Casting stainless steel ???

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I would love some feedback from those of you with experience casting stainless steel. I have been involved with casting aluminum, bronze and iron for several years but have never attempted SS. I was recently given @ 350 lbs of 316 SS fasteners which I want to melt and cast. I have constructed a coke-fired cupolette-style furnace w/ a 300lb capacity and barring any oversight, intend to melt in it. Im not certain what to expect when the 316 is melted. Im am certain that some factors will have to be weighed and ask your help pinpointing them.
eg.-When the SS is molten what measures must be taken (fluxes, additives) to retain (relatively- see below) the properties of the original materials??
My main concern for the cast objects is that they are weldable,machinable, corrosion- resistant, and can be finished to a degree of reflectivity that Im familiar with, with this material. As an art object, the casting need not adhere to any particular rigorous performance standard. I have obtained the ASM Handbook on Casting (vol 15) and will certainly conduct research into the subject. However, I feel its pertinent to go directly to the source- artists working in metal.
Thanks alot in advance,
McR


GeorgeMummert's picture

ss casting

I would double check to see if cupola melt will work for stainless.  Though I have never cast SS myself, I have been around foundries who do....all of them use Induction furnaces for SS. 

on another note...SS is much hotter than the other metals that you (and I) have experience with.  It is dangerous exponentially more so than bronze or aluminum..take extra caution.  Let me know what you find out.

 George

KeystoneArt.org


AbOmInOg's picture

Cast SS

Thanks George.
I am accustomed to melting cast iron in this furnace and have experienced the increased heat of the melt with that material. I certainly will gain as much knowledge as possible before attempting anything... if it is deemed entirely untenable, Ill not attempt it all. Anyone out there have any direct experience with this???


Rich Waugh's picture

I don't think you'll have

I don't think you'll have much joy with trying to melt SS in a cupola furnace for casting. You say tghat you desire the end product to be "weldable,machinable, corrosion- resistant, and can be finished to a degree of reflectivity that Im familiar with", yet you go on to say that the resultant product need not adhere to any "particular rigorous performance standard." That jseems contradictory; on the one hand you want it to be just like a standard ASM alloy (read, meet standards), while on the other hand you say it need not.

There is no rational hope of obtaining a consistent, dependable alloy from a cupola melt. The process is inherently fraught with uncertainty as regards the outcome. As noted previously, those who routinely casrt SS use induction melters, generally in a controlled atmosphere, to obtain pieces that are weldable, machinable, etc. I don't think you can possibly achieve that in a cupola.

If you do succeed, I would love to hear your process.


AbOmInOg's picture

Casting SS

Thanks for your comments. To clarify: the recycled metal forming the art casting need not adhere to the exacting performance testing such as those spec'd in ASTM and other such testing organizations. My concern is primarily aesthetic. Im quite certain that the metal composition and therefore its properties will be altered. These will likely complicate working with it. As long as I can fabricate with it (weld/ machine and finish) in a manner pleasing to me- I would consider it satisfactory- warts and all. At any rate the allure of even a modicum of success makes it worth trying. I built a cupolette-style furnace (w/ lid). This design is more of a batch melter than a continuous one which recoups more heat than a cupola. If run carefully the melt zone tends to oxidize less than a standard continuous melter.
Im wondering if you are able to expand on your comment regarding a controlled atmosphere??
Additionally, I am aware of the hazard posed by the melt's high heat and chromium content.


Rich Waugh's picture

Regarding the controlled

Regarding the controlled atmosphere:

When melting any ferrous metal, (and most non-ferrous), it is common in industry to perform the melt in a controlled atmosphere. Generally, an inert gas such as argon, helium, nitrogen or carbon dioxide is maintained in the induction furnace to prevent oxidation, absorption of undesirable elements or other variables during the melt. High carbon steel is particularly prone to losing carbon through oxidation, most steels are better without excess sulfur, etc.

In a cupola-type melt, the metal is essentially subjected to open flame and thus highly prone to oxidation if the atmosphere is not maintained in a reducing state by the addition of some material to consume free oxygen. Stainless steel, generally composed of iron, nickel and chromium, is only stainless if the chromium carbides are in suspension and the surface chromium is oxidized. If tramp elements are introduced, these balances can change. Thus the use of controlled atmospheres. The need for atmosphere control necessitates isolating the melt from the flame and free atmosphere, so induction furnaces are appropriate, or muffle-type furnaces or closed crucibles.

I'm not too knowledgeable about cupola melting, so I can't say how you could control the atmosphere in one effectively. Building a cupola that will withstand for a sufficient period of time the more than 2600F temps necessary to melt stainless may be a problem, too.

Finally, your desire fora michineable final product concern me. Typically, steel is cast into ingots large enough to be rolled down to billets and then into finished form aftera reduction in section of some 85% or thereabouts. This high degree of reduction is necessary to develp the tight grain structure necessary to have a piece that is both strong and dense enough for machining.

I wish you luck with your efforts and look forward to hearing how it comes out.


visitor's picture

melting stainless steel in a cupola

I just stumbled across this site. As a metallurgist in industrial investment casting foundry, I have a couple of thoughts. Temperatures for castings should be around 2800F for good flow. the thinner a section, the more heat you need to keep it from freezing off too soon. Also, stainless steel is a mushy freezer, more prone to shrinkage porosity than bronze. (I haven't worked with Al).

I don't think grain size will be a factor for machining castings. SS is gummy, so tends to wear cutters faster.

I agree that induction melting is better than cupola. I don't know much about cupolas: doesn't it work by burning carbon, so are mainly used for cast iron? If so, then that it going to change the composition of your SS if it is in direct contact with the carbon. 316 stainless is supposed to be low carbon. Some bad things can happen to 316, as far as carbides in the grain boundaries, and how it can react to heat treating.

No matter how much you shield, you will not be able to overcome h20 and excess oxygen in a combustion system. In induction heating, you can shield by a liquid nitrogen drip, or flowing gaseous Nitrogen over the melt, and keeping a lid on it as much as possible. You need to make sure you have good ventilation.


visitor's picture

Suggestion

You could check with www.tridentalloysinc.com for help with castings.


visitor's picture

Also just stumbled across

Also just stumbled across this site, sorry if it's out of date by now.
Couple of points regarding melting SS in a cupola/cupolette. You will pick up carbon in excess of what the material can handle, rendering the metal hard and brittle due to carbide formation.it might not even survive contraction stresses while cooling depending on complexity. You will lose a lot of chromium to oxidation, not only altering the metal chemistry but also blocking up the furnace (chrome oxide slag is not fluid).
BTW I am a foundry metallurgist, have produced SS and high chrome heat resistant steels(in induction and arc furnaces) and used to run a battery of 28" cupolas for white iron. For the latter we did alloy with ferrochrome but only produced the base iron in the cupolas, all alloying was done in holding furnaces.


visitor's picture

looking for stainless steel melters

I have some AISI 304 materials in sheet form of 690x755 mm (27 " x 30 ") and looking for a smelter who would be interested in purchasing.. total quantity = 115 tons (255.000 lbs) ..
can anyone recommend someone ? thanks
marc@helaxa.com


ScottTheSculptor's picture

brittle

All the extra carbon will react with the chromium to give you chromium carbide.
What little chrome is leftover from reacting with the oxygen in the burn.

The elevated temperatures need to melt the stuff will probably erode your cupolette lining and throw sparks far and wide when you tap it.

Haven't tried it