The term “Stainless Steel” came about 50 years ago when it was discovered that a minimum of 12% chromium would impart corrosion resistance and it came to define ferrous alloys. It is important to note that there are sub-categories of stainless steel plates and the appropriate grade should be selected for a particular application. Stainless steel is a common specification where corrosion or oxidation are a problem, it reduces maintenance requirements and the life expectancy is lengthy. The sub-categories and their applications are stated below.
Ferritic – Contains 11-17% chromium and has the lowest corrosion resistance, which is better than painted or galvanized steel. Commonly used for decorative trim, sinks, and automotive applications, but can also be used as a substitute for galvanized steel in some applications.
Martensitic – This class is similar to ferritic stainless steels, except it has a higher carbon content. They are straight chromium steels containing no nickel. They can be hardened with heat treatment and are most often used where hardness, strength, and wear resistance are required.
Austenitic – The most widely used of the stainless steels. Over 85% of the world’s stainless steel production is either 304 or 316. Austenitic grades have similar strength to mild steel with lower thermal conductivity and higher thermal expansion coefficients.
- 304 – Contains 18% chromium, 8% nickel. Often used for chemical processing equipment, for food and beverage industries, for heat exchangers, and for the milder chemicals.
- 316 – Contains 16-18% chromium, 11-14% nickel, and about 2% molybdenum. This type is used in chemical processing, the pulp and paper industry, for food and beverage processing and dispensing and in the more corrosive environments.
Duplex – The newest member of the stainless steel family. As the name implies, this material is a combination of austenitic and ferritic material. It promotes high strength and resistance to stress corrosion cracking. Used in demanding applications, available on order from mills.
The ferritic, martenistic, and duplex grades are magnetic while the austenitic grades are not. When deciding to purchase stainless steel plates it is necessary to take the project conditions into consideration. While a specific grade may be suitable for one project, it may be a disaster if specified in a different area.