Statistical evaluation of the measurement of residual stresses in the surface layer of CP1000 steel sheets using the magnetic Barkhausen noise and X-ray methods

The paper presents an analysis of the possibility of measuring the residual stresses of metal sheets with the application of the so-called Barkhausen effect. The aim of the research was to compare the residual stress levels measured by two methods of multiphase steel sheets (ferritic-martensitic-bainitic) in grade HCT980C after flattening on a roller leveller in industrial conditions. The measurements were carried out using two methods: the Barkhausen effect method and the X-ray method. The paper describes in detail the methodology used for testing the measurement of residual stresses. The residual stress testing of sheets made of the CP1000 steel group was supplemented with tests of chemical composition, microstructure and mechanical properties (Re, Rm, A80, HRC hardness). In the analysis of the research results, elements of statistics were also used, in the form of ordinary correlation. The research results showed that in the case of sheets after flattening on a roller leveller in industrial conditions, it is possible to replace the commonly used and recognized, but labour-intensive X-ray method, with a simple, innovative and cheap to use method using the Barkhausen effect. Stress measurement using the Barkhausen effect has already been found to be applicable in the diagnostics of tracking changes in the stress value in the material in industrial pipelines, where access to the other measurement methods is difficult or even impossible. Currently, the measurement of stress in sheets by the magnetic method is introduced on the transverse cutting line when cutting the sheet metal from coils to metal sheets. The measurement of stresses in the production of steel sheets is important because the difference in stress between the top and bottom sides of the sheet has a significant effect on the flatness of manufactured metal sheets.