Stainless steel is known for its ability to resist rust and corrosion. Not all stainless steels are identical; they are categorized into different “grades,” each with distinct characteristics. These grades are differentiated by their elemental composition, which influences their properties and suitability for specific applications. This article explains the differences between two common grades: 18-8 and 316 stainless steel.
Deciphering Stainless Steel Grades
The numerical designations for stainless steel grades, such as 18-8 and 316, relate to their chemical makeup. 18-8 stainless steel contains approximately 18% chromium and 8% nickel. This grade is also commonly referred to as Type 304 stainless steel, classifying it within the austenitic family. Chromium plays a primary role in corrosion resistance by forming a passive oxide layer on the surface, while nickel contributes to the material’s ductility, strength, and additional resistance to corrosion.
316 stainless steel shares a comparable chromium and nickel content with 18-8. The distinguishing feature of 316 is the inclusion of about 2% to 3% molybdenum in its alloy. This addition of molybdenum significantly enhances the material’s resistance to corrosion, particularly against chlorides and other aggressive chemicals.
Performance Distinctions
The differing chemical compositions, especially the presence of molybdenum in 316 stainless steel, lead to variations in performance. 316 stainless steel offers enhanced corrosion resistance, particularly in harsh environments such as those containing saltwater, acidic conditions, or chlorides. This makes it a suitable choice for applications where exposure to these aggressive elements is common. In contrast, 18-8 stainless steel performs well in general atmospheric conditions and freshwater exposure but exhibits less resilience when confronted with highly corrosive chemicals or marine environments.
Both grades demonstrate good formability and weldability. 316 stainless steel exhibits better strength at elevated temperatures compared to 18-8. While both are easy to work with for various manufacturing processes, 18-8 stainless steel is sometimes easier to form and weld in certain applications.
Common Applications
The performance characteristics of each stainless steel grade dictate their suitable applications. 18-8 stainless steel is widely used in everyday items and less corrosive settings due to its balanced properties and cost-effectiveness. Common applications include kitchen sinks, cookware, and food processing equipment. It is also found in architectural trim, certain automotive components, and indoor handrails where superior resistance to harsh chemicals is not a primary concern.
316 stainless steel’s enhanced corrosion resistance makes it suitable for demanding environments. It is frequently chosen for marine applications, such as boat fittings and railings, where exposure to saltwater is constant. This grade is also prevalent in chemical processing equipment, medical implants, and pharmaceutical manufacturing apparatus, as well as outdoor electrical enclosures, where its robustness against corrosive agents is important.
Making the Right Choice
Selecting between 18-8 and 316 stainless steel involves considering the specific demands of the intended application. A primary factor is the environment in which the material will operate; if it involves corrosive elements like saltwater or strong chemicals, 316 stainless steel is generally the more appropriate choice due to its molybdenum content. For less aggressive conditions, 18-8 stainless steel offers sufficient performance.
Cost is another important consideration, as 316 stainless steel is typically more expensive than 18-8 due to the inclusion of molybdenum and other alloying elements. It is generally advisable to avoid over-specifying a material if a less costly option, such as 18-8, can adequately meet the application’s requirements. The most suitable choice hinges on balancing the specific needs for corrosion resistance, strength, and budget constraints.