Prevent stainless steel picking up carbon ?

Discussion in 'Castings, finishing/ repair/ and patina's' started by metallab, Aug 12, 2020.

  1. metallab

    metallab Silver

    When making SS castings usually made from ANSI 304 , 18/8 steel, self alloyed from mild steel (iron), elemental Nickel and elemental Google metal with some discarded SS bolts, I use a DC welder where a cylindrical graphite (not clay-graphite, but pure) is connected with the anode (+) of the welder and a carbon rod with the cathode (-) of the welder. I use 140 Amp and about 100g of SS is molten witing five minutes. I use some sand+lime flux to keep the arc sustainable.

    That goes all well, the molten SS looks very nice and lustrous and is very fluid and pours easily and thin castings of 1mm in 'Delft clay' are no problem.

    But: it gets harder and even a bit brittle, not as brittle as cast iron. Probably due to carbon intake from the electrode and / or the crucible.

    How can I prevent this and how do large scale commercial EAFs in the steel industry handle this ? They also work with carbon rods.
     
  2. TRYPHON974

    TRYPHON974 Copper

    I'm far from an expert in metal treating but did you try to anneal your casting? Basically heating you part and letting it cool slowly.
     
  3. metallab

    metallab Silver

    I'll give it a try, but I already let the casting cool slowly in the sand after freezing.
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    But, does slow cooling of stainless cause hardening or annealing? Several sources advocate rapid cooling to achieve softening.
    Annealing of types SS304 and SS304L is achieved by heating to above 1900°F for 60 minutes per inch thickness followed by water quenching. The best corrosion resistance is achieved when the final annealing temperature is above 1900°F.”

    Most likely prolonged holding at 1900 is not required.
    Denis
     
  5. TRYPHON974

    TRYPHON974 Copper

    Very interesting, it depends of whether it's austenitic (quenching softens) or martensitic (slow cooling softens) if I get it right. Austenitic stainless steels are non magnetic, so it shouldn't be hard to find in which category your alloy fits.
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    Tryphon, see the first post.

    Denis
     
  7. Rasper

    Rasper Silver

    I have shaped and gas-welded a good bit of 304 stainless in my sculpture studio. I learned the basics from the Bible on stainless, published by International Nickel back about 1952. I learned the rest the hard way.

    Stainless work-hardens quickly. Welding seems to harden it even worse. To partially anneal 300 series stainless I heat it to 1900 F. (yellow hot) and quench it in water. To fully anneal it you must hold it at 1900 F. in an oven for an hour and then quench.

    [​IMG]
     
    Tobho Mott and Melterskelter like this.
  8. TRYPHON974

    TRYPHON974 Copper

    Well, it's embarrassing... :)

    The handbag is a nice piece of craft! Is it tig welded?
     
  9. Rasper

    Rasper Silver

    Thank you, sir. It was assembled with 56% silver solder. I don't have a TIG machine. I use oxy/acetylene for everything; steel, aluminum, stainless, and silicon bronze.

    Richard
     
  10. metallab

    metallab Silver

    I made another SS casting. It is a credit card sized (and thickness) knife of a wood scraper (bottom left).
    It is a tiny graphite crucible of about 10ml contents, and as seen, the inner walls are somewhat attacked by the arc (top left), so that's probably the reason it picks up carbon.
    The crucible was inside a shroud of Fiberfrax blanket to protect the heat.
    It took about five minutes to melt.

    SScasting.jpg
     

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