Stainless steel castings are an important type of metal product with broad application prospects and market demand. With the continuous development and progress of industrial technology, stainless steel castings will be better applied and developed in the future. Stainless steel castings have many advantages, such as sturdy and durable material, high temperature and corrosion resistance, smooth and clean surface, etc. They are widely used in fields such as automobiles, ships, engineering machinery, petrochemicals, and food processing, playing an important role.

During the production process, stainless steel castings need to undergo cleaning, slag removal, heat treatment, and surface treatment to further improve the quality and performance of the castings. Cleaning and slag removal is the process of removing oxides and impurities from the surface of castings, making them smoother and more uniform. Heat treatment is the process of improving the microstructure, wear resistance, and strength of castings by controlling their temperature and time. Surface treatment is to apply a protective coating or polish the surface of the casting to increase its aesthetics and corrosion resistance.

What are the characteristics of corrosion behavior of stainless steel castings in different media?

atmospheric environment 

General atmosphere: In a normal dry atmospheric environment, a thin and dense passivation film will naturally form on the surface of stainless steel castings. This passivation film can effectively isolate the metal from oxygen, moisture, etc. in the air, making it have good corrosion resistance. Usually, only slight oxidation occurs, and the surface color may gradually darken, but there is basically no obvious corrosion phenomenon.

Ocean atmosphere: The ocean atmosphere contains a large amount of salt, especially chloride ions, which have strong corrosiveness. Stainless steel castings in marine atmosphere will adsorb chloride ions on their surface and damage the passivation film, leading to localized corrosion such as pitting and crevice corrosion. Pitting corrosion is manifested as scattered small holes appearing on the surface of the casting, which may gradually deepen and expand over time; Gap corrosion often occurs in the gaps of castings, bolt connections, etc. Due to the accumulation of salt and water in these areas, a localized corrosion environment is formed, accelerating the corrosion process.

Industrial atmosphere: Industrial atmosphere usually contains corrosive gases such as sulfur dioxide, hydrogen sulfide, carbon dioxide, as well as pollutants such as dust. These substances will combine with moisture in the air to form acidic solutions, adhere to the surface of stainless steel castings, and corrode the passivation film. Stainless steel castings that are exposed to industrial atmospheric environments for a long time may experience comprehensive or localized corrosion, depending on factors such as pollutant concentration and humidity. The degree of corrosion is generally more severe than in ordinary atmospheric environments, and rust spots, corrosion pits, etc. may appear on the surface.

water environment

Freshwater: Stainless steel castings have good corrosion resistance in general freshwater. The passivation film on its surface can resist the erosion of fresh water to a certain extent, but if the water contains high concentrations of dissolved oxygen, trace amounts of chloride ions or other impurity ions, it may also cause local corrosion, especially in areas with defects or stress concentration on the casting surface. However, overall, its corrosion rate is relatively slow and its service life is long.

Seawater: Seawater is a complex and highly corrosive medium, containing a large amount of salt, with a high content of chloride ions. Stainless steel castings are prone to severe localized corrosion in seawater, such as pitting corrosion, crevice corrosion, and stress corrosion cracking. Chloride ions can damage the passivation film on the surface of stainless steel, exposing the metal substrate to seawater and causing corrosion reactions. In addition, factors such as the flow of seawater, temperature changes, and the attachment of marine organisms can also affect the corrosion behavior of stainless steel castings. For example, the attachment of marine organisms can create a local hypoxic environment, accelerating the occurrence of corrosion.

Acidic aqueous solution: When stainless steel castings come into contact with acidic aqueous solution, their corrosion resistance will be greatly affected. Different acids have different corrosiveness to stainless steel. For example, strong acids such as hydrochloric acid and sulfuric acid have stronger corrosiveness to stainless steel, quickly dissolving the passivation film on the surface of stainless steel and reacting chemically with the metal substrate, leading to rapid corrosion of castings. Some weak acids, such as carbonic acid and acetic acid, have relatively weak corrosiveness to stainless steel at lower concentrations, but the corrosion rate increases significantly with increasing acid concentration and temperature. In acidic aqueous solutions, stainless steel castings may experience various forms of corrosion such as overall corrosion and intergranular corrosion.

Alkaline aqueous solution: Generally, stainless steel castings have better corrosion resistance in alkaline aqueous solutions. Alkaline environment helps stabilize the passivation film on the surface of stainless steel, making it less susceptible to damage. However, if alkaline solutions contain high concentrations of chloride ions or other strong oxidants, it may also cause localized corrosion. In addition, stainless steel castings may experience stress corrosion cracking and other phenomena in high temperature and high concentration strong alkaline solutions, especially in the presence of residual stress.

Chemical media

Oxidative acid: For oxidizing acids like nitric acid, stainless steel castings have good corrosion resistance within a certain concentration and temperature range. Nitric acid can form a more stable passivation film on the surface of stainless steel, thereby preventing further corrosion reactions. But if the concentration of nitric acid is too high or the temperature is too high, exceeding the passivation ability range of stainless steel, it can also lead to intensified corrosion, which may cause over passivation corrosion and damage such as corrosion pits on the surface of castings.

Reductive acid: Stainless steel castings have poor corrosion resistance in reducing acids such as hydrofluoric acid, hydrochloric acid, and other media. These acids can quickly destroy the passivation film on the surface of stainless steel and undergo strong chemical reactions with the metal substrate, leading to rapid corrosion. Therefore, in the case of contact with reducing acids, it is usually necessary to use special stainless steel materials that are more corrosion-resistant or take effective protective measures such as lining, coating, etc.

Salt solution: Different types of salt solutions have significant differences in corrosiveness to stainless steel castings. Some neutral salt solutions, such as sodium chloride solution, are mainly corrosive to stainless steel due to the chloride ions in them, which can cause localized corrosion phenomena such as pitting corrosion and crevice corrosion. For some salt solutions containing oxidizing anions, such as chromate and nitrate, under certain conditions, it may enhance the passivation film on the surface of stainless steel and improve its corrosion resistance. But if multiple ions are present in the salt solution at the same time, its corrosion behavior will become more complex, and the interaction of various ions needs to be comprehensively considered.

Stainless steel castings refer to components made from stainless steel as raw material in the casting process. Stainless steel castings have excellent corrosion resistance, wear resistance, oxidation resistance, and aesthetics, and are widely used in fields such as mechanical manufacturing, aerospace, automotive manufacturing, and petrochemicals.

The production process of stainless steel castings includes two main steps: casting and processing. Firstly, the casting process involves injecting melted stainless steel into a mold, which is then cooled and solidified to form a molded casting. Next is the machining process, which involves cutting, grinding, polishing, and other methods to process the castings to achieve specific dimensions and surface requirements.