Study of magnetic signals behavior at groove defect by tensile stress during online measurement of Q345R steel

•The magnetic signals of Q345R steel containing groove defects at different stress stages during online loading were investigated, and the magnetic behavior of specimens with different initial magnetization strengths under stress was discussed from both theoretical derivations and experimental results.•By analyzing the magnetic signals at different stress stages, it is possible to assess the degree of damage and the remaining life of the damaged component at that stress state.•The microstructures of defective fracture interfaces corresponding to different stress stage pairs were analyzed. To study the influence of external loading on the magnetic signal at the defect location of the component, Q345R steel was selected to make a groove defect specimen for axial tensile testing. The magnetic behavior of the specimens containing different initial magnetization strengths under different stress states (elastic deformation stage, yielding stage, strengthening stage, and fracture stage) was studied in comparison. The result showed that the value of the tangential component Hxave in the nondestructive region gradually decreased with the increase of the stress loading in the elastic loading stage, however, the tangential component Hxave at the defect location of the specimens had different variation patterns due to the different initial magnetization strengths. When the load was loaded to the yielding stage, the magnetic signals remained stable, and Hxave increased again in the strengthening stage and completed the excitation of the magnetic signals in the fracture stage. By analyzing the magnetic memory field parameters throughout the loading process, it can be found that the variation patterns were consistent despite the different initial magnetization intensities of the specimens. The above findings are of great significance for assessing the stress state of defects in ferromagnetic materials.