What’s stainless steel and why is it called stainless?

October 14, 2022

Stainless steel is a special material with unique advantages such as stainless steel, heat resistance, corrosion resistance, easy processing, easy cleaning, recyclability, and low life cycle cost. is 405, 430, 304, 316 from weak to strong.

It is also a kind of green environmental protection material, which is widely used in industrial and civil fields.

What is stainless steel?

In metallurgy, stainless steel refers to alloy steel with high chromium content (usually 12%~30%) in the atmosphere and in corrosive media such as acid, alkali, and salt, which is passive, corrosion-resistant, non-rusting, and contains high chromium.

The most important metal element that determines the rust resistance of stainless steel is chromium. Usually, it also contains elements such as nickel, molybdenum, vanadium, manganese, tungsten, etc.

Why can stainless steel not rust?

The rusting process of ordinary steel

Ordinary carbon steel and oxygen in the atmosphere form an oxide film on the metal surface. Then, continue to oxidize, so that the rust continues to expand, forming a “thousand-layer cake”-type corrosion until it rots through.

Anti-rust process of stainless steel

The rust of stainless steel is related to the chromium content in the steel.

When the chromium content in the steel reaches 12%, a passivation film (Cr2O3) is formed on the surface of the stainless steel in contact with the atmosphere. It is a dense chromium-rich oxide that effectively protects stainless steel surfaces, especially against further reoxidation.

This oxide film is extremely thin (only a few microns), through which the natural luster of the steel surface can be seen, giving stainless steel a unique surface. Once the surface passivation film is destroyed, the chromium in the steel and the oxygen in the atmosphere will regenerate the passivation film and continue to play a protective role.

Is stainless steel always rust-proof?

Ordinary stainless steel encounters special environments, and some local corrosion will also occur, such as pitting corrosion (pitting corrosion), intergranular corrosion, stress corrosion, galvanic corrosion, etc.

In order to overcome these corrosions, elements such as molybdenum, nitrogen, titanium, or niobium were added to the steel, and new varieties of low-carbon, ultra-low-carbon, and duplex stainless steels were developed to improve the corrosion resistance of stainless steel. Therefore, stainless steel has many specifications, and different specifications have different corrosion resistance.

Common Stainless Steel Specifications and Corrosion Resistance

The corrosion resistance of common stainless steel Specifications is 405, 430, 304, and 316 from weak to strong.

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