Stainless steel is an important metal alloy, finding uses in thousands of applications in building construction and renovation, as well as in industry and domestic applications. The metal is prized for its ability to resist corrosion and admired for its beautiful yet sturdy appearance. Since stainless steel is an alloy created by mixing several different types of materials, its characteristics and appearance can be manipulated.
The stainless steel types are identified in the United States through the use of a 3-digit numbering system, dependent upon their internal crystalline structure type. The sections below will describe the most common types of stainless steel currently used in the building industry.
300 series steels are austenitic, which means that they are a solid solution of iron containing face-centered cubic crystals. The greatest contributor to alloy in austenitic stainless steels is chromium and nickel. These steels are easy to maintain, can withstand high temperatures and are very corrosion resistant. The 300 series stainless steels most commonly used in the construction industry are described below.
301 Stainless Steel
This type of stainless steel is often used in decorative interior and exterior applications due to a shiny surface and resistance to atmospheric corrosion. 301 steel is also extremely strong in tension yet remains readily workable at room temperature.
This steel, along with the other 300 series steels, has a variant with an added “L” in the name (for example, 301L). The “L” represents a low carbon content, which provides increased workability and increased corrosion resistance at weld locations when joining two or more stainless steel pieces together.
304 Stainless Steel
304 stainless steel is the most commonly used type of stainless steel alloy, is easily available and is found in a wide range of applications. This type of steel comprises over 50% of the stainless steel produced worldwide, and is sometimes known as “18-8” steel due to its 18% chromium, 8% nickel content. 304 stainless steel lends itself to easy shaping due to its balanced chemical structure, is highly resistant to corrosion and easy to weld.
304H stainless steel with an increase carbon content is also available -- this variant is suitable for applications in environments with elevated temperatures.
316 Stainless Steel
316 stainless steel contains a percentage of the element molybdenum (around 2-3%), which provides greater resistance to corrosion than 304 stainless steel. This type of steel is commonly used in applications where the metal will be exposed to corrosive environments (such as acidic vapors) or in situations where the steel would be exposed to saltwater. 316 steel is also known as “surgical stainless” and finds extensive use in the medical and food industry. Due to its increased corrosion resistance, 316 finds many uses in cold-weather climates where deicing salts are used to clear streets and sidewalks. The steel is highly resistant to the chemicals used in deicing and requires minimal polishing to retain its exterior finish.
317 Stainless Steel
Type 317 steel is not commonly used in the construction industry, but can be the best fit for projects and situations where the environment requires a stainless steel with even higher corrosion resistance than type 316. This increased potential for corrosion may stem from industrial pollution, excessive salt exposure, climates that are hot and humid with low rainfall, and for steel containing a high surface roughness. Type 317 steel contains molybdenum in a range of 3-4%.
To achieve even greater levels of corrosion resistance than 317L steel, there is another variant entitled “317 LMN”, which contains increased quantities of molybdenum and nitrogen in the alloy.
400 series steels contains ferritic (body-centered cubic crystal) and martensitic (lens-shaped crystal) steels. These steels contain approximately 11% more chromium than the 300 series, providing high strength and wear resistance but a greater susceptibility to corrosion than 300 steels. The most commonly used 400 series steel in the construction industry is 430.
430 Stainless Steel
430 stainless steel is ferritic and is often used in decorative applications , as it is relatively easy to form and the surface lends itself to easy cleaning and polishing. The steel has a magnetic field and is best suited to interior environments where it will not be subjected to a corrosive atmosphere.
904L Stainless Steel
Though typically confined to industrial applications, 904L stainless steel can be used in cases where extreme corrosion resistance is required, over and above that of 317 LMN stainless. 904L contains copper, which is what allows the metal to be more acid tolerant than other stainless steels. In addition, this steel is easier to weld than other low-carbon stainless steels, as it has a lower tendency to form precipitates during the welding process.