A correlation study between magnetic Barkhausen noise and intergranular residual stresses in steels

Stress has long been known to influence the magnetic properties of materials. Residual stresses, created by non-uniform plastic deformation, also affect the magnetic behaviour. On a microscopic level, the "intergranular" residual stresses were found to accumulate along the <100> crystallographic directions in steels. This result is particularly interesting from the magnetic point of view since <100> is the magnetic easy axis for steels. The goal of this thesis is to examine the relationship between intergranular residual stresses and magnetic behaviour and specifically to determine if the magnetic easy axis correlates with the {lcub}100{rcub} residual intergranular stresses.; Several mild and interstitial free steel samples were uniaxially deformed in the strain range of 0.5%-25% followed by unloading. The Magnetic Barkhausen Noise (MBN) technique was used to characterize magnetic behaviour induced by deformation. Neutron diffraction was used to measure directly the residual strains for the {lcub}200{rcub}, {lcub}211{rcub} and {lcub}220{rcub} crystallographic planes. The obtained residual strain data were compared against the predictions of residual strain from the Elasto-Plastic Self-Consistent (EPSC) theoretical model and good agreement was found at low strains.; A direct correlation between the magnetic easy axis and {lcub}200{rcub} intergranular residual stresses was found. The deformed mild steel samples exhibited Luders bands. In these bands, the {lcub}200{rcub} intergranular strain was very high and produced a corresponding magnetic easy axis. This thesis represents the first systematic study of residual strain in Luders bands.; Magnetic behaviour is also sensitive to the crystallographic texture in a material. Texture developed with deformation and this work is also the first study to present texture results in the Luders bands. The deformation texture was found to contribute to the magnetic easy axis in mild steel samples.; The relief of intergranular residual strain and the corresponding change in magnetic behaviour with annealing were also studied. Samples were annealed at temperatures up to 600°C to achieve residual stress relieving without recrystallization.; An analytical model based on {lcub}200{rcub} intergranular residual stresses, texture and annealing results was proposed to simulate the magnetic easy axis. The simulated and experimental results agreed very well for interstitial free samples and for low-deformation mild steel samples.