Official Answer
Answer
In MRI and sensitive aerospace electronics, materials with low magnetic permeability $\mu < 1.01$ are required to prevent field distortion. Standard carbon steels and 400-series stainless steels are ferromagnetic and unsuitable. 302/304 stainless steels are paramagnetic in the annealed state but can become slightly magnetic when cold-worked into springs. For strictly non-magnetic applications, Phosphor Bronze (ASTM B159) or Monel K-500 (UNS N05500) are used. Phosphor Bronze offers excellent conductivity but lower strength, while Monel K-500 provides high strength and excellent corrosion resistance while remaining non-magnetic even after heavy cold reduction.
