Effect of Stress on the Law of Approach to Saturation Magnetization in Carbon Steels

In high fields, standard theoretical treatment leads to formulas I = I_s - b/H² – c/H³ • •• or μ_rev = 1 + (2b/H³ + 3c/H⁴ + • ••)/u₀, which are referred to as the law of approach to saturation magnetization. Following the calculation by Becker and Döring, the coefficient b for a cubic crystal has been deduced as b = 0.0762/I_s[K + 1.5(λ.₁₀₀ – λ₁₁₁)σ]², where a is the applied stress and others are magnetic constants. The values of reversible permeability μ_rev under biasing field H were measured for carbon steels with applied stresses. The results showed that the square root of 2b changed linearly with the applied stress as the theory predicted. The values of magnetic constants K and λ₁₀₀ – λ₁₁₁ were calculated on the basis of the theoretical formulas. They agreed with the standard values, but they were affected by chemical composition and heat treatment of materials, especially in λ₁₀₀ – λ₁₁₁.