Long before the turn of the century, it was discovered that the addition of nickel and chromium could improve steel corrosion property. However, steel reinforced with these elements.
The name astm a182 f11is used internationally and indicated the ratio of alloys of chromium-nickel to stainless steel.
Material properties and benefits
Stainless steel 1.4301 is an acid-resistant 18/10 austenitic Cr-Ni alloy steel with low hydrogen content and excellent anti-corrosion properties. It was approved at temperatures up to 300 degrees Celsius. ansi b16.5 flange is resistant to water, steam, atmospheric humidity, and edible acids. It is best used in food industry, beverage manufacturing, pharmaceutical, and cosmetics industry.
The chromium component of stainless steel is created by contact with oxygen in air. It eliminates all corrosive substances. When damaged by certain external influences, it reshapes on the surface of the steel in a few microseconds. This quality can be improved by adding nickel and molybdenum and other alloying elements. Therefore, there are many types of stainless steel fasteners.
In addition, corrosion resistance also depends on the quality of the surface, the smoother and more homogeneous the resistance increases. Penetration and deposition of rust and dust particles can cause local corrosion, which can occur very rapidly.
In double steel, the ferrite and austenite parts are almost equal. This fusion provides metal with better mechanical properties than austenite or ferritic stainless steel. The breaking point elongation of double steel is about 40%. These are typically used in environments where the temperature is below 300 ° C.
The following types of corrosion can appear on stainless steel:
a) Crystal corrosion
This corrosion occurs when chromium carbide is critically released at the particle boundaries. Materials 1.4541, 1.4571, and 1.4435 can be considered resistant to inter crystal corrosion.
b) Pitching corrosion
In the case of this corrosion, the passivation layer breaks only at certain points. The result is one or more pits on the surface. Pitting corrosion is mainly caused by halogen ions, especially chlorine ions.
c) Galvanic corrosion
This corrosion is very common and occurs when metallic materials of different potentials come into contact in the presence of electrolytes. In this case, the metal is attacked by the electrolyte and melts. The degree of corrosion is proportional to the amount of electricity circulating in this galvanic element. This type of corrosion is very common. One of the best-known examples of this corrosion is the joining of steel and stainless steel flanges. This type of corrosion also occurs when bolting cast iron flanges with stainless steel bolts.
d) Cave
This corrosion occurs when the passivation layer of stainless steel is destroyed. For example, due to the presence of corrosive products and lack of oxygen. Therefore, this type of corrosion is common in narrow grooves and small hollow spaces, such as under gaskets and nut heads. The example mentioned here is an example of a gas cap in a fermentation tank. Among them are corrosive products in the form of fermentation gases but are completely deficient in oxygen. In that case, special care is required to avoid the formation of such corrosion.
