Stainless steel is steel that does not easily rust. The main alloying element in stainless steel is Cr (chromium). When the Cr content reaches a certain value, the steel has corrosion resistance, and the stainless steel generally has a Cr content of at least 10.5%.
The mechanism of corrosion resistance of stainless steel is the theory of passivation film, that is, its surface is formed with a very thin and strong and stable Cr-rich passivation film to prevent oxygen atoms from continuing to infiltrate and continue to oxidize, thereby achieving the ability to prevent corrosion.
The corrosion resistance mechanism of stainless steel is the theory of passivation film, that is, people think that "stainless steel does not rust, and rusty is not stainless steel. In fact, this is a one-sided misconception that stainless steel lacks understanding. Stainless steel will rust under certain conditions. If we can intuitively understand the various types of corrosion of stainless steel, in the face of corrosion of stainless steel can have corresponding measures to reduce losses. The following describes the common types of corrosion of stainless steel in combination with the actual situation of the project, briefly introduces the corresponding anti-corrosion measures, and focuses on the causes of stainless steel stress corrosion and prevention and control measures.
The corrosion damage occurred in stainless steel is mostly local corrosion damage, the most common being intergranular corrosion (9%), pitting corrosion (23%) and stress corrosion (49%).
Pitting is a very dangerous localized corrosion that occurs when small holes occur and then corrodes abruptly. In severe cases, perforation can occur. The main factors affecting pitting are:
1. Influence of Cl-, Cl- causes partial destruction of passivation film of stainless steel, resulting in preferential corrosion of the part;
2, the influence of temperature, the higher the temperature, the faster the corrosion;
3, surface adhesion of pollutants to prevent the circulation of oxygen.
For example, pitting corrosion often occurs in stainless steel (mostly 201 or 304 stainless steel) sinks in daily life. If some acidic or salty substances are placed in the tank and not treated in a timely manner, pitting of the stainless steel tank will occur.
The preventive measures are as follows:
1, to prevent Cl-adhesion;
2, a reasonable surface treatment, the formation of a stable passive film;
3. Select materials that are resistant to Cl-corrosion (such as 316L stainless steel with Mo.
