Two Passivation Processes for Stainless Steel Plates
Date:2023-04-03View:383Tags:
The dry passivation process includes normal temperature natural passivation process and high temperature passivation process, among which the normal temperature natural passivation process is suitable for austenitic stainless steel and should be used in a slightly corrosive environment. After degreasing, descaling, and polishing the stainless steel plate, then place the stainless steel plate in clean air and store it for 24 hours. Because the stainless steel plate has self-passivation ability, it has a strong passivation tendency in the air, and the surface A natural passivation film is formed.
The high-temperature passivation process is in a heat treatment furnace, and a passivation film can be obtained by heat treatment. The furnace can also be evacuated, or a protective gas, such as steam, argon, etc., can be introduced to prevent excessive oxidation. Before passivation, the surface of the part must be carefully cleaned to remove any dirt. At higher temperatures, a colorless passivation film can be obtained by changing the temperature and time. When the passivation film exceeds a certain thickness, a colored passivation film layer will be formed.
The stainless steel plate nitric acid passivation process needs to use the corresponding solution, which is composed of different concentrations of nitric acid, which can be applied to the passivation treatment of various stainless steel plates, and is a general-purpose passivation solution.
The characteristics of nitric acid passivation of stainless steel plate are as follows.
The first is that the stainless steel plate will be in a passive state in the nitric acid solution. A very thin passivation film is formed on the surface of the stainless steel plate, which determines that the color of the stainless steel does not change before and after treatment, that is, the reproducibility is good. The stainless steel plate shows no reaction state in the nitric acid solution. The passivation process of stainless steel in nitric acid solution, because it is chemical immersion method, room temperature or medium temperature treatment, it is in a non-reactive state in nitric acid solution, so that the nitric acid passivation solution is relatively stable, does not need to add materials frequently, and is relatively convenient to operate .
Secondly, the stainless steel plate does not need to be sealed after nitric acid passivation. Although the passivation film formed by the passivation of the stainless steel plate in the nitric acid solution is very thin, the film layer is very dense and the pore size is very small, so there is no need to do sealing treatment after passivation, which is not possible after other passivation processes. Less.
The main point of nitric acid passivation process for stainless steel plate is the treatment of stainless steel plate before passivation. Stainless steel plates must be degreased and pickled before passivation. The oil on the surface of the stainless steel plate must be completely removed before it can enter the nitric acid solution. Although the nitric acid in the passivation solution is an oxidizing agent, it has a certain ability to remove oil. There can be slight traces of floating rust on the surface of the stainless steel plate. Because the slight rust on the stainless steel plate is more negative than the stainless steel itself, the rust will not show a passive state and be dissolved in the nitric acid solution.
Neutralization treatment must be done after nitric acid passivation. After the stainless steel plate is passivated in nitric acid, for example, if it is not neutralized, the residual nitric acid adheres to the surface of the stainless steel plate. Although it is washed with water, the corresponding nitric acid content is obviously lower than the process range, but the passivation film of the stainless steel plate will still be destroyed. The damage is even worse than when it is not passivated.
