Characterization of damage-induced magnetization for 304 austenitic stainless steel

Experimental and analytical studies are carried out on features of damages-induced magnetization (natural magnetization) of the 304 austenitic stainless steel. Various tensile plastic deformations are introduced into test pieces with different initial discontinuities. The surface strain distributions and natural magnetic fields are measured during and after the tensile testings. The magnetization distributions inside the material are reconstructed from the measured natural magnetic field signals through inverse analysis. From the experimental and numerical results, it is clarified that at first, the magnetization direction of the material depends on the load direction and damage distribution and the distribution pattern of magnetization reflects the existence of concentrative damages. Second, the relationship between the intensity of damage-induced magnetization and the maximum plastic strain follows a simple formula proposed in this paper. Third, the magnetization intensity is correlated with the volume fraction of the martensitic phase. Finally, the theory of minimum energy is applicable to qualitatively explain the mechanism of the damage-induced magnetization for the 304 austenitic stainless steel. (C) 2011 American Institute of Physics. [doi:10.1063/1.3667288]