People are surprised when brown spots appear on the surface of 304 stainless steel. They believe that 304 stainless steel does not rust, and rust is caused by substandard quality. In fact, this is a misunderstanding of the lack of understanding of stainless steel 304. Stainless steel 304 can rust under certain conditions.
1. Fluoride ions exist in the use environment, such as salt, seawater, sea breeze and soil. Stainless steel corrodes rapidly in the presence of fluoride ions, even more than ordinary low carbon steel. That said, stainless steel 304 is basically immune to corrosion and rust, but it will still rust if it comes in contact with a lot of fluoride ions. In general, the corrosion rate of articles in a sealed condition is higher than that in an open environment. If the item is spliced with sheet, the corrosion rate will be greater at the splices than elsewhere. Therefore, if the device is in an environment rich in fluoride ions, the best approach is to replace the device's material.
2. After the 304 stainless steel plate and tube without solution treatment are drawn and bent, the surface passivation film and the crystal structure in the tube are destroyed; if there is no pickling protection, it will be oxidized and rusted.
Third, the intergranular corrosion does not contain titanium and niobium material has a natural intergranular corrosion tendency, the material is stable after adding titanium and niobium, which can reduce intergranular corrosion.