Should 100% stainless steel never rust?

[Brad93]

When talking of different stainless steel grades or any materials really it is important to know why they corrode.

There are 8 different forms of corrosion or should I say forms of attack.

There is basically the following:

• Uniform
• Galvanic
• Crevice (Under Deposit Corrosion)
• Pitting
• Intergranular
• Erosion
• Stress corrosion
• Selective Leaching

Uniform corrosion is what occurs with steel left out in the elements with no protection. It corrodes roughly equally across its surface. The same could be said if you put it in acid, it corrode until there was nothing left.

Most austentitic stainless steel is obviously highly resistance to the elements, with certain grades being better suited to marine use.

As has already been explained the chromium in the stainless steel creates a tough passive oxide layer that prevents the underlying layers from being exposed to oxygen or nitrogen.

However not all stainless alloys are resistant to the same environments, for example elevated temperatures, presence of acids or organic material etc can break down the passive layer.

When you get embedded iron particles on the surface of stainless steel, you get galvanic and crevice corrosion occurring. That little iron particle basically creates a localised potential forming an anode and cathode.

Similar occurs with chlorine, sulphur, vanadium and other elements on what would normally be very corrosion resistant materials.

I could talk about this all day but the best resource there probably is around is a book by Fontana & Green called Corrosion engineering.
I forget how many revisions there are, it’s been reprinted and updated many times. The guy was about in the 40s!

Bout £20-40 second hand online.

Once you’ve got the book look up a guy on YouTube his name is Thomas W Eagar, American Professor at MIT. His video series on corrosion is quite interesting.

 

[Pigeon_Droppings2]

Loved the wheeler dealer episode where Ed says his stainless won't rust because its stainless and there is no iron in its makeup!...I think thats how he said it . I know what he meant but was funny....but I forgive him because of everything else I've learned from him.

My mate told me not to use steel spanners on stainless....either stainless spanners or chrome.

I thought he was having a laugh....but I looked it up and he was right. I think it causes contamination which can lead to rust!

 

[Wozzaaah]

Stainless steel is usually chosen for its corrosion resistant properties, but it is important to know that different grades provide different amounts of corrosion resistance. Austenitic stainless steels generally provide the most corrosion resistance because of their high amounts of chromium. This makes grade 304 an excellent choice when corrosion resistance is important. Grade 316 is similar to grade 304, but it has molybdenum as part of its chemical makeup, further increasing its corrosion resistance. Ferritic stainless steels and martensitic are generally more affordable than austenitic stainless steel because they have less nickel and sometimes less chromium than austenitic stainless steels, which can result in a loss of corrosion resistance.

Basically, as long as there is sufficient chromium present, the chromium oxide layer will continue to protect the stainless steel and prevent it from corroding.

If you’re going to copy and paste at least give credit to the website you robbed it from.

 

[Nick67GT]

Google is your friend and helps consolidate the knowledge you already have, but can’t recall in exact terms......