The tensile strength of spring steel may be found as:

`S_"ut" = A/d^m`, where A and m are uniquely defined for American National Standards Institute (ASTM) materials (see Notes Page):

    A232 - Chrome Vanadium
     A401 - Chrome Silicone

The allowable stress `sigma` then for a spring of hardened and tempered carbon and low-alloy steel is then given by this equation as:
 `S_y = sigma = 0.87 S_ut`

Notes