistry is the same.
    Then the carbon problem should be the same, or is it removed in postprocessing in a ladle furnace ?
    Last edited by metallab; 12-24-2017 at 04:28 PM.

  4. #4
    Senior Member Jammer's Avatar
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    The rods aren't in the steel, just the arc. The only time we had a carbon problem was when the tip of one of the rods would break off and fall in the steel. Also, they used oxygen lances to lower the carbon and remove impurities. Just the act of pouring would put enough O2 in the melt to remove any carbon that was left. We didn't have a ladle furnace and would add alloys as we tapped and then trimmed it up at the stir station.
    You would have to have an analysis to see what the chemistry is but you could try to anneal your parts by heating it to red heat and bury it in vermiculite or just leave it in the furnace to cool slowly.

  5. #5
    @Jammer: indeed I also hover the carbon rod over the melt (otherwise it won't heat up), i only dip it a few seconds to stir it.
    Annealing might be an idea.
    I did a test by melting some mild steel over some underlying charcoal, but the liquid steel barely picked up the charcoal. It got harder, so it did pick up something but did not get brittle cast iron.

  6. #6
    Senior Member HT1's Avatar
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    What did you use for a crucible??? you most likely picked up carbon there unless you used a refractory material and at .08% max any carbon pick up is too much to be any "real" SS

    V/r HT1

  7. #7
    Senior Member Jammer's Avatar
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    There are some white iron alloys that are high carbon and high chrome. They would be very hard. Any photos of your castings?

  8. #8
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    I have not cast stainless, but I have shaped a lot of 300 series stainless sheet metal and bar stock in my sculpture studio. These shoes for instance:



    They are about 4 feet long. I made a pair of them.
    Shaping those heels was a serious education.

    The one characteristic stainless seems to enjoy above all else, to torment you, is that it work hardens almost instantly. So I have done a lot of annealing. International Nickel published the bible of stainless back in the early 1950's. There is a good section in it on annealing stainless. To anneal
    300 series stainless totally, you heat it to 1900 F. in an oven and let it soak there for an hour. Then quench it in water. I never did that. I would heat it to a bright yellow heat and quench it. That did a pretty fair job of annealing. (What I quickly learned though was that trying to cold work stainless is folly. I heat it red hot and hammer it to shape.)

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  9. #9
    Quote Originally Posted by Rasper View Post
    They are about 4 feet long. I made a pair of them. Shaping those heels was a serious education.[/SIZE][/TD]
    What a large feet does your wife / girlfriend have !

    @Jammer,here are the photos.
    It are just tiny castings as I can only melt tiny amounts because my welder is max 3kW and I have no three phase supply, only single phase 220V.
    The rosette is made from ANSI 304 SS and the other castings are from 420 SS.
    The second photo shows the crucible, which still contains some frozen slag and steel droplets, and the sprue for the rosette (304). This is a cilindrical pure graphite crucible of (outer) 60x40mm, contents about max. 30ml (1 fl oz). Pure graphite conducts better than the graphite clay ones which I use in gas furnaces. This is needed because I use the crucible (and the metal bath) as anode and hover a cathode carbon rod over it to arc it inside the crucible.

    Here a video of melt and pour of the 420 SS (the two wildboard heads bottom left) which lasten only three minutes from a cold crucible.
    Using refractory crucibles (SiC or alumina) is not an option as these do not conduct, unless I can afford an induction melter.

    https://www.metallab.net/jwplayer/vi...5tcDQ6Ojo2MDA=


    EDIT: I did a test this Christmas day.

    I melted a piece of mild steel in a ceramic (Hessian) crucible using two carbon rods, the anode touching the steel and the cathode hovering over it. In four minutes it was molten and poured out the steel which gave lots of sparks, much more than with cast iron.
    After freezing and cooling down, I filed it with a normal file and it felt like original mild steel, it was not harder.

    But the crucible cracked, as I had earlier with these crucibles in a gas furnace, hence I prefer graphite.

    https://www.metallab.net/jwplayer/vi...1wNDo6OjYwMA==
    Attached Images Attached Images
    Last edited by metallab; 12-25-2017 at 03:22 PM.

  10. #10
    Senior Member OCD's Avatar
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    Quote Originally Posted by metallab View Post
    What a large feet does your wife / girlfriend have !
    I think those are Rasper's.

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