There are chemical, electrochemical and mechanical methods to remove the oxide scale from stainless steel. No matter which method is used, it is necessary not only to remove the oxide scale, but also to make the surface clean and smooth. The oxide scale of stainless steel has a variety of oxide structures and different properties. This greatly increases the difficulty of removing the oxide scale on the surface of stainless steel. Generally speaking, for single-phase stainless steel, the above methods have different degrees of effect on removing the oxide scale according to different conditions. For some duplex stainless steels, when the oxide scale is removed by chemical or electrochemical methods, the ferrite phase in the steel will decay, but the surface will be rough and uneven, so mechanical grinding and polishing may be required. In this case, more consideration should be given to economic efficiency, and a more economical mechanical method can be directly adopted.
The oxide scale on the surface of stainless steel has a dense structure and strong bonding with the substrate. It must be removed before subsequent decorative treatments such as passivation, electroplating, and coloring.
(1) Chemical composition of stainless steel oxide scale. LappeenrantaStainless steel contains chromium, nickel, iron, a small amount of carbon and silicon, and may contain elements such as manganese, titanium, molybdenum, and tungsten. In the process of refining, melting, hot rolling, heat treatment, welding, etc., oxide scale will inevitably be produced, and there are various oxide structures in the oxide scale composition.
(2) Complexity and harmfulness of stainless steel oxide scale. The complexity of the stainless steel oxide scale structure destroys the integrity of the oxide scale, including the crystal structure and electronic structure of the oxide film. Incomplete oxide scale not only has no decorative appearance, but also accelerates the electrochemical corrosion of the metal surface. New oxides are formed in the oxide film, and stress will be generated on the metal surface due to the difference in volume. The thermal expansion coefficient of the oxide and the matrix will also generate corresponding stress. The existence of surface stress accelerates stress corrosion on the surface. Therefore, incomplete oxidation and oxide scale formed on the stainless steel surface due to various reasons are harmful and unhelpful. Removing the oxide scale on the stainless steel surface is of great practical significance for the next process, preventing corrosion of the stainless steel surface, keeping the stainless steel surface clean, and extending the service life of stainless steel parts.
