Microstructure- Assisted Changes in the Magnetic Barkhausen Emission of a Mild Steel Under the Influence of Various Mechanical and Environmental Loading Factors; a Semiquantitative Analysis

The aim of the present work is to introduce some novel possible ways for the semiquantitative analytical characterization of ferromagnetic steels. The characterization attempt focuses on microstructural changes occurring under the combined influence of certain mechanical loading as well as physico – chemical degradation factors such as applied stressstrain, tempering processing and salt water – induced electrochemical corrosion. In this direction, various conveniently simple developed functional modelling approaches are used to be able to analyse and estimate related experimental results obtained by means of micromagnetic Barkhausen emission measurements. The approaches are correlated to macroscaling as well as microscaling parameters such as stress-strain, dislocation – controlled cell size and pinning spacing – strength as well as internal cell flow stress. The needed correlations and estimations are made on the basis of an adopted specific micromagnetic activity parameter by which the obtained experimental data are compared and analysed. In this manner the opposite effects of internal flow stress and cell size reduction on the micromagnetic activity can reasonably be demonstrated where the first tends to stimulate an increase while the second a decrease in the specific micromagnetic parameter with progressive plastic deformation. One can further demonstrate that various physico-chemical degradation factors may markedly influence the microstructural as well as micromagnetic behaviour. For instance, hydrogen produced by corrosion of steel in NaCl – water solution and tempering processing lead to appreciable mechanical embrittlement as well as magnetic hardening of steel, expressed by an associated decrease in the specific micromagnetic parameter. With respect to this the tempering processing leads to a higher magnetic hardening compared to the corrosion process of steel.