Stainless steel refers to any stainless steel. For a material to be considered stainless, it must contain at least 10% chromium. There are austenitic and ferritic stainless steel grades. These are found in the 400 and 300 series, respectively. Ferritic steels are magnetic, whereas austenitic steels are not. Their metallurgical microstructures are distinct. Duplex steel’s metallurgical microstructure contains both ferritic and austenitic phases, combining the best qualities of ferritic and austenitic steel grades. Duplex steels are tough and corrosion-resistant. Modern duplex grades are used instead of more expensive, traditional metals. Two main types of duplex steel are standard duplex and super duplex.
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Pickling And Passivation Of Duplex And Stainless Steel
Pickling and passivation procedures improve a material’s corrosion resistance. Pickling involves cleaning the surface of any metal to remove contaminants. Pipes and tubes must be cleaned of inorganic pollutants and stains before being used in sensitive applications such as food grade and chemical applications. The passivation process renders the material’s surface inactive. An acid bath removes the surface of iron and oxides. The passivation process benefits items used in acidic applications and applications with other oxidizing agents. Metals are frequently pickled, machined, and passivated to achieve the best results and a clean surface.
Galvanic Corrosion Between Stainless Steel And Duplex Stainless Steel
Although stainless steel can withstand some corrosion, it is ineffective against highly corrosive substances. High chloride concentrations can be tolerated by austenitic stainless steel grades such as 316, but not acids. When exposed to acids, reducing agents, oxidizing agents, and chlorides, duplex grades are more corrosion resistant. The various duplex grades outperform the majority of austenitic stainless steel in terms of corrosion resistance. Much more flexible materials like Hastelloy are used in highly corrosive applications such as acid production facilities.
Advantages and Disadvantages of Duplex and Stainless Steel
Stainless steels are, without a doubt, less expensive than duplex grades. Stainless steel is widely used and widely available on the market. They were simple to machine, cut, mould, and weld. The market has limited access to duplex steel grades. They must be ordered and specified because they are less common than stainless steel. Duplex steel prices are also higher due to the higher alloying content in the composition. Specific welding techniques, such as preheating to a predetermined temperature before welding and post-weld heat treating, are required for the various duplex steel grades. Despite their higher price, duplex steels are still preferred for applications requiring strength, corrosion resistance, and high-temperature resistance.