Pickling and passivation of 304 stainless steel pipe
Stainless steel pipe is widely used in the processing of military product parts because of its good mechanical properties, high hardness and high wear resistance. The surface treatment of the material is performed after the heat treatment and solid solution aging, due to the thick oxide scale caused by the heat treatment process and The inherent special nature of the material makes it very difficult to carry out pickling and passivation processing, and it is necessary to have a good product.
1 pickling passivation process
Stainless steel tube surface treatment processing process is simple. However, in the actual processing, pickling passivation processing is quite difficult, mainly in the following two aspects:
(1) The stainless steel pipe material cannot remove the scale on the surface of the part according to the conventional stainless steel derusting method, and the stainless steel pickling and descaling is applied to this material.
(2) The material passivation process material does not corrode with air and destroy the part size and surface finish. However, during the processing process, the strong oxidant must be acid-passivated to passivate the surface of the component. Membrane, in order to achieve anti-corrosion. Remove heat treated scale: stainless steel mainly Ti, Cr, Ni, Si, V, Mn, Mo and other elements, these elements in the heat treatment process to form a thicker and denser Oxide scale, which can be composed of iron, chromium, nickel and oxygen dense oxide film with spinel structure (FeCrO4), the chemical properties are also very stable. Therefore, it is not easy to remove the oxide film.
2.304 stainless steel pipe for low temperature solid solution aging parts
Low-temperature solid-state aging parts of the thin oxide skin, usually lavender, oxide skin for such parts is relatively easy to handle. Parts according to stainless steel pickling passivation after pickling, the surface oxide scale has been basically removed, And do not corrode parts, parts of the surface without leaving ash, can be directly followed by passivation processing.
2.1.2 Parts for Aging at High Temperature
The parts with high temperature and solidification aging are thicker, usually blackish purple or even black. Because of the thicker, denser and more complex oxide scales on the surface of the parts, it is relatively complicated to remove oxide scales from these parts. The scale should be removed by loosening the oxide scale, pickling and removing ash.
(1) loose oxide scale:
(2) Pickling operation:
After the oxide scale is loosened, the surface of the part is often attached with a layer of ash. After the ash is removed, the oxide scale is passivated.
(3) The operating procedures for removing ash are as follows:
The stainless steel pipe passivation process pickling parts in the air corrosion resistance is poor, such as exposure to the air, the part surface will rust. In order to enhance the corrosion resistance of the parts, the part surface must generate a dense, corrosion resistance Good passivation film, in order to achieve the purpose of anti-corrosion. Passivation film quality will directly affect the service life of parts and product appearance. The factors that affect the quality of passivation film are mainly the composition of the material and the quality of the passivation solution. .