The effect of heat treatment on microstructure and magnetic domain related to magnetization characteristics in Q345R steels

•Revealing the magnetization kinetics under the influence of the microstructure of materials after heat treatment.•The material microstructure affects the magnetization properties by impeding the motion of magnetic domain wall.•The variation of the microstructure and magnetic properties are also related to the change of grain texture. The remanence and coercivity caused by micro-damage of standard specimens in calibration experiments will reduce the accuracy of magnetic non-destructive testing techniques (MNDT). By means of heat treatment, the micro-damage of the material can be effectively reduced to achieve accurate and efficient non-destructive testing. This paper aims to study the effects of heat treatment temperature on the microstructure and magnetic domains related to the magnetization properties by using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM). According to the study, when the heat treatment temperature increases, the proportion of recrystallized regions gradually increases and the deformation regions become smaller. Meanwhile, the kernel average misorientation (KAM) will become smaller and its distribution in the grains become more uniform. Further, as the heat treatment temperature increases, the low-angle grain boundaries (LAGBs) and medium-angle grain boundaries (MAGBs) are gradually transformed into high-angle grain boundaries (HAGBs). KAM and LAGBs decrease as the deformation region decreases. It is observed that temperature increase of the heat treatment leads to a change in grain texture from hard magnetization to easy one, and turns the disordered maze or stripe structure of the magnetic domains into an ordered stripe structure. Therefore, the heat treatment is beneficial to the movement of the domain walls during the magnetization process, which promotes the reduction of saturation magnetization, coercivity, and remanence.