Is it possible to rust stainless steel

Aluminium, for example, will have some serious pitting issues in a saline solution. The rule of thumb is that if you can limit the potential difference to 0. However, you may need to limit the potential difference to 0.

Note — removing the electrolyte will also stop the corrosion! Active stainless is where that passive barrier is abraded or otherwise not allowed to form.

Small particulates, plain steel for example, become embedded in the surface and cause surface staining on the stainless. If the part is machined on a CNC machine that also does steel parts, small particulates of steel can contaminate the coolants, and when the stainless part is machined, become embedded in the surface. Similarly, buffing wheels that have been used on steel parts and then on stainless can similarly embed steel particulates, as can other steel tools like wrenches.

Check with your machining house, and ensure that they are not cross-contaminating your stainless parts. For sensitive applications, electro-polishing can be used to resolve the issue, which can also improve the finish and abrasion of the stainless as well. Small iron nodules could also be within the stainless steel matrix itself if the steel was processed incorrectly. Metallurgical analysis may be required to determine the exact source, whether within the grain structure, or surface contamination.

Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time. To prevent stainless steel from rusting, you need to passivate it. Passivating stainless steel is a process that allows stainless steel to retain its corrosion resistance. There are a few factors that can affect the corrosion resistance of stainless steel.

The composition of the steel affects corrosion resistance. Even within grades of stainless steel, impurities in the steel can affect the corrosion resistance.

The environment is another big factor in stainless steel rust. When the passive layer is breached, it usually forms again spontaneously. In aggressive environments, such as very close to the beach, where there is a lot salt in the air, the passive layer may not be able to form, and some corrosion may take place.

The graph below shows the results of a year corrosion study from a very corrosive environment near a beach in South Africa: an even more severe environment than the most aggressive in Australia, such as Newcastle Beach. Stainless steel grade gave about 9, times the life of carbon steel. Grade would be similar, although not quite as much. And this in an environment where each millimetre of carbon steel would corrode away completely in about four years.

Of course, the passive layer that stainless steel relies on for protection has to be allowed to form. Blue and black visible oxides formed during heat treating, welding and heavy grinding interfere with the formation of the passive layer.

They must be removed to get the full corrosion resistance of each grade of stainless steel. Often, when stainless steel appears to be rusting, it has actually been contaminated with carbon steel — which rusts, of course!