Grain Sizes of Spring Materials

Material Grain Size

Standard grain sizes in spring materials are acceptable for most spring applications. Sometimes however, the additional investments of smaller grain size spring materials are beneficial.

Grain sizes are measure in grains per square inch of spring material. The numbers of grains for a specific spring material are designated by an ASTM number. Grains in material are counted by microscope under 100X. The numbers of grains in a material are determined by several variables including alloy content, cooling rate and mechanical vibration.

Benefits of using fine grain in spring material include increased yield strength as grain size decreases. Increased fracture toughness and resistance to crack growth also typically increase as grain size decreases. Reduced grain size or fine grain may increase the fatigue life of a spring, because microscopic cracks have more grain lines to pass through with finer-grained spring materials.

"Investing in Grain Size", Spring Manufacturers Institute, January 2005, Volume 44 Number 1, Pages 49-50.