Why does the material of stainless steel 304 still rust?
When the surface of stainless steel 304 comes out with brown spots, people are surprised, thinking that stainless steel 304 does not rust, and the rust is caused by unqualified quality. In fact, this is a wrong view of lack of understanding of stainless steel 304. Stainless steel 304 will also rust under certain conditions.
1. There are fluoride ions in the use environment
Fluoride ions exist widely, such as salt, seawater, sea breeze, soil, etc. In the presence of fluoride ions, stainless steel corrodes rapidly, even more than ordinary low carbon steel.
That is to say, stainless steel 304 will basically not corrode and rust, but if it encounters a large amount of fluoride ions, it will still rust, and in general, the corrosion rate of items in a sealed condition is greater than that in an open environment. If the item is spliced from plates, the corrosion rate at the splicing will be greater than the corrosion rate at the rest.
So if the equipment is in a fluoride ion-rich environment, it is a good idea to change the material of the equipment.
2. No solution treatment
After the stainless steel 304 pipe has been processed by wire drawing, pipe bending, etc., the surface passivation film and the internal crystal structure of the pipe have been destroyed; if it has not been protected by pickling and other protection treatments, it will also be oxidized and rusted.
3. Intergranular corrosion
Materials without titanium and niobium have an inherent tendency to intergranular corrosion. Adding titanium and niobium to the material, together with stabilization treatment, can reduce intergranular corrosion.
The above are some of the factors that cause stainless steel 304 to rust, so you need to pay attention to the following points when using stainless steel 304 pipe:
1. Try to prevent the appearance from being scratched
2. Keep the pipes clean
3. Avoid long-term exposure of the pipe to an environment containing acid and salt.
There are three main factors that affect stainless steel corrosion:
1. The content of alloying elements.
Generally speaking, the content of chromium is 10.5%, and the steel is not easy to rust. The higher the content of chromium and nickel, the better the corrosion resistance. For example, the content of nickel in 304 material is 8-10%, and the content of chromium is 18-20%. Such stainless steel will not rust under normal circumstances.
2. The smelting process of the manufacturer will also affect the corrosion resistance of stainless steel.
A large stainless steel plant with good smelting technology, advanced equipment and advanced technology can ensure the control of alloying elements, the removal of impurities, and the control of the cooling temperature of the billet, so the product quality is stable and reliable, the internal quality is good, and it is not easy to rust. On the contrary, some small steel mills have backward equipment and backward technology. During the smelting process, impurities cannot be removed, and the products produced will inevitably rust.
3. The external environment, the climate is dry and ventilated, and the environment is not easy to rust.
The air humidity is high, continuous rainy weather, or environmental areas with high pH in the air are prone to rust. 304 stainless steel, if the surrounding environment is too bad, it will rust.