Made of steel alloyed with at least 12% chromium and often nickel, stainless steel is a strong metal that fares well in a wide variety of environments and conditions.
Springs made of stainless steel are preferred in outdoor and water applications as well as in environments where sanitation is necessary. The aerospace, semi-conductor, heat exchanging, medical, food and beverage processing, marine, boat manufacturing, industrial manufacturing and oil industries all use stainless steel springs as components within machinery, equipment and vehicles. They always have a shiny, grey finish and can be fabricated into many different sizes and types of spring, including coil, compression, extension and torsion springs.
Small spring sizes generally have higher tensile strengths, which are similar to hard drawn carbon steel. They are made from cold drawn flat or round wire that have varying degrees of nickel. Springs that exhibit lower nickel content have better formability and flexibility but lower strength than those that have high amounts.
Like all stainless steel parts and products, heat treatment will not strengthen the metal. Instead, cold working, like cold extrusion to fabricate wire, strengthens the steel’s properties. After cold working, a low temperature heat treatment improves the spring properties, some of which are lost during cold working.
Most stainless steel springs are fabricated from austenitic stainless steel, which is unaffected by heat treatment. Grades 302 (18% chromium, 9% nickel), 304 (18% chromium, 8% nickel) and 316 (17% chromium, 12% nickel, 2.5% molybdenum) are used to manufacture springs, all of which offer different properties. They are able to withstand temperatures up to 650ºF, a property that no other spring metal exhibits.
These grades have a small degree of magnetism, a coefficient of thermal expansion 15% less than carbon steel and thermal conductivity only 30% of standard steel. While stainless springs are not likely to oxidize and rust, they sometimes become discolored when the spring wire is stress relieved.
This yellow-brown color only affects the spring’s aesthetics, not the function, life span or mechanical properties. In order to resume and maintain the spring’s appearance, passivation, which is a coating method, is applied. It improves tarnish resistance as well as removes any discoloration.