Back To Basics: What Makes Stainless Steel Rustproof?

Regular readers of our blog will already know the value of stainless steel as we sing its praises frequently. However, for our more curious readers, we’d like to dig a little deeper this week into the corrosion resistance of this metallic marvel. Have you ever asked the question - what makes stainless steel rustproof?

Do fully understand stainless steel’s anti-corrosion properties, we should go back to its roots. Stainless steel is an alloy made up of varying percentages of iron, chromium, manganese, silicon, carbon and often nickel and molybdenum. However, iron rusts. So what makes stainless steel so special?

The Nirvana Seeking Theory

According to the fascinating world of Materials Science and Engineering, a factor known as Equilibrium thermodynamics is at play in this battle against rust. In its simplest form, this theory basically tells us what a material’s goals are in life – the difference between where it is and where it wants to be, an equilibrium or balance. In the case of pure iron, if there is oxygen at an ambient temperature and a normal state of pressure, then it will oxidize. This will occur when the iron atoms are surrounded by oxygen atoms and form a very thin film over the iron. The red oxide produced (Fe₂O₃) reacts with the water atoms in the air and cause a fundamental change in the iron which results in its demise - blistering and flaking until there is no more iron to consume. This is the dreaded rust that we see.

What Makes Stainless Steel Rustproof?

However, once we introduce the above-mentioned mix of alloying elements this process is not given an opportunity to start. How so?

Along with some of its compatriots, Chromium plays an important role in reacting with oxygen to create a thin and stable film which acts as an almost invisible membrane between the steel and the water and oxygen particles in the air.

Including silicon or aluminium in this mix offers a self-healing element to this barrier, resulting in a strong, rustproof and beautiful product.

So there we have it, the layman’s version of the rustproof properties of stainless steel.

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