Effect of inclusion orientation upon acoustic emission-microstructural relationships in ferritic steels

A comparison of the acoustic emission, mechanical properties and fracture behaviour of three model low-alloy steels containing manganese sulphide inclusions of varying orientation has been made as a function of tempering conditions. The majority of the inclusions existed in elliptical clusters whose major axis was aligned with the rolling direction and whose plane lay on the rolling plane. Both the yield region acoustic emission activity and ductility in the through-thickness (short transverse) sample orientation were reduced compared with the longitudinal, and to a lesser extent, transverse orientation samples. These effects are shown to be a consequence of inter-inclusion cluster shear localization in material of high yield stress and low work-hardening capacity. Because of the wide range of yield strengths and work-hardening capacities used in this study, the results extend our insight of the interactions between inclusion distribution, stress state and work-hardening capacity during ductile fracture of this class of materials.