Stainless steel is an alloy of Iron with a minimum of 10.5% Chromium. Chromium produces a thin layer of oxide on the surface of the steel known as the 'passive layer'. This prevents any further corrosion of the surface. Increasing the amount of Chromium gives an increased resistance to corrosion.
Stainless steel also contains varying amounts of Carbon, Silicon and Manganese. Other elements such as Nickel and Molybdenum may be added to impart other useful properties such as enhanced formability and increased corrosion resistance.
Stainless steel is available in many varieties, though 300 Series or austenitic stainless steel is most commonly used for inserts. The properties of stainless steel vary dramatically from one alloy or family to the next and it is difficult to make general statements regarding performance. For this reason it’s a good idea to consult the application engineers at a reputable insert manufacturer when considering stainless steel or other special materials. Among stainless steel’ s advantages:
• Certain grades, such as 316, are superior to brass in more-aggressive marine environments such as fast-moving currents, but this does not apply to all grades. The most common turning stainless, free-machining 303, contains added sulfur that improves machinability in comparison to other 300 Series stainless steels. Conversely, sulfur significantly decreases corrosion resistance in seawater. Brackish or slow moving seawater may also increase crevice or pitting corrosion in various grades.
• Excellent resistance to petroleum products and many acids, and it can be passivated in either citric or nitric acid solutions. Avoid hydrochloric acids.
• Is typically stronger than brass, though actual comparisons depend on grade and alloy.
• Certain grades of austenitic stainless steel such as 302, 304, and 316 are FDA approved for food contact, and are, therefore, a good choice for food and beverage applications. Free-machining 303 stainless steel is not approved for use in contact with food.
• Austenitic stainless steel provides a higher service temperature than brass. It’s important to note that this offers limited benefit because the heat-deflection temperature of the plastic component is usually the limiting factor. The service temperatures for most plastic assemblies are within the acceptable service temperature for brass.