Research On The Corrosion Behavior Of Fe-Mn-Al-C Low-density High-strength Steel

Due to the need for environmental protection and energy conservation,the light weight of automobile had become the trend of automobile development in the world.The automobile lightening was mainly mainly reflected in two aspects:optimization of automobile structure and material alloying.This paper was to reduce the density of material alloying.Fe-Mn-Al-C low-density high-strength steel had a product of strength and elongation（product of strength and elongation 60GPa·%,the general elongation of up to 60%）,a lower density（far below 7.0g/cm³）,a better corrosion resistance,which was the most potential automotive steel.In this paper,the microstructure and mechanical properties of Fe-28.24Mn-9.97Al-0.81C and Fe-27.5Mn-13.35Al-0.81C experimental steels were studied by composition design,melting process,solution treatment and tensile deformation at room temperature.At the same time,the corrosion resistance and stress corrosion resistance of Fe-28.24Mn-9.97Al-0.81C steel were studied by electrochemical workstation and slow strain rate test machine.Two kinds of low-density steel strength steels,Fe-28.24Mn-9.97Al-0.81C and Fe-27.5Mn-13.35Al-0.81C,had a density of 6.75 g/cm³and 6.52 g/cm³,respectively,and their density was comparable to that of pure iron.It decreased by 14.5%and17.7%respectively.The phase transition or precipitation phase transition temperatures of the two experimental steels were discussed by differential thermal analysis（SDC）,and then the dissolution of the two experimental steels was provided,according to the corresponding differential thermal analysis data,and the different solution treatments were studied.The process of evolution of the microstructure and mechanical properties under the process conditions,combined with SEM,EDS and XRD testing techniques.Studies had shown that Fe-28.24Mn-9.97Al-0.81C is a single-phase austenite steel,Fe-27.5Mn-13.35Al-0.81C was an austenite-ferrite dual-phase steel.With the increase of solution temperature,austenite of single-phase austenitic steel grain coarsened,recrystallization grain growth,and grain boundary flatten,and a large number of annealing twins appeared throughout the austenite grain.Austenitic-ferritic dual-phase steels coarsened with austenite grain growth as the solution temperature increased,fine ferrite distributed at the grain boundaries or austenite,and then coarsened into massive.And a large number of annealing twins appeared and penetrated throughout the austenite grains.With the increase of solution temperature,product of strength and elongation and elongation of the two experimental steels increased first and then decreased.When the solid solution temperature of Fe-28.24Mn-9.97Al-0.81C steel is 1050℃for 1h,product of strength and elongation and extensibility of that was the highest,and it showed the best comprehensive mechanical properties（60.11GPa·%）;product of strength and elongation and extensibility of that was the highest when the solution temperature of Fe-27.5Mn-13.35Al-0.81C steel was 1100℃for 1 h,and it showed the best comprehensive mechanical properties（28.35GPa·%）.Compared to the two experimental steels,Fe-28.24Mn-9.97Al-0.81C steel met the practical application requirements.This paper put the Fe-28.24Mn-9.97Al-0.81C steel in a 3.5%NaCl solution at a temperature of 35℃to perform the immersion test.The results showed that the corrosion process of Fe-28.24Mn-9.97Al-0.81C steel can be divided into the the dominant period of pitting corrosion,the pitting-total corrosion transition period,and the overall corrosion leading period.,but also confirmed the evolution of corrosion products,the final corrosion products were Fe₂O₃,Fe₃O₄,Al₂O₃,Mn₂O₃,Mn₃O₄.Subsequently,the corrosion resistance was studied by weight loss and electrochemical tests.At the same time,the tensile test of slow strain rate was used to study the resistance to stress corrosion.It was found that the corrosion resistance of Fe-28.24Mn-9.97Al-0.81C steel was much higher than that of Fe-29.5Mn-3.2Al-1.5Si steel.The stress corrosion resistance was also much higher than Fe-29.5Mn-3.2Al-1.5Si steel.