Mechanism of Carbon Pickup in Stainless Steels

Contamination by Mild Steel

Contamination by Chloride

Contamination by Carbon

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Stainless Steel - Surface Contamination in Fabrication

This is easier than trying to explain it, although Milo can give more detail, if needed.

No carbon can be picked up by the SS just for contact in no high temperature is present (this rise the mobility of C atoms that can diffuse from the CS to the SS).

The recommended practice to avoid direct contact of CS with SS (or use in SS some tooling previously used in Cs, or even manufacture, welding, etc. CS and SS in the same room) is set to avoid surface contamination of ferritic small particles which can be the source of pitting corrosion.

Some industries who have a high cleaning requirements on SS use to make a test after the cleaning process to check for that. It consist in apply a filter paper wet with a solution freshly prepared with sodium ¿thiosulfate?, in oxidant and acid medium and look if some Prussia's blue dots appear. The blue dots are indications of ferritic contamination.

Kind regards

I agree that the issue is iron from the carbon steel setting up galvanic cell. It is not a carbon issue. To destroy something made of stainless steel, just scrub it down with regular steel wool. Will start rusting in a very short time.

Milo

Can anybody explain the mechanism of carbon pick up in stainless steel from carbon steel or other sources?

Worn steel pneumatic press dies punching out stainless steel washers. If I had a nickel for every time we have received a batch of rusted stainless steel washers (due to steel impregnation on the surface of said washers) I would have a lot of nickels.