What are the best materials for fatigue applications?

Since spring wire is primarily subjected to torsional stresses, maximum stress levels occur at the wire surface. As a result, material surface defects (i.e. seams, laps, pits, etc.) can dramatically reduce a spring’s fatigue life. Knowing this, wire manufacturers have developed surface preparation methods to restrict the size of wire surface defects as it leaves the mill. Wire produced with these methods is rated for fatigue applications and is often referred to as “valve spring quality”. Since these methods often involve costly processes, fatigue-rated spring wire is often significantly more expensive than its commercial-grade counterpart.

The two most popular materials for fatigue applications today are Music Wire (ASTM A228) and Chrome-Silicon Wire (ASTM A401). At wire sizes below approximately 0.080" (2.0 mm), Music Wire offers higher tensile strength; however, Music Wire’s maximum service temperature is less than that of Chrome-Silicon.