Stainless steel classification


Classification of stainless steel:

1. Classified stainless steel according to the rate of corrosion:

The stainless steel resistant is base on ability of corrosion in different environments. Accordingly to that property and depending corrosive environments, stainless steel in general is classified according to the corrosion rate as follows:
Rust on stainless steel
Rust on stainless steel

In corrosive environments: freshwater, air ...
  • No more than 0.01 mm / year: Stainless steel is considered to be completely stainless.
  • Not more than 0.1 mm / year: Stainless steel is considered to be stainless.
  • Greater than 0.1 mm / year: Stainless steel is considered to be corrosive.
In strong corrosive environments: sea water, salt, acid ...
  • Not more than 0.1 mm / year: Stainless steel is considered to be resistant to salt, acid (Good)
  • Not more than 1 mm / year: Stainless is considered (satisfactory)
  • Greater than 1 mm / year: Stainless steel is considered to be corrosive.

Stainless steel Kitchenware Corrosion
Stainless steel Kitchenware Corrosion

If you want to understand clearly of how does stainless steel be rusted, you may discover this post of detail.

stainless-rust-on-pipe
Stainless-rust-on-pipe


2.Classified Stainless steel according to the structure of the steel:

Based on the influence of alloying elements to the structure of the steel, we divided stainless steel into two groups: stable austenite structure elements (characterized by content of Ni) and stable ferrite structure (Characterized by content of Cr). This definition is shown in the Schaeffler diagram of the structure of stainless steel with vertical axis is % of Ni equivalent, horizontal axis is %  of Cr equivalent.

Schaeffler diagram for stainless steel structure


Schaeffler diagram for stainless steel structure

According to the diagram of the stainless steel structure, there are three main groups of stainless steel (single phase) is: stainless steel mactensite, stainless steel austenite and ferrite stainless steel. In addition, there are other related stainless steel groups but they have a little use in our life.