Alloy steel being added more than 12% of Cr for securing
    corrosion resistance
Once being added Cr over 12%, a passivity layer Cr203 is
    formed on the surface
For better properties of the steel such as corrosion
    resistance and plasticity, various kinds of alloy are added
    such as Ni, Mo, and N.

 

13Cr steel and 18Cr-8Ni steel are main kinds of STS, a main component Cr forms a very thin Cr203 layer on
the surface acting a passivity layer blocking oxygen to entering into the metal, so gives the steel a nature of
a corrosion resistance quality.

 

Item

Stainless Steel

Carbon Steel

Formation

Features

The layer is thin and dense, so
    prevents Oxygen from penetrating
    into the steel.
In some sever environment such as     exposure to radiation, it could rust
    by the layer damage.

The layer is thick and porous, so
    Oxygen penetration is easy.
It is easy to rust in the normal
    atmospheric environment and
    impossible to prevent the rust     basically.