Why is stainless steel rust proof?

Question

Hi, I need to know why stainless steel is rust proof please tell me its for my science project. :)

Answer 1

First I think you need to know about Rust and Stainless Steel , so read this.

http://en.wikipedia.org/wiki/Rust

http://en.wikipedia.org/wiki/Stainless_steel

Why doesn't stainless steel rust?
Nancy Avery,
New London, Conn.

Metallurgical engineer Michael L. Free of the University of Utah offers this explanation:
Stainless steel remains stainless, or does not rust, because of the interaction between its alloying elements and the environment. Stainless steel contains iron, chromium, manganese, silicon, carbon and, in many cases, significant amounts of nickel and molybdenum. These elements 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. Chromium plays a dominant role in reacting with oxygen to form this corrosion product film. In fact, all stainless steels by definition contain at least 10 percent chromium.

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. Because the film forms so readily and tightly, even only a few atomic layers reduce the rate of corrosion to very low levels. The fact that the film is much thinner than the wavelength of light makes it difficult to see without the aid of modern instruments. Thus, although the steel is corroded on the atomic level, it appears stainless. Common inexpensive steel, in contrast, reacts with oxygen from water to form a relatively unstable iron oxide/hydroxide film that continues to grow with time and exposure to water and air. As such, this film, otherwise known as rust, achieves sufficient thickness to make it easily observable soon after exposure to water and air.

In summary, stainless steel does not rust because it is sufficiently reactive to protect itself from further attack by forming a passive corrosion product layer. (Other important metals such as titanium and aluminum also rely on passive film formation for their corrosion resistance.) Because of its durability and aesthetic appeal, stainless steel is used in a wide variety of products, ranging from eating utensils to bank vaults to kitchen sinks.

Answer 2

Stainless steel is an alloy of iron and other metals, notably Chromium and vanadium.

You do not see it with the naked eye but at the surface of any stainless steel (SS) there are iron atoms and chromium atoms that are exposed. However, the chromium reacts preferentially to form an oxide. In essence, think of chromium sacrificing itself for iron so that iron will not rust. What a nice guy huh! This is called passivation just like most responders said.

However, more than that the chromium oxide forms a tight protective layer that forms a physical barrier preventing Oxygen or any oxidant to reach and attack the iron underneath it. Also, the chromium oxide formed is not FLAKY and porous, so it does not mar much of the surface as an iron oxide (rust) would.

For science project, you may not make it too technical but you can make a reference or make an ANALOGY of rust prevention to high school or social situations as "being there for your friend or classmate"

But in real life, when the odds are too great, that protection afforded by chromium may not be enough. Because eventually all steel exposed to very oxidizing atmospheres will rust. Just a little break in the surface is enough to start the process of rusting.

Answer 3

Stainless steel is characterized by the presence of chromium. Chromium oxidizes like aluminium does, by passivation, that is, it forms a though oxide layer that sticks to the metal underneath and protects it. On the other hand, iron oxidizes by turning into rust, which is a brittle material that flakes off, exposing the metal under for more oxidation.
Now, what happens when you have a metal that is made of both iron and chromium? Any iron on the surface will "rust" and flake off (at the atomic level, so do not expect to see much rusting) until the surface is a pure chromium layer (again, we are talking about a layer that is a few atoms thick) and that chromium will oxidize but stay put.
Then rust then has no way of getting deeper, and the metal will remain clean.

Answer 4

Rust Proof Metal

Answer 5

When steel is made, nickel is added to the mix of iron and carbon. There are several different mixes for stainless. Sometimes chromium is used as well.
Some of the different types are 10-10-321 and 14-10 stainless steel.

Answer 6

Actually stainless steel will rust like an ordinary steel, but figuring the percentage, an ordinary steel will rust 100% and stainless steel have a say 5% chance to rust, that is why the name itself STAIN--LESS or less chance to have a rust stain. Otherwise if really the steel is rust proof, we will call it as STAINZERO STEEL.....PEACE

Answer 7

Stainless steel is a type of alloy (different metals mixed together. For ex. Gold and other metals make up, well, gold, but not the squishy kind, since plain gold is very soft). Stainless steel can be used in medicine (for ex. joint replacements) and silverware, so we can't be poisoned (i'm not sure we will actually be poisoned, but we can get really ill) from rust.

Answer 8

High oxidation resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.[2] The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, meaning the metal remains lustrous.

But it is NOT rust-proof. Just more resistant than other metals.

Answer 9

This Site Might Help You.

RE:
Why is stainless steel rust proof?
Hi, I need to know why stainless steel is rust proof please tell me its for my science project. :)

Answer 10

The chromium in stainless steel oxidizes in a very thin layer at the surface. The layer of chromium oxide protects the metal below it, which consists of a combination of chromium, iron, and varying amounts of nickel and/or molybdenum depending on the type of steel.