Why does stainless steel cartridge heater rust?
Stainless steel cartridge heater will not rust under normal circumstances, but when exposed to chlorine or harsh environments, especially after the passivation layer on the surface is mechanically or chemically damaged, the cartridge heater will rust more easily than usual in this environment. The surface of the stainless steel products we usually use is passivated. The thickness of the chromium oxide film on the surface is much thicker and denser than the natural oxide film formed on the fresh surface. Therefore, the stainless steel cartridge heater will rust.
Let us introduce to you some stainless steel materials:
All metals in life will oxidize with oxygen in the atmosphere, forming an oxide film on the surface. However, the iron oxide formed on ordinary carbon steel will continue to oxidize, causing the corrosion to continue to expand and eventually forming holes. Paint or oxidation-resistant metals (such as zinc, nickel, and chromium) can be used for electroplating to protect the surface of carbon steel, but, as people know, this protection is only a thin film. If the protective layer is destroyed, the steel below will begin to corrode. Chromium is the basic element for the corrosion resistance of stainless steel. When the chromium content in the steel reaches about 12%, the chromium interacts with the oxygen in the corrosive medium to form a surface on the steel surface. A very thin oxide film (self-passivation film) can prevent further corrosion of the steel matrix. In addition to chromium, commonly used alloying elements include nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the requirements of various uses for the structure and performance of stainless steel.
The corrosion resistance of stainless steel decreases with the increase of carbon content. Therefore, the carbon content of most stainless steels is low, and the carbon content of some steels is even lower than 0.03% (such as 00Cr12). The main alloying element in stainless steel is chromium. When the chromium content reaches a certain amount, the stainless steel will have corrosion resistance. Therefore, stainless steel generally contains more than 13% chromium. Stainless steel also contains elements such as Ni, Ti, Mn, N, and Nb.
The above are the reasons why the stainless steel cartridge heater will rust.