AMS5678 (17/7PH) / ASTM A313 Type 631 is by far the most commonly used material for most of the ‘new’ springs we see. AMS5678 is a precipitation hardenable stainless steel which performs nearly as well as some high carbon steels in terms of strength and fatigue but has the added advantage of being a stainless.
One possible area of concern with this material in the most demanding applications is its surface finish and we would recommend in some of these cases that the springs are vapour blasted or shot peened to reduce the risk of crack propagation. We always however recommend that this material is Dye Penetrant Flaw Detected to a standard such as ASTM E1444.
BS 2S205 is another commonly used aerospace stainless grade which is still very much in use. S205 (as it is more commonly known) is a standard 18/8 stainless and although not having quite the same strength or fatigue performance as a 17/7 ph Steel is cheaper to both procure and process. Where your application does not demand extreme performance this is a good material to specify.
There is a commercial version 18/8 stainless called X10CrNi18/8 (302S26) however this material cannot normally be bought with a polished finish and the Tensile strength is lower than S205 giving reduced performance, we would not advise using this as an alternative to S205 without thoroughly checking the designs cycle life prior to use.
