In some cases, a certain type of stainless steel may have good corrosion resistance in many media, but if it is placed in some other medium, it may be corroded due to low chemical stability. Therefore, a stainless steel is not likely to resist corrosion on all media.
Metal corrosion, according to the mechanism can be divided into special corrosion, chemical corrosion and electrochemical corrosion three. Most of the metal corrosion in actual life and engineering practice belongs to electrochemical corrosion.
The main corrosion types of stainless steel are uniform corrosion (surface corrosion), pitting corrosion, crevice corrosion, intergranular corrosion, and stress corrosion.
Uniform corrosion refers to the phenomenon that all metal surfaces exposed to the corrosive medium are corroded. According to different usage conditions, different indicators are required for corrosion resistance, which can be generally divided into two categories of three corrosive
Corrosion resistant steels are steels that are resistant to corrosion in a variety of aggressive media.
1. Point corrosion
Point corrosion refers to the fact that most of the surface of the metal material is not corroded or corroded by light, and localized corrosion occurs with a high degree of dispersion. The size of the common corrosion point is less than 1.00mm, and the depth is often greater than the surface pore size, and lighter ones have shallow pits, and even severe ones. Form a perforation.
2. Crevice corrosion
Crevice corrosion refers to the occurrence of spot-like or ulcer-like macroscopic pits at the crevices of metal components, which is a type of localized corrosion.
3. Intergranular corrosion
Intergranular corrosion is a selective corrosion damage. It differs from general selective corrosion in that the locality of corrosion is microscopic and not macroscopically local.