Stainless steel sheet suppliers offer many grades of stainless steel for consumers to choose from. The choices can be overwhelming to the uninitiated. However, knowing what grade to use will ultimately be determined by the environment in which the stainless steel will be used. In other words, the degree of corrosion resistance needed by the consumer depends on the industry and application. Will it be an indoor or outdoor environment? Will it be used in a bathroom, a kitchen, for architectural paneling, or automotive parts? Herein is a concise guide to assist our customers in choosing the right size, grade, and finish of stainless steel for any job.
Let’s consider first that stainless steel sheet metal is formed by an industrial process into thin, flat pieces, which can be cut and formed into a variety of shapes. Many everyday objects around us are fabricated from stainless sheet metal. The thicknesses of the sheets vary up to 6mm (0.25 inches). Any thickness higher is classified as plate and is used for other industrial or commercial purposes.
The grades are determined by a chemical formula. Of all the stainless steel alloys, the 300 series grade is the most commonly used, with the 304 alloy austenitic steel being the most prevalent type. Its versatility and strength make it the most widely used, and it is available in more forms and finishes than any other grade of stainless steel. Approximately 70% of all stainless steel made is austenitic, a nonmagnetic, solid solution of mostly iron and carbon, which relates to its primary crystalline structure.
The 300 series grade is the most corrosion-resistant, most ductile, and can be easily formed and welded. The 304-grade stainless steel is the ideal grade to use not only because of its incredible welding characteristics but also because of its balanced austenitic structure. It’s widely used in many industrial, architectural, and transportation-related applications.
The level of corrosion resistance, or what makes stainless steel stainless, is related to the amount of carbon and chromium used in the finished alloy. The corrosion resistance of the many grades of stainless steel stems from alloying the base iron with at least 10.5% chromium and a maximum of 0.15% carbon. The chromium provides a passive film of chromium oxide that rises to the surface, coats the steel, and blocks corrosion from spreading into the metal’s internal structure. Therefore, increasing the amount of chromium gives an increased resistance to corrosion.
In addition to the many grades of stainless steel, the sheets come in a variety of finishes depending on the application that stainless steel is used for. The finishes are numbered or alpha-coded: 1, 2B, 2D, 2BA (Bright Annealed), 3, 4, 6, 7, 8, and TR (Temper Rolled).
The #4 “Brushed” finish is the most common. Easily recognizable, you’ll find this finish on nearly all stainless steel appliances. The brushed look has a bright finish and is characterized by short, uniform, parallel polished lines, with a visible directional “grain.” It is designed for daily use and to hide scuff marks, fingerprints, scratches, etc.
The #8 mirror-like finish has the most reflective, highly polished surface of any stainless steel. The finish is achieved by polishing with successively finer abrasives and then buffing extensively until all grit lines from preliminary grinding operations are removed.
Finally, stainless steel sheet is typically sold in the annealed condition. This means that when stainless steel is annealed, it is heated to a temperature below its melting point and then cooled slowly to make it less brittle and more malleable. This process brings the sheets to the desired consistency, texture, or hardness.
