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Refine Stainless Steel from 316 to 316L

Q. I am interested in refining SS316 to have less/no carbon content (i.e., from 0.08% in SS316 to 0.03% SS316L or lower). Is there some standard way of doing this, or am I onto unexplored waters here?

Sebastian Marin
- Menlo Park, California
May 24, 2024

A. For what reason are you wanting to reduce the carbon from 316 to 316L levels, as opposed to purchasing 316L? What equipment do you have to "refine" the steel, and what geometries are you looking to process?

You could decarburize the steel but this would be difficult to control the outcome and would call for solution treatments to reduce the carbides formed to return the corrosion resistance. This I would doubt to be commercially viable, but may be reasonable a hobbyist with the right equipment and knowledge. That said I would only expect it to be at all viable for small cross-sections and even then it would very likely just be easier to get 316L.

Commercially you would be bubbling pure oxygen through the molten steel, but at that point you would be making new steel and not bother with refining 316.

Andrew Speer
- Ballarat, Australia

Q. This is for a research project. I'm just interested in studying the chemical properties of stainless steel as a function of carbon. I only have two data points (ie 304 vs 304L) so I'm wondering if I can tune the carbon content myself. The form factor I'm purchasing is specific to my experimental setup.

How do you suggest that I decarburize the stainless steel while in solid form? Carbide formation would be fine for now.

Sebastian Marin [returning]
- Menlo Park, California

A. Sebastian, if you were to heat up steel in the presence of oxygen then you would form a layer of carbon poor steel at the surface of the piece, the degree of carbon loss is a function of both temperature and time. You may be able to find some literature on this topic, however it will mostly be focussed on stopping it or under welding topics where exclusion of oxygen is cost prohibitive.

The method of heating steel coupons in a muffle furnace would require experimentation to determine how much carbon is reduced from the coupon for specific combinations of time and temperature. You would want to maximise the exposed steel, and likely want a normalizing treatment after your decarbonizing treatment.

If you are not familiar with Time Temperature Transposition I would look into that as the theories behind it will play a large roll.

I would be interested in what chemical properties you are interested in where the sequestering of chrome into carbides would be inconsequential to you. That said you could minimize the carbide formation by decarburizing above the chromium carbide solution temperature and following the appropriate cooling sequence for the steel.

Andrew Speer
- Ballarat, Australia
May 29, 2024

thumbs up sign This is very helpful, Andrew. Thanks so much, great starting points.

I imagine that Chromium carbide WILL affect my results (I'm looking at electrochemical properties), but studying that effect is an area of interest as well, so I don't mind testing it if it will make my life easier initially.

Sebastian Marin [returning]
- Menlo Park, California

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