Ferromagnetic iron based alloys are used in many important steel products including electrical steels, oil and gas pipelines, naval structures, aircraft landing gear and automotive components. Magnetic properties of these materials are vital for such applications as electrical motors and transformers, where they have direct implications for energy efficiency. Many inspection methods rely on measurement of magnetic response including magnetic particle inspection, magnetic flux leakage, metal magnetic memory, magnetic adaptive testing and magnetic Barkhausen noise (MBN). Understanding the dependence of magnetic properties on material condition is particularly important for detection of residual stress using MBN. This paper examines MBN response in a high strength naval steel, Q1N, undergoing magnetization, including domain structure, which is modified by application of tensile stress, and its interaction with pinning sites within grains, as provided by impurity elements and carbides, whose density is varied by isothermal tempering treatment. A physical basis for modifying domain structure and experimentally examining its interaction with changing pinning site density via temper embrittlement is presented to investigate stress dependent behaviour of MBN in such steel materials. The introduction of this experimental process will facilitate the potential of MBN sensing technology for advanced monitoring of steel structure condition.