A CORRELATION STUDY BETWEEN INTERGRANULAR STRAINS AND MAGNETIC PROPERTIES OF MILD STEEL

Abstract: Residual stresses appear due to non-uniform plastic deformation that occurs, for example, during the manufacture of engineering materials. The importance of a complete understanding of the residual stress mechanisms is vital since they add to the external applied stresses leading to unexpected failures. The microscopic residual stresses are caused by the complex grain-grain interaction in a deformed polycrystalline material. These residual stresses, which are named intergranular residual stresses (IS) were found, using neutron diffraction, to be large along the <100> crystallographic directions [1-4]. Interestingly, <100> is the magnetic easy axis in steels as determined by the Magnetic Barkhausen Noise (MBN) method. Our work focuses on finding the correlation between the IS and magnetic behaviour of steels based on MBN, neutron diffraction and stress relief experimental data. Several mild steel samples were deformed at different plastic deformation levels then unloaded. We have found that the magnetic easy axis detected in these samples is strongly related to the <100> IS. Introduction: Residual stresses are present in a material after the plastic deformation of this material followed by unloading. In the presence of residual stresses, materials will yield plastically at a lower applied stress then a specimen free of residual stresses and thus, the resistance to fracture will be affected. There are mainly two types of residual stresses: Type 1 stresses which are the macroscopic residual stresses appearing on the length scale of the sample and the recently recognized Type 2 intergranular residual stresses (IS) which develop on the scale of th