Full definition
Stainless steel is a versatile iron-based alloy that contains at least 10.5% chromium (Cr), which enables the formation of a passive oxide layer on its surface. This layer provides exceptional corrosion resistance compared to carbon steel, making stainless steel a preferred choice in various industrial applications. The alloy's composition can be adjusted to achieve specific properties, such as improved strength, corrosion resistance, or machinability. The most commonly used grades include 304 and 316, which cater to different environments and requirements. Grade 304, known for its general-purpose usability, contains approximately 18% chromium and 8% nickel, making it suitable for food processing and chemical vessels. Grade 316, with its higher molybdenum content (2%), offers superior resistance to chlorides and acids, making it ideal for marine and chemical applications.
Additionally, there are specialized grades such as 316L, which has a lower carbon content allowing for better weldability without the risk of sensitization, and 420, which is a hardenable martensitic stainless steel used for cutlery and tools. The duplex stainless steel 2205 combines the benefits of austenitic and ferritic structures, providing high strength and excellent corrosion resistance, particularly useful in pipelines and pressure vessels. The yield strengths of stainless steels can vary significantly, ranging from 205 MPa for annealed 304 to over 450 MPa for duplex grades.
The use of stainless steel spans diverse industries, including food processing, pharmaceuticals, chemicals, marine environments, medical devices, and architecture. In all these applications, the corrosion resistance and mechanical properties of stainless steel are critical for ensuring product longevity and reliability. Proper surface treatment, such as passivation, is recommended as per ASTM A967 after fabrication to enhance corrosion resistance by removing free iron and promoting the formation of the protective oxide layer.