When you think of stainless steel, what’s the first thing that comes to mind? For many, the first image that leaps to mind is that of a gleaming metal object, one that has a near mirror-like surface.
What most people don’t think of when they hear the term stainless steel is rust or decay of any kind. After all, stainless steel earned its name by being free of blemishes, right?
However, the question “will my stainless steel basket rust?” is still a legitimate one. Just because an alloy is referred to as “stainless” doesn’t necessarily mean that it’s proof against all forms of corrosion or rust.
So, the short answer to the title question of this article is: “it’s possible.” Many forms of stainless steel are very resistant to corrosion and oxidation, but there are limits to how resistant these materials can be to the effects of certain chemical and temperature combinations.
Why is it Called Stainless Steel?
The popular term stainless steel is a reference to the alloy’s tendency to resist rust under normal conditions.
As pointed out in an article featured on scientificamerican.com, the chemical elements in stainless steel “react with oxygen from water and air to form a very thin, stable film that consists of such corrosion products as metal oxides and hydroxides.”
How does this film of corrosion products prevent rust? As stated in the article, “the presence of the stable film prevents additional corrosion by acting as a barrier that limits oxygen and water access to the underlying metal surface.” In essence, this stable, microscopic layer of rust keeps other corrosives from attaching to the steel.
This layer of rust is so thin that the human eye typically cannot see it without aid, giving the surface appearance of the steel its characteristic “stainless” appearance.
So, Why Would Stainless Steel Rust?
There are many reasons why a given piece of stainless steel might start to develop rust. However, it’s important to remember that there are hundreds of different alloys of stainless steel. What might cause one stainless steel alloy to corrode might not affect another one.
According to a publication by Sperko Engineering, one cause of rust on stainless steel would be “when a condition develops in which the metal molecules at the surface are not sufficiently alloyed with chromium to create or maintain the required oxide layer.” In other words, rust can occur if the protective film that covers the steel dissipates.
So, what can cause the protective oxide layer to dissipate?
One reason that the oxide layer might dissipate is if plain iron is deposited onto the surface of the stainless steel. This can happen if the stainless alloy comes into contact with plain iron or ordinary, non-stainless steel alloys.
When plain iron is deposited onto stainless steel, this iron lacks the chromium content that is so integral to the formation of the protective film that keeps stainless alloys from rusting. This allows rust to attach to the surface of the stainless steel. Yet, as pointed out in the Sperko document, “the rusted surface looks bad, but, the chromium in the stainless steel under the rust film forms a suitable corrosion-resistant oxide layer, and further corrosion does not continue once that film of unalloyed steel turns to rust.
The British Stainless Steel Association points out another situation where corrosion can occur on stainless steel, a phenomenon they refer to as crevice corrosion. As stated in the bssa.org article, “stainless steel requires a supply of oxygen to make sure that the passive layer can form on the surface. In very tight crevices, it is not always possible for the oxygen to gain access to the stainless steel surface thereby causing it to be vulnerable to attack.” The “passive layer” referenced in the article being the oxide layer that typically protects stainless steel.
Certain caustic chemicals can eat away at the steel itself, causing what the bssa.org article refers to as general corrosion. According to the article “with some chemicals, notably acids, the passive layer may be attacked uniformly… hydrochloric acid and [sulfuric] acid at some concentrations are particularly aggressive towards stainless steel.”
So, while stainless steel alloys are generally resistant to rust under normal conditions, there may be situations that can cause the stainless steel alloys to begin to corrode and develop rust. Some specific alloys might resist exposure to certain conditions better than others, which is why it’s important for the design engineer creating your custom steel wire basket to know the specifics of your application when choosing the specific alloy to use for your parts washing or materials handling baskets.