EFFECT OF MAGNETIZATION ON MECHANICAL PROPERTIES AND FORMABILITY OF STEEL SHEETS

Abstract

The current study discusses how a change in tensile characteristics with an applied magnetic field improves the formability of a dual phase steel sheet. The work also reports a novel design of an electromagnetic uniaxial tensile test tool and its performance analysis to assess the effect of magnetic field on tensile properties. The electromagnetic tool is developed as an external attachment to a conventional uniaxial tensile test specimen while testing in a universal testing machine. For the simulations, five different configurations of electromagnetic tools are modelled with different magnetic flux density. Based on the predicted results of magnetic flux density distribution, obtained from simulations and analytical model, the electromagnetic tools are designed and fabricated. Furthermore, uniaxial tensile tests were performed with electromagnetic tools to analyze the tensile properties, and the optimal tool was identified based on the results. For the effect of magnetization on the steel sheet two grades of steels were select DP590 and ZC440 in three different directions. The experimental results obtained from tensile tests show a significant improvement in the tensile strength and normal anisotropy due to magnetic field. A negligible change in strain hardening exponent with a slight decrease in percentage elongation was also observed due to the magnetic field. The effect of magnetic field was observed in the higher thicknesses of both steels in term of ultimate tensile strength and anisotropy. It was observed that higher magnetization of material ZC440 steel gives the better results when compared to the DP590 steel sheet. The samples for microstructural investigations using electron backscattered diffraction technique were taken from the middle of the specimens tested with 20% of plastic strain in all the cases of experiments performed with and without the magnetic field. The magnetic force microscopy frequency analysis was also performed to evaluate the evidences of magnetic field on the tensile tested specimens. A significant increase in the values of strengths and anisotropy but a slight decrease in ductility and strain hardening exponent were observed vi in the specimens tested with the magnetic field. A modified electromagnetic tool was also developed as an attachment with sheet samples for conducting experiments on an Erichsen cupping machine to evaluate the forming behavior of the sheet. The results of Erichsen cupping experiments were obtained with and without magnetic field and it is observed that the magnetic field increases the values of Erichsen Index suggesting an enhanced formability. The value of Erichsen Index increased in both material but the value of ZC440 Erichsen index was higher when compared to the DP590. Numerical simulations were carried out using a finite element (FE) method-based software to simulate Erichsen cupping test and predict punch force and Erichsen Index in both parent of ZC440 and DP590 sheets. The predicted results were validated with experimental work. The FE results showed a value of reduction in sheet thickness during stretching was validated with the experimental data. The experimental reading of sheet thickness was measured by the Creo software by putting the image of the samples. The increasing value of punch force was validated in the FE results. Comparison of the experimental versus simulation results of the Erichsen cupping test confirmed that the MF increased the formability of the sheet. It was also confirmed that the MF has more effected on the ZC440 material as compared to the DP590 material. This newly developed electromagnetic tool setup worked on the basic of the magnetization behaviour of the material as well the sheet thickness of the material.