Investagations Of Microstructure And Magnetic Domain During Uniaxial Tensile For Pressure Vessel Steel

Crystallographic orientation and magnetic domain of typical pressure vessel steel (Q235 and 16MnR) in different strain were investigated by electron microscopic analysis and Bitter powder methods to analyze the intrinsic relationship of stress and crystallographic orientation and magnetic domain under different conditions of uniaxial tensile.Magnetic fluid which can get clear magnetic domain images of carbon steel was compounded by controlling the parameters of reaction temperature, the quality of oleic acid coated and the concentration of Magnetic fluid.The sample deformation level was characterized by grain average misorientation(GAM).Trends of GAM transformation were greatly consistent with the three stages of uniaxial tensile. The maximum value of GAM (Q235) or fluctuating near a value (16MnR) appeared in the yield point, while the minimum value appeared near strengthening point,the GAM value increased linearly with strain during strengthen stage.The GAM increasing with the increase of strain in deformation state means that material deformation level can be qualitatively characterized by the parameter of GAM.The rotation of several grains were analyzed under different strain, the results showed that rotation statistics of grains were different under different deformation stages.Simultaneity, the conclusion gained by GAM analysis under different tensile stages verified the mechanism of deformation. The performance of grain rotation revealed that the rotate angle had large value before yield, then decreased after yield, and the minimum rotate angle appeared at about 1.0% strain close to strengthing point.Through the crystal orientation graph accurately determine each grain orientation, for the selection of every possible sliding grain schmid factor value of calculation, according to law, judge slipping schmid is in the process of starting and changes in deformation.Q235 and 16MnR magnetic domain images were obtained through the Bitter powder method. The transformation characteristics of magnetic domain orientation in different strain were obtained. The decisive function of stress energy and magnetocrystalline anisotropy energy to magnetic domain orientation was analyzed. The angles between magnetic domain orientation and stress derectionθ1, easy magnetization directionθ₂ were analyzed. When the strain reached a certain value,θ1 got stable at about 45°, Revealed that the magnetic domain orientation distribution was confirmed. With the increase of strain,θ2 tend to stabilize at 45°and 0°. The magnetic domain rotation of the whole grains did not happen at the same time means that the sensitive degree of magnetic domain with different orientations to stress is different. Magnetic domain orientation vibrated between the original orientation and stress in tension process, especially in the elastic and the early yield stages. It means that the difference between stress energy and magnetocrystalline anisotropy energy determines the orientation of the magnetic domain. When stress energy is dominant, magnetic domains tend to stress direction.When the magnetic anisotropy energy is dominant, the magnetic domains tend to the orientation which determined by the grain-oriented.Finally,the phenomenon of magnetic memory test curve pasting zero point, corresponding stress concentration and slope change were explained by the experiment conclusion and fundamental ferromagnetic theory.