Study On Corrosion Resistance Of Oxide Film On IF Steel Surface For Automobile

The Interstitial-Free Steel has been widely used in automotive industry due to its drawability,high-impact,no-aging performances.These merits are major reasons of improving dent resistence and redcing automobile weight,which meet the requirement of security,lightweight and environment friendliy.However,there are so long time during transition that the Interstitial-Free Steel may be corroded by the dewdrop formed among its surface.Therefore,it's meaningful to research the mechanism of the Interstitial-Free Steel corrosion so that improve the corrosion resistance.In this paper,the effects of Mn content and heat treatment on the corrosion resistance of IF steel plates are studied by using the Interstitial-Free Steel as reasearchful materials,and the differences in corrosion resistance of different types of IF steel plates are compared.The corrosion resistance of 3.5%NaCl and.0.1 × 104mol/L Na2SO4 electrolytes is characterized by electrochemical test,and the composition of the surface oxide film is analyzed by XPS.The microstructures of the samples are characterized by metallographic,XRD and EBSD techniques.Finally,the thermal experiments are carried out to make the macroscopic observation and comparison of the corrosion resistance of IF steel.The conclusions are shown as following.(1)The following conclusions are obtained by comparing the corrosion resistance of IF steel plates with different Mn contents.In the 3.5%NaCl electrolyte,the self-corrosion potential,the resistance and the donor density of the IF steel samples with different Mn contents are very close.So the Mn content of the IF steel substrate have a little influence on corrosion resistance.In the 0.1×10-4mol/LNa2SO4 electrolyte,with the increase of Mn content,the selfcorrosion potential of the template is less corrected,the resistance is smaller and the donor density is lower.At the same time,we can draw the conclusion that the corrosion degree of the model before heat treatment is lower by damp heat experiment.XPS analysis showed that the type and content of Mn in the oxide film on the surface of the template increased with the increase of Mn content,which indicated that Mn was more easily enriched with the template surface.The results of XRD and EBSD show that the texture of the template tends to be stable with the increase of Mn content,and the main orientation of corrosion resistance(111)<110>and ?111}<112>is affected.Indicating that the increase in Mn content makes the surface oxide film less dense,less resistant to corrosion.(2)The results of corrosion resistance of IF steel samples before and after heat treatment are shown as following.In the 3.5%NaCl electrolyte,the corrosion potential,the resistance and the donor density of the IF steel samples before and after the heat treatment are very close.As a result,the heat treatment on the IF steel substrate corrosion resistance is minimal.In the 0.1×10-4 mol/L Na2SO4 electrolyte,the self-corrosion potential of the template before the heat treatment is more corrected,the resistance of the passivation film is larger and the donor density is lower.It can also be found to have a lower degree of corrosion before the heat treatment by observing the macroscopic morphology of the damp heat experiment.XPS analysis showed that the oxide content of Mn in the oxide film on the surface of the template increased and the oxide content of Fe decreased sharply after heat treatment.XRD and EBSD analysis show that the grain orientation preference of the template after annealing is not obvious,and the main orientations of the corrosion resistance of IF steel {111}<110>and {111}<112>are reduced.The difference of the large angle is the main difference.The conclusion is drawn that the corrosion resistance of the model is reduced after heat treatment.(3)Comparison of different types of IF steel plate corrosion resistance can be drawn the following conclusions.In the 3.5%NaCl electrolyte,the corrosion resistance,the resistance and the donor density of the different types of IF steel plates are very close.So that different types of IF steel base corrosion resistance is very close.In the 0.1 × 10-4 mol/L Na2SO4 electrolyte,the self-corrosion potentials of the DQ-IF and 590CQ-IF templates are more correct than those of other templates,and the passive film resistance is larger and the donor density is lower.The macroscopic morphology of the DQ--IF and 590CQ-IF models are less corrosive.The order of strength is:DQ-IF steel plate>590CQ-IF steel plate>SEDDQ-IF steel plate>340DDQ-IF steel plate>340BH-IF steel model.(4)The 340DDQ-IF steel with the worst corrosion resistance was optimized.The optimal heat treatment conditions were obtained:the soaking temperature was 800?,the outlet temperature was 180?,and the cooling water was distilled water at room temperature.The soaking temperature and cooling water type have a great influence on the corrosion resistance of 340DDQ-IF steel.