|Stainless Steel is a common name for metal alloys that consist of 10.5% or more Chromium (Cr) and more than 50% Iron (Fe). Although it is called "Stainless", a better term for it is "highly stain resistant". A somewhat dark metal, it looks bright because it reflects light. Stainless Steel differs from Carbon Steel by the amount of Chromium present. Carbon Steel rusts when exposed to air and moisture. This Iron Oxide film (the rust) is active and accelerates corrosion by forming more Iron Oxide. Stainless Steels contain sufficient Chromium to form a passive film of Chromium Oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure.
It is important to know that there are different grades, different types, and also different finishes of Stainless Steel. Pemko's Stainless Steel products such as thresholds, gasket retainers, and Hinge fasteners, are made from type 304 Stainless Steel, which is part of the Austenitic Grade. The Austenitic Stainless Steels, because of their high Chromium and Nickel content, are the most corrosion resistant of the Stainless Steel Grades. Type 304 (also known as 18-8 Stainless Steel) contains approximately 18% chromium and 8% nickel. It is commonly used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchangers, and for a great number of chemicals applications. Stainless steel finishes range from a #1, a somewhat dull finish, to a #8, a highly reflective mirror finish. Pemko's Stainless Steel products have a #4 brush finish. It is the easiest finish to maintain. It is not highly reflective, but it is a good general purpose finish for products that may have fairly rough handling in service (eg restaurant equipment, door thresholds, etc).
General use Stainless Steel Fasteners are made from type 410 Stainless Steel. Type 410 is a basic Martensitic Grade Stainless Steel. Martenstic Stainless Steels like most non-Stainless Steels can be hardened by a "quench-and-temper" heat treatment. It contains a minimum of 11.5% Chromium, just sufficient to give corrosion resistance properties. It achieves maximum corrosion resistance when it has been hardened and tempered. Type 410 Stainless Steel is commonly used in screws, nuts, and bolts.