What do the numbers on stainless steel mean?

Do stainless steel names like 304, 18/8, or 18/10 seem like a confusing code? Wondering what they actually mean? Let's decode these numbers simply.

These numbers refer to the approximate percentages of two key components: chromium (Cr) and nickel (Ni). The first number (like 18) is the chromium content. The second number (like 8 or 10) is the nickel content. These metals give stainless steel its special properties.

Let's break this down further. These numbers are essentially a shorthand way to talk about the grade or type of stainless steel, focusing on the elements that most affect its performance, especially its ability to resist rust and corrosion.

Why Chromium (Cr)?
The “18” in 18/8 and 18/10 refers to a chromium content of approximately 18%. Chromium is super important. When it's exposed to oxygen (even just the oxygen in the air), it forms a very thin, invisible, protective layer on the surface of the steel. This layer is called a passive film. It protects the iron in the steel from rusting.To some extent, the higher the chromium content, the stronger the corrosion resistance. This is the fundamental reason why stainless steel is not as prone to rust as ordinary carbon steel.

Why Nickel (Ni)?
The second number (8 or 10) tells you about the nickel content.
18/8 and 18/10: These contain about 8% and 10% nickel, respectively. Nickel significantly boosts corrosion resistance, especially against certain acids. It also makes the steel more ductile (easier to form and shape without breaking) and keeps it strong at high temperatures. Importantly, adding enough nickel often demagnetizes the steel.

Connecting Names: 18/8 is Often 304
In the industry, especially when talking about common grades, you'll hear '18/8' used interchangeably with '304 stainless steel'. They are essentially the same grade – the most widely used stainless steel in the world. As I mentioned in my insights, you might also see it designated by different standards:

06Cr19Ni10: Often indicates production according to Chinese GB standards.
304: Typically refers to the American ASTM standard.
SUS304: Refers to the Japanese JIS standard.

They all point to the same basic composition and properties. Knowing this helps when sourcing products, like the vacuum bottles we manufacture.