Introduction to various processes of 304 stainless steel pipe

Pickling and passivation process of 304 stainless steel pipe
   Stainless steel pipes are widely used in the processing of military product parts due to their good mechanical properties, high hardness and high wear resistance. The surface treatment of this material is carried out after heat treatment and solid solution aging. Due to the thick oxide scale and Due to the inherent particularity of the material, it is very difficult to perform pickling and passivation processing, so good products are necessary.
   1 Pickling and passivation process
   The surface treatment process of stainless steel pipes is simple. However, in the actual processing process, pickling and passivation processing is quite difficult, mainly focusing on the following two aspects:
   (1) Stainless steel pipe materials cannot remove oxide scale on the surface of parts according to conventional stainless steel rust removal methods. This article introduces the application of stainless steel pickling to remove oxide scale from this material.
   (2) This material passivation processing technology will not corrode the material when it encounters air, and will damage the size and surface finish of the parts. However, during the processing process, strong oxidants such as pickling and passivation are used to form a passivation film on the surface of the parts. , to achieve corrosion resistance. Remove oxide scale after heat treatment: Stainless steel mainly contains elements such as Ti, Cr, Ni, Si, V, Mn, Mo, etc. These elements form thicker and denser oxides during the heat treatment process. Skin, and can be composed of iron, chromium, nickel and oxygen to form a dense oxide film (FeCrO4) with a spinel structure. The chemical properties are also very stable. Therefore, the oxide film is not easy to remove.
   2.304 stainless steel pipe for low temperature solid solution aging parts
   The oxide scale of parts subjected to low-temperature solid solution aging is thinner, generally lavender, and it is relatively easy to treat the oxide scale of such parts. After the parts are pickled according to stainless steel pickling passivation, the oxide scale on the surface has been basically removed. It does not corrode parts, leaves no dust on the surface, and can be directly processed for subsequent passivation.
   2.1.2 For parts subject to high temperature solid solution aging
   The oxide scale of parts subjected to high temperature solid solution aging is thicker, usually black-purple, or even black. Since the surface of the part generates thick, dense and complex oxide scale, it is relatively complicated to pickle and remove the oxide scale of such parts. Removing this type of scale is relatively complicated. The oxide scale should be removed according to the steps of loosening the oxide scale, pickling and removing hanging dust.
   (1) Loose oxide scale:
   (2) Pickling operation:
   After the oxide scale is loosened, a layer of ash is often attached to the surface of the part. After the ash is removed, the oxide scale is passivated.
   (3) The operating procedures for removing hanging dust are as follows:
   The parts pickled by the passivation process of 304 stainless steel pipes have poor corrosion resistance in the air. If exposed to the air, the surface of the parts will rust. In order to enhance the corrosion resistance of the parts, a dense, corrosion-resistant layer is formed on the surface of the parts. A good passivation film is required to achieve corrosion resistance. The quality of the passivation film will directly affect the service life of the parts and the appearance of the product. The factors that affect the quality of the passivation film mainly include the composition of the material and the quality of the passivation solution.